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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