What is endocrine system? ,diseases

ENDOCRINE SYSTEM:

       The system of endocrine gland (ductless gland) in all vertebrates is called the endocrine system. These glands produce some Chemicals (hormones) and pour them directly into blood. Endocrine system consists of 20 endocrine glands found in different parts of the body.

 Endocrine gland: 

       There are 20 different endocrine glands in the body but the main endocrine glands in the body are,

1)Pituitary gland

2)Thyroid gland

3)Pancreas

4)Adrenal gland

5)Gonads

(1)Pituitary gland:

       Pituitary gland is also called master gland because of its secret various types of hormones. 

Shape: 

       Pituitary gland is oval in shape attached to the hypothalamus of the brain. 

 Size:

       It is about the size of the pea seed.

Weight:  

       In adults its weight is about 0.5gm. 

Parts: 

       There are two lobes of pituitary gland. 

1)Interior lob 

2)Posterior lob 

(1) Anterior lobe: 

       Anterior lobe of the pituitary secretes four types of hormones.

(i) Somatotropic hormone (STH) or growth hormone: 

       It controls the growth and development of the body. It is secreted more in childhood but in adults secretion becomes normal. 

DISORDER: 

       Hyposecretion in early life causes gigantism and hyposecretion in early life causes dwarfism. 

(ii) Thyroid stimulating hormone: 

       These hormones control the development and secretion of thyroid gland. 

(iii) Adrenocorticotropic hormone (ACTH):

        The function of this hormone is to stimulate the adrenal cortex to release adrenal hormones.

(iv) Gonadotropic hormone(GTH): 

         These hormones control the function and development of gonads. 

(v) Posterior lobe: 

       Posterior lobe secretes two hormones.

(a) Antidiuretic hormone ADH or vasopressin: 

        It controls the reabsorption of water in Renal tubules of nephrons. 

(b) Oxytocin: 

        This hormone causes strong contraction of the uterus muscles during delivery.

 (2) Thyroid gland: 

        Thyroid gland is situated about the larynx. It consists of two lobes present on each side of the trachea. 

Hormone:

        It secretes a hormone called thyroxin which works only in the presence of iodine.

Function: 

        This hormone influences metabolism, growth, development and also produces heat in the body. It promotes growth hence secreted more in young age. 

Disorder: 

☆ Hyposecretion after oxygen increased Heartbeat, blood pressure, excessive sweating, loss of weight.

☆ Hyposecretion causes goiter. This disease becomes endemic among the people living at high altitude because they do not have sufficient iodine in their diet.

(3) Pancreas:

 

      Pancreas has a dual function; it acts as an exocrine gland that secretes digestive enzymes which help in digestion of food. It also acts as an endocrine gland which secrete hormones.

 Location:

        It is present near the liver and stomach. Pancreas contain special cells called Islets of Langerhans.

       It secrete two hormones.

(A) Insulin:

      Insulin lowers the Glucose level in the blood by converting glucose into glycogen. The deficiency of insulin leads to a condition called Diabetes mellitus. 

(B)Glucagon: 

       Work opposite to insulin increases blood glucose level by the breakdown of glucose into glucose in the liver and muscle. 

(4) Adrenal gland:

       Adrenal glands are two in number present on the top of each kidney.

Parts:

      Each gland has two parts; 

(a)Adrenal cortex 

(b)Adrenal medulla 

(a)Adrenal cortex: 

       The outer yellowish portion of adrenal gland is called adrenal cortex. It works under the action of ACTH secreted by anterior pituitary. It secretes many hormones collectively known as corticosteroids. 

FUNCTION:

        It controls the metabolism of minerals in glucose etc. 

(b)Adrenal medulla: 

         Inner light portion of the adrenal gland is called adrenal medulla. The adrenal medulla produces two hormones called adrenaline and noradrenaline also called epinephrine and norepinephrine respectively.

Function: 

☆Adrenaline secreted in emotion and anger also called flight and flight hormone. It causes vasodilation (dilation of blood vessels) hence the face becomes red. 

☆Noradrenaline secreted in fear therefore also called fright hormone. It causes vasoconstriction (contraction of the blood vessels) hence the face become pale and white. 

 (5)Gonads: 

        Gonads are collective terms for male and female reproductive organs. There are two types of gonads. 

(1) Testes 

(2) Ovaries 

(2) Testes: 

       Testes are male gonads. They are two in number and are located in a sac like structure called scrotum. 

Hormone:

        Produce male sex hormone called testicular hormone or testosterone. 

Function:

☆Before puberty this hormone acts to slowly grow the male genitalia. 

☆In puberty it brings the male secondary sexual characteristics such as appearance of beard, moustaches, appearance of hair on chest and armpit, deepness of sound. 

(2) Ovaries: 

        Ovaries are female gonads. These are two in number. Ovaries present in the pelvic region of the lower abdomen. 

Hormones: 

        They secrete two types of hormones. 

1) Estrogen 

2) Progesterone 

(1) Estrogen:

        The bring about development of secondary sexual characters in the female. 

2) Progesterone: 

         Progesterone maintains pregnancy and development of placenta.

MECHANISM OF HORMONE SECRETION

 NEGATIVE AND POSITIVE FEEDBACK MECHANISM 

MECHANISM OF HORMONE SECRETION:                

         Different endocrine secretions act as a system of check and balance for each other. For the proper function of the body two opposing systems are required. If there are accelerators, there must be inhibitors. Same is the case of hormones. 

NEGATIVE FEEDBACK MECHANISM: 

        The increasing amount of one hormone decreases the secretion of another hormone. This kind of feedback is known as a negative feedback mechanism. 

EXAMPLE: 

         The glucose level increased the blood after a meal. When this glucose rich blood passes through the pancreas, it starts secreting insulin in the blood. Insulin converts excess glucose to glycogen that can be stored in the liver, muscle etc. This results in a decrease in blood glucose level. When this low glucose blood passes through the pancreas, it stops releasing insulin. This process is known as the negative feedback mechanism of hormones. 

POSITIVE FEEDBACK MECHANISM: 

         In this mechanism, increasing the amount of one hormone increases the secretion of another hormone. This type of feedback is called a positive feedback mechanism. 

EXAMPLE: 

         The Sucking action of her baby stimulates the production of the hormone in the mother. Sucking action of a baby stimulates the production of hormones in the mother. This hormone helps in the production of more milk. More sucking action means more hormones and more production of milk.

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