Puberty and Lactation

Question 1

Adrenarche

Answer 1

Increase in production of androgens by adrenal cortex.

Question 2

Gonadarche

Answer 2

Physical and functional maturation of the gonads by gonadotrophins

Question 3

Puberty Definition

Answer 3

Developmental stage during which adolescents reach sexual maturity and become capable of reproduction.

Question 4

What does puberty result in?

Answer 4

• Growth in stature
• Change in body composition
• Development of secondary sexual characteristics (pubarche)
• Achievement of fertility

Question 5

Thelarche

Answer 5

Onset of breast development

Question 6

Pubarche

Answer 6

First appearance of pubic hair

Question 7

Menarche

Answer 7

Onset of menstruation

Question 8

Primary Sexual Characteristics

Answer 8

Reproductive organs which are present at birth

Question 9

Secondary Sexual Characteristics - Female

Answer 9

• ## Develop during puberty and not directly required for reproduction

Question 10

Secondary Sexual Characteristics - Male

Answer 10

• Develop during puberty and not directly required in reproduction

Question 11

Hypothalamic-Pituitary-Adrenal Axis (Adrenarche)

Answer 11

• 6-8 years of age
• Adrenocorticotropic hormone is produced by pituitary.
• Stimulates adrenal glands to secrete androgens - predominantly Dehydroepiandrosterone Sulphate (DHEAS).
• Increased androgen levels responsible for pubarche, development of pilosebaceous unit in skin (acne), increases cortical bone density.

Question 12

Tanner Stages of Female Puberty

Answer 12

• Breast development - first sign - usually occurs between ages 8.5 and 12.5 years
• Pubic hair growth and rapid height spurt - occur almost immediately after breast development
• Menarche - average age 13 years, on average occurs 2.5 years after start of puberty and signals the end of growth (only around 5cm remaining).
• Some normal variation in order and timing.

Question 13

Tanner Stages of Male Puberty

Answer 13

• Testicular Enlargement to greater than 4mls volume - first sign, 10-15yrs (mean is 11yrs).
• Pubic hair growth and penile enlargement - normally 2 year interval between onset of pubic hair and axillary and facial hair.
• Spermarche - appearance of sperm in seminal fluid - mean age is 13.4 years (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 is later and of greater magnitude which accounts for a greater final height in males.

Question 14

Initiation of Puberty

Answer 14

• Gonadotropin (LH/FSH) release - suppressed by continuous infusion of GnRH, pulsatile administration will lead to gonadal stimulation, maturation and production and production of steroid hormones.
• Pulses of GnRH are detectable in the childhood years but mostly during sleep and if low frequency and amplitude therefore do not stimulate gonadotropin release.
• Unknown signal is the GnRH pulse generator
• Nocturnal secretion of GnRH pulses become more pronounced leading to gonadotropin release.

Question 15

Factors Contributing to Early Puberty

Answer 15

• Genetics - timing correlates with mother and sisters
• Social Factors - lower social class and obesity tends to lead to earlier menarche
• Geographic Factors - closer to the equator, lower altitudes and 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.

Question 16

“Breast is best” for baby

Answer 16

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

Question 17

Anatomy of the Breast

Answer 17

• 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 fully develops during pregnancy
• Secretory Alveoli - milk producing cells, stimulated by prolactin
• Each alveolus is surrounded by contractile myo-epithelial cells and stimulated by oxytocin.

Question 18

Milk Secretion

Answer 18

5 Major routes for production of milk

• Secretory pathway
• Transcellular endocytosis/exocytosis
• Lipid pathway
• Transcellular salt and water transport through channels and transporters
• Paracellular pathway for ions and water

Question 19

Breast Development

Answer 19

• At birth the breast consists of lactiferous ducts without any alveoli (same in male breast)
• At puberty under influence of oestrogen the ducts proliferate and masses of alveoli form at the ends of the branches.
• Each cycle involves proliferative changes in the alveoli and there may be some secretory activity.
• During pregnancy under the influence of oestrogen, progesterone and prolactin the glandular portion of the breast undergoes hypertrophy - replacing the adipose tissue.
• From week 16 the breast tissue is fully developed for lactation but is inactive awaiting activation.
• After parturition the breast produces Colostrum before mature milk production begins.

Question 20

Breast Alveoli Development

Answer 20

• 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 21

Suckling Reflex - The Role of Prolactin

Answer 21

• Stimulus from suckling travels from breast, through the spinal cord to the hypothalamus.
• Neurons from the spinal cord inhibit dopamine release from the arcuate nucleus. The decreased level of dopamine removes the inhibition that dopamine normally produces on lactotrophs in the anterior pituitary, leading to prolactin release. Prolactin stimulates milk production in the breast.

Question 22

Milk Ejection Reflex - Role of Oxytocin

Answer 22

• Neurons from the spinal cord also stimulate the production and release of oxytocin from the paraventricular and supraoptic nuclei. Oxytocin is released in the posterior pituitary and into the systemic blood, where it then makes its way to the breast and myoepithelial cells.
• Neurons from the spinal cord inhibit neurons in the arcuate nucleus and the preoptic area of the hypothalamus, causing a fall in GnRH production. The reduced stimulation of gonadotrophs inhibits the cycle.

Question 23

How is lactation inhibited during pregnancy?

Answer 23

Prolactin levels increase during pregnancy which stimulates growth and development of mammary tissue. Prolactin controls/promotes milk production and is secreted during pregnancy from the anterior pituitary. However, its action is inhibited by the high levels of progesterone, oestrogens and human placental lactogen (hPL). These steroid levels fall after parturition and milk production begins.

Question 24

Lactational Amenorrhoea

Answer 24

Women who exclusively breast feed their baby will delay the onset of menstrual cycles. Prolactin suppresses hypothalamic release of GnRH and therefore pituitary FSH and LH. It prevents follicular growth, ovulation and menstruation. Lactational Amenorrhoea Method effective so long as: amenorrhoeic, baby less than 6 months old and baby exclusively breast fed.

Question 25

“Breast is best” for mother

Answer 25

• Promotes recovery from childbirth
• Promotes return to normal body weight
• Promotes a period of infertility
• Reduces risk of postmenopausal breast cancer
• Reduces risk of ovarian cancer
• Possibly improves bone mineralisation.

Question 26

Colostrum

Answer 26

Colostrum is the first form of milk produced by the mammary glands of mammals immediately following delivery of the newborn. Most species will begin to generate colostrum just prior to giving birth. It is rich in antibodies.

Question 27

Lactation

Answer 27

Milk production and ejection controlled by neurohormonal reflexes, Prolactin being the hormone responsible. It is initiated by the precipitous drop in oestrogen and progesterone after delivery. Prolactin surges each time mother nurses baby due to nerve impulses from the nipples to the hypothalamus. Without this 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.