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Endocrine System Biology 2122 Introduction (1) What are hormones? (2) What are the functions of hormones? (3) What are the types of hormones? – Amino Acids – Steroids – Eicosanoids How do Hormones Work? (1) Action on Target Cells – Membrane permeability – Synthesis of proteins or enzymes • Or inhibits – Induces secretory activity – Stimulates mitosis (2) Target-Specific – Target cell receptor sites – “Turns on cell” – “Dynamic” How do Hormones Work? (3) Half-Life (4) Interaction – Target Cells – Permissive – Synergistic – Antagonistic (5) Control of Release – Negative feedback – Endocrine Gland Stimuli • Humoral stimuli • Neural stimuli • Hormonal stimuli Plasma Membrane Receptors (1) Second Messenger System – All amino acid hormones (except thyroid) Plasma Membrane Receptors (2) Intracellular – Direct Gene Activation – – – – Lipid soluble; steroid Binds to intracellular receptors Binds to DNA Activates a gene Anterior Pituitary Hormones-HGH (1). Somatotroph cells produce GH (2). Secretion – GHRH – stimulates release (GHIH) inhibits – Produced in the hypothalamus (3). Effects – Anabolic – protein synthesis – Targets bones and muscles – Stimulates epiphyseal plates during development (4). Disorders – Gigantism and Acromegaly Thyroid-Stimulating Hormone • (1). Also referred to as thyrotropin. – Produced by thyrotroph cells • (2). Secretion – TRH or thyrotropin releasing hormone stimulates the release of TSH – Negative feedback – rising levels of thyroid hormones • ANIMATION • (3). Effects – Moderates normal thyroid gland activity. Adrenocorticotropic Hormones • (1). ACTH – adrenocorticotropic hormone secreted – corticotroph cells • (2). Stimulation-Secretion – CRH – corticotropin-releasing hormone – hypothalamus • Levels peak in the morning – Negative feedback • (3). Effects – Stimulates the Adrenal gland (cortex) to release Glucocorticoids • Cortisol (stress hormone) Gonadotropins (1). FSH and LH – gonadotrophic cells (2). Stimulus-Secretion ◦ Puberty ◦ GnRH – prompts the anterior pituitary to release hormones ◦ ANIMATION (3). Effects ◦ (a). LH FSH - maturation of follicle Ovulation Stimulates interstitial cells - testosterone in males ◦ (b). FSH – stimulates gamete production; follicle development. Prolactin (1). PRL or prolactin is a protein hormone. – Produced by the lactrotroph cells (2). Stimulus – Secretion – PRH and PRH – PRH plays dominant role – dopamine prevents secretion (3). Effects – Stimulate milk production in the breasts Acromegaly Posterior Pituitary Gland Hormones (1). Production- hypothalamic neurons (2). ADH or Antidiuretic Hormone – Reabsorption of water – collecting tubules – Release stimulated by – increasing osmolarity • Diabetes insipidus (3). Oxytocin – Stimulated release by positive feedback – contractions during birth – Milk ejection – Synthetic – induce contractions Thyroid Gland (1). Produces TH or thyroid hormones ◦ T4 or thyroxin; T3 or triiodonthyronine (2). Stimulus – Secretion ◦ Hypothalamus (TRH) - Pituitary (TSH) -- TH ◦ Stress - cold, pregnancy – cause hypothalamus to produce TRH. ◦ Rising TH levels – negative feedback to hypothalamus-pituitary axis. (3). Effects ◦ Increases BMR ◦ body heat production (stimulates enzymes to increase glucose oxidation) Synthesis of TH Thyroid Imbalances • (1). Myxedema – hypothyroid • (2). Goiter • (3). Cretinism – Infant hypothyroidism • (4). Grave’s Disease – Hyperthyroid Calcitonin (1). Polypeptide hormone – Parafollicular cells of the thyroid – Lowers calcium blood levels – Reabsorption back into the bones (2). Stimulus for release – 20% above normal levels for calcium blood levels – Lower than normal – inhibitory effect (3). More important in childhood – Due to developing bones and keeps calcium levels in check Parathyroid Hormones (1). Cells in the parathyroid gland – Oxyphil and chief cells (secretes ) PTH (2). Stimulus and Secretion Increases calcium absorption Kidney Osteoclast activity increased Intestines Bone – Hypocalcemia ----- PTH Increases calcium reabsorption Adrenal Hormones (1). Adrenal gland has two distinct regions ◦ (a). Cortex - outer region ◦ (b). Medulla - inner region (2). Hormones produced – corticosteroids ◦ 12 total (3). Steroid Hormones – Not stored in cells – rate of release depends on productivity (4). Cortical regions ◦ (a). Zona glomerulosa – mineralocorticoids ◦ (b). Zona fasciculata – glucocorticoids ◦ (c). Zona reticualaris – adrenal sex hormones called gonadocorticoids. Mineralocorticoids (1). Produced in the zona glomerulosa of the cortex ◦ Mostly aldosterone ◦ Balances ions and water (2). Stimulus and Secretion ◦ Renin-angiotensin mechanism ◦ Elevated K+ levels (3). Disorders ◦ Aldosteronism ◦ Addison’s disease Glucocorticoids (1). Produced in the zona fasciculata – Metabolic hormones (2). Cortisol is the main hormone – Gluconeogenesis; lipolysis; protein metabolism (3). Stimulation and secretion – ACTH from the anterior pituitary (low levels of hormones) (4). Disorders – Cushing’s syndrome – Addison’s disease Gonadocorticoids (1). Androgens produced in the zona reticularis – Converted to testosterone and estrogen (2). Stimulus and secretion – ACTH released from anterior pituitary (3). Effects – Males – Female libido; pubic and axillary hair in females; estrogen after menopause