PubertyDr. G CornwallHuman Reproductive Biology

Changes with Puberty• Tanner Stages

– Five stages used to measure progression of pubertal changes• Breast development in females• Pubic hair distribution in males and females• External genitalia in males• Figures 8.1 – 8.3 (tables 8.1 and 8.2)

• Tanner Stages are correlated with endocrinological milestones– Andrarch: (males and females) activation of the adrenals

• Secretion of DHEA and DHEAS leads to pubic and axillary hair

– Thelarch: (females) onset of breast development• Dependent on andrarch• Adrenal androgens are converted to estrogens

– Menarch (females) & Gonadarch (males)• Menarch is usually the last distinctive sign in females• Gonadarch (enlargement of testes) is usually the earliest sign in males

• Development of secondary sex characteristics– Changes in reproductive and somatic tissues– Resulting from increased production of gonadal sex steroids

• Targets include:– Genitourinary ducts– Hair follicles– Apocrine glands– Fat and Muscle cells– Bones – Brain– Growth Spurt

• initiated earlier in females (ends sooner)• Increased estrogen production• Ends with fusion of the epiphysial plates

– Body Composition changes

• In females fat deposition begins sooner and remains• In males it begins later and then is lost• Males experience upto 56% more muscle growth than males

– Body Composition changes• In females fat deposition begins sooner and remains• In males it begins later and then is lost• Males experience upto 56% more muscle growth than males

– Increased androgens result in a number of changes in both sexes (less in females)• Appearance of pubic and axillary hair• Darkening of hair • Maturation of sweat and apocrine glands• Acne – due to conversion of T to DHT by skin cells• Deepening of the voice

– Psychological and Behavioral changes• Intellectual ability• Preference for abstraction• Increased capacity for making judgements• Interest in sexual activity• Sexual orientation and Gender identity

The Timing of Puberty• The timing of puberty is extremely variable and dependent on several factors– Thinking from an evolutionary perspective, maturity is important

• Female must be large enough and well nourished enough to sustain a pregnancy• Male must be strong enough and skilled enough to protect and ptroduce• Must be intellectually and psychologically prepared for participation in society

– Industrialized countries, puberty occurs much earlier than this

– Regardless, certain metabolic / nutritional status is requisite for puberty to ensue.

• Averages– Menarch = 12.3 years (range 9.7 – 16.7)– Thelarch = 7.9 – 13.9 years– Gonadarch = 8.5 – 15.9 years

• Mean age of puberty is decreasing in Western Europe and the US– Average age of menarch is decreasing (stabilized

in the 90’s)– Environmental factors must play a big role

The Onset of Puberty• The Hypothalamus is responsible for the initiation of puberty– Reactivation of the GnRH pulse generator– Results in increased LH and FSH levels

• Inhibited during childhood ???• Sleep entrainment

– Possible cause of nocturnal emissions

Metabolic Cues• Reactivation of the GnRH pulse generator must be

controlled by the biological clock– Nutritional status appears to be critical– “critical weight” / “critical fat” hypothesis

• 22% body fat (< 20% = inhibition of pulse generator)

– Strenuous physical activity appears to delay menarch

• Leptin may play a role in the onset of puberty– Leptin levels increase at puberty– Leptin deficiency leads to obesity in mice– In umans leptin levels increase as weight increases?– Certain leptin levels may be necessary