Effects of Hormones on Target Cells

1) Metabolic effect. In this case hormones induce a change in metabolism in target cells. These changes may be associated with increase in permeability of biological membranes, synthesis of some enzymes or a change in their activity. For example, thyroid hormones possess a pronounced metabolic effect.

2) Morphogenetic effect. Here, hormones control alteration of target cells during individual development of a human. For example, somatotropin, a hormone of adenohypophysis, influences the height of an individual. Sex hormones contribute to formation of the secondary sex signs.

3) Kinetic effect. This effect is associated with ability of hormones to trigger physiological processes. For example, oxytocin (a hormone produced in the hypothalamic region) activates contraction of smooth muscles of uterus, and antidiuretic hormone triggers mechanism of reabsorption in kidneys.

4) Corrective effect. This action of hormones is associated with their ability to modify the current activity of target cells, tissues and organs. For example, adrenaline influences the heart rate.

5) Reactogenic effect. This effect is associated with ability of hormones to change response of cells, tissues and organs to different stimuli including other hormones. For example, gastrin and cholecystokinin modify excitability of feeding and satiety nervous centers located in the hypothalamic region.

Concept of Endocrine Glands. Classification of Endocrine glands.

Endocrine glands have no excretory ducts for excretion of biologically active substances synthesized by them. Endocrine glands release (secrete) the synthesized substances into the internal environment of the body to be propagated throughout the body.

1) By localization the endocrine glands are divided into central and peripheral. Central glands include epiphysis, hypothalamic region, pituitary. Peripheral glands include thyroid, parathyroid, adrenals, thymus, pancreatic islets, reproductive glands and others.

2) By controlling mechanism endocrine glands are divided to pituitary-dependent and non-pituitary-dependent. The pituitary-dependent glands include thyroid, adrenal cortex, reproductive glands, epiphysis. The non-pituitary-dependent glands include parathyroid glands, thymus, pancreatic islets and adrenal medulla.

Date: 2015-01-02; view: 942