Puberty and lactation Flashcards
What is the first stage of puberty?
Adrenarche
- Increase in production of androgens by adrenal cortex
What is gonadarche?
- Activation of the gonads by gonadotrophins
What are examples of gonadotrophins?
LH and FSH
What is thelarche?
Onset of breast development
What is pubarche?
First appearence of pubic hair
WHat is menarche?
Onset of menstruation
What are secondary sexual characteristics?
- Developing during puberty
- Not directly required for reproduction
How long does puberty take?
4 - 5 years
When does adrenarche begin?
6 - 8 years of age
What is the hypothalamic-Pituitary-Adrenal axis which is involved in Adrenarche?
- Hypothalamus produces CRH
- Anterior pituitary releases ACTH
- Adrenal gland produces adrenal androgens
What are increased androgen levels responsible for?
- Development of pubic and axillary hair (pubarche)
- Development of pilosebaceous unit in skin - acne
- Increases cortical bone density
What is the first sign of puberty in females and when is this?
Breast development
- Between 8.5 - 12.5 years
What usually follows immediately after breast development?
Hair growth and rapid height spurt
What signals the end of growth?
Menarche
How long after the start of puberty is menarche?
2.5 years
What is the average age for menarche?
13
What is a way we are able to tell what point in puberty a girl/boy is in?
Tanner stages (1 - 5)
What is usually the first sign of puberty in men?
Testicular enlargement (greater than 4ml volume)
When is testicular enlargement in males usually?
10 - 15 years (mean 11)
How long is the interval between the onset of pubic hair and axillary and facial hair?
2 years
When is spermarche on average in men?
13.4
What promotes testicular enlargement?
FSH
What promotes penile enlargement?
Testosterone
What hormones cause male secondary sexual characteristics?
Testosterone and its metabolite DHT
What are the androgen-dependant secondary sexual characteristics?
- Facial, underarm, pubic hair
- Deepening of voice (due to growth of larynx)
- Thick secretion of skin oil glands (can cause acne)
- MAsculine pattern offat distribution
- Bone growth via growth hormone secretion (then termination via closure of epiphyseal plates)
- Stimulation of muscle protein synthesis
- EPO stimulation giving higher haematocrit in males
What initiates puberty?
Pulsitile secretion of LH
What stops puberty from happening in children?
Gonadotrophins are suppressed by a continous infusion of GnRH
What factors contribute to early onset of puberty?
- Genetics
- Social factors
- Obesity
- Geographical factors (lower altitudes, urban setting, close to equator)
- Enviromental exposures (endocrine disrupting chemicals - industry uses
- Race - earlier in black compared to white children
- Exact mechanism is unknown
What happens prior to menopause?
Peri-menopause (5 -7 years)
What happens to the follicle supply in menopause?
- Diminishes but does not ‘run out’
- Remaining follicles not sensitive to LH and FSH
What happens to hormone levels in menopause?
Estrogen levels fall
- Positive feedback on pituitary
- Increase in FSH and LH
How long is a woman advised to breastfeed for for optimal benefits?
Exclusively for 6 months
What are the benefits of breastfeeding for the baby?
- Reduced incidence of GI, respiratory and middle ear infection
- Decreased risk of childhood diabetes, asthma and eczema
- Reduced risk of lactose intolerance
- Improved intellectual and motor development
- Decreased risk of obesity in later life
- Possible reduced autoimmune disease
- 27% reduced risk of sudden infant death syndrome
What are the benefits of breastfeeding for the mother?
- Promotes recovery from childbirth
- Promotes return to ‘normal’ body weight
- Promotes a period of infertility
- Reduces risk of premnopausal breast cancer
- Reduces risk of ovarian cancer
- Possibly improves bone mineralisation
When does glandular tissue develop fully?
During pregnancy
What do modified sebaceous glands (alveoli) empty via?
Lactiferous ducts that are dilated to form lactiferous sinuses which open on the surface of the nipple
What cells produce milk?
Secretory alveoli
What stimulates the secretory alveoli (milk producing cells)?
Prolactin
What are the alveoli surrounded by?
Contractile myo-epithelial cells
What are contractile myo-epithelial cells stimulated by?
Oxytocin
What hormone stimulates the ducts to proliferate and form alveoli at the ends of the ducts?
Estrogen (at puberty)
What do the breasts contain before puberty?
Laxctiferous ducts without alveoli (also in male breasts)
What happens to the breasts during pregnancy?
Under the influence of estrogen, progesterone and prolactin the glandular portion of the breast undergoes hypertrophy replacing adipose tissue
When does the breast tissue become fully developed?
- From week 16 fully developed but quiescent
- After parturition the breast produces colostrum before mature milk production begins
What are the alveoli replaced with after lactation?
Adipose tissue
How is prolactin initiated?
- Precipitous drop in estrogen and progesterone after delivery
- Prolactin surges each time mother nurses baby due to nerve impulses from nipples to hypothalamus
What is produced by the hypothalamus when not nursing child?
Prolactin inhibitory hormone
What does lactation inhibit?
FSH and LH thus interfereing with reproductive function
What does the sucking stimulus inhibit and release?
- Inhibits hypothalamic release of dopamine
- Prolactin is released in proportion to the strength and duration of suckling
- Baby essentially orders up its next meal as it suckles at its current one
- Stimulates neurons in hypothalamus to synthesise oxytocin which is carried to pituitary
- Oxytocin then released anf acts on myo-epithelial cells in alveoli causing ‘let down’ of milk
What can inhibit the oxytocin let down release?
Stress - catecholamines
What can trigger the oxytocin let down release other than sucking?
Cry of baby
How is lactation inhibited during pregnancy?
- Prolactin secreted during pregnancy but action inhibited by high levels of progesterone and estrogen and hPL (human placental lactogen)
- Steroid levels fall after parturition and milk production begins
What does prolactin suppress?
Hypothalamic release of GnRH and therefore pituitary FSH and LH
- Prevets follicular growth, ovulation and menstrauation
When does LAMs effectiveness depend on?
- Must be ammenorrhoeic
- Baby must be exclusively breast fed
- Baby less than 6 months old
