Chapter 18: The Endocrine System

1. Chapter 18: The Endocrine System BIO 211 Lecture Instructor: Dr. Gollwitzer

2. Today in class we will: • Compare intercellular communication in the endocrine and nervous systems • Learn the differences and similarities in each system’s function(s) and how they are important with regard to homeostasis in the body • Talk about hormones • The 3 major structural classes and examples of each • The secretion, distribution, and elimination of hormones • The mechanisms that allow hormones to affect target cells and organs • Identify the organs of the endocrine system • Learn the names of the hormones that each endocrine organ produces

3. Intercellular Communication • Cellular activities in the body must be coordinated to maintain homeostasis (a stable internal environment within the body) • Homeostasis is the key to survival in an ever changing environment • Failure to maintain homeostasis eventually leads to illness or death • Activities in the human body are coordinated through intercellular communication (communication between cells)

4. Table 18-1 Mechanisms of Intercellular Communication

5. Endocrine System vs. Nervous SystemDifferences • Endocrine system • Endocrine communication • Via hormones • Thru circulatory system • Affects target cells in other tissues/organs distant to tissue of origin • Slow response, but lasts much longer • Nervous System • Neural (synaptic) communication • Via neurotransmitters • Across synaptic cleft • Affects limited, specific area (post-synaptic) • Fast response, short-term crisis management

6. Endocrine System vs. Nervous SystemSimilarities • Both systems: • Share many chemical messengers • Use chemical messengers that must bind to specific receptors on their target cells • Share the common goal of maintaining homeostasis

7. Endocrine System • One of the body’s two coordination/communication systems • Nervous system is the other • Endocrine glands are ductless glands • Communicate with other cells/organs/ systems in the body through release of hormones • Endocrine cells  hormone (chemical messenger)  interstitial fluid or circulatory system  target cells  effect(s)

8. Examples of Endocrine Control • Growth and maturation • Sexual development (puberty) • Reproduction • Response to environmental stress 24 hours/day for a lifetime

9. Hormone Structure • Divided into 3 major groups based on chemical structure • Amino acid derivatives • Peptide hormones • Produced as inactive prohormones; converted to active hormones • Lipid derivatives

10. Hormone Structure:Amino Acid Derivatives • Small molecules structurally related to amino acids • Derivatives of tyrosine • Thyroid hormones – T3, T4 • Catecholamines – epinephrine and norepinephrine, dopamine • Derivative of tryptophan • Melatonin

11. Figure 18–2

12. Hormone Structure:Peptide Hormones • Chains of amino acids • Synthesized as prohormones • Inactive molecules converted to active hormones before or after secretion • 2 Groups • Glycoproteins • Short polypeptides and small proteins

13. Figure 18–2

14. Glycoproteins • More than 200 amino acids long, with carbohydrates • Released by: • Anterior pituitary: LH, FSH, TSH • Reproductive organs: inhibin • Kidneys: erythropoietin

15. Short Polypeptides andSmall Proteins • All other hormones secreted by: • Hypothalamus • Anterior pituitary • Posterior pituitary • Pancreas • Parathyroid gland • Thymus, heart, and digestive tract

16. Hormone Structure:Lipid Derivatives • 2 Classes • Steroid hormones • Synthesized from cholesterol • Eicosanoids • Synthesized from arachidonic acid

17. Figure 18–2

18. Steroid Hormones • Produced by: • Male and female reproductive organs • Testes  androgens (testosterone) • Ovaries  estrogens and progestins (progesterone) • Adrenal glands  corticosteroids • Kidneys  calcitrol • Bound to transport proteins in plasma (albumins, globulins) so remain in circulation longer than peptide hormones

19. Eicosanoids • Small molecules with 5-C ring at one end • Important local (paracrine) hormones secreted by all cells except RBCs • Primarily affect neighboring cells • Coordinate cellular activities • Affect enzymatic processes in extracellular fluid • 2 Types • Leukotrienes (from WBCs or leukocytes) • Coordinate tissue response to injury or disease • Protaglandins (produced by most tissues of the body) • Coordinate local cellular activities

20. Hormone Distribution and Transport • Hormones secreted/released into: • Interstitial space • Capillaries • Circulate/distributed through bloodstream as: • Free hormones • Bound hormones

21. Free Hormones • Proteins, polypeptides, amino acid derivatives • Rapidly removed from bloodstream • Diffuse out of bloodstream and bind to receptors on target cells • Absorbed by liver or kidney and broken down • Broken down by enzymes in plasma or interstitial fluids • Functional for <1 hr

22. Bound Hormones • Thyroid and steroid hormones • Bound to transport proteins in blood, i.e., albumins and globulins • Remain in circulation much longer (weeks)

23. Hormone Function and Mechanism of Action on Target Organs • Alter cellular operations • Change biochemical properties or physical structure of target cells • Activate genes in nucleus that code for synthesis of enzyme or structural protein • Turn existing enzyme on or off by changing its shape or structure • Increase/decrease rate of synthesis of enzyme or other protein

24. Hormone Function and Mechanism of Action • Hormone effect depends on: • Type of target cell • Type of receptor = protein molecule to which particular hormone binds strongly • Requires interaction of hormone with appropriate receptor • Presence or absence of specific receptor determines cell’s hormonal sensitivities • Receptor present  response • Receptor absent  no response

25. Hormone Receptors • On cell membrane (extracellular) • For water-soluble hormones (can’t cross membrane) • Catecholamines (E and NE) • Peptide hormones • Hormones can’t have direct effect inside cell • Act as first-messenger • Causes second-messenger to appear in cytoplasm (cAMP, cGMP, Ca++) • Second messenger  changes in rates of metabolic reactions

26. Figure 18–3

27. Hormone Receptors • Inside cell (intracellular) • For lipid-soluble hormones (can cross membrane) • Steroid and thyroid hormones • Cross cell membrane and bind to receptors in cytoplasm or nucleus • Hormone/receptor complex activates/inactivates specific genes and changes protein/enzyme synthesis, e.g., • Testosterone stimulates production of enzymes and protein in skeletal muscle, causing increased muscle mass and strength • Thyroid hormones increase/decrease concentrations of enzymes and bind to mitochondria and increase ATP production

28. Figure 18–4

29. Endocrine Organs • Hypothalamus • Pituitary gland • Thyroid gland • Parathyroid glands • Adrenal glands • Pineal gland • Pancreas • Kidneys • Other: heart, thymus, adipose tissue • Reproductive organs (gonads and placenta)

30. Fig 18-1

31. Today in class we will: • Discuss the hormones (and each hormone’s function) along with the general effects of abnormal levels of each hormone produced by the: • Hypothalamus • More in depth info on the hypothalamus: • The structural relationship of the hypothalamus and pituitary gland • Learn about the hypophyseal portal system and its importance • Learn how the hypothalamus controls endocrine function • Pituitary gland • Identify hormones secreted by the posterior pituitary gland and produced and secreted by the anterior pituitary gland • Thyroid gland • Parathyroid glands

32. Hypothalamus:A Neuroendocrine Organ • Neural effects • Controls feeding reflexes, heart rate, blood pressure, body temp, day-night activity cycles • Endocrine contribution • Hormone synthesis (for release by posterior pituitary), i.e., ADH and OT • Transported via axons of neurosecretory cells to posterior pituitary for release • Hormone synthesis and release, i.e., RHs • Transported via hypophyseal portal system to anterior pituitary

33. Hypothalamus Figure 14–10a

34. Hypothalamic Hormones • Hypothalamus produces: • ADH (antidiuretic hormone) • OT (oxytocin) • RHs (regulatory hormones)

35. Hypothalamic Hormones • ADH (antidiuretic hormone) • Produced by supraoptic nuclei (released by posterior pituitary) • Effects • Decreases water lost at kidneys by increasing reabsorption • Elevates blood pressure through vasoconstriction • Release inhibited by alcohol why you urinate a lot while drinking

36. Diabetes Insipidus • Inadequate amounts of ADH released from posterior pituitary • Impairs water conservation at kidneys  watery urine

37. Hypothalamic Hormones • OT (oxytocin) • Produced by paraventricular nuclei (released by posterior pituitary) • Produced during: • Sex, breastfeeding, and other bonding experiences (increases trust and compassion) • Labor • Stimulates smooth muscle in: • Mammary gland  milk ejection • Uterus to promote labor and delivery • Male and female reproductive tracts • Plays a role in sexual function

38. Hypothalamic Hormones • RHs (regulatory hormones) • Produced by median eminence (tuberal area) • Stimulate/inhibit anterior pituitary hormone synthesis and release

39. Hypophyseal Portal System • Prevents dilution of very small quantities of RHs by systemic circulation • Ensures RHs entering portal vessels will reach target cells in anterior pituitary

40. Fig 18-7

41. Control of Endocrine Organs • Involves endocrine reflexes, i.e., stimulus  hormone secretion • In most cases, controlled by negative feedback mechanisms • Hormones released in response to one or more of the following stimuli: • Humoral • Neural • Hormonal

42. Control of Endocrine Organs • Humoral stimuli • From local changes in composition of extracellular fluid • Hormones released continually, but rate rises and falls in response to humoral stimulation • e.g., pancreatic hormones increased blood glucose  increased extracellular glucose  increased insulin

43. Control of Endocrine Organs • Neural stimuli • Via arrival of neurotransmitters at neuroglandular junctions • e.g., hypothalamic control of adrenal medullae via action potentials along efferent nerve fibers (also have hormonal component) • Hypothalamus has autonomic centers that exert direct neural control over endocrine cells of adrenal medullae • When sympathetic division activated, adrenal medullae release E and NE into bloodstream

44. Control of Endocrine Organs • Hormonal stimuli • Via arrival/removal of hormones from other endocrine glands • Hypothalamus • Highest level of endocrine control • Secretes regulatory hormones/factors that stimulate synthesis and secretion of anterior pituitary hormones and/or prevent the synthesis and secretion of hormones • Anterior pituitary • Hormones it secretes controls activities of other endocrine organs (thyroid, adrenal cortex, reproductive organs)

45. Hypothalamic Control ofEndocrine Function • Involves most complex responses • Integrates activities of nervous and endocrine systems • 3 mechanisms • Secretion of AP regulatory hormones • Production of ADH and oxytocin • Control of sympathetic stimulation of adrenal medullae

46. Figure 18–5

47. Hypothalamic Control ofEndocrine Function • Secretion of AP regulatory hormones • Neurosecretory cells in median eminence of Hth secrete RHs • Delivered to AP thru hypophyseal portal system • Control release of AP hormones (e.g., TSH, ACTH, FSH, LH) that control other endocrine organs • Rate of RH release controlled by negative feedback

48. Hypothalamic Regulatory Hormones Figure 18–8a

49. Hypothalamic Control ofEndocrine Function • Production of ADH and oxytocin • Hth acts as endocrine organ by producing ADH and oxytocin that are released by PP • Neurosecretory cells connect Hth to PP • ADH and oxytocin packaged in vesicles and transported along axons to PP where they are stored in axon terminals • When neurosecretory cells stimulated, action potential triggers release of stored ADH and oxytocin from PP

50. Hypothalamic Control ofEndocrine Function • Control of sympathetic stimulation of adrenal medullae • Hth contains autonomic centers • Exert direct control over adrenal medullae  E and NE