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The following points will highlight the activities of hormones in vertebrate body. The activities are: 1. Growth and Development 2. Reproduction 3. Maintenance of Internal Environment 4. Metabolism and Store.
Hormone Activity # 1. Growth and Development:
Some hormones play an important role in overall growth and development. In vertebrate body, growth regulating hormones are STH of anterior pituitary, thyroid hormone, androgens etc. STH helps to increase the rate of all growing cells of the body.
As a result the rate of cellular mitosis is increased and this seems to be due to increased rate of synthesis of all the individual cellular constituents. Injection of thyroxine to the tadpole larva will convert the tadpoles into the adult frogs within a very short time than of its normal schedule and thereby it stimulates cellular metamorphosis.
Hormone Activity # 2. Reproduction:
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Reproduction includes maturation of gonads, accessory sex organs, gametogenesis, etc. Pituitary gonadotrophic hormone maintains the structure and function of gonads. In male, testosterones are secreted from the testis and maintain the growth of seminiferous tubules and spermatogenesis.
Female sex hormone estrogen maintains the reproductive cycle. Pituitary FSH maintains the growth ovarian follicles in female and seminiferous tubule in male. Pituitary LH helps in ovulation.
Hormone Activity # 3. Maintenance of Internal Environment:
Homeostasis maintains the internal steady state condition of vertebrate. Hormones maintain this mechanism, like blood glucose level, blood Ca++ level, blood pressure etc.
For example, hyper-glycaem.ia stimulates beta cells of endocrine pancreas for secretion of insulin, which in turn lowers the blood glucose level by glycogenesis. Again hypoglycaemia stimulates alpha cells for secretion of glucagon which elevates blood glucose by glycogenolysis in liver.
Hormone Activity # 4. Metabolism and Store:
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Hormones affect metabolic processes, both catabolic and anabolic in most cells. The synthesis and degradation of carbohydrates, lipids and proteins are controlled by hormones to meet specific energy or growth requirements of the individual.
For instance, insulin increases the uptake of glucose by muscle, adipose tissue etc. It also increases the glycogen synthetase activity. Adrenocorticosteroid increases gluconeogenesis in the liver as a result of mobilization proteins. While adipose tissue (unilocular type of adipose cells) produce a protein hormone peptide leptin which increases the energy expenditure (Fig. 3.5).
