24-03-23 – Puberty and Lactation Flashcards
Learning outcomes
- Recognise that puberty is a process which takes 4-5 years and begins with adrenarche
- List the sequence of events in the process of puberty in girls and boys
- Explain that pulses of LH released at night bring about the secretion of increasing levels of gonadal steroid hormones
- Recognise some of the causes of the trend towards earlier age of onset of puberty
- Describe the physiological development of human female breast tissue
- Explain the factors which control milk production during pregnancy and lactation
- Describe the neurohumoral reflexes that occur in the mother during breastfeeding
What is puberty?
What 2 physiological processes does puberty involves?
What are androgens?
What do androgens function in?
What 4 things does puberty result in?
- Puberty is a developmental stage (physical changes) during which adolescents reach sexual maturity and become capable of reproduction
- 2 physiological processes puberty involves:
1) Gonadarche
* Physical and functional maturation of the gonads by gonadotrophins
* Gonadotrophins are FSH & LH released from pituitary in both males and females
2) Adrenarche
* Increase in production of androgens by adrenal cortex
* Androgens are steroid hormones e.g. dehydroepiandrosterone (DHEA) and tesosterone
* Although androgens are commonly thought of only as male sex hormones, females also have them, but at lower levels: they function in libido and sexual arousal.
* Also, androgens are the precursors to oestrogens in both men and women
- 4 things puberty results in:
1) Growth in stature
2) Change in body composition
3) Development of secondary sexual characteristics (pubarche)
4) Achievement of fertility
What are primary and secondary sexual characteristics?
What is Thelarche, Pubarche, and Menarche?
- Primary sexual 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
What is Adrenarche?
At what age does this occur?
How does this start?
What 3 processes are Increased androgen levels responsible for?
- Adrenarche means “the awakening of the adrenal gland.” (Hypothalamic-Pituitary-Adrenal Axis)
- This occurs at 6-8 years of age
- This starts when ACTH is produced by the pituitary, which stimulates adrenal glands to secrete androgens – predominantly DHEAS (dehydroepiandrosterone sulphate)
- 3 processes Increased androgen levels are responsible for:
1) Development of pubic and axillary hair (pubarche)
2) Development of pilosebaceous unit in the skin - acne
3) Increases cortical bone density
What are the 3 Tanner Stages of Female Puberty?
At what age does each usually stage occur?
What process occurs at the end of growth?
How long does it take for regular ovulatory cycles to develop?
- 3 Tanner Stages of Female Puberty:
1) Breast development
* First sign
* Usually between 8.5 and 12.5 years
2) Pubic hair growth and rapid height spurt
* Occurs almost immediately after breast development
3) 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)
- Some normal variation in order and timing
- End of growth - gonadal steroids (oestrogen and testosterone) triggers closure of epiphyseal plates
- Up to 18 months for regular ovulatory cycles to develop
What are female Secondary Sexual Characteristics dependent on?
What are 6 examples of hormone-dependent female secondary sexual characteristics?
- Virtually all female secondary sexual characteristics are dependent on oestrogen and progesterone
- 6 examples of female hormone-dependent secondary sexual characteristics:
1) Facial, underarm, pubic hair
2) Thick secretion of skin oil glands (can cause acne)
3) Female pattern of fat distribution (breasts, hips, buttocks, thighs, upper arms)
4) Hips and pelvis widen
5) Uterus and cervix enlarge, secretory function increases
6) Bone growth via growth hormone secretion then termination via closure of epiphyseal plates
What are the 4 Tanner Stages of Male Puberty?
At what age does each stage usually occur?
- 4 Tanner Stages of Male Puberty:
1) Testicular enlargement to greater than 4mls volume
* First sign
* 10-15 years (mean 11)
2) Pubic hair growth and penile growth
* Normally 2-year interval between onset of pubic hair and axillary and facial hair
3) Spermarche
* Appearance of sperm in seminal fluid
* Mean age 13.4 (stage 3-4 of testicular growth)
4) 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 8
What is the Prader Orchidometer? What is it used for?
- The Prader Orchidometer is a String of twelve numbered wooden or plastic beads of increasing size from about 1 to 25 millilitres.
- The beads are compared with the testicles of the patient, and the volume is read off the bead which matches most closely in size.
- Discrepancy of testicular size with other parameters of maturation can be an important clue to various diseases. e.g. Small testes can indicate either primary or secondary hypogonadism
What are male Secondary Sexual Characteristics dependent on?
What are 7 examples of androgen dependent male secondary sexual characteristics?
What is the role of GH in male puberty?
Describe the graph for plasma testosterone levels throughout male life (in picture)
- Virtually all male secondary sexual characteristics are dependent on testosterone and its metabolite dihydrotestosterone (DHT)
- 7 examples of androgen dependent male secondary sexual characteristics:
1) Facial, underarm, pubic hair
2) Deepening of voice (due to growth of larynx)
3) Thick secretion of skin oil glands (can cause acne)
4) Masculine pattern of fat distribution
5) Bone growth via growth hormone secretion then termination via closure of epiphyseal plates
6) Stimulation of muscle protein synthesis
7) Erythropoietin stimulation giving higher haematocrit in males
- Sex steroids stimulate growth spurt by stimulating GH release but also promote the closure of epiphyseal plates so that growth in height ceases at the end of puberty
- Graph for plasma testosterone levels throughout male life (in picture)
Initiation of Puberty.
How does continuous and pulsatile release of GnRH affect Gonadotropin (LH/FSH) release?
When is GnRH release detected in childhood years?
What does this not stimulate?
What is the signal for this release?
How does this GnRH release start to change?
- Initiation of Puberty
- Gonadotropin (LH/FSH) release is suppressed by continuous infusion of GnRH
- Pulsatile administration of GnRH will lead to gonadal stimulation, maturation and production of steroid hormones
- 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 signals from the hypothalamus act as a GnRH pulse generator
- Nocturnal secretion of GnRH pulses become more pronounced leading to gonadotropin release
How is pulsatility of GnRH inferred?
Describe the Gonadotropin (LH/FSH) levels in females in:
1) Foetal life
2) Childhood
3) Early-mid puberty
4) Mid to late puberty
5) Adult pattern
What is needed to suppress gonadotropin output in childhood and adulthood?
How does GnRH pulse frequencies affect LH and FSH synthesis and secretion?
- GnRH too short a half-life to measure so the pulsatility is inferred from LH levels measured (half-life of 30mins compared to 300mins for FSH) responds to GnRH so can infer what it’s doing
- Gonadotropin (LH/FSH) levels in females in:
1) Foetal life
* LH and FSH peak and again during early infancy, before falling to low levels throughout the rest of childhood
2) Childhood
* Low FSH and LH levels, low LH pulse amplitude and frequency. Minor pulses mostly at night, not sufficient to trigger gonadotrophin release
3) Early-mid puberty
* Amplification of nocturnal pulses of LH reflects the re emergence of the GnRH pulse generator and beginning of puberty
4) Mid to late puberty
* Daytime pulses increase
5) Adult pattern
* Roughly one pulse/hour with significant variation throughout the menstrual cycle
- In childhood very low sex steroid levels are sufficient to fully suppress gonadotropin output.
- In adolescence and adults higher levels of sex steroids are required to suppress gonadotropin release.
- High GnRH pulse frequencies favour LH synthesis and secretion, while low GnRH pulse frequencies favour FSH synthesis and secretion
What are 5 factors that contribute to earlier puberty?
What mechanism signals start of puberty?
- 5 factors that contribute to earlier puberty:
1) Genetics
* Timing correlates with mother and sisters
* Genetics accounts for the majority of variability in the timing of pubertal onset in developed countries
2) Social factors
* Lower social class & obesity tends to lead to earlier menarche
* Diet may be one component but may be other factors in play.
3) Geographic factors
* Closer to equator, lower altitudes, urban setting
4) Environmental exposures
* Endocrine disrupting chemicals – industry uses e.g. plastics, agriculture, fuels
5) 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
What is WHO/UN advice regarding breast feeding?
What are 7 benefits in the baby for breast feeding exclusively for 6 months?
- WHO/UN advises women to breast feed exclusively for 6 months for optimal lifetime benefits
- 7 benefits in the baby for breast feeding exclusively for 6 months
1) Reduced incidence of GI, respiratory and middle ear infection
2) Decreased risk of childhood diabetes, asthma and eczema
3) Reduced risk of lactose intolerance
4) Improved intellectual and motor development
5) Decreased risk of obesity in later life
6) Possible reduced autoimmune diseases
7) 27% reduced risk of sudden infant death syndrome
What are 6 benefits in the mother for breast feeding exclusively for 6 months?
- 6 benefits in the mother for breast feeding exclusively for 6 months:
1) Promotes recovery from childbirth
2) Promotes return to ‘normal’ body weight
3) Promotes a period of infertility
4) Reduces risk of premenopausal breast cancer
5) Reduces risk of ovarian cancer
6) Possibly improves bone mineralisation
Describe 2 features in the anatomy of the breast.
What is dormant in the non-lactating breast?
When does glandular tissue fully develop?
- 2 features in the anatomy of breasts:
1) Nipple is surrounded by pigmented skin (areola)
2) 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 nonlactating breast
- Glandular tissue only develops fully during pregnancy
What do secretory alveoli in the breast contain?
What are milk producing cells stimulated by?
What is each alveolus of the breast surrounded by?
What are myo-epithelial cells stimulated by?
- Secretory alveoli in the breast contain milk producing cells
- They are stimulated by prolactin
- Each alveolus of the breast is surrounded by contractile myo-epithelial cells
- Myo-epithelial cells are stimulated by oxytocin, which leads to milk being pushes out of the alveolus into the lactiferous ducts, out the nipple, and into the baby
What are the 5 major routes for production of milk?
- 5 major routes for production of milk:
1) Secretory pathway
2) Transcellular endocytosis/exocytosis
3) Lipid pathway
4) Transcellular salt and water transport through channels and transporters
5) Paracellular pathway for ions and water
Describe the 5 steps of the breast alveoli development during pregnancy
- 5 steps of the breast alveoli development during pregnancy:
1) Prior to pregnancy, ducts with few alveoli exist
2) In early pregnancy, alveoli grow
3) In mid-pregnancy, alveoli enlarge and acquire lumen
4) During lactation, alveoli dilate
5) After weaning, gland regresses
Suckling Reflex – Role of Prolactin.
What inhibits the release of dopamine in breast feeding?
What is prolactin release in proportion to?
- Suckling Reflex – Role of Prolactin
- Suckling stimulus inhibits the hypothalamic release of dopamine (PIF - Prolactin Inhibitory Factor)
- Prolactin is released in proportion to the strength and duration of the suckling
Milk Ejection Reflex – Role of Oxytocin.
What does suckling stimulate in the hypothalamus?
What does oxytocin act on?
What kind of reflex is the milk ejection reflex?
How is it triggered?
What is oxytocin release inhibited by?
What can inhibit the milk ejection reflex?
- Milk Ejection Reflex – Role of Oxytocin
- Suckling stimulates neurones in hypothalamus to synthesise oxytocin - carried to posterior pituitary
- Release of oxytocin into blood stream acts on myo-epithelial cells in alveoli – causing ‘let down’ (ejection) of milk
- The milk ejection reflex is a conditioned reflex
- It is triggered in response to the cry of a baby
- Oxytocin release is inhibited by catecholamines - stress can inhibit the reflex
How are prolactin levels affected during pregnancy?
What does this stimulate?
What does prolactin control?
How is prolactin’s action inhibited in pregnancy?
When do steroid levels fall again?
- 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
