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The Endocrine System

The Endocrine System. Chapter 15. Hormones. Secreted by endocrine glands, endocrine cells, and certain neurons Travel through the bloodstream to nonadjacent target cells. Other Signaling Molecules. Neurotransmitters Local signaling molecules Pheromones. Discovery of Hormones.

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The Endocrine System

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  1. The Endocrine System Chapter 15

  2. Hormones • Secreted by endocrine glands, endocrine cells, and certain neurons • Travel through the bloodstream to nonadjacent target cells

  3. Other Signaling Molecules • Neurotransmitters • Local signaling molecules • Pheromones

  4. Discovery of Hormones • Bayliss and Starling severed nerves to dog’s intestine; left blood vessels intact • Pancreas still responded • Extracts of glandular epithelium also provoked pancreatic response • Extracts contained secretin

  5. Hormone Interactions • Opposing interaction • Synergistic interaction • Permissive interaction

  6. Endocrine System Main Sources • Pituitary gland • Adrenal glands • Thyroid gland • Parathyroid glands • Pineal gland • Thymus gland

  7. Responses to Hormones Vary • Different hormones activate different responses in the same target cell • Not all types of cells respond to a particular hormone

  8. Two Main Hormone Types • Steroid hormones • Derived from cholesterol • Estrogens, progestins, androgens (such as testosterone), cortisol, aldosterone • Peptide hormones • Peptides, proteins, or glycoproteins • Glucagon, ADH, oxytocin, TRH, insulin, somatotropin, prolactin, FSH, LH, TSH

  9. Steroid Hormones hormone • Most diffuse across the plasma membrane and bind to a receptor • Hormone-receptor complex acts in nucleus to inhibit or enhance transcription receptor hormone-receptor complex gene product

  10. Protein Hormone glucagon • Hormone binds to a receptor at cell surface • Binding triggers a change in activity of enzymes inside the cell glucagon receptor cyclic AMP + Pi ATP cAMP activates protein kinase A Protein kinase A converts phosphorylase kinase to active form and inhibits an enzyme required for glucagon synthesis.

  11. The Hypothalamus hypothalamus • Region in the forebrain • Contains hormone-secreting cells • Interacts with pituitary pituitary gland

  12. Pituitary Gland • Pea-sized gland at base of hypothalamus • Two lobes • Posterior lobe stores and secretes hormones that were synthesized in the hypothalamus • Anterior lobe produces and secretes its own hormones

  13. Posterior Lobe cell body in hypothalamus • Antidiuretic hormone (ADH) • Oxytocin (OCT) axons to the general circulation

  14. Anterior Pituitary • ACTH • TSH • FSH • LH • PRL • STH

  15. Normal Hormone Production • Generally, the body produces only very small amounts of hormones • To isolate 1 milligram of TRH, researchers dissected 7 metric tons of hypothalamic tissue

  16. Abnormal Somatotropin Output • Gigantism • Pituitary dwarfism • Acromegaly

  17. Feedback Mechanisms • Negative feedback • An increase in concentration of a hormone triggers activities that inhibit further secretion • Positive feedback • An increase in concentration of a hormone triggers activities that stimulate further secretion

  18. Cortisol • Cortisol secretion • Inhibits blood glucose uptake by muscle and other tissues • Causes breakdown of proteins to amino acids and conversion to glucose • Causes degradation of adipose tissue to fatty acids for use as energy source

  19. Feedback Control of Cortisol Secretion • Hypothalamus senses rise in glucose and secretes less releasing hormone (CRH) • Anterior pituitary responds by secreting less ACTH • Adrenal cortex slows its secretion of cortisol

  20. Localized Feedback in Adrenal Medulla • Norepinephrine secreted by neurons in the medulla accumulates in the synaptic gap • Some molecules bind to receptors on the axon endings that secreted them • This prevents further secretion of norepinephrine by that axon

  21. Thyroid Gland Disorders • Goiter • Hyperthyroidism • Hypothyroidism

  22. Calcium Regulation • Parathyroid hormone (PTH) is the main regulator of calcium in the blood • It is secreted when calcium levels drop • PTH causes bone cells to digest bone tissue and release calcium • PTH also stimulates calcium reabsorption by the kidneys and absorption by the gut

  23. Control of Glucose Metabolism insulin Glucose uptake Glucose to glycogen Glucose falls Glucose is absorbed Cells use glucose Glucose rises Glycogen to glucose glucagon

  24. Diabetes Mellitus • Disease in which excess glucose accumulates in blood, then urine • Effects include • Excessive urination • Constant thirst • Weight loss • Ketone formation and acid-base imbalances

  25. Two Types of Diabetes • Type 1 • Autoimmune disease • Usually appears in childhood • Treated with insulin injections • Type 2 • Target cells don’t respond • Usually appears in adults • Treated with diet, drugs

  26. The Pineal Gland • Photosensitive gland embedded in brain • In the absence of light, secretes melatonin • Affects the human biological clock • May also play a role in human puberty and in seasonal affective disorder

  27. Local Signaling Molecules • Prostaglandins • Produced and secreted in response to local changes • Sixteen types with a variety of effects • Growth factors • Affect cell division rates in tissues

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