Puberty and Lactation Flashcards
Puberty
is a developmental stage (physical changes) during which adolescents reach sexual maturity and become capable of reproduction
puberty Involves physiological processes of
– Gonadarche = physical and functional maturation of the gonads by gonadotrophins • Gonadotrophins are FSH & LH from pituitary
– Adrenarche = increase in production of androgens by adrenal cortex • Androgens are steroid hormones e.g. dehydroepiandrosterone (DHEA)
what does puberty result in
– Growth in stature
– Change in body composition
– Development of secondary sexual characteristics (pubarche)
– Achievement of fertility
primary reproductive characteristics
– Reproductive organs, present at birth
Secondary sexual characteristics
– Develop during puberty, not directly required for reproduction
Thelarche
onset of breast development
Pubarche
first appearance of pubic hair
Menarche
onset of menstruation
Hypothalamic-Pituitary-Adrenal Axis (Adrenarche)
- 6-8 years of age
- ACTH produced by pituitary
- Stimulates adrenal glands to secrete androgens – predominantly DHEAS (dehydroepiandrosterone sulphate)
• Increased androgen levels responsible for
– Development of pubic and axillary hair (pubarche)
– Development of pilosebaceous unit in the skin - acne
– Increases cortical bone density
Breast development
– first sign
– usually between 8.5 and 12.5 years
Pubic hair growth and rapid height spurt
– occur almost immediately after breast development
• Menarche
– average age 13
– on average 2.5 years after the start of puberty
– signals the end of growth (only around 5cm height gain remaining)
Secondary Sexual Characteristics development in women
• Virtually all dependent on oestrogen and progesterone
• Hormone-dependent secondary sexual characteristics
– Facial, underarm, pubic hair
– Thick secretion of skin oil glands (can cause acne)
– Female pattern of fat distribution (breasts, hips, buttocks, thighs, upper arms)
– Hips and pelvis widen
– Uterus and cervix enlarge, secretory function increases
– Bone growth via growth hormone secretion then termination via closure of epiphyseal plates
• Testicular enlargement to greater than 4mls volume
– first sign, 10-15 years (mean 11)
Pubic hair growth and penile growth
– Normally 2 year interval between onset of pubic hair and axillary and facial hair
Spermarche – appearance of sperm in seminal fluid
– mean age 13.4 (stage 3-4 of testicular growth)
Growth spurt
– when testicular volume is 12-15mls, after a delay of around 18 months
– Growth spurt in males later and of greater magnitude accounting for greater average final height in males
Secondary Sexual Characteristics development in men
• Virtually all dependent on testosterone and its metabolite dihydrotestosterone (DHT)
• Androgen-dependent 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 of fat distribution
– Bone growth via growth hormone secretion then termination via closure of epiphyseal plates
– Stimulation of muscle protein synthesis
– Erythropoietin stimulation giving higher haematocrit in males
Initiation of Puberty
• Gonadotropin (LH/FSH) release
– Suppressed by continuous infusion of GnRH
– Pulsatile administration will lead to gonadal stimulation, maturation and production of steroid hormones
initiation of puberty method
- 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 gonadotropin release
Factors Contributing to Earlier puberty
• Genetics
– Timing correlates with mother and sisters
• Social factors
– Lower social class & obesity tends to lead to earlier
menarche
• Geographic factors
– closer to equator, lower altitudes, urban setting • Environmental exposures
– endocrine disrupting chemicals – industry uses e.g. plastics, agriculture, fuels
• Race
– onset earlier in Afro-Carribean and African-American
children compared to white children
• Exact mechanism that signals start of puberty is unknown but body weight and other metabolic factors may play a key role
WHO/UN advises women to breast feed exclusively for
6 months for
optimal lifetime benefits
• 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 diseases
• 27% reduced risk of sudden infant death syndrome
wha benefits does lactation have for the mother
- Promotes recovery from childbirth
- Promotes return to ‘normal’ body weight
- Promotes a period of infertility
- Reduces risk of premenopausal breast cancer
- Reduces risk of ovarian cancer
- Possibly improves bone mineralisation
Anatomy of the Breast
- Nipple is surrounded by pigmented skin (areola)
- Modified sebaceous glands (alveoli) empty via lactiferous ducts that are dilated to form lactiferous sinuses which open on the surface of the nipple
- Adipose tissue is dominant in the non- lactating breast
- Glandular tissue only develops fully during pregnancy
• Secretory alveoli
– milk producing cells
– stimulated by prolactin
• Each alveolus
– surrounded by contractile myo-epithelial
cells
– stimulated by oxytocin
Prolactin
• Initiated by precipitous drop in oestrogen and progesterone after delivery
• Prolactin surges each time mother nurses baby due to nerve impulses from nipples
to hypothalamus
• Without nursing stimulation, no prolactin surge and loss of milk production
• When not nursing, hypothalamus produces prolactin inhibitory hormone
• Lactation inhibits FSH and LH and thus lactation interferes with reproductive function
How is Lactation Inhibited During Pregnancy?
- Prolactin levels increase during pregnancy - stimulates growth and development of the mammary tissue
- Prolactin controls / promotes milk production
- Prolactin is secreted during pregnancy (from anterior pituitary), but its action is inhibited by high levels of progesterone and oestrogens and hPL (human placental lactogen)
- These steroid levels fall after parturition and milk production begins
