ENDOCRINOLOGY. For Biochemistry Diploma Students Faculty of Science Cairo University. Classical definition of a hormone. Chemical messengers Synthesized by living cells and Secreted by a specific gland Secreted directly into the blood stream Carried by the blood
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For Biochemistry Diploma Students
Faculty of Science
"Any substance released by a cell and which acts on another cell, near or far, regardless of the means of conveyance"
Activation of specific enzymes: acetate cholesterol pregnenolone to the diff hormones.
The SER, mitochondria and cytoplasm contain the enzymes required for the transformations
They are sterol hormones and have much in common to other steroid hormones
Its precursor, cholecalciferol, is obtained from diet or synthesized by the ultraviolet irradiation of provitamin D in the skin
Cholecalciferol, by a series of enzymes in the liver and kidney, is hydroxylated to the active hormone, calcitriol
I.Thyroid hormones: is a unique process
II. Catecholamines: They are synthesized from tyrosine by a number of enzymes in the cytoplasm and chromaffin granules
From fatty acid (arachidonic acid) released from phospholipids in cell membrane by means of a number of enzymes.
A dynamic equilibrium exists between the concentrations of free (unbound) hormone, plasma protein, and the hormone-protein complex:
Where K is the dissociation constant
Some biologically active hormones are converted to other equally active hormones in peripheral tissues such as liver, breast adipose tissue, brain etc
Thyroxine (T4) triiodothyronine (T3)
Estradiol acts on ovarian follicles to promote granulosa cell differentiation, on uterus to stimulate its growth and maintain the cyclic change of uterine mucosa, on mammary gland to stimulate ductal growth, on bone to promote linear growth and closure of epiphyseal plates, on HPA to regulate secretion of gonadotropins and prolactin, on metabolic processes to affect adipose tissue distribution, volume of ECF, etc
Release of fatty acids (lipolysis) from adipose tissue stimulated by catecholamines, glucagon, secretin, prolactin and B-lipotropin
Development of mammary gland, under infleunce of prolactin, estradiol & progesterone and the permissive influence of glucocorticoids, thyroid hormones and insulin