Plant Hormones: (Phytohormone)
Definition
Certain chemical produced by plants have profound effect on their subsequent growth and development. Such chemicals are called Plant Hormones or Phytohormone.
Phytohormone are synthesized by plants in minute concentration and exert their effect by activating gene expression or inhibiting enzyme or changing properties of membrane.
Types of Phytohormone
There are five kind of plant hormones
1. Auxins
2. Gibberellins
3. Cytokinins
4. Abscisic Acid
5. Ethene
1. Auxins
Discovery
the first auxin was discovered by Fret Went in 1926.
Chemical Nature
Indol Acetic Acid (I.A.A)
Indol Acetic Acid (I.B.A)
Nephthalene Acetic Acid (N.A.A)
Site of Synthesis
It is synthesize at the apices of stem and foot, young leaves and young embryo.
Role of Auxin
i. Cell division and cell enlargement
It stimulate teh cell division and cell enlargement and plant in increase the length of plant.
ii. Initiation of Root
Auxins also initiates development of adventitious roots when applied at the cut base of stem.
iii. Abscission
In mature leaves and fruits when auxin production diminishes, a layer of thin walled cells is formed at the base of petiole and stake of fruit. This layer is called Abscission layer and causes fall of leaves and fruit with slight jerk.
iv. Growth of Fruit
Auxins produced in young embryo promotes the growth of fruit.
v. Parthenocarpy
Use of auxin helps in producing parthenocarpic or seedless fruits.
vi. Apical Dominance
Besides growth promoting function on Auxin, also has inhibitory effect on growth. Growth of apical bud inhibits growth of lateral buds beneath the stem. This phenomenon is termed as apical dominance removal of apical buds initiates growth of lateral buds with more leaves and axillary bud.
vii. Weedicide
Auxins are selective weed killer 2-4 dichlorophenoxy acetic acid (-2-4-D) is used to kill weeds in lawn’s and cereal crops.
2. Gibberellins
Discovery
Gibberellins was discovered by T.Yabuta and I.Hayashu in a fungus called Gibberellins funjikuroi. This fungus causes foolish seedling (Bakanae) disease in rice. In this disease the infected rice seedling elongated and ultimately fallover without producing grains.
Chemical Nature
The chemical nature of Gibberellins is Gibberellins acid 70 types of gibberellins have been discovered.
Role of Gibberellins
i. Cell division and cell enlargement
Like auxins Gibberellin also promotes cell division and elongation.
ii. Control of Dwarfism
Gibberellins can control genetic and physiological dwartism plants.
iii. Seed Germination
They promote the synthesis of a-amylase enzyme is dorman seeds due to the production of this enzyme, the seed starts germination.
iv. Parthenocarpy
These hormones help in the formation of seedless fruit which are called Parthenocarpic fruits.
v. Increase of Crop Yield
The crop yield of sugar can can be increased by the application of gibberellin about 50 tons/ acre.
vi. Formation of Flower and Growth of Pollen Tube
They stimulate flowering and the growth of pollen tubes during fertilization
3. Cytokinins
Discovery
Cytokinins are discovered by Miller in coconut milk.
Chemical Nature
Chemically there are two types of cytokinins.
Kinetin It is found in coconut milk etc.
Zeatin It is found in maize.
Role of Cytokinins
i. Cell Division
They initiate rapid cell division only in the presence of auxin.
ii. Delay in Senescence
They also caused delayed senescence (old age).
iii. Breaking of Seed Dormancy
They break seed dormancy and promote fruit development some species.
4. Abscisic Acid (A.B.A)
In contrast to growth promoting hormones, abscisic acid is growth inhibitor, produced by plants during adverse environment conditions such as drought conditions.
Role of Abscisic Acid
It is a gas which also acts as a growth inhibitor.
Role of Ethene
Changes in environmental conditions are the big threats for living organisms especially for plants. These factors which change the normal condition of light, CO2, nutrients, temperature etc. causes severe stresses on plants. The common environmental stresses for plants are
1. Water Shortage (Drought condition)
2. Less Oxygen Supply
3. High Concentration of Salt in the Soil
4. High Temperature
5. Low / Cold Temperature
6. Herbivory / Over Grazzing
1. Water Shortage
In plants there are two methods to tolerate the heat stress.
Diseases of plants may arise from infections by viruses, bacteria or fungi and other pathogens in most cases. Against these diseases the plants produce immune system in their body.
First Line Efence
The outer layer epidermis is a protective covering around the body of plant. This is the First Line Defence.
Second Line Defence
When pathogens enter the body through stomata or any other way, then plants produce certain chemicals to kill them. This is called Second Line Defence.
Phytoalexins
In infected plants an antibiotic phytoalexins is produced which is effective to all micro-organisms.
Biological Clocks
Definition
A control system is found in all living organisms which controls physiological and metabolic and metabolic functions according to time is called Biological Clock.
Biological Rhythms OR Biorhythms
Definition
In living things the behavior activities occur at regular intervals which are called biological rhythms OR biorhythms.
Circadian Rhythms
Definition
[Circa => about; dies => day]
Biorhythms may occur, showing periodicity of about 24-Hours. These are called Circadian Rhythm, which means about one day, so they are also called diurnal rhythms.
Causes of Biorhythm
Biorhythms occurs due to the following reasons.
1. Exogenous Stimuli
2. Endogenous Stimuli
1. Exogenous Stimuli
There may be direct response to various changes in the external (exogenous) stimuli.
2. Endogenous Stimuli
These rhythms can be controlled internally by an efficient time measuring system and are independent of light and temperature effects. These types of rhythms are called endogenous.
Co – Ordination
Definition
The working together of all parts of the body or system is called Co-ordination.
Types of Co-Ordination
There are two types of Co-ordination.
1. Nervous Co-Ordination
2. Chemical Co-Ordination
1. Nervous Co-Ordination
Definition
Co-Ordination brought about by the nervous system. It is quickest way of communication take place by electro-chemical messages called Nerve Impulse within the body of all animals is called Nervous Co-Ordination.
Elements of Nervous System
The elements o nervous system which help in co-ordination are
i. Receptor
ii. Central Nervous System (CNS)
iii. Effector
i. Receptor
The sensory tissues or organs which receive any change in their external as well as internal environment (stimuli) are called Receptors.
ii. Central Nervous System
The receptors convey the stimuli to the control centre, the nervous system (Central Nervous System) through sensory nerves.
iii. Effector
The central nervous system (CNS) analyses stimuli and sends an appropriate command, through it motor nerves to either endocrine organ to release hormones into the blood or to muscles called Effectors.
Pathway in Nervous System
There are two types of pathway in the nervous system.
i. Afferent Nerve Pathway
ii. Efferent Nerve Pathway
i. Afferent Nerve Pathway
From receptor the messages are carried to the Central Nervous System i.e. brain and spinal cord, this pathway is called Afferent Nerve Pathway.
ii. Efferent Nerve Pathway
From central nervous system the messages are transferred to the effector. This pathway is called Efferent Nerve Pathway.
Nervous Tissues
There are two types of nervous tissues
1. Neurons
2. Neuroglia OR Glial Cells
1. Neurons
Definition
The nervous system consist of special cells which can generate and conduct electric current are called Neurons.
OR
The chief structural and functional unit of nervous system is called Neurons.
Structure of Neurons
Neurons are different from each other according to size and shape but the structure of neuron consists of three parts.
i. Some or Cell Body
ii. Dendrites
iii. Axon
i. Soma OR Cell Body
Each neuron has a cell body or soma containing nucleus and various organelle embedded in the cytoplasm. Nissl’s granules which are group of ribosomes, associated with rough E.R. and Golgi apparatus are present in the cell body.
Functions
The cell body or soma is the main nutritional part of the cell necessary for growth of neuron.
Soma receive message to dendrites and convey it to axon.
ii. Dendrites
From the soma, a large number of small threads like terminal branches are arises are called Dendrites.
Functions
Dendrites receive stimuli and convey it to the soma.
iii. Axon
The unbranched, single elongated cytoplasm process which usually arises opposite to dendrites called Axon.
Axon Hillock
Axon originates from a pyramid like area of soma called Axon-Hillock.
Axon Terminal
At the terminal end of axon many fine branches are present called Axon Terminals.
Myelin Sheath
The axon of some neurons is enclosed by a layer of fatty substance known as Myelin Sheath.
This serve as insulating layer.
Functions
Axon is specialized for conducting impulses to other neurons.
Types of Neurons
According to the function, neurons are of the three types.
i. Sensory Neuron
ii. Motor Neuron
iii. Inter Neuron
i. Sensory Neuron
The neurons which transmit impulses from receptor to the central nervous system is called Sensory Neuron or Receptor Neurons.
ii. Motor Neuron
The neurons which transmit instructions of the central Nervous System to the effector are called Motor Neurons or Effector Neurons.
iii. Inter Neurons
The neurons present between sensory and motor neurons are called Inter Neurons. They are found in Central Nervous System.
Functions of Neurons
Neurons is the functional unit of nervous system which receives stimuli, transfers them to the Central Nervous System (CNS).
It transfers the messages from CNS to the body parts effector.
Reflex Action
Definition
The automatic involuntary responses which occur either due to internal or external stimuli are called Reflex Action.
OR
An immediate response to a specific stimulus without conscious control is called a Reflex Action.
Parts of Reflex Action
Reflex action consists of
i. Receptor: (Skin) receive stimuli.
ii. Sensory Neuron: It carries message from receptor to the Central Nervous System (CNS).
iii. Motor Neuron: It carries message from Central Nervous System (CNS) to the effector.
iv. Effector: (Muscle of gland) which perform action.
Reflex Arc
Definition
The pathway of passage in impulse during a reflex action is called Reflex Arc.
Reflexes may be monosynaptic or polysynaptic.
Monosynaptic
The reflex action in which only one synapse is involved is called Monosynaptic.
Example: Knee Jerk
Polysynaptic
The reflex action in which many synapses are involve due to presence of inter neurons between sensory and motor neurons is called Polysynaptic.
Example: Hand withdrawal on the painful stimuli.
Examples of Reflex Actions
Definition
The electrochemical signals developed by a neuron for communication is called Nerve Impulse.
Method of Development of Nerve Impulse
The neurons develop impulse in the following way.
1. Resting Membrane Potential (RMP)
2. Action Potential
3. Propagation of Impulse
4. Synapse
Resting Membrane Potential
Definition
A typical neuron at rest is more positive electrically outside than inside the cell membrane. This net difference in charge between the inner and outer surface of a non conducting neuron is -65mv is called the Resting Membrane Potential.
Factors Involved in Resting Membrane Potential
This popularity is due to the unequal distribution of ions across the neurolemma. The major factors which are involved in resting membrane potential are
Sodium and Potassium Ions
Definition
When neuron is stimulated reversal of the polarity of the neurolemma occurs, first changes to +40mv and then restores to -65mv again is called Action Potential.
This action potential is extremely rapid as it occurs in a few milliseconds.
Factors Involved in Action Potential
Sodium and Potassium Ions
Sequence of membrane potential changes associated with an Action Potential.
Definition
When the action potential develops and spreads along the entire length of neurolemma, it is called propagation of nerve.
Synapse
Definition
The region where the impulse moves from one neuron to another is called a Synapse.
Components of Synapse
It consists of three components
1. Pre Synapting Membrane
2. Synaptic Cleft
3. Post Synaptic Membrane
1. Pre Synaptic Membrane
The membrane of axon terminal is called Pre Synaptic Membrane.
2. Synaptic Cleft
The narrow space between neurons is called Synaptic Cleft.
3. Post Synaptic Membrane
The membrane of dendrites of another neuron is called Post Synaptic Membrane.
Motor End Plate
When it is the membrane of muscle cell it is called motor end plate.
Neurotransmitter
The chemicals present in the vesicles which are released at the axon ending of the neurons, at synapse are called Neurotransmitter.
Mechanism of Impulse Through Synapse
Many different types of neurotransmitter are known. These are acetylcholine, norepinephrine, glycine, gab a, serotonin, dopamine etc.
Evolution of Nervous System
In different group of animals two types of nervous systems can be recognized, which are
1. Diffused Nervous System
2. Centralized Nervous System
1. Diffused Nervous System
Diffused Nervous System is found in cnidarians and Echinoderms.
Nervous System of Hydra
Centralized Nervous System found to varying degrees in more complex organisms from platyhelminthes to chordates including humans.
Nervous System of Planaria
The nervous system of man is the most advanced, highly developed. It controls all functions of the body. It consists of two parts
1. Central Nervous System (CNS)
2. Peripheral Nervous System (PNS)
1. Central Nervous System (CNS)
Definition
The nervous system consists of brain and spinal cord (hollow nerve cord) and also consists of upto 100 billion inter neurons is called Central Nervous System (CNS).
Components of Central Nervous System
The central nervous system consists of
Brain
Spinal Cord
Protection of Central Nervous System
Brain and spinal cord both are protected in three ways
i. Cranium
ii. The Vertebral Column
iii. Meninges
iv. Cerebrospinal Fluid (CSF)
i. Cranium
Cranium, which is part of skill, protects the brain.
ii. Vertebral Column
Neural arches of vertebrate of vertebral column protect the spinal cord.
iii. Meninges
Beneath the cranium, the brain and spinal cord are protected by triple layers of tough connective tissues called meninges.
iv. Cerebrospinal Fluid (CSF)
Between the layers of meninges, there is a plasma like fluid which bathes the neurons of brain and spinal cord is called Cerebrospinal Fluid (CSF).
It cushions against the bumps and jolts.
2. Peripheral Nervous System (PNS)
Definition
The nerves arises from brain and spinal cord that are spread in various part of body which transmits the signals between CNS and body parts make a nervous system called Peripheral Nervous System.
The peripheral nervous system consists of two types of nerves.
i. Cranial Nerves
ii. Spinal Nerves
i. Cranial Nerves
In humans, there are 12 pairs of nerves which arise from the brain or lead to the brain these nerves are called cerebral or cranial nerves.
ii. Spinal Nerves
In humans, there are 31 pairs of nerves which arise from the spinal cord or lead to the spinal cord are called spinal nerves.
Types of Peripheral Nervous System
The peripheral nervous system is divided into two types according to their functions.
1. Somatic Nervous System
2. Autonomic Nervous System
1. Somatic Nervous System
The peripheral nervous system which controls all the voluntary activities of the body such as contraction of skeletal muscles and movement of joint is called Somatic Nervous System.
2. Autonomic Nervous System
The autonomic nervous system which controls involuntary activities of the body such as smooth muscles, glands, muscles of heart and other internal organs is called Autonomic Nervous System.
Types of Autonomic Nervous System
Autonomic nervous system divided into two types
i. Para Sympathetic Nervous System
ii. Sympathetic Nervous System
i. Para Sympathetic Nervous System
The autonomic nervous system formed by some cranial nerves, vagus nerves and the spinal nerves that are arising from the sacral vertabrate are called Para Sympathetic Nervous System.
ii. Sympathetic Nervous System
The autonomic nervous system whose nerves arise from the thoracic and lumber regions of spinal nerves is called Sympathetic Nervous System.
Functions
This system is important during emergency situation and is associated with “flight or fight”. It increases the heart beat, breathing rate, slows digestion, dilates pupil etc.
Brain
Definition
The most important part of Central Nervous System develops from dorsal, hollow nerve cord well protected in the cranium of skull and composed of inter neurons and is the seat of our intelligence, learning and memory is called Brain.
Part of Brain
The brain consists of three parts
1. Fore Brain
2. Mid Brain
3. Hind Brain
1. Fore Brain
Fore brain can be divided into two regions
i. Telencephalon
ii. Diencephalon
i. Telencephalon
The largest part of fore-brain which is differentiated into two cerebral hemisphere or cerebrum is called Telencephalon.
Cerebrum
Cerebrum is the largest part of the brain and is divided into two halves called Cerebral Hemisphes.
Cerebral Hemisphere
Each hemisphere consist of an outer grey matter or cerebral cortex and an inner white matter.
Cerebral Cortex
The two cerebral hemisphere communicate with each other by means of large band of axons called Corpus Callosum.
Part of Cerebrum
Functionally, the cerebrum is differentiated into four lobes.
The diencephalons consists of two parts
i. Thalamus
ii. Limbic System
i. Thalamus
The clearing house for sensory impulses is called Thalamus.
Functions
The limbic system is located in an are between the thalamus and cerebrum.
Parts of Limbic System
The limbic system consists of
i. Hypothalamus
ii. Amygdala
iii. Hippocampus
i. Hypothalamus
Hypothalamus is the part of limbic system which is called Thermostal of the body.
Functions
The amygdala produces sensation of pleasure, punishment or sexual arousal stimulation.
It also involve in the feelings of fear.
iii. Hippoc Ampus
Hippocampus is involved in long term memory.
Mid Brain
In mammals mid brain is relatively very small. It consists of the optic lobes which are represented by four small bodies.
Functions
It receives sensory information like vision, odour etc. It receives sensory information from spinal cord and sends them to the fore brain.
Hind Brain
Hind brain consists of
1. Medulla Oblongata
2. Cerebellum
3. Pons
4. Reticular Formation
1. Medulla Oblongata
Medulla oblongata lies on the top of spinal cord.
Function
It controls involuntary actions like blood pressure, heart beat, sneezing, coughing, breathing rate, hicupping, swallowing etc.
2. Cerebellum
The cerebellum lies dorsally behind the optic lobes. It is highly convoluted. It is large in mammals than other animal.
Functions
Pons regulates activities like muscular co-ordination, facial expressions, breathing and sleeping.
4. Reticular Formation
Reticular formation lies in pons, medulla and mid brain.
Functions
It monitors the messages to the brain which should be ignored or should be realized.
Brain Stem
The oldest tissues formed by the combination of medulla oblongata, pons and mid brain is called as Brain Stem.
Functions
It involved in the control of sleep and wakening.
Spiral Cord
Definition
A thick whitish nerve cord that lies below the medulla oblongata and extends down through the neural canal of vertebrate upto the hips is called Spinal Cord.
Cross Section of Spinal Cord
In cross section, the spinal cord is differentiated into two areas.
White Matter
Gray Matter
Unlike brain, spinal cord has grey matter inside surrounded by white matter on the outside. They grey matter has the shape of an “H”. The first synapse of each sensory neuron is located in the grey matter.
Central Canal
The narrow central containing cerebrospinal fluid runs through the middle of the spinal cord. This fluid brings nutrients to the spinal cord.
Spinal Nerves
The nerve arises from spinal cord is called Spinal Nerves.
Each spinal nerve divides into two roots just before it joins spinal cord.
1. Dorsal Root
2. Ventral Root
1. Dorsal Root
The dorsal root joints the dorsal part of the spinal cord and it contains axons of sensory neurons.
Dorsal Root Ganglion
The cell bodies of these neurons aggregate in a small swelling known as the dorsal root ganglion.
2. Ventral Root
The ventral root which is attached to the ventral part of the spinal cord carrying axons of motors neurons, arised from the spinal cord.
Functions of Spinal Cord
Spinal cord serves as an express way for signals between autonomic nervous system.
It is also the control centre for many reflexes.
Receptors
Definition
The single or group of either modified neurons or epithelial cells which receive stimuli either from external environments and relaying them in the form of impulses to the CNS are called Receptors.
Receptionists
The receptors are acts as receptionist of nervous system because they receive any kind of change, which is then transferred to the brain and spinal cord.
Sensation
Receptor converts stimuli into nerve impulses, this stage awareness of stimulus is called Sensation.
Perception
In the control centre of the nervous system, the impulses are converted into perception.
Types of Receptors
Receptors are classified according to type of stimulus which they can detect and give response. Following are some types of receptor.
1. Thermoreceptor
The receptors which detect and respond to temperature fluctuations (heat and cold) are called Thermoreceptor.
2. Chemoreceptor
The receptors which can detect and respond to presence of certain chemicals in their surrounding are called Chemoreceptor.
3. Mechanoreceptor
The receptors which can detect the stimuli of sound, motion, touch, pressure gravity and movement are called Mechanoreceptor.
4. Photoreceptor
The receptors which respond to the stimulus of light and ultraviolet rays are called Photoreceptor.
5. Pain Receptor
The receptors which produced sensation of pain or damage tissues are called the Pain Receptor.
Working of Sensory Receptors in Skin
In human, the receptors in skin are concerned with at least five different senses i.e., touch, pressure, cold, warm and pain.
Types of Sensory Receptor in Skin
There are two types of sensory receptors in the skin.
i. Free Nerve Ending Receptors
ii. Encapsulated Receptors
i. Free Nerve Ending Receptors
The simplest types of receptor which contain free end without any protective capsule and are located just beneath the epidermis are called Free Nerve Ending Receptors.
Functions
Free nerve ending receptors adapt very slowly to stimulation.
Types
They are of different types
a. Mechanoreceptors Receive touch and pressure.
b. Nociceptors Feel pain
c. Thermoreceptors Feel change in temperature
ii. Encapsulated Receptors
The type of receptor contain a protective capsule of connective tissues at their ends and lie in skin are called Encapsulated Receptors.
Types
Encapsulated receptor are of following two types
i. Meissner’s Corpuscles
ii. Pacinian Corpuscles
i. Meissner’s Corpuscles
The encapsulated receptors that are found in those parts which do not have hairs such as finger tips, eyelids, lips palms, soles, nipples etc are called Meissner’s Corpuscles.
Structure of Capsule
Their capsules consists of thick collagen fibers with spiral and highly coiled nerve endings.
Function
There are touch receptors means very sensitive to touch.
ii. Pacinian Corpuscles
The encapsulated receptors which are found in dermis layer and also in some internal organs and moveable joints are called Pacinian Corpuscles.
Structure
Their nerve endings are surrounded by an onion like capsule made of concentric layers of membrane. Between the membranes fluid filled spaces are present.
Functions
They are pressure receptor and detect rapid and deep pressure changes produced by vibration and touch.
Sensory Receptors with Reference to Arteries
The aortic arch and the carotid artery contain many receptor which are
Mechanoreceptor
They detect the pressure changes in arteries.
Baroreceptor
They detect the pulse pressure
Function
These receptors transfer these changes to the medulla oblongata which controls blood pressure.
Aortic Body and Carotid Body
The aortic arch and the carotid sinus also contain chemoreceptor called Aortic body and carotid body.
Function
They are sensitive to CO2 concentration and hydrogen ion concentration of the blood.
Effects of Drugs on Co-Ordination
Drugs
A chemical substance that causes the specific physiological response in the body are called drugs.
Importance
The abnormalities appear in brain, spinal cord, central nervous system and peripheral nervous system causes diseases called Nervous Disorders.
Some common disorders of nervous system are as follows
1. Parkinson’s Disease
2. Alzheimer’s Disease
3. Epilepsy
1. Parkinson’s Disease
It is a brain disorder.
Causes
It either caused by degeneration or damage of nerve tissues within the basal ganglia of the brain.
Symptoms
It is characterized by involuntary tremors, diminishing motor power and rigidity. It causes stiffness, weakness and trembling of the muscles. The mental faculties are not affected.
Treatment
Leopoda is the effective medicine which is helpful in minimizing the symptoms by can not halt the degeneration of neurons of brain.
2. Alzheimer’s Disease
It is the progressive degeneration of neurons of brain, especially cortex and hippocampus.
Causes
There is a genetic pre-disposition to the disease in some people, so it tends to run in families.
Stages of Diseases
The disease progresses in three broad stages.
First Stage
At first, the patient notices his forgetfulness.
Second Stage
In second phase, there is a severe loss of memory particularly for recent events. Anxiety increases with sudden changes in mood.
Third Stage
In the third and last stage the disease become severe. He losses memory, hears voices or see faces in the absence of any person. This disease is called Hallucination. He does not share his ideas and does not accept ideas of other persons, such disease is called paranoid delusions.
Symptoms
The main symptom of the disease is the loss of memory called dementia.
Treatment
Definition
The co-ordination brought about by the endocrine gland system. It is not very rapid, but shows slow and prolonged effect takes place by chemical substances called hormones and neurotransmitter within the body of all animals is called Chemical Co-ordination.
Endocrine glands secreat their secretions (hormones) directly into the blood stream. They are transported by the blood to the target cells.
Types of Hormones
Chemically the hormones are organic compounds which are classified into three types.
1. Peptide Hormones
2. Modified Amino Acids Hormones
3. Steroid Hormones
1. Peptide Hormones
The hormones which are composed of protein are called Peptide Hormone. There are two types of peptide hormones.
i. Small Chain Amino Acids
ii. Large Chain Amino Acids
i. Small Chain Amino Acids
The peptide hormones consists of small chain of amino acids are called Small Chain Amino Acids.
Examples
Glucagon
Antidiuretic Hormone (ADH)
Oxytocin
ii. Large Chain Amino Acids
The peptide hormones consists of long chain of amino acids are called Large Chain Amino Acids.
Example
Insulin
Preleclin
2. Modified Amino Acid Hormones
The hormones consists of modified amino acids are called Modified Amino Acid Hormones.
Example
Thyroxine
Epinephrine
Nor-epinephrine
3. Steroid Hormones
The hormones which are composed of lipid are called Steroid Hormones.
Example
Estrogen
Progesterone
Testosterone
Aldisterone
Hormone Action
To explain the action of hormones two models have been proposed.
1. First Model
2. Second Model
Similarity Between Both Models
Both model agree that the plasm membrane of cells contain certain receptors to accept the hormones.
Dissimilarity Between Both Models
After receiving the hormones continue their way of action called signal transduction pathway. It is different in both models.
1. First Model
According to the first model peptide hormones are involved. The receptor molecule is attached to an enzyme adenylate cyclase in the inner part of plasma membrane. The hormone is attached to the receptor. By the activity of enzyme ATP molecule is changed into cyclic adenosine monophosphate (AMP) in the cytoplasm. The cyclic (AMP) acts as a second messenger and activates the particular enzyme which actually helps in the function. Some other messenger molecules also take part in the process.
2. Second Model
According to the second model, steroid hormones are involved. These hormones are fat soluble, so they enter the cell directly through the plasma membrane, so they do not need second messenger. In the cytoplasm they are attached to the particular receptors which transfer into the nucleus. In the nucleus. In the nucleus hormone receptor complex activities the genes due to which actual function is started.
Functions of Hormones
Definition
Endo => Inside => Krinein => separate i.e. to secrete.
In the body of vertebrates there are certain dustless gland which poured their secretions (hormones) directly into the blood or in body fluids are called endocrine glands or ductless glands constitute a system called Endocrine System.
Endocrine Glands of Man
In the body of man and other mammals, following important endocrine glands are mostly found.
1. Hypothalamus
2. Pituitary Gland
3. Thyroid Gland
4. Parathyroid Gland
5. Pancreas
6. Adrenal Gland
7. Thymus Gland
8. Pineal Gland
9. Gonads
1. Hypothalamus
The part of forebrain which forms a connection between Nervous System and endocrine system is called Hypothalamus.
Hormones
The hypothalamus contains specialized nerve cells called neurosecretory cells which produced two types of hormones.
i. Releasing Hormone
ii. Inhibitory Hormone
i. Releasing Hormones
The hormones which are produced to increase the secretion of another glands are called Releasing Hormones.
Function
Releasing hormone control the secretion of hormones from pituitary gland.
ii. Inhibitory Hormones
The hormones which are produced to prevent the extra secretion of hormones are called Inhibitory Hormones.
Function
Hypothalamus produced two hormones which are
2. Pituitary Gland (Hypophysis)
Pituitary gland is called “master gland” because it controls the secretion of other endocrine glands.
Location
The pituitary gland is located in the brain. It is attached to the base of hypothalamus by short.
Size
The pituitary gland is small pea size gland.
Lobes of Pituitary Gland
Pituitary gland has three lobes
i. Anterior Lobe
ii. Median Lobe
iii. Posterior Lobe
i. Anterior Lobe
Anterior lobe produces three types of hormones which are
a. Tropic Hormone
b. Growth Hormone or STH
c. Prolactin
a. Tropic Hormone
The hormones which control the activity of other hormones are called Tropic Hormones.
Kinds of Tropic Hormone
The tropic hormone secreted by the pituitary gland are as follows
Thyroid Stimulating Hormone (TSH)
It control the working of thyroid gland including secretion of thyroxin.
Adreno-Cortico Tropic Hormone (ACTH)
In controls the activity of outer part of cortex of adrenal gland.
Follicle Stimulating Hormone (FSH)
FSH in females stimulate follicle developing and secretion of oestrogens from the ovaries.
In males it stimulates development of the germinal epithelium of the testis and sperm production.
Leutinizing Hormone (LH)
This hormone helps in the formation of sperms and testosterone hormone in male. In female it takes part in ovulation i.e. release of ovum from the ovary.
b. Growth Hormone OR Somatotropin Hormone (STH)
It regulates the normal growth by controlling many metabolic processes, such as protein synthesis, involved in growth of bones and soft tissue.
c. Prolactin Hormone
This hormone stimulate mammary glands and production of milk.
ii. Median Lobe
Median lobe produced one hormone called Melanocyte Stimulating Hormone (MSH).
Functions
This hormone controls darkening of skin in many vertebrates. In human, very small amount of MSH is produced by the anterior pituitary rather than median.
iii. Posterior Lobe
From posterior lobe of pituitary gland following hormones are secreted.
a. Antidiuretic Hormone (ADH)
b. Oxytocin
a. Antidiuretic Hormone (ADH)
It stimulates the re-absorption of water by tubules of kidney and thus decreases the amount of urine passed.
b. Oxytocin
It stimulates contraction of muscles of uterus during child birth and release of milk during breast feeding.
Abnormal Conditions Due to Pituitary Gland
Due to abnormal production of somato tropic hormone (STH) or growth hormone, following abnormalities occur.
i. Gigantism
ii. Dwarfism
iii. Acromegaly
i. Gigantism
It is disease of childhood.
Causes
It occurs due to over secretion of somatotropic hormones (STH) or growth hormone.
Symptoms
The affected individuals becomes abnormally tall.
ii. Dwarfism
It is a disease of childhood.
Causes
It caused due to less secretion of somato tropic hormone or growth hormone.
Symptoms
The affected individuals becomes abnormally short.
iii. Acromegaly
It is a disease of adulthood.
Causes
It occurs due to overproduction to somatotropic homrone (STH).
Symptoms
In this condition, hands, feet and jaw bones and cartilages and soft muscles become larger in size and swollen.
3. Thyroid Gland
Location
Thyroid gland is located in the neck region in front of trachea. It consists of two lobes, one on either side of trachea.
Shape
It is butterfly in shape.
Secretions
It secreats three main main hormones.
i. Thyroxine or T4 (Tetra lodo Thyroxine)
ii. T3 (Tri lodo Thyroxine)
iii. Calcitonin
i. Thyroxine OR T4
Thyroxin increases the metabolic rate and promotes both physical growth and mental development.
It increases the oxygen consumption and production of heat.
ii. T3 Hormone
Tri lodo thyroxine performs the same function as that of thyroxine or Tetra lodo Thyroxine.
iii. Calcitonin
There are two conditions of abnormalities of Thyroid Gland.
i. Hyperthyroidism
ii. Hypothyroidism
i. Hyperthyroidism
The state of deficiency of T4 and T3 hormones is called Hypothyroidism.
It causes following diseases
i. Myxedema
ii. Goiter
iii. Cretinism
i. Myxedema
It occurs in adult stage.
Causes
It occurs due to the deficiency of T3 and T4 Hormones
Symptoms
Causes
It occurs due to deficiency of iodine in diet which results in decreased level of thyroxin hormones (T3 and T4).
Symptoms
Thyroid gland works more than normal to produce more thyroxine. As a result of which they become swollen and enlarged.
iii. Cretinism
It is disease of childhood.
Causes
It occurs due to deficiency of thyroxin hormone in early age, such persons are called cretinism and the mechanism is known as cretinism.
Symptoms
Location
Parathyroid glands are present in the neck regiort with two parts of thyroid gland.
Size
Their size is like pea seeds.
Secretion
Parathyroid gland secrete only one hormone called Parathyroid Hormone (PTM).
Function
Abnormalities in parathyroid gland usually produces two diseases.
i. Tetany
ii. Rickets
i. Tetany
Deficiency causes a drop in blood Ca++ which in turn leads to muscular tetancy.
ii. Rickets
Over production would lead to a progressive demineralization of the bones similar to tickets, as well as to the formation of massive kidney stones.
5. Pancreas
Pancreas is a gland which acts as both exocrine and endocrine gland.
Location
ii. Beta Cells
i. Alpha Cells (α-cells)
Alpha cells secreat hormone called Glucagon.
ii. Beta Cells (β-cells)
Beta cells secreat hormone called Insulin.
Glucagon
ii. It also stimulates both lipid and protein synthesis which reduces glucose level.
iii. Insulin inhibits the hydrolysis of glycogen in the liver and muscles.
Disorders of Insulin Deficiency
Due to deficiency of insulin, a diseased appeared called Diabetes mellitus.
Diabetes Mellitus
When there is deficiency of insulin, the amount of sugar is increased in blood, it is called Diabetes Mellitus.
Symptoms
There are two types of Diabetes Mellitus.
i. Insulin Dependent Diabetes
ii. Insulin Independent Diabetes
6. Adrenal Gland
Location
A pair of adrenal gland is present, one on the top of each kidney.
Structure
Each adrenal gland has two distinct parts
1. Adrenal Cortex
2. Adrenal Medulla
1. Adrenal Cortex
The outer layer of adrenal gland is called Adrenal Cortex. It is controlled by the adrenocorticotropic hormone (ACTH) secreted from Pituitary Gland.
Secretions
Adrenal cortex produces many hormones which are collectively called as Corticosteriods.
Functions
2. Aldosterone
3. Androgen
1. Cortisol
Over secretion of cortisol causes a disease called Cushing’s Syndrome.
Cushing’s Syndrome
Symptoms
It is due to defect in auto immune system.
Symptoms
This hormone helps in the reabsorption of Na++ and Cl- ions by the help of kidney.
It raises the blood pressure and blood volume.
Androgen
It causes development of the secondary male characteristics, such as hairs on face, depending of voice and increase in muscle size. It is like a testosterone.
When their amount in female in increased, hairs are produced on the face of female.
2. Adrenal Cortex
The inner layer of adrenal gland is called Adrenal Medulla.
Adrenal medulla works under the influence of sympathetic nervous system.
Secretions
Adrenal Medulla produces many hormones which are collectively called as Emergency Hormones. Both are secreted in stress situation.
The important emergency hormones are
i. Adrenaline OR Epinephrine
ii. Nor-Adrenaline OR Nor-Epinephrine
i. Adrenaline OR Epinephrin
Location
It is present in the upper region of thorax, behind the breast bone. It consists of two parts which are attached together in the front region of trachea.
Structure
It secret hormone called Thymosine.
Function
Thymosine controls the production of Thymphocytes and also their differentiation. These are the cells of immune system and control the infection of virus bacteria.
8. Pineal Gland
Location
Pineal gland is a tiny gland present at the upper side of diencephalons in the brain.
Secretion
Pineal gland secretes a hormone called Melatonin.
Functions
The testes and ovaries also functions as endocrine glands and produce sex hormone chemically sex hormones are steroids. Secretion of gonadial hormones is controlled by gonadotropic hormones pituitary gland.
i. Testes
Testes are the male reproductive organs.
Secretion
Testes produced male sex hormone called Testosterone.
Functions
Tests is responsible of sexual maturity and development of secondary sexual characts such as appearance of beard and moustache in males.
It also stimulates the growth of bones and muscles.
ii. Ovaries
Ovaries are female reproductive organs but they acts as endocrine glands.
Secretion
Ovaries secrete two hormones called as
i. Oestrogen
ii. Progesterone
i. Oestrogen
Oestrogen causes development of female secondary sexual characters.
It also helps in thickening of the wall of uterus and prepare it for implantation of fertilized ovum.
ii. Progesterone
It is concerned with maintenance of pregnancy by preventing the contraction of walls of uterus.
Certain chemical produced by plants have profound effect on their subsequent growth and development. Such chemicals are called Plant Hormones or Phytohormone.
Phytohormone are synthesized by plants in minute concentration and exert their effect by activating gene expression or inhibiting enzyme or changing properties of membrane.
Types of Phytohormone
There are five kind of plant hormones
1. Auxins
2. Gibberellins
3. Cytokinins
4. Abscisic Acid
5. Ethene
1. Auxins
Discovery
the first auxin was discovered by Fret Went in 1926.
Chemical Nature
Indol Acetic Acid (I.A.A)
Indol Acetic Acid (I.B.A)
Nephthalene Acetic Acid (N.A.A)
Site of Synthesis
It is synthesize at the apices of stem and foot, young leaves and young embryo.
Role of Auxin
i. Cell division and cell enlargement
It stimulate teh cell division and cell enlargement and plant in increase the length of plant.
ii. Initiation of Root
Auxins also initiates development of adventitious roots when applied at the cut base of stem.
iii. Abscission
In mature leaves and fruits when auxin production diminishes, a layer of thin walled cells is formed at the base of petiole and stake of fruit. This layer is called Abscission layer and causes fall of leaves and fruit with slight jerk.
iv. Growth of Fruit
Auxins produced in young embryo promotes the growth of fruit.
v. Parthenocarpy
Use of auxin helps in producing parthenocarpic or seedless fruits.
vi. Apical Dominance
Besides growth promoting function on Auxin, also has inhibitory effect on growth. Growth of apical bud inhibits growth of lateral buds beneath the stem. This phenomenon is termed as apical dominance removal of apical buds initiates growth of lateral buds with more leaves and axillary bud.
vii. Weedicide
Auxins are selective weed killer 2-4 dichlorophenoxy acetic acid (-2-4-D) is used to kill weeds in lawn’s and cereal crops.
2. Gibberellins
Discovery
Gibberellins was discovered by T.Yabuta and I.Hayashu in a fungus called Gibberellins funjikuroi. This fungus causes foolish seedling (Bakanae) disease in rice. In this disease the infected rice seedling elongated and ultimately fallover without producing grains.
Chemical Nature
The chemical nature of Gibberellins is Gibberellins acid 70 types of gibberellins have been discovered.
Role of Gibberellins
i. Cell division and cell enlargement
Like auxins Gibberellin also promotes cell division and elongation.
ii. Control of Dwarfism
Gibberellins can control genetic and physiological dwartism plants.
iii. Seed Germination
They promote the synthesis of a-amylase enzyme is dorman seeds due to the production of this enzyme, the seed starts germination.
iv. Parthenocarpy
These hormones help in the formation of seedless fruit which are called Parthenocarpic fruits.
v. Increase of Crop Yield
The crop yield of sugar can can be increased by the application of gibberellin about 50 tons/ acre.
vi. Formation of Flower and Growth of Pollen Tube
They stimulate flowering and the growth of pollen tubes during fertilization
3. Cytokinins
Discovery
Cytokinins are discovered by Miller in coconut milk.
Chemical Nature
Chemically there are two types of cytokinins.
Kinetin It is found in coconut milk etc.
Zeatin It is found in maize.
Role of Cytokinins
i. Cell Division
They initiate rapid cell division only in the presence of auxin.
ii. Delay in Senescence
They also caused delayed senescence (old age).
iii. Breaking of Seed Dormancy
They break seed dormancy and promote fruit development some species.
4. Abscisic Acid (A.B.A)
In contrast to growth promoting hormones, abscisic acid is growth inhibitor, produced by plants during adverse environment conditions such as drought conditions.
Role of Abscisic Acid
- It increases dormancy in buds and seeds.
- It causes stomata to close.
- It turn leaf primordia into scale.
It is a gas which also acts as a growth inhibitor.
Role of Ethene
- It triggers ripening of fruits.
- It contributes in leaf abscission and also breaks the dormancy of seeds and buds.
- It also initiates flowering in plants e.g. pineapple.
Changes in environmental conditions are the big threats for living organisms especially for plants. These factors which change the normal condition of light, CO2, nutrients, temperature etc. causes severe stresses on plants. The common environmental stresses for plants are
1. Water Shortage (Drought condition)
2. Less Oxygen Supply
3. High Concentration of Salt in the Soil
4. High Temperature
5. Low / Cold Temperature
6. Herbivory / Over Grazzing
1. Water Shortage
- In dry condition, the guard cells of leaf become flaccid to close the stomata.
- In this way the transpiration is stopped.
- The dry condition also stimulates increased synthesis and release of abscisic acid.
- This hormone help in keeping stomata close.
- These plants produce deeper root system.
- Those plants which grow in wet habitat or marshes, they develop aerial roots to absorb oxygen.
- Some plants developed air tubes that provide oxygen to submerged roots.
- The plants especially halophytes, have salt glands in their leaves where desalination occurs.
In plants there are two methods to tolerate the heat stress.
- Transpiration has a cooling effect on the plant body. By this method the effects of heat are reduced.
- Above 40oC plants cell start synthesizing relatively large quantities of special protein called heat shock proteins.
- Plants respond to cold stress by altering the lipid composition, changes in solute composition is altered also by producing different polymers of pentose (Fructose) which allow the crystals to super cool without compound formation.
- Plants overcome excessive herbivory by developing horns and production of distasteful or toxic compounds.
Diseases of plants may arise from infections by viruses, bacteria or fungi and other pathogens in most cases. Against these diseases the plants produce immune system in their body.
First Line Efence
The outer layer epidermis is a protective covering around the body of plant. This is the First Line Defence.
Second Line Defence
When pathogens enter the body through stomata or any other way, then plants produce certain chemicals to kill them. This is called Second Line Defence.
Phytoalexins
In infected plants an antibiotic phytoalexins is produced which is effective to all micro-organisms.
Biological Clocks
Definition
A control system is found in all living organisms which controls physiological and metabolic and metabolic functions according to time is called Biological Clock.
Biological Rhythms OR Biorhythms
Definition
In living things the behavior activities occur at regular intervals which are called biological rhythms OR biorhythms.
Circadian Rhythms
Definition
[Circa => about; dies => day]
Biorhythms may occur, showing periodicity of about 24-Hours. These are called Circadian Rhythm, which means about one day, so they are also called diurnal rhythms.
Causes of Biorhythm
Biorhythms occurs due to the following reasons.
1. Exogenous Stimuli
2. Endogenous Stimuli
1. Exogenous Stimuli
There may be direct response to various changes in the external (exogenous) stimuli.
2. Endogenous Stimuli
These rhythms can be controlled internally by an efficient time measuring system and are independent of light and temperature effects. These types of rhythms are called endogenous.
Co – Ordination
Definition
The working together of all parts of the body or system is called Co-ordination.
Types of Co-Ordination
There are two types of Co-ordination.
1. Nervous Co-Ordination
2. Chemical Co-Ordination
1. Nervous Co-Ordination
Definition
Co-Ordination brought about by the nervous system. It is quickest way of communication take place by electro-chemical messages called Nerve Impulse within the body of all animals is called Nervous Co-Ordination.
Elements of Nervous System
The elements o nervous system which help in co-ordination are
i. Receptor
ii. Central Nervous System (CNS)
iii. Effector
i. Receptor
The sensory tissues or organs which receive any change in their external as well as internal environment (stimuli) are called Receptors.
ii. Central Nervous System
The receptors convey the stimuli to the control centre, the nervous system (Central Nervous System) through sensory nerves.
iii. Effector
The central nervous system (CNS) analyses stimuli and sends an appropriate command, through it motor nerves to either endocrine organ to release hormones into the blood or to muscles called Effectors.
Pathway in Nervous System
There are two types of pathway in the nervous system.
i. Afferent Nerve Pathway
ii. Efferent Nerve Pathway
i. Afferent Nerve Pathway
From receptor the messages are carried to the Central Nervous System i.e. brain and spinal cord, this pathway is called Afferent Nerve Pathway.
ii. Efferent Nerve Pathway
From central nervous system the messages are transferred to the effector. This pathway is called Efferent Nerve Pathway.
Nervous Tissues
There are two types of nervous tissues
1. Neurons
2. Neuroglia OR Glial Cells
1. Neurons
Definition
The nervous system consist of special cells which can generate and conduct electric current are called Neurons.
OR
The chief structural and functional unit of nervous system is called Neurons.
Structure of Neurons
Neurons are different from each other according to size and shape but the structure of neuron consists of three parts.
i. Some or Cell Body
ii. Dendrites
iii. Axon
i. Soma OR Cell Body
Each neuron has a cell body or soma containing nucleus and various organelle embedded in the cytoplasm. Nissl’s granules which are group of ribosomes, associated with rough E.R. and Golgi apparatus are present in the cell body.
Functions
The cell body or soma is the main nutritional part of the cell necessary for growth of neuron.
Soma receive message to dendrites and convey it to axon.
ii. Dendrites
From the soma, a large number of small threads like terminal branches are arises are called Dendrites.
Functions
Dendrites receive stimuli and convey it to the soma.
iii. Axon
The unbranched, single elongated cytoplasm process which usually arises opposite to dendrites called Axon.
Axon Hillock
Axon originates from a pyramid like area of soma called Axon-Hillock.
Axon Terminal
At the terminal end of axon many fine branches are present called Axon Terminals.
Myelin Sheath
The axon of some neurons is enclosed by a layer of fatty substance known as Myelin Sheath.
This serve as insulating layer.
Functions
Axon is specialized for conducting impulses to other neurons.
Types of Neurons
According to the function, neurons are of the three types.
i. Sensory Neuron
ii. Motor Neuron
iii. Inter Neuron
i. Sensory Neuron
The neurons which transmit impulses from receptor to the central nervous system is called Sensory Neuron or Receptor Neurons.
ii. Motor Neuron
The neurons which transmit instructions of the central Nervous System to the effector are called Motor Neurons or Effector Neurons.
iii. Inter Neurons
The neurons present between sensory and motor neurons are called Inter Neurons. They are found in Central Nervous System.
Functions of Neurons
Neurons is the functional unit of nervous system which receives stimuli, transfers them to the Central Nervous System (CNS).
It transfers the messages from CNS to the body parts effector.
Reflex Action
Definition
The automatic involuntary responses which occur either due to internal or external stimuli are called Reflex Action.
OR
An immediate response to a specific stimulus without conscious control is called a Reflex Action.
Parts of Reflex Action
Reflex action consists of
i. Receptor: (Skin) receive stimuli.
ii. Sensory Neuron: It carries message from receptor to the Central Nervous System (CNS).
iii. Motor Neuron: It carries message from Central Nervous System (CNS) to the effector.
iv. Effector: (Muscle of gland) which perform action.
Reflex Arc
Definition
The pathway of passage in impulse during a reflex action is called Reflex Arc.
Reflexes may be monosynaptic or polysynaptic.
Monosynaptic
The reflex action in which only one synapse is involved is called Monosynaptic.
Example: Knee Jerk
Polysynaptic
The reflex action in which many synapses are involve due to presence of inter neurons between sensory and motor neurons is called Polysynaptic.
Example: Hand withdrawal on the painful stimuli.
Examples of Reflex Actions
- If our hand touch any hot object, it is quickly withdrawn.
- Secretion of juices from the gland.
- Blinking of eyes.
- Contraction and expansion of lungs.
- If a strong light is flashed across the eye, the eyelids are at once closed or start blinking.
Definition
The electrochemical signals developed by a neuron for communication is called Nerve Impulse.
Method of Development of Nerve Impulse
The neurons develop impulse in the following way.
1. Resting Membrane Potential (RMP)
2. Action Potential
3. Propagation of Impulse
4. Synapse
Resting Membrane Potential
Definition
A typical neuron at rest is more positive electrically outside than inside the cell membrane. This net difference in charge between the inner and outer surface of a non conducting neuron is -65mv is called the Resting Membrane Potential.
Factors Involved in Resting Membrane Potential
This popularity is due to the unequal distribution of ions across the neurolemma. The major factors which are involved in resting membrane potential are
Sodium and Potassium Ions
- There is a greater concentration of sodium ions outside than inside the membrane.
- Similarly potassium ions are concentrated muscle inside than outside the membrane.
- This is attributed to the activity of ATP driven sodium potassium pump in the neurolemma.
Definition
When neuron is stimulated reversal of the polarity of the neurolemma occurs, first changes to +40mv and then restores to -65mv again is called Action Potential.
This action potential is extremely rapid as it occurs in a few milliseconds.
Factors Involved in Action Potential
Sodium and Potassium Ions
- The change in potential across the membrane is due to the presence to sodium and potassium channels in the neurolemma.
Sequence of membrane potential changes associated with an Action Potential.
- Resting Potential
- Sodium gates open and Na+ diffuses into the cell causing a depolarization of the membrane from negative to zero and then proceeds upto +40mv.
- Sodium gates close and potassium gates open.
- K+ diffuses out, causing a repolarization of the membrane.
- Sodium potassium pump restores original ion gradients and resting potential.
Definition
When the action potential develops and spreads along the entire length of neurolemma, it is called propagation of nerve.
Synapse
Definition
The region where the impulse moves from one neuron to another is called a Synapse.
Components of Synapse
It consists of three components
1. Pre Synapting Membrane
2. Synaptic Cleft
3. Post Synaptic Membrane
1. Pre Synaptic Membrane
The membrane of axon terminal is called Pre Synaptic Membrane.
2. Synaptic Cleft
The narrow space between neurons is called Synaptic Cleft.
3. Post Synaptic Membrane
The membrane of dendrites of another neuron is called Post Synaptic Membrane.
Motor End Plate
When it is the membrane of muscle cell it is called motor end plate.
Neurotransmitter
The chemicals present in the vesicles which are released at the axon ending of the neurons, at synapse are called Neurotransmitter.
Mechanism of Impulse Through Synapse
- When an impulse is reached at axon terminals, the calcium channels are opened.
- From synaptic cleft calcium ions are diffused into the calcium channels.
- Due to this synaptic vesicles fuse with the pre-synaptic membrane, causing the release of neurotransmitter molecules into the synaptic cleft.
- The neurotransmitter bind to the receptors on the post-synaptic membrane, which generate action potential in the post-synaptic cell.
- The neurotransmitters are then reabsorbed by the pre-synaptic cells for reuse.
Many different types of neurotransmitter are known. These are acetylcholine, norepinephrine, glycine, gab a, serotonin, dopamine etc.
Evolution of Nervous System
In different group of animals two types of nervous systems can be recognized, which are
1. Diffused Nervous System
2. Centralized Nervous System
1. Diffused Nervous System
Diffused Nervous System is found in cnidarians and Echinoderms.
Nervous System of Hydra
- In these animals, no anterior and posterior ends is present and their body is radially symmetrical.
- The nerves cells are found in the form of network throughout the body.
- The flow of information is not highly directional and it diffuses in all directions.
- The transmission of impulses is slow because of synapses involved.
- There is no brain but the nerve cells constitute the nervous system.
Centralized Nervous System found to varying degrees in more complex organisms from platyhelminthes to chordates including humans.
Nervous System of Planaria
- In these animals, definite anterior and posterior ends is present and their body is bilaterally symmetrical animals.
- It consists of an anterior brains (a concentration of neurons) which is connected with the Sensory Organs.
- From the brain arise two cord like nerves running longitudinally through the body.
- The two nerve cords are connected with each other at several points through the transverse nerves.
- They co-ordinated the movement of the two lateral sides of the body.
The nervous system of man is the most advanced, highly developed. It controls all functions of the body. It consists of two parts
1. Central Nervous System (CNS)
2. Peripheral Nervous System (PNS)
1. Central Nervous System (CNS)
Definition
The nervous system consists of brain and spinal cord (hollow nerve cord) and also consists of upto 100 billion inter neurons is called Central Nervous System (CNS).
Components of Central Nervous System
The central nervous system consists of
Brain
Spinal Cord
Protection of Central Nervous System
Brain and spinal cord both are protected in three ways
i. Cranium
ii. The Vertebral Column
iii. Meninges
iv. Cerebrospinal Fluid (CSF)
i. Cranium
Cranium, which is part of skill, protects the brain.
ii. Vertebral Column
Neural arches of vertebrate of vertebral column protect the spinal cord.
iii. Meninges
Beneath the cranium, the brain and spinal cord are protected by triple layers of tough connective tissues called meninges.
iv. Cerebrospinal Fluid (CSF)
Between the layers of meninges, there is a plasma like fluid which bathes the neurons of brain and spinal cord is called Cerebrospinal Fluid (CSF).
It cushions against the bumps and jolts.
2. Peripheral Nervous System (PNS)
Definition
The nerves arises from brain and spinal cord that are spread in various part of body which transmits the signals between CNS and body parts make a nervous system called Peripheral Nervous System.
The peripheral nervous system consists of two types of nerves.
i. Cranial Nerves
ii. Spinal Nerves
i. Cranial Nerves
In humans, there are 12 pairs of nerves which arise from the brain or lead to the brain these nerves are called cerebral or cranial nerves.
ii. Spinal Nerves
In humans, there are 31 pairs of nerves which arise from the spinal cord or lead to the spinal cord are called spinal nerves.
Types of Peripheral Nervous System
The peripheral nervous system is divided into two types according to their functions.
1. Somatic Nervous System
2. Autonomic Nervous System
1. Somatic Nervous System
The peripheral nervous system which controls all the voluntary activities of the body such as contraction of skeletal muscles and movement of joint is called Somatic Nervous System.
2. Autonomic Nervous System
The autonomic nervous system which controls involuntary activities of the body such as smooth muscles, glands, muscles of heart and other internal organs is called Autonomic Nervous System.
Types of Autonomic Nervous System
Autonomic nervous system divided into two types
i. Para Sympathetic Nervous System
ii. Sympathetic Nervous System
i. Para Sympathetic Nervous System
The autonomic nervous system formed by some cranial nerves, vagus nerves and the spinal nerves that are arising from the sacral vertabrate are called Para Sympathetic Nervous System.
ii. Sympathetic Nervous System
The autonomic nervous system whose nerves arise from the thoracic and lumber regions of spinal nerves is called Sympathetic Nervous System.
Functions
This system is important during emergency situation and is associated with “flight or fight”. It increases the heart beat, breathing rate, slows digestion, dilates pupil etc.
Brain
Definition
The most important part of Central Nervous System develops from dorsal, hollow nerve cord well protected in the cranium of skull and composed of inter neurons and is the seat of our intelligence, learning and memory is called Brain.
Part of Brain
The brain consists of three parts
1. Fore Brain
2. Mid Brain
3. Hind Brain
1. Fore Brain
Fore brain can be divided into two regions
i. Telencephalon
ii. Diencephalon
i. Telencephalon
The largest part of fore-brain which is differentiated into two cerebral hemisphere or cerebrum is called Telencephalon.
Cerebrum
Cerebrum is the largest part of the brain and is divided into two halves called Cerebral Hemisphes.
Cerebral Hemisphere
Each hemisphere consist of an outer grey matter or cerebral cortex and an inner white matter.
Cerebral Cortex
- Cerebral cortex is the largest and the most complex part of human brain.
- It is highly convulated to occupy the greater number of inter neurons.
The two cerebral hemisphere communicate with each other by means of large band of axons called Corpus Callosum.
Part of Cerebrum
Functionally, the cerebrum is differentiated into four lobes.
- Anterior Frontal Lobe
- Lower Central Temporal Lobe Parietal Lobe
- Dorsal Occipital Lobe
- Cerebrum is concerned with intelligence memory, learning, resoning and overall control of all voluntary actions.
- It involved in all conscious activities.
- It co-ordinated different senses together.
The diencephalons consists of two parts
i. Thalamus
ii. Limbic System
i. Thalamus
The clearing house for sensory impulses is called Thalamus.
Functions
- It receives them from different parts of brain and relays them to the appropriate part of the motor cortex.
- It also involves in the perception of pleasure and pain.
The limbic system is located in an are between the thalamus and cerebrum.
Parts of Limbic System
The limbic system consists of
i. Hypothalamus
ii. Amygdala
iii. Hippocampus
i. Hypothalamus
Hypothalamus is the part of limbic system which is called Thermostal of the body.
Functions
- The hypothalamus is important in regulation of homeostasis.
- It regulates pituitary gland.
- It also regulate body temperature, blood pressure, hunger, thirst, aggression, pleasure and pain.
The amygdala produces sensation of pleasure, punishment or sexual arousal stimulation.
It also involve in the feelings of fear.
iii. Hippoc Ampus
Hippocampus is involved in long term memory.
Mid Brain
In mammals mid brain is relatively very small. It consists of the optic lobes which are represented by four small bodies.
Functions
It receives sensory information like vision, odour etc. It receives sensory information from spinal cord and sends them to the fore brain.
Hind Brain
Hind brain consists of
1. Medulla Oblongata
2. Cerebellum
3. Pons
4. Reticular Formation
1. Medulla Oblongata
Medulla oblongata lies on the top of spinal cord.
Function
It controls involuntary actions like blood pressure, heart beat, sneezing, coughing, breathing rate, hicupping, swallowing etc.
2. Cerebellum
The cerebellum lies dorsally behind the optic lobes. It is highly convoluted. It is large in mammals than other animal.
Functions
- The cerebellum plays an important part in controlling muscular co-ordination.
- It specially maintains balance and also position of the body in space.
Pons regulates activities like muscular co-ordination, facial expressions, breathing and sleeping.
4. Reticular Formation
Reticular formation lies in pons, medulla and mid brain.
Functions
It monitors the messages to the brain which should be ignored or should be realized.
Brain Stem
The oldest tissues formed by the combination of medulla oblongata, pons and mid brain is called as Brain Stem.
Functions
It involved in the control of sleep and wakening.
Spiral Cord
Definition
A thick whitish nerve cord that lies below the medulla oblongata and extends down through the neural canal of vertebrate upto the hips is called Spinal Cord.
Cross Section of Spinal Cord
In cross section, the spinal cord is differentiated into two areas.
White Matter
Gray Matter
Unlike brain, spinal cord has grey matter inside surrounded by white matter on the outside. They grey matter has the shape of an “H”. The first synapse of each sensory neuron is located in the grey matter.
Central Canal
The narrow central containing cerebrospinal fluid runs through the middle of the spinal cord. This fluid brings nutrients to the spinal cord.
Spinal Nerves
The nerve arises from spinal cord is called Spinal Nerves.
Each spinal nerve divides into two roots just before it joins spinal cord.
1. Dorsal Root
2. Ventral Root
1. Dorsal Root
The dorsal root joints the dorsal part of the spinal cord and it contains axons of sensory neurons.
Dorsal Root Ganglion
The cell bodies of these neurons aggregate in a small swelling known as the dorsal root ganglion.
2. Ventral Root
The ventral root which is attached to the ventral part of the spinal cord carrying axons of motors neurons, arised from the spinal cord.
Functions of Spinal Cord
Spinal cord serves as an express way for signals between autonomic nervous system.
It is also the control centre for many reflexes.
Receptors
Definition
The single or group of either modified neurons or epithelial cells which receive stimuli either from external environments and relaying them in the form of impulses to the CNS are called Receptors.
Receptionists
The receptors are acts as receptionist of nervous system because they receive any kind of change, which is then transferred to the brain and spinal cord.
Sensation
Receptor converts stimuli into nerve impulses, this stage awareness of stimulus is called Sensation.
Perception
In the control centre of the nervous system, the impulses are converted into perception.
Types of Receptors
Receptors are classified according to type of stimulus which they can detect and give response. Following are some types of receptor.
1. Thermoreceptor
The receptors which detect and respond to temperature fluctuations (heat and cold) are called Thermoreceptor.
2. Chemoreceptor
The receptors which can detect and respond to presence of certain chemicals in their surrounding are called Chemoreceptor.
3. Mechanoreceptor
The receptors which can detect the stimuli of sound, motion, touch, pressure gravity and movement are called Mechanoreceptor.
4. Photoreceptor
The receptors which respond to the stimulus of light and ultraviolet rays are called Photoreceptor.
5. Pain Receptor
The receptors which produced sensation of pain or damage tissues are called the Pain Receptor.
Working of Sensory Receptors in Skin
In human, the receptors in skin are concerned with at least five different senses i.e., touch, pressure, cold, warm and pain.
Types of Sensory Receptor in Skin
There are two types of sensory receptors in the skin.
i. Free Nerve Ending Receptors
ii. Encapsulated Receptors
i. Free Nerve Ending Receptors
The simplest types of receptor which contain free end without any protective capsule and are located just beneath the epidermis are called Free Nerve Ending Receptors.
Functions
Free nerve ending receptors adapt very slowly to stimulation.
Types
They are of different types
a. Mechanoreceptors Receive touch and pressure.
b. Nociceptors Feel pain
c. Thermoreceptors Feel change in temperature
ii. Encapsulated Receptors
The type of receptor contain a protective capsule of connective tissues at their ends and lie in skin are called Encapsulated Receptors.
Types
Encapsulated receptor are of following two types
i. Meissner’s Corpuscles
ii. Pacinian Corpuscles
i. Meissner’s Corpuscles
The encapsulated receptors that are found in those parts which do not have hairs such as finger tips, eyelids, lips palms, soles, nipples etc are called Meissner’s Corpuscles.
Structure of Capsule
Their capsules consists of thick collagen fibers with spiral and highly coiled nerve endings.
Function
There are touch receptors means very sensitive to touch.
ii. Pacinian Corpuscles
The encapsulated receptors which are found in dermis layer and also in some internal organs and moveable joints are called Pacinian Corpuscles.
Structure
Their nerve endings are surrounded by an onion like capsule made of concentric layers of membrane. Between the membranes fluid filled spaces are present.
Functions
They are pressure receptor and detect rapid and deep pressure changes produced by vibration and touch.
Sensory Receptors with Reference to Arteries
The aortic arch and the carotid artery contain many receptor which are
Mechanoreceptor
They detect the pressure changes in arteries.
Baroreceptor
They detect the pulse pressure
Function
These receptors transfer these changes to the medulla oblongata which controls blood pressure.
Aortic Body and Carotid Body
The aortic arch and the carotid sinus also contain chemoreceptor called Aortic body and carotid body.
Function
They are sensitive to CO2 concentration and hydrogen ion concentration of the blood.
Effects of Drugs on Co-Ordination
Drugs
A chemical substance that causes the specific physiological response in the body are called drugs.
Importance
- Many drugs are useful medically to treat emotional stress or certain illness.
- Drugs which people take to alter the mood or emotional state affect body functional interfering with the working of neurotransmitters.
- Therefore their abuse often causes harmful effects.
- It is a drug found in tobacco.
- It acts as a stimulant and is widely used as a neurological agent.
- Nicotine affects post synaptic membrane in CNS and PNS.
- It minimize the action of acetylcholine on nicotine receptors. So it is stimulant to nerve impulse.
- It increase the heart beat, rate, blood pressure and digestive tract mobility.
- Nicotine may induce vomiting and diarrhea.
- It may cause water retention relation by kidneys.
- It stimulate the nervous system thereby reducing fatigue, increasing, alertness and improving the concentration.
The abnormalities appear in brain, spinal cord, central nervous system and peripheral nervous system causes diseases called Nervous Disorders.
Some common disorders of nervous system are as follows
1. Parkinson’s Disease
2. Alzheimer’s Disease
3. Epilepsy
1. Parkinson’s Disease
It is a brain disorder.
Causes
It either caused by degeneration or damage of nerve tissues within the basal ganglia of the brain.
Symptoms
It is characterized by involuntary tremors, diminishing motor power and rigidity. It causes stiffness, weakness and trembling of the muscles. The mental faculties are not affected.
Treatment
Leopoda is the effective medicine which is helpful in minimizing the symptoms by can not halt the degeneration of neurons of brain.
2. Alzheimer’s Disease
It is the progressive degeneration of neurons of brain, especially cortex and hippocampus.
Causes
There is a genetic pre-disposition to the disease in some people, so it tends to run in families.
Stages of Diseases
The disease progresses in three broad stages.
First Stage
At first, the patient notices his forgetfulness.
Second Stage
In second phase, there is a severe loss of memory particularly for recent events. Anxiety increases with sudden changes in mood.
Third Stage
In the third and last stage the disease become severe. He losses memory, hears voices or see faces in the absence of any person. This disease is called Hallucination. He does not share his ideas and does not accept ideas of other persons, such disease is called paranoid delusions.
Symptoms
The main symptom of the disease is the loss of memory called dementia.
Treatment
- Effective medicines should be used.
- Psychological treatment is better to control the disease.
- Personal care of patient is necessary otherwise he may get any harm.
Definition
The co-ordination brought about by the endocrine gland system. It is not very rapid, but shows slow and prolonged effect takes place by chemical substances called hormones and neurotransmitter within the body of all animals is called Chemical Co-ordination.
Endocrine glands secreat their secretions (hormones) directly into the blood stream. They are transported by the blood to the target cells.
Types of Hormones
Chemically the hormones are organic compounds which are classified into three types.
1. Peptide Hormones
2. Modified Amino Acids Hormones
3. Steroid Hormones
1. Peptide Hormones
The hormones which are composed of protein are called Peptide Hormone. There are two types of peptide hormones.
i. Small Chain Amino Acids
ii. Large Chain Amino Acids
i. Small Chain Amino Acids
The peptide hormones consists of small chain of amino acids are called Small Chain Amino Acids.
Examples
Glucagon
Antidiuretic Hormone (ADH)
Oxytocin
ii. Large Chain Amino Acids
The peptide hormones consists of long chain of amino acids are called Large Chain Amino Acids.
Example
Insulin
Preleclin
2. Modified Amino Acid Hormones
The hormones consists of modified amino acids are called Modified Amino Acid Hormones.
Example
Thyroxine
Epinephrine
Nor-epinephrine
3. Steroid Hormones
The hormones which are composed of lipid are called Steroid Hormones.
Example
Estrogen
Progesterone
Testosterone
Aldisterone
Hormone Action
To explain the action of hormones two models have been proposed.
1. First Model
2. Second Model
Similarity Between Both Models
Both model agree that the plasm membrane of cells contain certain receptors to accept the hormones.
Dissimilarity Between Both Models
After receiving the hormones continue their way of action called signal transduction pathway. It is different in both models.
1. First Model
According to the first model peptide hormones are involved. The receptor molecule is attached to an enzyme adenylate cyclase in the inner part of plasma membrane. The hormone is attached to the receptor. By the activity of enzyme ATP molecule is changed into cyclic adenosine monophosphate (AMP) in the cytoplasm. The cyclic (AMP) acts as a second messenger and activates the particular enzyme which actually helps in the function. Some other messenger molecules also take part in the process.
2. Second Model
According to the second model, steroid hormones are involved. These hormones are fat soluble, so they enter the cell directly through the plasma membrane, so they do not need second messenger. In the cytoplasm they are attached to the particular receptors which transfer into the nucleus. In the nucleus. In the nucleus hormone receptor complex activities the genes due to which actual function is started.
Functions of Hormones
- They do not initiate new biochemical reactions but produce their effects by regulating the enzymatic and other chemical reactions, already present.
- They may either stimulate or inhibit a function.
- Hormones may also control some long term changes, such as rate of growth, rate of activity and sexual maturity.
Definition
Endo => Inside => Krinein => separate i.e. to secrete.
In the body of vertebrates there are certain dustless gland which poured their secretions (hormones) directly into the blood or in body fluids are called endocrine glands or ductless glands constitute a system called Endocrine System.
Endocrine Glands of Man
In the body of man and other mammals, following important endocrine glands are mostly found.
1. Hypothalamus
2. Pituitary Gland
3. Thyroid Gland
4. Parathyroid Gland
5. Pancreas
6. Adrenal Gland
7. Thymus Gland
8. Pineal Gland
9. Gonads
1. Hypothalamus
The part of forebrain which forms a connection between Nervous System and endocrine system is called Hypothalamus.
Hormones
The hypothalamus contains specialized nerve cells called neurosecretory cells which produced two types of hormones.
i. Releasing Hormone
ii. Inhibitory Hormone
i. Releasing Hormones
The hormones which are produced to increase the secretion of another glands are called Releasing Hormones.
Function
Releasing hormone control the secretion of hormones from pituitary gland.
ii. Inhibitory Hormones
The hormones which are produced to prevent the extra secretion of hormones are called Inhibitory Hormones.
Function
Hypothalamus produced two hormones which are
- Oxytocin
- Antidiuretic Hormones (ADH)
2. Pituitary Gland (Hypophysis)
Pituitary gland is called “master gland” because it controls the secretion of other endocrine glands.
Location
The pituitary gland is located in the brain. It is attached to the base of hypothalamus by short.
Size
The pituitary gland is small pea size gland.
Lobes of Pituitary Gland
Pituitary gland has three lobes
i. Anterior Lobe
ii. Median Lobe
iii. Posterior Lobe
i. Anterior Lobe
Anterior lobe produces three types of hormones which are
a. Tropic Hormone
b. Growth Hormone or STH
c. Prolactin
a. Tropic Hormone
The hormones which control the activity of other hormones are called Tropic Hormones.
Kinds of Tropic Hormone
The tropic hormone secreted by the pituitary gland are as follows
Thyroid Stimulating Hormone (TSH)
It control the working of thyroid gland including secretion of thyroxin.
Adreno-Cortico Tropic Hormone (ACTH)
In controls the activity of outer part of cortex of adrenal gland.
Follicle Stimulating Hormone (FSH)
FSH in females stimulate follicle developing and secretion of oestrogens from the ovaries.
In males it stimulates development of the germinal epithelium of the testis and sperm production.
Leutinizing Hormone (LH)
This hormone helps in the formation of sperms and testosterone hormone in male. In female it takes part in ovulation i.e. release of ovum from the ovary.
b. Growth Hormone OR Somatotropin Hormone (STH)
It regulates the normal growth by controlling many metabolic processes, such as protein synthesis, involved in growth of bones and soft tissue.
c. Prolactin Hormone
This hormone stimulate mammary glands and production of milk.
ii. Median Lobe
Median lobe produced one hormone called Melanocyte Stimulating Hormone (MSH).
Functions
This hormone controls darkening of skin in many vertebrates. In human, very small amount of MSH is produced by the anterior pituitary rather than median.
iii. Posterior Lobe
From posterior lobe of pituitary gland following hormones are secreted.
a. Antidiuretic Hormone (ADH)
b. Oxytocin
a. Antidiuretic Hormone (ADH)
It stimulates the re-absorption of water by tubules of kidney and thus decreases the amount of urine passed.
b. Oxytocin
It stimulates contraction of muscles of uterus during child birth and release of milk during breast feeding.
Abnormal Conditions Due to Pituitary Gland
Due to abnormal production of somato tropic hormone (STH) or growth hormone, following abnormalities occur.
i. Gigantism
ii. Dwarfism
iii. Acromegaly
i. Gigantism
It is disease of childhood.
Causes
It occurs due to over secretion of somatotropic hormones (STH) or growth hormone.
Symptoms
The affected individuals becomes abnormally tall.
ii. Dwarfism
It is a disease of childhood.
Causes
It caused due to less secretion of somato tropic hormone or growth hormone.
Symptoms
The affected individuals becomes abnormally short.
iii. Acromegaly
It is a disease of adulthood.
Causes
It occurs due to overproduction to somatotropic homrone (STH).
Symptoms
In this condition, hands, feet and jaw bones and cartilages and soft muscles become larger in size and swollen.
3. Thyroid Gland
Location
Thyroid gland is located in the neck region in front of trachea. It consists of two lobes, one on either side of trachea.
Shape
It is butterfly in shape.
Secretions
It secreats three main main hormones.
i. Thyroxine or T4 (Tetra lodo Thyroxine)
ii. T3 (Tri lodo Thyroxine)
iii. Calcitonin
i. Thyroxine OR T4
Thyroxin increases the metabolic rate and promotes both physical growth and mental development.
It increases the oxygen consumption and production of heat.
ii. T3 Hormone
Tri lodo thyroxine performs the same function as that of thyroxine or Tetra lodo Thyroxine.
iii. Calcitonin
- Calcitonin plays and important role in calcium homeostasis.
- Calcitonin is produced when calcium Ca++ level is increased in blood.
- It respond to decreased the blood calcium level by stimulating the deposition of excess calcium in bones.
There are two conditions of abnormalities of Thyroid Gland.
i. Hyperthyroidism
ii. Hypothyroidism
i. Hyperthyroidism
- The state of over secretion of hormones by thyroid gland is called Hyperthyroidism.
- Due to hyperthyroidism following symptoms usually appear.
- High blood pressure
- Increase body temperature
- Intolerance to heat
- Profuse sweating
- Loss in weight etc
The state of deficiency of T4 and T3 hormones is called Hypothyroidism.
It causes following diseases
i. Myxedema
ii. Goiter
iii. Cretinism
i. Myxedema
It occurs in adult stage.
Causes
It occurs due to the deficiency of T3 and T4 Hormones
Symptoms
- Myxedema produces following symptoms
- Overweight (Obesity)
- Loss of hairs
- Dry Skin
- Mental activity or body movement become slower
- Intolerance to cold
Causes
It occurs due to deficiency of iodine in diet which results in decreased level of thyroxin hormones (T3 and T4).
Symptoms
Thyroid gland works more than normal to produce more thyroxine. As a result of which they become swollen and enlarged.
iii. Cretinism
It is disease of childhood.
Causes
It occurs due to deficiency of thyroxin hormone in early age, such persons are called cretinism and the mechanism is known as cretinism.
Symptoms
- This disease shows following symptoms
- Mental retardation
- Stunted growth
- Physical weakness
- Abnormal facial features
Location
Parathyroid glands are present in the neck regiort with two parts of thyroid gland.
Size
Their size is like pea seeds.
Secretion
Parathyroid gland secrete only one hormone called Parathyroid Hormone (PTM).
Function
- Parathyroid hormone plays an important role in calcium’s homeostasis.
- Parathyroid hormone is produced when calcium Ca++ level is decreased in blood.
- It response to increased the calcium ion in blood in two ways.
- It increase the absorption of calcium ions in kidney.
- It induces the bone cells (Osteoblasts) to released calcium from bones into the blood. This process is called Demineralization.
Abnormalities in parathyroid gland usually produces two diseases.
i. Tetany
ii. Rickets
i. Tetany
Deficiency causes a drop in blood Ca++ which in turn leads to muscular tetancy.
ii. Rickets
Over production would lead to a progressive demineralization of the bones similar to tickets, as well as to the formation of massive kidney stones.
5. Pancreas
Pancreas is a gland which acts as both exocrine and endocrine gland.
Location
- Pancreas is located in abdominal cavity below the liver.
- Islets of Langerhans
- The cells of pancreas are called Islets of langerhans.
- They perform the function of endocrine gland.
- This is under control of the pituitary trophic hormones STH and ACTH and responds directly to the level of blood glucose which is normally 90ms/100mg.
- The islets of langerhans are of two distinct types.
ii. Beta Cells
i. Alpha Cells (α-cells)
Alpha cells secreat hormone called Glucagon.
ii. Beta Cells (β-cells)
Beta cells secreat hormone called Insulin.
Glucagon
- It is secreted in response to decrease sugar level in blood.
- It increase the blood glucose level mainly by promoting breakdown of glycogen to glucose in the liver and muscles.
- It also increase the rate of breakdown of fats.
- It is secreted in response to increase sugar level in blood.
- It decrease the blood glucose level mainly by following mechanism:
ii. It also stimulates both lipid and protein synthesis which reduces glucose level.
iii. Insulin inhibits the hydrolysis of glycogen in the liver and muscles.
Disorders of Insulin Deficiency
Due to deficiency of insulin, a diseased appeared called Diabetes mellitus.
Diabetes Mellitus
When there is deficiency of insulin, the amount of sugar is increased in blood, it is called Diabetes Mellitus.
Symptoms
- High level of blood sugar
- Sugar in the urine
- Disturbance of the body’s osmotic equilibrium
- Dehydration
- Derangement of the nervous system
There are two types of Diabetes Mellitus.
i. Insulin Dependent Diabetes
ii. Insulin Independent Diabetes
6. Adrenal Gland
Location
A pair of adrenal gland is present, one on the top of each kidney.
Structure
Each adrenal gland has two distinct parts
1. Adrenal Cortex
2. Adrenal Medulla
1. Adrenal Cortex
The outer layer of adrenal gland is called Adrenal Cortex. It is controlled by the adrenocorticotropic hormone (ACTH) secreted from Pituitary Gland.
Secretions
Adrenal cortex produces many hormones which are collectively called as Corticosteriods.
Functions
- These hormones are very important for regulating carbohydrates metabolism.
- They are also essential for maintaining mineral balance in the body.
- The important corticosteroid hormones are as follows.
2. Aldosterone
3. Androgen
1. Cortisol
- This hormone is produced at the time of fever and diseases.
- It converts protein of muscles into amino acids, which are changed into glucose by the activity of liver.
- In this way there is continue supply of energy in the body.
- It reduces pain and inflammation in the body.
Over secretion of cortisol causes a disease called Cushing’s Syndrome.
Cushing’s Syndrome
Symptoms
- Obesity
- Breakdown of Muscles
- Diabetes
- Deficiency of Cortisol
- Deficiency of cortisol causes a diseases called Addison’s Disease.
- Addison’s Disease
It is due to defect in auto immune system.
Symptoms
- Loss in weight
- Weakness
- Low level o sugar
- Low blood pressure
This hormone helps in the reabsorption of Na++ and Cl- ions by the help of kidney.
It raises the blood pressure and blood volume.
Androgen
It causes development of the secondary male characteristics, such as hairs on face, depending of voice and increase in muscle size. It is like a testosterone.
When their amount in female in increased, hairs are produced on the face of female.
2. Adrenal Cortex
The inner layer of adrenal gland is called Adrenal Medulla.
Adrenal medulla works under the influence of sympathetic nervous system.
Secretions
Adrenal Medulla produces many hormones which are collectively called as Emergency Hormones. Both are secreted in stress situation.
The important emergency hormones are
i. Adrenaline OR Epinephrine
ii. Nor-Adrenaline OR Nor-Epinephrine
i. Adrenaline OR Epinephrin
- It increase heart rate, amount of glucose in blood, rapid respiration and metabolism during emotions and emergency.
- It also takes part in the contraction of blood vessels in intestine and dilation of blood vessels in muscles.
- It also functions like epinephrine, but its main function is control of blood pressure during fight and flight.
- The over secretion of both these hormones causes high blood pressure.
Location
It is present in the upper region of thorax, behind the breast bone. It consists of two parts which are attached together in the front region of trachea.
Structure
It secret hormone called Thymosine.
Function
Thymosine controls the production of Thymphocytes and also their differentiation. These are the cells of immune system and control the infection of virus bacteria.
8. Pineal Gland
Location
Pineal gland is a tiny gland present at the upper side of diencephalons in the brain.
Secretion
Pineal gland secretes a hormone called Melatonin.
Functions
- Metatonin regulates the seasonal reproductive cycles.
- It also regulates the growth and development of gonad in many mammals.
- It controls the sensation of light and darkness of eyes.
- It produced a/c to the time of day, night or weather.
The testes and ovaries also functions as endocrine glands and produce sex hormone chemically sex hormones are steroids. Secretion of gonadial hormones is controlled by gonadotropic hormones pituitary gland.
i. Testes
Testes are the male reproductive organs.
Secretion
Testes produced male sex hormone called Testosterone.
Functions
Tests is responsible of sexual maturity and development of secondary sexual characts such as appearance of beard and moustache in males.
It also stimulates the growth of bones and muscles.
ii. Ovaries
Ovaries are female reproductive organs but they acts as endocrine glands.
Secretion
Ovaries secrete two hormones called as
i. Oestrogen
ii. Progesterone
i. Oestrogen
Oestrogen causes development of female secondary sexual characters.
It also helps in thickening of the wall of uterus and prepare it for implantation of fertilized ovum.
ii. Progesterone
It is concerned with maintenance of pregnancy by preventing the contraction of walls of uterus.
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