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Endocrine System

Endocrine System. Chapter 16. The Endocrine System. Specialized glands throughout the body Regulates metabolic activity Secrete hormones into ECF Slow acting Long living Act on target cells Signaling molecules Other tissues produce hormones too. Categories of Hormones.

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Endocrine System

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  1. Endocrine System Chapter 16

  2. The Endocrine System • Specialized glands throughout the body • Regulates metabolic activity • Secrete hormones into ECF • Slow acting • Long living • Act on target cells • Signaling molecules • Other tissues produce hormones too

  3. Categories of Hormones • Amino acid based • Chains of AA’s • Not membrane soluble (hydrophilic) • Regulatory G proteins and 2nd messengers • e.g. oxytocin, insulin, and prolactin • e.g. epinephrine, norepinephrine, and thyroxine • Derived from AA tryptophan and tyrosine • Steroids • Lipids made from cholesterol • Membrane soluble (hydrophobic) • Direct gene activation • e.g. testosterone, estrogen, and cortisol

  4. Amino Acid Action (cAMP) • Binds to PM receptors (1st messenger) • Conformation change binds inactive G protein • Activated by GTP replacing GDP • Active G protein binds to adenylatecyclase(effector) • Stimulatory (Gs) or inhibitory (Gi) • cAMP (2nd messenger) from ATP • cAMP activates protein kinase A • Phosphorylates proteins causing signaling cascade • Target cell specificity produces/inhibits hormone production • Phosphodiesterase rapidly degrades

  5. Amino Acid Action (PIP2) • Binds to PM receptors (1st messenger) • Conformation change binds inactive G protein • Activated by GTP replacing GDP • Active G protein binds to phospholipase C (effector) • Stimulatory (Gs) or inhibitory (Gi) • DAG and IP3 (2nd messengers) from PIP2 • DAG activates protein kinase C • IP3 triggers Ca2+ (2nd messenger) release

  6. Steroid Action • Binds to intracellular receptors • Hormone-receptor complex binds to DNA • Activates or inhibits • Gene transcription (mRNA production) • mRNA translated into proteins

  7. Hormonal Functioning • Stimulating release • Humoral: concentration of ions & nutrients in blood • Drop in Ca2+ signals PTH or increased glucose signals insulin • Neural: nerve fibers • Stress (SNS) signals NE and Epi • Hormonal: other endocrine gland secretions • Hypothalamus signals anterior pituitary • Interactions at target cells • Permissiveness: requirement of 1+ hormone for full effect • Reproductive hormones need thyroid hormone • Synergism: 1+ hormone produces same effect  both amplifies • Glucagon and epinephrine signal liver to release glucose • Antagonism: hormones oppose one another • Glucagon increases and insulin decreases blood glucose levels • Generally regulated by negative feedback • Oxytocin is positive feedback

  8. Pituitary Gland • Posterior lobe is neural tissue • Store hypothalamic hormones • Exocytic release on demand • Anterior lobe is glandular tissue • Produce hormones • Release of hormones to blood portal system • Hypothalamic control • Releasing or inhibiting hormones

  9. Posterior Lobe • Oxytocin • Uterine contractions (smooth muscle) • Milk letdown (glandular muscle) • Sexual arousal, satisfaction, and ‘bonding’ behavior in males & nonlactating females • Antidiuretic hormone • Water balance and loss • Vasoconstriction of visceral blood vessels • Raises blood pressure  vasopressin

  10. Anterior Lobe • Tropic hormones • TSH • ACTH • FSH • LH • Non-tropic • GH • PRL • Melanocyte-stimulating hormone (MSH): controls appetite

  11. Growth Hormone • Growth hormone releasing (GHRH) and inhibiting (GHIH) hormones regulate • Increase size of multiple target cells • Promotes protein synthesis/growth • Primarily skeletal muscle mass and bone length • Metabolic effects (glucose conservation) • Mobilize fat from adipose • Hypersecretion • Gigantism: in children; tall stature w/ normal body proportions • Acromegaly: in adults; disproportionately large hands, feet, face • Hyposecretion • Pituitary dwarfism: in children; short stature w/normal body proportions • TSH, LH, and FSH reduced can misproportioned and/or delay sexual maturity • Artificial production w/ pros and cons

  12. Prolactin • Prolactin inhibiting hormone (PIH) regulates • Stimulates milk production • Rise and fall w/ estrogen levels in females • Breast tenderness prior to menstrual period • Elevates at end of pregnancy; suckling maintains • Role in males is not understood • Hypersecretion • Inappropriate lactation, lack of menses, impotence in males • Hyposecretion only problem for nursing females

  13. Thyroid Gland • Thyrotropin-releasing hormone (TRH) regulates TSH release to regulate • Anatomy • Bilobed structure w/connecting isthmus • Composed of follicles surrounded by follicular cells w/ thyroglobin • Colloid in lumen is thyroglobin bound to iodine  thyroid hormone • Parafollicularcells w/i follicular epithelium secretes calcitonin • Inhibits osteoclast activity and Ca 2+ release; stimulates Ca 2+ uptake

  14. Thyroid Hormone (TH) • Most processes in body (table 16.2) • Steroid hormone action • Oxidizes glucose to up metabolic rate & heat production • Maintains blood pressure • Regulates tissue growth and development • Skeletal and nervous system development • Reproductive maturation • Thyroxine (T4) primarily produced, but converted to triiodothytonine (T3) by targets

  15. Thyroid Imbalances • Hypothyroidism • Myxedema in adults • Low metabolic rate, chills, dry skin, puffy eyes, lethargy, edema • Goiter from lack of iodine • Gland enlargement • Cretinism when severe in infants • Mental retardation and short, disproportionate body • Hyperthyroidism • Graves’ disease from autoimmune attack of follicle cells • Elevated metabolic rate, sweating, rapid heart rate, weight loss, protruding eyeballs

  16. Adrenal Gland • Adrenal cortex is glandular tissue • Long-term stress responses • Corticosteroids derived from cholesterol • Corticotropic releasing hormone (CRH) regulates ACTH to regulate • Adrenal medulla is neural tissue • Short-term stress responses • Epinephrine (Epi) • Norepinephrine (NE) • Hypothalamic neural signal (SNS)

  17. Adrenal Cortex • Zonaglomerulosa produce mineralcorticoids • Aldosterone (chpts. 25 & 26) • Zonafaciculataproduce glucocorticoids • Cortisol stimulates gluconeogenesis • Excessive levels cause anti-inflammatory and –immune functions • Zonareticularisproduce sex steroids (androgens) • Onset of puberty, hair production, and sex drive in women • Testosterone (and estrogen) precursors

  18. Adrenal Cortex Imbalances • Hyposecretion • Addison’s disease (mineral- and glucocorticoids) • Loss of weight, drop in glucose and Na+, increase in K+ • Dehydration and hypotension are common • Hypersecretion • Cushing’s disease (glucocorticoids) • Chronic elevated blood glucose, loss of muscle and bone, H2O and NaCl retention • Hypertension, edema, swollen face, neck hump, bruise tendency • Masculinizationprepubescently (sex steroids) • Strong sex drive in males • Masculine body hair patterns and clitoris resembling a penis in females

  19. Adrenal Medulla • SNSregulates • Secrete epinephrine (Epi) and norepinephrine (NE) • Similar effects • Tyrosine  dopamine  NE  Epi • Hypersecretion increases SNS effects

  20. Gonads • Gonadotropin-releasing hormones (GnRH) regulates FSH and LH to regulate • Ovaries and testes contain all types, but ratios vary • Estrogens (estradiol) • Maintain female system • Development of 2° sex characteristics • Derived from androgens • Masculinize male brain in early development • Progesterone • Prepare and maintain uterus • Breast development • Can be converted to testosterone • Testosterone • Maintain and stimulate development of male system • Development of 2° sex characteristics and sex drive • 7th week level determines sex

  21. Parathyroid Gland • Tiny glands on the posterior thyroid • Chief cells secrete parathyroid hormone (PTH) • Regulates blood Ca2+ levels (fig 16.12) • Skeleton: stimulates osteoclast activity • Intestine: increases Ca2+ reabsorption (vitamin D) • Kidneys: activates vitamin D and enhances Ca2+ reabsorption in nephrons • Hyperparathyroidismis rare • Ca2+ leaches from bones causing softening and deformation • Elevated Ca2+ depresses nervous system and kidney stones form • Hypoparathyroidism • Low Ca2+ levels increases excitability of neurons

  22. Pancreas • Acinar cells produce enzyme rich digestive juices • Islets of Langerhans produce hormones • Alpha (α) cells produce glucagon w/ fasting • Beta (β) cells produce insulin w/feeding

  23. Diabetes Mellitus • Blood glucose levels high after feeding • Type I (insulin dependent) • Autoimmune disease • WBC’s attack beta cells (hyposecretion) • Type II (non-insulin dependent) • Older onset • Cells can’t use insulin (hypoactivity)

  24. Other Hormone Producing Structures • Heart: ANP reduces blood pressure, volume, and [Na+] • GI tract: enteroendocrine cells release local digestive hormones (gastrin, secretin, CCK) • Placenta: human chorionic gonadotrophic (hCG) to sustain fetus and pregnancy • Kidneys: secrete erythropoietin (EPO) to signal erythropoiesis

  25. Other Hormone Producing Structures • Skin: choleocalciferolproduce precursor of vitamin D • Adipose tissue: leptin signals stored energy levels and satiety; increase activity levels • Thymus: large in children, diminishes in size w/age; thymosin and thymopoietins stimulate T-cells • Pineal gland: releases melatonin to regulate rhythmic variation of physiological processes

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