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Puberty and associated changes. Puberty Sexual maturity –Physical –Behavioral –Physiological.

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Presentation on theme: "Puberty and associated changes. Puberty Sexual maturity –Physical –Behavioral –Physiological."— Presentation transcript:

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

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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

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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 years old

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17 Production of adrenal steroids –Androgens (DHEA) Specific –No increase in glucocorticoids or mineralocorticoids –Adrenarche Starts around 8 years of age and continues until 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 GnRH Hypothalamus Pituitary gland FSH E (-) GnRH Hypothalamus Pituitary gland FSH E (+) Prepubertal period Puberty

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

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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


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