I. General features!A. Endocrine gland= an organ that makes and secretes into BLOOD specific chemical substances having well-defined effects on body function. Often have counter-reg. agents.!B. Subclasses of endocrine glands!1. Endocrine: specialized endocrine cells that secrete product --> capillaries and hormone transported to target order by BLOOD!2. Neuroendocrine: spec. nerve cells that secrete their product into capillaries and hormone is transported to target organ by blood!3. Paracrine (and autocrine= special): spec. endocrine cells that secrete their product into the interstitium and hormone has local action on neighboring cells!C. Hormones= the secretory products of endocrine glands. 3 classes:!1. Derivatives of tyrosine (catelcholamines and thyroid hormones), adrenaline!2. Peptides and proteins (products of the pituitary gland)!- Start out at pro-hormone, made from RER, conversion in golgi, stored in secretion grans!3. Steroids (Ch backbone)!D. Correlation between germ layer of origin of endocrine tissue and class of hormone produced!1. Catelcholamines made by ectodermally derived glands!2. Polypeptides made by either ectoderm or endoderm derivatives!3. Steroids made by mesodermally derived glands!II. Synthesis and Secretion of Hormones!A. Derivs of tyrosine (thyroid gland, adrenal medulla)!B. Peptide hormones:!C. Steroid hormones:!III. Cytological features of endocrine glands:!A. Catecholamine and peptide glands: (things for making proteins for export) !- well developed RER, golgi, e- dense secretion granules where the hormones are stored until the cell is stimulated to release them !- regulated secretion --> exocytosis --> capillary (fenestrated)!B. Steroid glands: !- Do NOT store their secretory product, so NO secretion granules!- Enzyme for steroid syn. are in mitochondria and smooth ER. Cells have lots of mitochondria, well dev. SER. !- Ch= precursor for steroid hormone syn. is stored in lipid droplets in the cells.!- Constitutive secretion= you make the amt of hormone you want to release!C. Stroma!- ALL endocrine glands= highly VASCULAR (fenestrated caps)!- Cells supported by reticular fibers!IV. Target Organs and Receptors!A. Target organs can be endocrine glands or other organs!B. Hormones comm. w/target cells thru receptors!1. Catecholamine and peptide receptors are on the plasma membrane and incl.:!- Receptors coupled to G proteins --> activation generates cAMP as 2nd messenger!- Receptors coupled to activation of phospholipase C, diacylglycerol and IP3 are 2nd messengers!- Receptors coupled to activation of tyrosine kinase!- Cytokine receptors --> activate STAT molecules --> translocate to nucleus!V. Regulation and Integration of Hormone Secretion!A. Hormone secretion occurs as result of chemical or nervous stimulus!B. Stimulus secretion coupling!C. Endocrine secretions affect their target organs --> target organ can give pos or neg feedback signal to primary gland!!Pituitary Gland I. Gross structure!A. Location and size: 1 cm diameter!B. Divisions and subdivisions!1. Anterior (adenohypophysis)!- Pars distalis!- Pars intermedia!- Pars tuberalis !2. Posterior (neurohypophysis)!- Pars nervosa!- = an extension of the hypothalamus!- median eminence and infundibulum!C. Blood supply!1. Superior hypophyseal a.!2. Inferior hypophyseal a.!3. Portal System: w/the hypothalamus (who is making lots of hormones too), cnxn between the brain and hypothalamus --> influences pituitary gland!- Blood goes in median eminence (post pit g) via inf. and sup. hypophyseal a. --> distribute to cap. bed --> effluent from capi bed collects into veins --> enter 2nd cap bed --> supplies anterior pituitary gland --> venous blood leaves via hypophyseal v.!- hypothalamo-hypophyseal portal system carries reg. hormones from hypothalamus to anterior pituitary!D. Histogenesis!1. Derived from both oral ectoderm and floor of 3rd ventricle (diencephalon, hypothalamus) of the brain!2. Oral ectoderm in roof of mouth prolifs and outpockets above Rathke's pouch, developing ant. pituitary thickens (pars distalis) reducing pouch to cleft (Rathke's cysts), separating pars distalis from pars intermedia, developing gland constricts at base and separates from oral cavity!3. Diencephalon (hypothalamus) forms a pocket --> neural growth from the hypothalamus median eminence grows into the infundibular stalk and main body of Pars nervosa (post. pituitary)!II. Anterior Pituitary (Adenohypophysis)!A. Cell types (LM classification)!1. Chromophobes: 50%, don't stain!- Some: stain poorly, contain a few secretion granules, resting stage cells (or are very active and have released everything...)!- Follicular cells: stellate shaped, appear to be supportive and phagocytic!2. Chromophils: 50%, stain well!- Acidophils: 40%, PAS -!- Somatotropes (GH)!- Mammotropes (PRL= prolactin) - Basophils: 10%, PAS + due to glyoproteins in their hormones!- Corticotropes (ACTH, MSH)!- Secreted by same cell:!- FSH gonadotropes (FSH= follicle stimulating)!- LH gonnadotrops (LH= leuteninzing)!- Thyrotropes (TSH= thyroid stimulating)!- ALL chromophils have many e- dense secretion granules B. EM and Histophysiology of the Anterior Pituitary (Pars distalis)!1. Somatotropes!- acidophil, protein secreting (lots of secretion granules)!- syn. and secretes Growth Hormone !- GH affects epiphyseal cartilage, stimulates growth, but doesn't act directly!- GH stims liver and kidney to make somatomedins which maniest GH effects!- GH has direct effects on other cells!- Abnormal secretion:!- Hypersecretion (acidophil tumors)!- gigantism (child), acromegaly (adult), GH diabetes!- Hyposecretion!- hypopituitary dwarfism (child) 2. Mammotropes!- Acidophil!- Syn. and secrete prolactin (PRL)!- PRL stims mammary gland development in prep for lactation!- PRL --> synthesis of milk!- Enlarge during pregnany under influence of estrogen, pregnancy cells --> secrete more PRL!- PRL regs glucose sensitivity of islet B-cells during pregnancy!- PRL plays role in immune function!3. Gonadotropes= 1 cell type, secretes 2 diff. hormones!- Gonadotrope (FSH)!- Basophils!- Syn. and secretion Follicle Stimulation Hormone (glycoprotein)!- Female: Follicular dev.!- Male: Gametogenesis!- Castration --> hypertrophy of "castration cell" - Gonadrotrope (LH)!- Basophil!- Syn. and secrete luteinizing hormones (LH)/interstitial cell secreting hormone (ICSH) (glycoprotein)!- Female: maturation of Graafian follicle, dev. of corpus luteum, and progesterone and estrogen secretion!-
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