Anatomy and Physiology: The Endocrine System

1. Anatomy and Physiology: The Endocrine System

2. Overview • Endocrine System Overview • Hormone Secretion/Pos. & Neg. Feedback • Hypothalamus and Anterior Pituitary • Posterior Pituitary • Thyroid Gland • Parathyroid Glands • Adrenal Cortex • Pancreas • Gonads • Pineal Gland

3. Essential Terms hormone • chemical mediator that helps maintain homeostasis target cell • cell with a receptor that responds to the presence of a hormone

4. General Characteristics • Glands that secrete chemical signals (hormones) into circulatory system • Hormone characteristics • Produced in small quantities • Secreted into intercellular space • Transported some distance in circulatory system • Acts on target tissues elsewhere in body • Regulate activities of body structures

5. Endocrine System Functions • Metabolism and tissue maturation • Ion regulation • Water balance • Immune system regulation • Heart rate and blood pressure regulation • Control of blood glucose and other nutrients • Control of reproductive functions • Uterine contractions and milk release

6. Endocrine Glands • exocrine glands secrete products onto a surface • endocrine glands secrete products into the body fluids • hormones are carried to target tissues where activity is carried out • pituitary, thyroid, parathyroid, adrenal, pineal • Other hormone secreting structures • hypothalamus, thymus, pancreas, ovaries, testes, kidneys, stomach, liver, small intestine, skin, heart, adipose tissue, placenta

7. Figure 17.1

8. Regulation of Activities: Comparison of Endocrine and Nervous Systems • Endocrine: amplitude modulated signals. • Amount of hormone determines strength of signal • Onset within minutes of secretion of hormone • Nervous: frequency-modulated signals. • Frequency of action potentials produced by neurons determines strength of signal. • Onset within milliseconds • Two systems actually inseparable • Nervous system secretes neurohormones into circulatory system • Nervous system uses neurotransmitters and neuromodulators as ligands • Some parts of endocrine system innervated directly by nervous system

9. Intercellular Chemical Signals • Hormones: type of intercellular signal. Produced by cells of endocrine glands, enter circulatory system, and affect distant cells; e.g., estrogen • Autocrine: released by cells and have a local effect on same cell type from which chemical signals released; e.g., prostaglandin • Paracrine: released by cells and affect other cell types locally without being transported in blood; e.g., somatostatin • Pheromones: secreted into environment and modify behavior and physiology; e.g., sex pheromones • Neurohormone: produced by neurons and function like hormones; e.g., oxytocin • Neurotransmitter or neuromodulator: produced by neurons and secreted into extracellular spaces by presynaptic nerve terminals; travels short distances; influences postsynaptic cells; e.g., acetylcholine.

10. Functional Classification of Intercellular Chemical Signals

11. Functional Classification of Intercellular Chemical Signals

12. Control of Secretion Rate • Most hormones controlled by negative feedback systems • Most hormones are not secreted at constant rate, but their secretion is regulated by three different methods • The action of a substance other than a hormone on an endocrine gland. • Neural control of endocrine gland. • Control of secretory activity of one endocrine gland by hormone or neurohormone secreted by another endocrine gland

15. Table 17.1

16. Receptors • hormones only affect target cells • water soluble hormone receptors on outside surface and trigger response inside the cell • lipid soluble hormone receptors on inside of cell and trigger response inside cell • target cells generally have between 2,000 and 100,000 receptors for a given hormone

17. Chemical Classes of Hormones • water soluble • amino acid based • lipid soluble • steroids • thyroid hormones • nitric oxide • transported in blood by transport proteins • slow rate of loss in kidneys • ready reserve of hormone in blood stream

18. Table 17.2 pt 1

19. Table 17.2 pt 2

20. Hormone Action • variable depending on hormone and target cell • various targets respond differently to same hormone • some hormones activate synthetic or stimulatory processes • others activate degradation or inhibitory processes

21. Figure 17.2

22. Figure 17.3

23. Hormone Interactions • permissive effects • one hormone allows the other to function • synergistic effects • one hormone intensifies the effects of the other • antagonistic effects • one hormone inhibits or reduces the effects of the other

24. Control of Hormone Secretion • hormones secreted in bursts • as stimulation increases bursts increase in frequency • in absence of stimulation, bursts are minimal or inhibited • regulated by • neural signals • chemical changes in blood • other hormones

25. Hypothalamus & Pituitary Gland

26. Hypothalamus • controls the activity of the pituitary gland • major integrating link between the nervous and endocrine systems • hormones that stimulate anterior pituitary are all either releasing hormones or inhibiting hormones

27. Releasing and Inhibiting Hormones • Tropins or tropic hormones: hormones that regulate the hormone secretions of target endocrine tissues. All anterior pituitary hormones are tropins. • Releasing hormones: • GHRH. Growth hormone-releasing hormone. Causes the anterior pituitary to release growth hormone. • TRH. Thyroid-releasing hormone. Causes the anterior pituitary to release thyroid-stimulating hormone (TSH). • CRH. Corticotropin-releasing hormone. Causes anterior pituitary to produce adrenocorticotropic hormone. • GnRH. Gonadotropin-releasing hormone. Causes anterior pituitary to produce FSH (follicle stimulating hormone) and LH (luteinizing hormone). • PRH. Prolactin-releasing hormone. Causes the anterior pituitary to release prolactin. • Inhibiting hormones: • GHIH. Growth hormone-inhibiting hormone, somatostatin. Causes the anterior pituitary to decrease release of growth hormone. • PIH. Prolactin-inhibiting hormone. Causes the anterior pituitary to decrease release of prolactin.

28. Figure 17.4

29. Pituitary Gland • two lobes • anterior lobe • stimulated by tropic hormones from hypothalamus • hypophyseal portal system • posterior lobe • neural tissue that releases hormones produced in the hypothalamus • neurosecretory cells

30. Table 17.3

31. Figure 17.5

32. Figure 17.6

33. Figure 17.11

34. FSH & LH • released by the anterior pituitary • triggered by GnRH • target tissue gonads • FSH • in females initiates development of ovarian follicles • in males stimulates sperm production • LH • in females triggers ovulation • in males triggers testosterone secretion

35. PRL • released by the anterior pituitary • trigger is PRH and PIH from hypothalamus • initiates and maintains milk secretion and production by mammary glands in females • in males can cause erectile dysfunction

36. ACTH • secreted by anterior pituitary • triggered by CRH • also triggered by stress • controls production and secretion of hormones called glucocorticoids • cortisol from adrenal cortex • cause negative feedback regulation of CRH and ACTH release

37. Figure 17.16

38. MSH • secreted by anterior pituitary • function unknown in humans • presence of MSH receptors in brain suggests it may influence brain activity • excessive CRH stimulates MSH release • PIH inhibits MSH release

39. Table 17.4 pt 1

40. Table 17.4 pt 2

41. Posterior Pituitary

42. Posterior Pituitary • AKA neurohypophysis • store and release two hormones produced by hypothalamus • ADH • OT

43. Figure 17.4

44. OT • oxytocin • targets uterus and mammary glands during and after delivery • uterus contracts • milk ejection (“let down”) • function in non-reproducing women and in men is unknown • animal studies seem to indicate parental caretaking behavior toward offspring • sexual pleasure during and after intercourse

45. ADH • antidiuretic hormone • decreases urine production • kidneys return water to blood • decreases sweating • causes constriction of arterioles • increases blood pressure • AKA vasopressin

46. Figure 17.8

47. Table 17.5

48. Thyroid Gland

49. TSH • follicular cells produce • thyroxine (T4) • triiodothyronine (T3) • parafollicular cells produce • calcitonin • involved in calcium homeostasis • brings calcium levels down when too high

50. Figure 17.11