Puberty and Lactation

Question 1

Define puberty and the processes involved

Answer 1

• a developmental stage during which adolescents reach sexual maturity and become capable of reproduction

Involves:

• gonadarche: physical and functional maturation of the gonads by gonadotrophins
• adrenarche: increase in production of androgens by adrenal cortex

Question 2

What are the outcomes of puberty?

Answer 2

• growth in stature
• change in body composition
• development of secondary sexual characteristics
• achievement of fertility

Question 3

Define thelarche, pubarche and menarche

Answer 3

• thelarche: onset of breast development
• pubarche: first appearance of pubic hair
• menarche: onset of menstruation

Question 4

Describe the process of adenarche and the outcome of it is

Answer 4

• occurs 6-8 years old
• ACTH produced by pituitary
• stimulates adrenal glands to secrete androgens (predominantly DHEAS)

Increased androgens cause:

• development of pubic and axillary hair
• development of pilosebaceous unit in skin (acne)
• increases cortical bone density

Question 5

Describe the Tanner stages of female puberty

Answer 5

• first sign: breast development (8.5-12.5 years)
• then pubic hair growth and rapid growth spurt
• then menarche which signals end of growth (avg age 13)

Question 6

What are the hormonal dependent secondary sexual characteristics?

Answer 6

• facial, underarm, pubic hair
• thick secretion of skin oil glands
• female pattern of fat distribution
• hips and pelvis widen
• uterus and cervix enlarge, secretory function increases
• bone growth (and closure of epiphyseal plates)

Question 7

Describe the Tanner stages of male puberty

Answer 7

• testicular enlargement to over 4mls (10-15 yrs)
• then pubic hair growth and penile growth
• then spermarche (sperm in seminal fluid - 13.4yrs)
• growth spurt (when testicular volume 12-15mls, later and of greater magnitude than females)

Question 8

What are the androgen-dependent secondary sexual characteristics?

Answer 8

• facial, underarm and pubic hair
• deepening of voice
• thick secretion of skin oil glands
• masculine pattern of fat distribution
• bone growth
• stimulation of muscle protein synthesis
• erythropoietin stimulation

Question 9

What are the factors that contribute to earlier puberty?

Answer 9

• genetics: timing correlates with mother and sisters
• social factors: lower social class and obesity
• geographic factors: closer to equator, lower altitudes, urban setting
• environmental exposures: endocrine disrupting chemicals like in industry
• race: afro-carribean and african-american

Question 10

Describe the important anatomical features of the breast

Answer 10

• nipple which is surrounded by pigmented skin (areola)
• modified sebaceous glands (alveoli) that contain milk producing cells stimulated by prolactin which empty by lactiferous sinuses that open onto the surface of the nipple
• alveoli surrounded by contractile myoepithelial cells stimulated by oxytocin
• adipose tissue dominant in non-lactating breast
• glandular tissue only develops during pregnancy

Question 11

What are the 5 major routes for milk production?

Answer 11

• secretory pathway: proteins made and processed in Golgi, pinched off and stored as vesicles then exocytosed
• transcellular endocytosis/exocytosis: proteins pinched through endocytosis then transported across cell then exocytosed across lumen
• lipid pathway: epithelial cells synthesise short chain fatty acids, gets pinched off and dumped within alveolar lumen
• transcellular salt and water transport through channels and transporters
• paracellular for ions and water

Question 12

Describe the development of the breast

Answer 12

• birth: lactiferous ducts but no alveoli
• puberty: oestrogen causes ducts to proliferate and masses of alveoli form at end of branches
• each cycle involves proliferative changes in alveoli
• preganancy: oestrogen, progesterone and prolactin causes glandular portion of breast to hypertrophy replacing adipose tissue
• from week 16: breast tissue ready for lactation waiting activation (parturition produces colostrum which causes mature milk production)

Question 13

Describe breast alveoli development

Answer 13

• prior to pregnancy ducts with few alveoli exist
• in early pregnancy alveoli grow
• in mid-pregnancy alveoli enlarge and acquire lumen
• during lactation alveoli dilate
• after weaning, gland regresses

Question 14

Summarise lactation

Answer 14

• involve milk production and let down
• controlled by neurohumoral reflexes (from prolactin)
• initiated by drop in oestrogen and progesterone after delivery
• prolactin surges each time mother nurses baby due to nerve impulses from nipples to hypothalamus
• without nursing no prolactin surge and so loss of milk production
• when not nursing, hypothalamus produces prolactin inhibitory hormone
• lactation inhibits FSH and LH so interferes with reproductive function

Question 15

What is the role of prolactin in the suckling reflex?

Answer 15

• suckling stimulus inhibits the hypothalamic release of dopamine/PIF (prolactin inhibitory factor)
• allows prolactin to be released in proportion to strength and duration of suckling

Question 16

What is the role of oxytocin in the milk ejection reflex?

Answer 16

• suckling stimulates neurones in hypothalamus to synthesise oxytocin
• carried to posterior pituitary
• release of oxytocin into bloodstreatm acts on myoepithelial cells in alveoli causing a let down of milk
• can be stimulated by cry of baby
• inhibited by stress and catecholamines

Question 17

How is lactation inhibited during pregnancy?

Answer 17

• prolactin stimulated growth and development of mammary tissue and promotes milk production in pregnancy
• however is inhibited by high levels of oestrogen, progesterone and hPL (human placental lactogen)

Question 18

Describe the role of prolactin in lactational amenorrhoea

Answer 18

• prolactin suppresses hypothalamic release of GnRH and therefore FSH and LH
• prevents follicular growth, ovulation and menstruation