Endocrine system
Endocrine system is the system of chemical coordination with the help of hormones which is secreted by endocrine glands present in different parts of the body. The gland is of two types.
(1) Exocrine gland
It is also called ducted glands. These types of glands secretes their secretions outside the body or into the digestive cavity through a duct called Exocrine glands e.g Sweat glands. Mammary gland etc.
(2) Endocrine glands
Those types of glands which secrete their secretions directly into the blood stream without a duct called endocrine glands. It is also called ductless gland because it has no duct. The secretions of such glands are collectively called hormones.
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| Endocrine glands |
HARMONES as chemical messengers
It is a Greek word Hormao" means "to excite". These are chemical molecules released from endocrine glands directly into the blood stream and transported to their target sites which are physiochemical programed to detect and respond to them.
Chemical nature of hormones
Hormones can be classify into the four main groups on the basis of their
chemical structures.
(1) Peptide hormones
Most of the hormones are chemically protein which are form from a chain of amino acids. e.g. Insuline, Glucogon etc.
(2) Steroid hormones
These hormones chemically resemble to cholesterol, from which most of them are synthesized. E.g. Estrogen, progesterone etc.
(3) Modified Amino acid hormones
Some hormones are form of single modified amino acid e.g. Adrenaline form from "Tyrosine".
(4) prostaglandine
These are modified fatty acids which are produces in almost all cells of our body.
Functions of Hormones
The hormones in general, regulate or control the following types of activities in our body.
i). Growth, maturation and regeneration.
ii). Metabolism and homeostasis.
iii). Reproductive activities.
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Names of Endocrine glands
Some of the most important endocrine glands are as follow:
(1) Pituitary gland
(2) Thyroid gland
(3) Parathyroid gland
(4) Adrenal glands
(5) Pancreas
(6) Gonads
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1) PITUITARY GLAND
It is located in the brain under the hypothalamus. It is called master gland because it secretes numerous hormones, many of which regulate the activity of other endocrine glands. It has 2 portions.
(1) Anterior
(2) Posterior
These two portions secretes different hormones.
(1) Hormones of Anterior pituitary
It secretes the following hormones.
(a) Growth hormones or Somatotrophic hormone
It is protein in nature. It's secretions is under the control of a secretion
from hypothalamus called SRF (Somatotrophic releasing factor).
Functions
- It is hyperglycemic hormone, because it increases the blood glucose level.
- It affects the protein synthesis and thus affecting the cell division. It is secreted out throughout of life but at adolescence stage its secretion increases due to which growth occurs rapidly.
- It increases retention of phosphorus and calcium in body fluid by increasing absorption from GIT.
Abnormalities
- Under secretion at child hood stage leads to DWARFISM. Development is much lower. However such individual has normal mental level. Over secretions at earlier stages of life leads to "Gigantism", in which much gain height than normal. Over secretions at adult stages leads to ACROMEGALY in which there is abnormal growth of the bones such as hands, head, jaws and feet.
(b) THYROID STIMULATING HORMONE (TSH)
TSH effects the growth of thyroid gland. Synthesis of thyroxin and its secretions.
(C) Diabetogenic hormone
Functuons
- It influences the secretion of Glucogon from pancreas. The secretion of Diabetogenic hormone is influenced by blood sugar level.
(D) Adrenocorticotrophic hormone (ATCH)
Function
- ACTH effect the growth and secretary function Cortax region of adrenal gland.
(E) Gonadotrophic hormone
Functions
- These are under the control of hypothalamus. This hormone is of two types.
(i) Follicle stimulating hormone (FSH).
(ii) Leutinizing hormone (LH)
These hormones efects the gonads of an individual (both male and female).
(F) Prolactine
Function
- This hormone control the development of mammary gland and milk production.
(2)Hormones of posterior pituitary
(a) Antidiuretic hormone (ADH) or vasopressin
Function
- lt affects the reabsorption of water in the last part of nephron and thus it's function is to maintain the water balance in the body. It also helps in maintaining blood pressure of the body.
(b) Oxytocin
Function
- It effects the milk secretion from mamary gland that is stimulates by sucking of baby. It helps in the delivery of the baby at the end of pregnancy by contacting the uterus during the process, thus expelling the baby.
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2) THYROID GLAND
Thyroid gland has two lobes which is located interior to the trachea just below the larynx.
HORMONES OF THYROID GLAND
A. Thyroxine
B. Triiodothronin
C. Calcitonin
Functions
- It increases the carbohydrate metabolism to release energy. It also affect the protein and fat metabolism.
- It increases the peristalsis in GIT, increase heart rate, breathing rate and oxygen consumption in cells.
- It also affect the physical, mental and sexual development.
- T4 is necessary for conversion of beta carotene to vitamin A.
- It promotes galactopoiesis (formation of milk).
Abnormalities
Hypothyroidism
Under secretion of thyroxine.
i). Cretinism
It is due to deficiency of thyroxine, appear at infant stage.
ii). Myxoedama
It is due to deficiency of thyroxine, appear at adult stage. Such individual have lower metabolism rate, disturbance of sexual function, mind become dull.
iii). It is due to the deficiency of iodine in water and food. In goitre enlargement of thyroid gland occur.
Hyperthyridism
Over secretion of thyroxine.
Grave'S disease
lt is due to over secretion of thyroxine. There is increase in peristalsis, high metabolic rate of heart and breathing, sweating, decrease in sleep.
Calcitonin
Function
- It is secreted by thyroid gland for Ca++ balance.
- It is secreted in larger quantity when the blood Ca++ level increase, because they are responsible to store Ca++ in bones.
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3) PARATHYROID GLAND
In humans there are four parathyroid glands. All four glands are located on
the thyroid gland.
Hormones of parathyroid gland
It secrete parathoormone or parathyroid hormone (PTH).
Functions
- The main function of parathormone is to maintain the normal calcium and
- phosphate level of blood. It is do so by different mechanisms such as:
- A) Movement of Ca++ and po4 out of the bone to maintain normal blood Ca++ level. Calcium plays important role in bone formation, muscle contraction, nerve impulse and acts as coenzyme.
- B) Activation of "vitamin D" to increase the absorption of Ca++ in intestine from food.
- C) Reabsorption of Ca++ in kidneys.
Abnormalities
HYPOPARATHYRIDISM
Under secretion of parathormone it causes a decrease in blood ca++ level which leads to the following abnormalities.
1). Low blood Ca++ level slow down the growth of bones.
2). Low ca++ level effect nervous and muscular system.
3). A disease called Tetany in which muscles remain in contracted state.
HYPERPARATHYRIDISM
Over secration of parathormone. High calcium and po4 level in blood will leads the following abnormalities.
1). The bones become weak due to extraction of Ca++.
2). Kidney stones and Gall bladder stones formation may occur.
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4) ADRENAL GLAND
Adrenal glands are pair of glands present above the kidney one on each kidney and secrete a variety of hormones. Adrenal gland has two main parts.
(A) Adrenal cortex
(B) Adrenal medulla
(A) Hormones of Adrenal cortex
These secretes many hormones (about 50 different hormones). All of them are chemically steroids and are collectively called Corticosteriods.
The Adrenocortical hormones are functionally of the following three types.
(1) Mineralocorticoids
(2) Glucocorticoids
(3) Androgens.
(1) Mineralocorticoids
It is a group of different hormones. The most important among them are:
(i) Aldosterone
(ii) Deoxycarticosterone
Functions
- Aldosterone controls the balance between Na+ ion and water in the body.
- It increase absorption of Nacl form GIT.
- It causes increase in cardiac output upto 10-20%.
Abnormalities
Under secretion of Mineralocorticoids leads to nervous and muscular disorders while its over secretion will lead to hypertension.
(2) Glucocorticoids
It is also a group of different hormones. The most important among them are:
(i) Cortisole
(ii) Carticosterone
(iii) Cortisone
Fuctions
- It stimulates the "Glucogenesis" (Formation of glucose) from amino acids and fatty acids as a result blood glucuse level increas.
- Increase " Glycogenesis" (Formation of glucose from stored glycogen).
- Increase protein metabolism.
- Helps in fat metabolism.
Abnormalities
Under secretion of Glucocarticoids leads to " Addison's disease" in which the patient have low blood sugar, weak and cannot cope with the stress conditions.
Over secretion of Glucocorticoids leads to " "Cushing disease" that leads increase the break down of protein due to which the muscles become weak high blood glucose level and hypertension due to retention of water.
Androgens
A small amount of male and female sex hormones ( e.g Testosterone and Estrogen) is secreted by inner cortex portion. In female it is responsible for the production of male characteristics especially at old age.
Andrenal Medulla
It consist of nerve like cell that secretes two hormones.
(i) Adrenaline
(ii) Nor-Adrenaline
(i) Adrenaline
It is released in emotional conditions. such as stress, anxiety, fear, emergency etc.
Functions
- Increase blood glucose level by the conversion of stored glycogen to glucose.
- Increase oxygen consumption to release more energy.
- Increase heart beat and raises B.P.
- Increase the breathing rate and dilates the air passage to lungs.
(ii) Nor-Adrenaline
It acts in the same way as adrenaline but it is less powerful than adrenaline. It is normally secreted in the blood that helps to keep the B.P. normal, promotes the blood glucose level. constriction of blood vessels of some parts of the body.
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