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 cell Ex.: 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 with pituitary dwarfism; 45” tall
Achondroplastic Dwarfism (genetic dwarf) due to failure of cartilage to form in epiphyseal plate

25. Thyroid Location

26. Thyroid Follicle Parafollicular cells  calcitonin
(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
(buffalo hump)
Obesity of trunk

41. Adrenogenital syndrome
A 15 yo girl, note typical masculine build, under developed breasts, and excessive 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