Question

a. How do peripheral endocrine glands regulate pituitary gland? b. Describe the functions of different peripheral endocrine hormones (preferably using flow-diagrams).

Answer 1

a. The peripheral endocrine glands are the endocrine glands that lie outside of the nervous system. Pituitary glands release hormones that stimulates or inhibits the peripheral endocrine glands. Peripheral endocrine glands regulate the pituitary by positive and negative feedback loops.

Pituitary hormones stimulate the release of peripheral endocrine gland hormones. Most of the endocrine activities are regulated by complex feedback loops. In negative feedback loop the excess of a hormone in the blood stream released by peripheral endocrine gland. The excess of this hormone will send signals to the pituitary to stop releasing the stimulatory hormone. The glands, which do not constantly secrete hormones, rely on the presence or absence of hormones in the blood to turn their secretions on and off. If there is not enough hormone circulating in the blood, the endocrine glands make more, increasing blood hormone levels. If there is too much hormone, the glands stop producing it, leading to lower blood hormone levels. For example if blood calcium levels are high and the bone calcium and phosphorus density is low then the pituitary will release thyroid stimulating hormone that will stimulate thyrocalcitonin release from thyroid gland, when this hormone gets in excess in the blood leading to low blood calcium level then it will send a signal to pituitary to stop releasing TSH.A positive feedback loop occurs when the product of a reaction leads to an increase in that reaction. In endocrine system it occurs when a hormone stimulates the pituitary to release its stimulatory hormone. It is very rare as compared to the negative feedback loop in the endocrine system.

b. Thyroid gland-

This releases teraiodothyronine (T4) and triiodothyronine (T3). These play and important role in basal metabolic rate and also support RBC formation, Thyroid hormone control metabolism of carbohydrate, fats and proteins. Thyroid gland also secretes thyrocalcitonin that regulates the blood calcium levels.

Parathyroid gland-

The parathyroid gland secretes parathyroid hormone that increases calcium ion levels in the blood and stimulates bone reabsorption and renal reabsorption of calcium.

Thymus

It secretes thymosine that plays a major role in T-lymphocyte formation and promote antibody production by B lymphocytes.

Adrenal gland-

Adrenal medulla secretes 2 hormones- epinephrine and nor epinephrine. These are released in stressful situations and increase alertness, pupil dilation, contraction of heart, respiratory rate, etc. These also stimulate glucose breakdown and thus provide energy during stress.

Pancreas-

The alpha cells of pancreas secrete glucagon and beta cells secrete insulin. Glucagon is a peptide hormone and plays an important role in maintaining blood glucose levels . It acts in liver and promotes glycogenesis and increase blood sugar levels.

The beta cells secrete insulin which is a peptide hormone and enhance cellular glucose uptake by acting on hepatocytes and adipocytes.

Testis-

These release androgens mainly testosterone that regulate development, maturation and functions of male sex hormones.

Ovaries-

These release Estradiol and Progesterone. Estradiol have many actions including stimulation of growth and activities of female sex organs, development of growing ovarian follicles, appearance of female secondary sex characters and female sexual behavior.

Progesterone supports pregnancy and acts on mammary glands to stimulate alveoli formation.

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Hypothalamig GnRH release Negative Pituitary Feedback K FSH & LH release excess Testosterone/ Estrogen - Progesterone Release

Adrenocortico troplico Hormone (anterior pituitary stimulates release of Epinephrine & norepinephine C Adrenal cortex) increase Vasocone increased HR; fiction, respiratory rate, increased pupel ditation

decreased & Blood calcium levels -- cond Hormone Parathyroid gland Release P Parathyroid I absorption from bones & in → Kidneys

Thyroid Releasing Hammoue Chypothalamus ih Thyroid (Pituitary) stimulating Hormone Thyroid gland TA To -> Thy no calcitonin Regulate blood "basal calcun leuds Regulate metabolic rate & Red Blood lell Production