ENDOCRINE PHYSIOLOGY

ENDOCRINE PHYSIOLOGY Overview • Multiple activities of cells, tissues and organs of the body are coordinated by the interplay of several types of chemical messengers among them being HORMONES. • Hormone: a chemical messenger released by glands into the blood stream to influence biological activity of distant structures. • Adjacent image shows the locus of major endocrine glands Classification of hormones • Protein and peptide hormones • Include hormones produced by the pituitary gland, pancreas, parathyroid gland, calcitonin, hCG, renin, EPO, ADH, gastrin, secretin, CCK, leptin • Steroids • Produced by the adrenal cortex, ovaries, testes and placenta • Derivatives of amino acids • They are derivatives of the amino acid tyrosine e.g. thyroid hormones, epinephrine, norepinephrine Synthesis and secretion of peptide hormones Synthesis and secretion of steroid hormones • The chemical structure of steroid hormones is similar to that of cholesterol (they are cholesterol derivatives) thus they are lipid soluble • There is very little storage of steroid hormones by secretory cells but large pools of cholesterol can be mobilized (from plasma or de novo synthesis) rapidly for hormone synthesis Synthesis and secretion of amino acid hormone