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Puberty and associated changes. Puberty. Sexual maturity Physical Behavioral Physiological. Signs of puberty Females Ovulation Menstruation Males Somewhat unclear First ejaculation with viable sperms Minimum number required to achieve successful conception. Puberty and fertility

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puberty
Puberty
  • Sexual maturity
    • Physical
    • Behavioral
    • Physiological
slide3
Signs of puberty
    • Females
      • Ovulation
      • Menstruation
    • Males
      • Somewhat unclear
      • First ejaculation with viable sperms
        • Minimum number required to achieve successful conception
slide4
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
Physical changes
  • Rapid growth
    • Phases
      • Minimum growth
      • Peak growth velocity (PGV)
        • Rapid growth
      • Epiphseal fusion
        • End of growth
    • Earlier in females
slide6
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
slide7
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
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
slide9
Role of steroid hormones
    • Estradiol
      • Breast development
        • Development of mammary alveolar tissue
      • Female external genitalia
    • Progesterone
      • Breast development
        • Development of mammary ducts
slide10
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
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
slide14
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)
slide15
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
slide17
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
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
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
slide20
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
slide21
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
slide22

Prepubertal period

Puberty

E (+)

E (-)

Hypothalamus

Hypothalamus

GnRH

GnRH

FSH

FSH

Pituitary gland

Pituitary gland

hypothalamus maturation model
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
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
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
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
slide29
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
slide30
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
slide31
Metabolic signals
    • Leptin
      • Hormone produced by fat cells
      • Satiety factor
        • Decreases appetite
        • Energy levels within the body
      • Unclear linkage