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The Endocrine System

The Endocrine System. chapter 16. Endocrine System: Definitions. Endocrine – releasing substances into blood Endo = within or internal Contrast with Exocrine – releasing substances outside the body Hormone – a chemical that influences the function of a remote tissue (acts at a distance).

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The Endocrine System

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  1. The Endocrine System chapter 16

  2. Endocrine System: Definitions • Endocrine – releasing substances into blood • Endo = within or internal • Contrast with Exocrine – releasing substances outside the body • Hormone – a chemical that influences the function of a remote tissue (acts at a distance)

  3. 9 glands in total Endocrine glands pituitary thyroid parathyroid adrenal pineal thymus Mixed glands produce both hormones and exocrine products pancreas gonads produce hormones and has neural functions hypothalamus Endocrine System: Overview

  4. Pineal gland Hypothalamus Pituitary gland Thyroid gland Parathyroid glands (on dorsal aspect of thyroid gland) Thymus gland Adrenal glands Pancreas Ovary (female) Testis (male)

  5. Hormones • How they work • Regulate the metabolic function of other cells • Have lag times ranging from seconds to hours • Tend to have prolonged effects • Are classified as amino acid-based hormones, or steroids

  6. 2 M ain Types of Hormones • Amino acid based • Water-soluble • Do not enter the cell • e.g., insulin, norepinepherine, epinephrine • Steroids • Lipid soluble • Act intracellularly and activate genes • e.g., testosterone, estrogen, cortisol

  7. Mechanism of Hormone Action • Act on receptors in the plasma membrane • Amino acid–based hormones • e.g., epinephrine- binds to smooth muscle cells in blood vessels - causing contraction • Direct gene activation • Steroid hormones, thyroid hormones • e.g., growth hormone - stimulates cells to increase in size and divide • The precise response depends on the type of the target cell • The ONLY tissue to respond is the Target Tissue (may be very specific (1) tissue, or multiple tissues)

  8. Hormone Blood Concentrations • Concentrations of circulating hormone reflect: • Rate of release • Speed of inactivation and removal from the body • Hormones are removed from the blood by: • Degrading enzymes • The kidneys • Liver enzyme systems

  9. Hypothalamic Control • Hypothalamus “releasing hormones” and “inhibiting hormones” tells of central control by brain • GHRH (growth hormone RH) and GHIH (growth hormone IH) control GH from Ant. Pituitary • PRH (prolactin RH) and PIH control PL from Ant. Pit. • TRH  thyrotropin RH – release of TSH from Ant. Pit. • CRH  corticotropin releasing hormone – release of hormones from adrenal cortex  Stress • GnRH  gonadotropin RH – release of gonadal hormones from Ant. Pit.  LH and FSH

  10. Pituitary (Hypophysis) • Pituitary gland • two-lobes • secretes 9 major hormones • Connected to the hypothamus by • Posterior Lobe • Neurohypophysis – neural tissue) and the infundibulum • Receives, stores, and releases hormones from the hypothalamus • Anterior Lobe • Adenohypophysis – made up of glandular tissue • Synthesizes and secretes a number of hormones

  11. Pituitary (Hypophysis) Figure 16.6

  12. Anterior Pituitary Hormones • regulate other endocrine glands • GH – growth hormone • TSH – thyroid stimulating hormone • ACTH – adrenocorticotrophic hormone • FSH – follicle stimulating hormone • LH – luteinizing hormone • PRL - prolactin (latter 3 are called gonadotropins)

  13. Growth Hormone (GH) • Underproduction in children  dwarfism • Overproduction in children  gigantism • Overproduction in adults  acromegaly

  14. Posterior Pituitary Hormones • Posterior pituitary • stores antidiuretic hormone (ADH) and oxytocin • ADH and oxytocin are synthesized in the hypothalamus • Oxytocin stimulates smooth muscle contraction in breasts and uterus • “cuddle hormone” • Both are amino acid based • Receptor location?

  15. Pancreas • both exocrine and endocrine cells, • Acinar cells  enzyme-rich juice used for digestion (exocrine product) • Pancreatic islets (islets of Langerhans) produce hormones (endocrine products) • The islets contain two major cell types: • Alpha () cells that produce glucagon • Beta () cells that produce insulin

  16. Regulation of Blood Glucose Levels • hyperglycemic  glucagon  glucose uptake • hypoglycemic  insulin  glucose release Figure 16.18

  17. Diabetes Mellitus (DM) • Results from hyposecretion or hypoactivity of insulin • The three cardinal signs of DM are: • Polyuria – huge urine output • Polydipsia – excessive thirst • Polyphagia – excessive hunger and food consumption

  18. Thyroid Gland • thyroid hormone metabolism, BP, growth • T3 (10x) • T4 • calcitonin response to rising blood calcium – inhibit gut absorption and kidney reabsorption of Ca++

  19. Thyroid Disorders • Hypothyroidism • Thyroid gland defect, inadequate TSH, lack of iodine • Low metabolic rate, feeling chilled • Goiter formation ( if cause is lack of iodine) • Cretinism = Hypothyroidism in infants • Stunted growth, low mentality • can be prevented by hormone replacement therapy

  20. Grave’s Disease • Hyperthyroidism • Autoimmune disease- body attacks and stimulates the thyroid cells - increased thyroid hormone • High BMR, Weight loss, Increased heart rate, Protrusion of the eyeballs, goiter • Treated by surgical removal of the thyroid gland

  21. Parathyroid Glands • PTH (parathormone) • response to falling calcium in blood – promotes gut absorption and kidney reabsorption of Ca++ • Question: • what two hormones regulate calcium in blood?

  22. Adrenal (Suprarenal) Glands • Adrenal glands • cope with stressful events • Structurally and functionally, they are two glands in one • Adrenal cortex – glandular tissue • Adrenal medulla – neural tissue that acts as part of the SNS

  23. Adrenal Cortex Hormones • Aldosterone - dehydration • causes kidney to reabsorb Na+  reabsorb water • stimulated by angiotensin (remember Renin) • Cortisol - stress • increases blood glucose levels & reduces edema of tissues • prolonged high levels  changes in neural and circulatory function, depressed bone/cartilage growth, suppressed immune response

  24. Adrenal Cortex Hormones • Androgens (masculinizing hormones) • most important is testosterone • the onset of puberty • secondary sex characteristics • sex drive in females • testosterone can be converted to estrogen in females after menopause

  25. Disorder • Addison’s disease • Hyposecretion of the adrenal cortex • Deficiency in cortisol and aldosterone • Low BP • Hypoglycemia • Cushings disease • Hypersecretion of adrenal cortex (tumor of the adrenal cortex) • Hyperglycemia • “buffalo hump” (fat on upper back)

  26. Adrenal Medulla • secretes the catecholamines • epinephrine • norepinephrine • “Fight or Flight” secretion causes: • blood glucose levels to rise • blood vessels to constrict • faster heart rate • blood diversion to brain, heart, and skeletal muscle

  27. Adrenal Medulla • Epinephrine is the more potent stimulator of the heart and metabolic activities • Norepinephrine is more influential on peripheral vasoconstriction and blood pressure

  28. Stress and the Adrenal Gland Figure 16.16

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