78 Puberty Flashcards
What is puberty?
• Developmental stage during which adolescents reach sexual maturity and become capable of reproduction
• Involves physiological processes of adrenarche and gonadarche
• Results in:
- growth of stature
-change in body composition
-development of secondary sexual characteristics
-achievement of fertility
Definition of adrenarche?
- Increase in production of androgens by adrenal cortex
* Androgens = steroid hormones e.g. testosterone
Definition of gonadarche?
- Activation of the gonads by gonadotrophin
* Gonadaotrophins = FSH and LH from pituitary
Difference between primary and secondary sexual characteristics?
- Primary sexual characteristics
• Reproductive organs, present ar birth - Secondary sexual characteristics
• Develop during puberty, not directly required for reproduction
Definition of thelarche?
Onset of breast development
Definition of pubarche?
First appearance of pubic hair
Definition of menarche?
Onset of menstruation
What area of adrenal gland releases androgens?
Zona retiulcaris of adrenal cortex
What occurs in Adrenarche (Hypothalamic-Pituitary-Adrenal axis)?
• Primary stimulus = enhanced adrenal sensitivity to ACTH
• Maturational increase in adrenal androgen (DHEA-S) production
• Around age 6 in boys and girls
• Occurs in conjunction with gonadal maturation
• Increased androgen levels responsible for:
- Development of pubic and axillary hair (pubarche)
- Development of pilosebaceous unit in the skin (acne)
- Increases cortical bone density
Events of puberty in females?
- Breast development:
• 1st sign
• Between 8.5 - 12.5 years
2.Pubic hair growth and rapid height spurt:
• Occurs almost immediately after breast development
- Menarche:
• Average age 13
• On average 2.5 years after start of puberty
• Signals the end of growth (only ~5cm height gain remaining)
List the female secondary sexual characteristics?
- Breast budding (Thelarche)
- Onset of pubic hair (Pubarche)
- Maximal growth velocity
- Menarche
- Development of axillary hair
- Attainment of the adult breast type
- Adult pubic hair pattern
In total, thelarche, growth spurt, pubarche and menarche requires how many years?
4.5 years (range 1-6)
What is the tipping point to the beginning of menarche?
- As the ovaries mature, becomes more sensitive to gonadotrophin and release more steroid hormones
- Early cycles may be anovulatory
- Up to 18 months for regular ovulatory cycles to develop
Tanner Stages in females?
Scale (I-V) of physical development in children, adolescents and adults
• Breast and pubic hair
What is the HPA axis?
Hypothalamic- Pituitary- Adrenal axis
What is the HPO axis?
Hypothalamus pituitary ovarian axis
Signs of male puberty?
- Testicular enlargement to greater than 4mls volume:
• 1st sign
• 10-15 years (mean 11) - Pubic hair growth and penile growth:
• Normally 2 year interval between the onset of pubic hair and axillary and facial hair - Spermarche -appearance of sperm in seminal fluid
• Mean age 13.4 - Growth spurt:
• When testicular volume is 12-15mls, after a delay of ~ 18 months
• Growth spurt in males later and of greater magnitude accounting for greater average final height in males
Tanner stages in males?
Scale (I-V) of physical development in children, adolescents and adults
• Testes, scrotum, penis, pubic hair
What is a Prader Orchidometer?
Medical instrument used to measure the volume of the testicles
What is the HPG axis?
Hypothalamic Pituitary Gonadal (HPG) axis
- FSH/ LH promotes testes to produce sex steroids - testosterone
- FSH promotes testicular enlargement
- Testosterone promotes penile enlargement
- Testosterone criitcal for spermatogenesis
Male androgen-dependent secondary sexual characteristics?
Virtually all dependent on testosterone and its metabolite DHT
- Facial, underarm, pubic hair
- Deepening of voice (due to growth of larynx)
- Thick secretion of skin oil glands (can cause acne)
- Masculine pattern of fat distribution
- Bone growth via growth hormone secretion - then termination via closure of epiphyseal plates
- Stimulation fo muscle protein synthesis
- Erythropoietin stimulation giving higher haematocrit in males
How is puberty initiated (hypothalamic-Pituitary-Gonadal axis)?
• Gonadotrophin (LH/ FSH) release:
- Suppressed by continuous infusion of GnRH
- Pulsatile administration will lead to gonadal stimulation, maturation and production of steroid hormones
• ‘Juvenile pause’ characteristic of all higher primates
• Pulses of GnRH are detectable in the childhood years but mostly during sleep and of low frequency and amplitude therefore do not stimulate gonadotropin release
• Unknown signal - GnRH pulse generator
• Nocturnal secretion of GnRH pulses become more pronounced leading to gonadotrophin release
4 phases of human growth?
- Fetal:
• Uterine environment
• Fastest
• 30% of eventual height determined - Infantile:
• Nutrition, general health, happiness and thyroid function • Birth - 18 months - rapid but decreasing growth rate
• 15% - Childhood:
• Dependent on thyroid hormones, growth hormone, general health and happiness, genetics
• Slow steady prolonged - Pubertal:
• Sex hormones esp. testosterone and oestrogen, growth hormones and insulin-like growth factor
What is the peak velocity of girls and boys?
- Girls mean age 11.5 (9cm/y)
- Boys mean age 13.5 (10c/y)
• PHV occurs relatively earlier in girls (tanner stage 2-3) compared to boys (tanner stage 3-4)
Why are boys taller?
Late onset of growth spurt in boys (~ 2 years) accounts for overall greater final height as they achieve more growth before peak velocity
Why does puberty limit heights?
Puberty limits adult height as gonadal steroids lead to epiphyseal closure of long bones
Difference in male and female body composition?
In adults:
- Males
• Gain greater amounts of fat-free mass and skeletal mass
• Changes in body composition from ~9y - Females
• Acquire significantly more fat mass
• Changes in body composition from ~6y
Factors contributing to earlier puberty?
- Genetic:
• Fhx of early puberty
• TIming correlates with mother and sisters
2. Social factors: • Lower social class and obesity = earlier menarche
- Geographic factors:
• Close to equator, lower altitudes, urban setting - Environmental exposure:
• Endocrine disrupting chemical s
• Industry uses e.g. plastics, agriculture, fuels - Race:
• Onset earlier in Afro-Carribean and African-American children compared to white children
Describe link between nutrition and pubertal development?
• Some evidence that obesity accelerates onset in girls
• Progression affects by prepubertal body composition (fat mass and BMI) in boys and girls
• Increase in body fat may play a critical role int he turning on of the adrenal androgen secretion and adrenarche:
- Leptin may be link between adipose tissue, energy homeostasis centres in hypothalamus and the reproductive system
What are the stages of ovarian failure in menopause?
- Cycles become regular as women reach climacteric age 40 (10 years of change that leads to menopause)
- Between 45-55 years (average 51.5)
- Follicle supply diminishes
- Follicle cells gradually become insensitive to FSH and LH
- Ovarian steroid levels fall
- No -ve feedback to the pituitary therefore dramatic increase in levels of FSH (10-20x: excreted in urine) and LH (3x)
- Low levels of sex steroids are produced by the adrenals
Menopause symptoms?
• Vascular instability - night sweats and hot flushes
• Atrophy of all oestrogen dependent tissues:
- Breast, uterus, vagina, bladder, urethra (atrophic vaginitis)
- Skin collage loss
- Bone catabolism with loss of Ca2+ leads to osteoporosis
- LDL rises (increases risk of coronary thrombosis)
• Rise in adrenal androgens may lead to hirsutism
• Loss of libido
• Depression, anxiety, mental confusion
Treatment of menopause?
HRT replaces steroids, maintains oestrogen dependent tissues and delays osteoporosis
