The posterior pituitary gland or neurohypophysis or pars nervosa stores and release two hormones :
1. Vasopressin (ADH or Antidiuretic Hormone)
2. Oxytocin
1. Function of Vasopressin hormone. Vasopressin hormone controls urine output. When there is more water in the body then this hormone is secreted in less amount. When amount of water is less inside the body then it is secreted in more amount so the urine output is less. The ADH hormone reduces water loss.
2. Function of Oxytocin :
(i) It acts on smooth muscles and results in their contraction .
(ii) It stimulates rigorous contraction in the uterine walls during the child birth.
(iii) It stimules ejection of milk from the mammary glands.
Explain the following :
(1) Insulin lowers the blood sugar level.
(2) Adrenal medulla and the sympathetic nervous system function as a closely integrated system.
(3) Pituitary gland regulates the reproductive system.
(4) Feed back system controls the blood level of many hormones.
(1) Insulin is reponsible for lowering the blood sugar level by converting excess of glucose to gylcogen which is stored in muscles and liver.
(2) Adrenal medulla and the sympathetic nervous system are closely integrated systems as noradrenaline is secreted during danger when nerve impulse reaches adrenal medulla via the sympathetic nerves.
(3) Gonadotrophic hormone secreted by pituitary gland controls spermatogenesis in male and ovulation of mature follicles , growth and development of ovarian follicles and maintenance of corpur luteum in females.
(4) Hormones maintain homeostasis. Hormones produced in body are under the control of hormones secreted by pituitary gland and hormones of pituitary gland are further controlled by hormones of hypothalamus. All this control of hormones is done by feed back mechanism. For example, if thyroxin amount is more in blood then it stimulates hypothalamus to secrete less thyrotropin releasing hormones which decreases thyroxine secretion. On decrease in amount of thyroxine below normal, thyrotrophin releasing hormone accelerates the release of thyroxine secretion. This is feed back control.
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Hormones |
Enzymes |
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1. Glands |
These are secreted by endocrine glands. |
These are secreted by exocrine glands. |
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2. Transportation |
They are transported by blood. |
They are transported by ducts. |
|
3. Amount : |
The hormones are needed in less amount. |
The enzymes are needed in more amount. |
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4. Chemical nature: |
The hormones may be formed from amino acids, proteins, peptides and steroids. |
Enzymes are only proteinous. |
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5. Change of nature : |
Hormones undergo changes during chemical reaction. |
Enzymes do not undergo any change. |
The steroid hormones bring changes in their target cells in the following manner :
1. Steroid hormones are lipid soluble hormones and can readily pass through the plasma membrane of a target cell.
2. After reaching the cytoplasm they bind to specific intracellular receptor proteins. They form a complex that enters the nucleus and binds to specific regulatory sites on chromosomes.
3. The binding alters the pattern of gene expression, initiating the tanscription of some genes (DNA), while repressing the transcription of others.
4. This results in the production of specific mRNA translation products such as proteins and usually enzymes, thus causing the required effects.
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