Hormonal Influences on Human Body Composition

1. Hormonal Influences on Human Body Composition

2. Hormones • Hormones exert major, determining effects on body composition.

3. The Endocrine System • Gland • Hormone • Target organ or tissue.

4. Hormones • Hormones can be classified as either steroidal or nonsteroidal. • Steroid hormones are lipid soluble, and most are formed from cholesterol. • Nonsteroid hormones are proteins, peptides, or amino acids.

5. Hormones • Hormones are generally secreted into the blood and then circulate through the body to exert an effect only on their target cells.

6. Hormones • Steroid hormones pass through cell membranes and bind to receptors inside the cell. • They use a mechanism called direct gene activation to cause protein synthesis.

7. Hormones • Non-steroidal hormones cannot enter cells easily, so they bind to receptors on the cell membrane. • This activates a second messenger within the cell which in turn can trigger numerous cellular processes.

8. Hormones • Secretion of most hormones is regulated by a negative feedback system.

9. Hormones • The number of receptors for a specific hormone can be altered to meet the body’s demands.

10. Hormones • Key point - the pituitary gland was once thought to be the master endocrine gland solely in control of many other glands and organs.

11. Control • It is now recognized that the pituitary gland is largely controlled by the hypothalamus.

12. Hormones • Both peptide and steroid hormones, alone or in combination, exert profound changes on both the lean and fat compartments of body composition.

13. Hormones • The main physiological steroid hormones affecting body composition include: cortisol, testosterone, and 17-beta-estradiol.

14. Hormones • The effects of these steroid hormones are dependent on the interactions of GH and insulin.

15. Pituitary Hormones Anterior Lobe • Somatotropin (hgH) - Impacts all cells of the body. • Major role in maturation, protein synthesis, use of fat, and CHO sparing.

16. Thyroid Hormone • Thyroxine and triiodothyronine - Impact all cells in the body. • Increases rate of cellular metabolism, increases heart rate and force of contraction.

17. Adrenal Hormones Medulla • Epinephrine - Impacts most cells of the body. • Mobilizes glycogen, increases skeletal muscle blood flow, increases heart rate and contractility, increases oxygen consumption.

18. Adrenal Hormones Medulla • Norepinephrine - impacts most cells of the body through vasoconstriction which increases blood flow, increases heart rate and contractility, increases VO2.

19. Adrenal Hormones Cortex • Glucocorticoids (cortisol) - impacts most cells of the body. • Controls metabolism of all fuels and has an anti-inflammatory action.

20. Adrenal Hormones Cortex • Androgens and estrogens - impacts sex organs. • Responsible for development of secondary sexual characteristics.

21. Pancreatic Hormones • Insulin - impacts all cells of the body. • Regulates blood glucose levels. • Increases the utilization of glucose and the synthesis of fat.

22. Pancreatic Hormones • Glucagon - impacts all cells of the body. • Increases blood glucose levels and stimulates the breakdown of protein and fat.

23. Gonadal Hormones Testes • Testosterone - affects sex organs and muscles. • Responsible for the development of male secondary sexual characteristics.

24. Gonadal Hormones Ovaries • Estrogen - affects sex organs and adipose tissue. • Responsible for the development of female secondary sexual characteristics.

25. Cortisol • Excess cortisol secretion causes wasting of lean body mass, particularly muscle.

26. Cortisol • The interactions of insulin become important for the net effect of glucocorticoids on muscle mass as well as on adipose tissue mass and distribution.

27. Cortisol • In human adipose tissue, the acute short-term effects of cortisol seem to be essentially absent.

28. Cortisol • In long-term (days) experiments under fully controlled conditions, the effects are easier to detect.

29. Cortisol • In the presence of insulin, cortisol by itself has a rather weak inhibitory effect on cathecholamine-induced lipolysis, but cortisol induces a marked “permissive” effect by GH on lipolysis. • Result – decreased fat mass and muscle mass

30. Cortisol • The integrated effect of cortisol on lipolysis would not be expected to increase lipolysis because, with cortisol excess, GH secretion is blunted.

31. Cortisol • Furthermore, insulin secretion is elevated, with its consequences for lipid mobilization.

32. Cortisol • The effects of glucocorticoids on adipose tissue are regionally specific.

33. Testosterone • The effects of testosterone on lean body mass are well established, e.g., the elevation of muscle mass and reduction of adipose tissue stores.

34. Testosterone • The effects of T on total adipose tissue mass are apparently not very marked in normal adults or in aging men.

35. Testosterone • Adipose tissue distribution is, however, probably regulated by T.

36. Testosterone • T-deficiency has been suggested to be associated with centralization of body mass.

37. Testosterone • This might be the explanation for well known tendency of aging men with decreased T-secretion to develop central fat accumulation.

38. Testosterone • The cellular effects of T on adipocytes have been surprisingly little studied.

39. Testosterone • Androgens are also produced by women, albeit in much smaller amounts.

40. Testosterone • The effects of T on adipose tissue might be weaker, due to the lower concentrations of T.

41. Growth Hormone • Pituitary growth hormone (GH) or somatotropin is obviously a major regulator of body composition.

42. Growth Hormone Effects on Body Composition: • increases in muscle mass • increases in extracellular water volume • and a marked decrease in body fat.

43. Growth Hormone Effects on Cell Differentiation • GH seems to promote the conversion of pre-adipocytes to fully differentiated adipocytes.

44. Growth Hormone • It is unclear if this growth promoting effect of GH on pre-adipocytes is important in human beings after puberty, since effects of GH on pre-adipocyte conversion to adipocytes have not been observed indicating that these cells may be already “committed” in adult life.

45. Growth Hormone Effects on Adipose Tissue Metabolism: • The long-term effects of GH on adipose tissue metabolism are undoubtedly a stimulation of lipolysis and inhibition of lipogenesis, reflected in the marked changes in body composition with GH excess or deficiency.

46. Growth Hormone Interactions with other hormones: • The metabolic effects of GH are also dependent on insulin and glucocorticoids.

47. Growth Hormone • GH has no growth promoting effect in the absence of insulin, and the metabolic effects of GH in adipose tissue also seem to be dependent on the presence of insulin.

48. Growth Hormone • In human, GH secretion is dependent upon age and gonadal function. • Another important observation is the consistent decrease in GH secretion in obesity.

49. Female Sex Hormones • Female sex steroid hormone concentrations also regulate adipose tissue mass, although it is not clear whether these effects are direct or mediated via energy intake and/or expenditure.

50. Female Sex Hormones • It is clear that these hormones affect body fat distribution in women. • With menopause, VAT increases, but this is preventable by hormonal replacement therapy.