Puberty and associated changes

1. Puberty and associated changes

2. Puberty • Sexual maturity • Physical • Behavioral • Physiological

3. Signs of puberty • Females • Ovulation • Menstruation • Males • Somewhat unclear • First ejaculation with viable sperms • Minimum number required to achieve successful conception

4. Puberty and fertility • First menstruation/ejaculation • Not the sign of fertility • Signs of gonadal development • Changes in gonadotropin secretion • Changes in gonadotropin responsiveness • Changes in steroid hormone production • Changes in gametogenesis

5. Physical changes • Rapid growth • Phases • Minimum growth • Peak growth velocity (PGV) • Rapid growth • Epiphseal fusion • End of growth • Earlier in females

6. Involvement of skeletal and muscular system • Regional differences in rate of growth • Dimorphism • Changes in body composition • Amount of fats within the body • Distribution of fats • Changes take place before puberty • Earliest difference in males and females during puberty

7. Endocrine regulation • Synergism between growth hormone (GH) and steroid hormones (estradiol or testosterone) • Increased secretion of GH • Increased responsiveness to GH • GH receptors

8. Activation of gonads • Development of secondary sex characteristics • Breasts • External genitalia • Hair distribution • Pubic hair • Facial hair • Axillary hair • Larynx (vocal cord) and laryngeal muscles • Deepening of voice

9. Role of steroid hormones • Estradiol • Breast development • Development of mammary alveolar tissue • Female external genitalia • Progesterone • Breast development • Development of mammary ducts

10. Role of steroid hormones • Androgens • Male genitalia • Hair growth and distribution • Male and female • Larynx and laryngeal muscles • Events associated with puberty • Sequential • Critical for clinical examination

12. Endocrine control of puberty • Secretion of gonadotropin • Very low during childhood • Increase in FSH and LH secretion • Stimulation of follicular development • Stimulation of steroidogenesis • Circadian pattern of gonadotropin secretion

14. Secretion of prolactin • Increased in females • Response to increased estradiol level • Steroidogenesis • Increased testosterone production • Follows LH pattern • Increase by 12 folds (0.2 ng/ml to 2.4 ng/ml)

15. Production of estradiol • Increase during puberty in females • Similar level with adult • Production of adrenal steroids • Androgens (DHEA) • Specific • No increase in glucocorticoids or mineralocorticoids • Adrenarche • Starts around 8 years of age and continues until 13-15 years old

17. Production of adrenal steroids • Androgens (DHEA) • Specific • No increase in glucocorticoids or mineralocorticoids • Adrenarche • Starts around 8 years of age and continues until 13-15 years old • Very high concentrations compared to gonadal steroids • Promotion of hair growth and distribution in both sexes

18. Changes in secretion of gonadotropins • Two theories • Gonadostat theory • Progressive maturation of feedback action of steroids • Changes in responsiveness of the anterior pituitary gland to GnRH • Central maturational role to the CNS • Hypothalamus

19. Gonadostat theory • Prepubertal period • Ovaries • Some antral/tertiary follicles • Estradiol production (very low) • Negative feedback of estradiol on gonadotropin secretion • Greater sensitivity to estradiol • Low threshold

20. Pubertal period • Changes in sensitivity to estradiol • Increased threshold • Decreased sensitivity • Increased responsiveness of pituitary gland to GnRH stimulation • All of these are secondary response • Leads to increased production of steroid hormones • Increased secretion of gonadotropins

21. Delayed appearance of positive feedback • Reproductive cycle during early puberty • May not accompanied by ovulation • Capacity to evoke LH surge • Requires repeated exposure to high concentrations of estradiol • Ovulatory LH surge • Later portion of puberty • Estradiol concentrations may be too low

22. Prepubertal period Puberty E (+) E (-) Hypothalamus Hypothalamus GnRH GnRH FSH FSH Pituitary gland Pituitary gland

23. Hypothalamus maturation model • Pubertal activation of hypothalamus • Increased output of GnRH • The CNS rather than gonadal axis • Changes in GnRH pulsatility • No alteration in pituitary or ovarian response • Independent of steroid exposure

26. Effects of environment • Decreasing age to the first menstruation and male puberty • Western countries • Advanced health care • Economics • Wellness • Majority of women will experience menopause • Increased life expectancy • Other health issues

27. Role of light exposure • Critical for animals with breeding seasons • Requires exposure to increasing length of daylight (long-day breeders) • Horses • Requires exposure to decreasing length of daylight (short-day breeders) • Sheep • Wild species

28. Role of nutrition • Attaining critical body weight • Critical for initiation of the reproductive cycle • Domestic species (i.e. cattle) • Body weight rather than actual age determines when animals reach puberty • Humans • Same as the domestic species • Activation of hypothalamus-pituitary-gonad axis • Growth spurt

29. Body size (weight and height) • May be critical • Pregnancy • Women with eating disorder (anorexia) • Maintenance of critical body weight (47 kg) • Irregular/cessation of menstrual cycle

30. Actual body weight vs. fatness of the body • Lean people (i.e. athletes) • Later initiation of menstrual cycle compared to moderately obese individuals • Low body fat content • Irregular menstrual cycle • Cessation of menstrual cycle

31. Metabolic signals • Leptin • Hormone produced by fat cells • Satiety factor • Decreases appetite • Energy levels within the body • Unclear linkage