Puberty and associated changes. Puberty Sexual maturity –Physical –Behavioral –Physiological.
Post on 16-Dec-2015
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• Signs of puberty– Females
• Ovulation• Menstruation
– Males• Somewhat unclear• First ejaculation with viable sperms
– Minimum number required to achieve successful conception
• 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
Physical changes
• Rapid growth– Phases
• Minimum growth• Peak growth velocity
(PGV)– Rapid growth
• Epiphseal fusion– End of growth
– Earlier in females
• 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
• Endocrine regulation– Synergism between growth hormone (GH)
and steroid hormones (estradiol or testosterone)
• Increased secretion of GH• Increased responsiveness to GH
– GH receptors
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
• Role of steroid hormones– Estradiol
• Breast development– Development of mammary alveolar tissue
• Female external genitalia
– Progesterone• Breast development
– Development of mammary ducts
• 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
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
• 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)
• 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
• 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
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
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
• 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
• 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
GnRHHypothalamus
Pituitary gland
FSH
E (-)
GnRH
Hypothalamus
Pituitary gland
FSH
E (+)
Prepubertal period Puberty
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
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
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
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
• 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
• 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
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