Endocrine System
Endocrine System

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exocrine glands (both examples abo ve) - epithelial glandular cells secrete into ducts lined by ductal cells, with secretions released at epithelial cell surface - sweat glands, salivary glands, breast, pancreas, etc. - embryologically, from either ectoderm or en doderm - secrete a hormone into capillary blood vessels (endocrine secretion) affecting distant cells, or secrete into tissue interstitium affecting neighboring cells (paracrine secretion) - some hormones affect many types of cells - examples: thyroid hormone, steroid hormones, insulin, adrenalin, etc. - some hormones affect limited types of target organ cells - examples: pituitary hormones, parathyroid hormone, sex hormones, etc. - embryo logically, endocrine gland cells are derived from either: - ectoderm: anterior pituitary cells (adenohypophysis) - endoderm: thyroid cells, “C cells” of thyroid interstitium (calcitonin), parathyroid cells, islet c ells of pancreas (insulin, etc.), as well as enteroendocrine cells of bronchial/gut epithelium [Kulschitky cells (serotonin) of bronchial mucosa and APUD cells of gastrointestinal mucosa (secretin, etc.)], and hepatocytes (a ngiotensin) - mesoderm: steroid hormones from adrenal cortex; and steroid sex hormones from follicular cells of ovary and from interstitial (Leydig) cells of testis, as well as some peptide hormones: renin from p ericytes (perivascular cells) of the juxtaglomerular apparatus and erythropoietin from interstitial cells of renal medullae - neuroectoderm: - modified neurons of hypothalamus - act on endocr ine cells of adenohypophysis via pituitary venous portal system - modified neurons of the posterior pituitary (neurohypophysis) - modified neurons of the pineal gland - neural crest cells migrate during embr yonic development, differentiate according to the final location, and include chromaffin cells of adrenal medullae, Cajal pacemaker cells of gut mucosa, Merkel cells of skin (discriminative touch), et cetera © ▲ breast gland lobule - lobular duct and gland acini with central apocrine secretions ◄ salivary gland acini and duct - two kinds of secretory cells - clear cytoplasm = mucus - dark cyt oplasm = serous endocrine glands