Endocrine System

1. Endocrine System Biology 211: Anatomy & Physiology 1 Tony Serino, Ph.D. Biology Department Misericordia University

2. Endocrine System • Controls and modifies the internal environment by releasing chemicals (hormones) into the blood • Slower response time but longer duration of action compared to nervous system

3. Chemical Messengers (hormones) • Hormone –secreted by cell into blood and acts on another cell some distance away • Neurohormone –secreted by neuron into blood to affect a target cell some distance away • Local hormones –secreted by cell into interstitial fluid to affects cells nearby • Paracrines –affect neighboring cells • Autocrines –affect the secreting cell • Pheromones –secreted by cell onto body surface to affect cells of another individual

4. Hormones • Chemical Classification • Amines –single or few amino acids, most water soluble • Epinephrine, Thyroxine (but water insoluble), Melatonin • Proteins –short to long chains of amino acids; water soluble • GH, FSH, LH, Insulin, Glucagon, ADH, etc. • Steroids –derivatives of cholesterol; water insoluble • Estrogen, Testosterone, Progesterone, Cortisol, Aldosterone

5. Steroid Hormones

6. Characteristics Common to all Hormones • Must have target cell with appropriate receptor molecules • Receptor-hormone complex must trigger events in target cell that changes its physiology • Mechanisms for deactivating the hormone response must be present

7. Controlling Hormone Response • Half-life of the hormone • Physiological range • Modifying target cell response • Up and down regulation • Turning off secretion • Negative feedback • Control by other hormones, neurons and metabolites

8. Control of Hormone Secretion

9. Mechanisms of Hormone Action 2nd messengers Water Soluble Water Insoluble Carrier protein

10. 2nd Messengers: cAMP

11. 2nd Messengers: IP3 and Ca++-Calmodulin

12. Steroid Hormone Transduction

13. Different Styles of Secretion • Prohormone –a hormone that is made as a larger (inactive form) that must be changed prior to secretion (allows for storage of hormone in secreting cell)Ex.: proinsulin, pro-opiomelanocortin • Prehormone –a hormone that is secreted in an inactive form that must be changed near or in the target cellEx.: Thyroxine, Angiotensinogen

14. Proinsulin

15. Types of Endocrine Disorders • Hypersecretion • Too much secretion of the hormone • Hyposecretion • Too little secretion of hormone • Hyporesponsiveness • Normal secretion, but little to no response by target cells

16. Endocrine Glands

17. Hypothalamus Control of Pituitary

18. Posterior Pituitary

19. Anterior Pituitary

20. Control of Growth • Growth periods: prenatal and postnatal (consists of pre-puberal (especially the first 2 years –infancy) and puberty • Several factors influence growth: genetics, diet, health, and hormonal balance • Prenatal growth dominated by insulin secretion, post-natal dominated by GH, thyroxine, and sex hormones

21. GH secretion and effects GH secretion stimulated by exercise, fasting, sleep (diurnal rhythm), stress, decreased plasma glucose, increased plasma AA (such as after a high protein meal) Increase protein synthesis Increase differentiation (increase mitosis)

22. GH interactions with other Hormones • Thyroxine: essential and permissive for GH • Needed to maintain energy levels for growth • Increases sensitivity of target cells to GH effects • Insulin: essential for GH effects • Dominant hormone for pre-natal growth • Estrogen and Testosterone: surge at puberty stimulates GH release, synergistic with GH anabolism; also trigger epiphyseal closure • Cortisol: anti-growth effects; decrease GH secretion, cell division, and increase catabolism

23. GH pathologies • Hypersecretion: • Gigantism –in children with responsive epiphyseal plates • Acromegaly –in adults, with closed epiphyseal plates

24. GH pathologies • Hypofunction: • Dwarfism –in children • Pituitary –decreased GH secretion • Laron –decreased responsiveness due to lack of GH receptors 28 yo woman withpituitary dwarfism; 45” tall Achondroplastic Dwarfism (genetic dwarf) due to failure of cartilage to form in epiphyseal plate

25. Thyroid Location

26. Thyroid Follicle (follicular cells  thyroxine) Parafollicular cells  calcitonin

27. T3 & T4 Formation and Secretion

28. T3 & T4

29. Control of Thyroxine Secretion Short loop Long loop

30. Thyroid Malfunction • Hypothyroidism • Endemic goiters –due to iodine deffeicency • Cretinism –i thyroxine in child results in igrowth (dwarf) and severe mental retardation • Myxedema –i thyroxine in adult, leads to swelling of tissues plus other symptoms

31. Cretinism

32. Thyroid Malfunction • Hyperthyroidism • Toxic goiters (Graves disease) –Ab may stimulate thyroid without negative feedback control • Exophthalmos –symptom present in many hyperthyroid patients

33. Parathyroid Location

34. Parathyroid

35. PTH Actions • Stimulates resorption of bone  hCa+ and PO4- in blood • Stimulates Ca+ absorption in intestine (active Vit. D3 necessary for Ca+ absorption) • Stimulates Ca+ reabsorption and PO4- excretion in kidney • Stimulates Vit. D3 formation (skin) and activation (kidney) • Vital for life

36. Adrenal Location and Structure

37. Adrenal Layers (Epinephrine (adrenalin)) (Androgens) (Glucocorticoids (cortisol)) (Mineralocorticoids,(Aldosterone))

38. GAS (General Adaptation Syndrome)

39. Adrenal Malfunction • Hypersecretion Cushing’s syndrome –increase in glucocorticoids • Usually due to over secretion of ACTH by pituitary or from adrenal cortex tumors stimulating an increase in glucocorticoids. Characteristic obesity of trunk only and development of “buffalo hump” (a fat pad behind the shoulders). Will develop hypertension, atherosclerosis, muscular weakness and fatigue. Conn’s syndrome –excess amount of aldosterone • Salt imbalance, water retention, hBP, muscle weakness Adrenogenital syndrome –too much androgen • Premature sexual development in children or masculinization in women

40. Cushings Obesity of trunk (buffalo hump)

41. Adrenogenital syndrome A 15 yo girl, note typical masculinebuild, under developed breasts, andexcessive body hair

42. Adrenal Cortex Malfunction • Hyposecretion –Addison’s disease • Due to decrease amounts of mineral and glucocorticoids • Can be due to over use of steroids or an autoimmune mechanism resulting in destruction of the gland • Dehydration, K+ loss, iBP, fatigue, pigmentation deepening (bronzing of skin) may be symptom of loss of negative feedback

43. Pineal Gland • Plays a major role in circadian rhythm control through its sympathetic connection to the hypothalamus • Melatonin increases at night and decreases during daylight • Implicated in the control of major life changes (such as the onset of puberty and adulthood

44. Thymus Gland • Bilobed organ that is largest in children, but begins to regress sharply at the onset of puberty (around age 11) • It is the site of T-cell lymphocyte production and produces hormones (such as, thymosin) that modifies their physiology