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2. Control of anterior pituitary

Hypothalamus controls the anterior pituitary gland by secreting releasing hormones and inhibitory hormones. It secretes seven hormones.

  1. Growth hormone releasing hormone (GHRH).

  2. Growth hormone releasing polypeptide (GHRP).

  3. Growth hormone inhibitory hormone (GHIH) or somatostatin.

  4. Thyrotropic releasing hormone (TRH).

  5. Corticotropin releasing hormone (CRH).

  6. Gonadotropin releasing hormone (GnRH).

  7. Prolactin inhibitory hormone (PIH).

These hormones are secreted by discrete areas of hypothalamus and transported to the anterior pituitary by the hypothalamo-hypophyseal portal blood vessels.

3. Control of adrenal cortex

The adrenal cortex is regulated by adrenocorticotropic hormone (ACTH). ACTH secretion is in turn regulated by corticotropic releasing hormone (CRH) which is secreted by the paraventricular nucleus of hypothalamus.

4. Control of adrenal medulla

Dorsomedial and posterior hypothamic nuclei are excited by emotional stimuli. These hypothalamic nuclei, in turn, send impulses to adrenal medulla through sympathetic fibers and cause release of catecholamines, which are essential to cope up with emotional stress.

5. Regulation of body temperature

Hypothalamus has two centers, which regulate the body temperature. These centers are the heat loss center and the heat gain center. Heat loss center is in anterior hypothalamus and heat gain center is in posterior hypothalamus.

Mechanism of Temperature Regulation

In addition to temperature receptors present in skin, abdomen and other structures, there are some heat sensitive nerve cells in the preoptic area of hypothalamus. The heat sensitive nerve cells are called thermoreceptors.

When body temperature increases, blood temperature also increases. When blood with increased temperature passes through hypothalamus, it stimulates the thermoreceptors present in the preoptic area. The thermoreceptors of hypothalamus are stimulated and cause heat loss in two ways.

  1. Preoptic thermoreceptors stimulate sweat glands and increase the secretion of sweat. When more sweat is secreted, more water is lost from skin. Along with water, heat is lost from body.

  2. The preoptic thermoreceptors inhibit the posterior hypothalamus, which controls the sympathetic nervous system. This decreases the activity of vasomotor center so that the vasomotor tone to cutaneous blood vessels is decreased. This leads to cutaneous vasodilatation and increase in blood

6. REGULATION OF AUTONOMIC NERVOUS SYSTEM

Hypothalamus controls the autonomic nervous system (ANS). The sympathetic division of ANS is regulated by posterior and lateral nuclei of hypothalamus. The parasympathetic division of ANS is controlled by anterior group of nuclei. Cerebral cortex also influences ANS but, only through hypothalamus.

7. REGULATION OF HEART RATE

Hypothalamus regulates heart rate through vasomotor center in the medulla oblongata. Stimulation of posterior and lateral nuclei of hypothalamus increases the heart rate. Stimulation of preoptic area decreases the heart rate.

8. REGULATION OF BLOOD PRESSURE

Hypothalamus regulates the blood pressure also by acting on the vasomotor center. Stimulation of posterior and lateral hypothalamic nuclei increases arterial blood flow to the skin. Due to increased blood flow through skin, more heat is lost from the skin directly or indirectly through sweat.

9. REGULATION OF FOOD INTAKE

To regulate the food intake, hypothalamus has two centers namely the feeding center and satiety (satiation) center.

Feeding Center

It is in the lateral hypothalamic nucleus. The stimulation of this center in animals leads to increased food intake (hyperphagia), and uncontrolled hunger. It causes obesity. The destruction of feeding center leads to loss of appetite-anorexia.

Satiety Center

It is in the ventromedial nucleus of the hypothalamus. Stimulation of this in animals causes cessation of food intake. Destruction of satiety center leads to hyperphagia. Normally, the feeding center is always active and its activity is inhibited by satiety center after food intake.

Mechanism of Regulation of Food Intake

There are some receptors called glucostats in the ventro-medial nucleus of hypothalamus. The glucostats give response to increased glucose content in blood. During food intake, the blood glucose level is increased. The glucostats are activated and stimulate the satiety center. This, in turn, inhibits the feeding center causing stoppage of food intake. But in diabetes, because of deficiency of insulin, hyperglycemia occurs. Hyperglycemia cannot stimulate the satiety center. So, tne satiety center will not inhibit the feeding center. This increases the frequency of food intake - polyphagia.

Few hours after meals, the blood glucose level is reduced. Now, the glucostats are not excited, and thus the satiety center is not activated. This causes release of inhibition over feeding center leading to hunger and food intake.

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