Anatomy of the Breast and Physiology of Lactation Flashcards
The breasts lie over which muscle?
The pectoralis major
What extends from the upper outer corner of the breast up into the axilla?
The axillary tail of Spence
Why do breasts vary in size?
Due to differing amounts of adipose tissue.
What are nipples composed of?
Connective tissue.
Describe the surface of the nipple.
Nipples are covered in pigmented stratified squamous epithelium, which contain papillae. Papillae allow bundles of unmyelinated nerve endings to lie close to the skin.
What are Montgomery’s tubercles and where can they be found?
Montgomery’s tubercles are sebaceous glands that produce sebum to lubricate the nipple. They are found in the areola.
What is the functional substance of the breast, the glandular tissue, also known as?
Parenchyma
How is parenchyma arranged?
Glandular tissue is arranged in lobes that radiate out from nipple. Each lobe is divided into smaller lobules.
What two things are contained in lobules?
Alveoli and ductules.
Where can acini cells (or lactocytes) be found?
In each alveolus.
Describe the arrangement of cells in the alveoli.
Cells are arranged in a single layer. They rest on the basal lamina and myoepithelial cells.
What is the basal lamina?
The basal lamina is the basement membrane dividing the epithelial and stromal parts of breast tissue.
Ducts consist of an inner lining of ____ cells and an outer lining of ____ cells.
epithelial
myoepithelial
How many groups of alveoli drain into a small duct?
10-100.
Ducts from lobules unit to form what?
The main lactiferous duct for each lobe.
What is the stroma?
The stroma refers to everything in the breast that is not the functional glandular tissue: connective tissue, adipose tissue, blood and lymph vessels, nerve tissues and surrounding skin.
What holds breasts in position?
Suspensory ligaments of Astley-Cooper.
What is the average amount of ducts exiting the nipple?
9
What is the ratio of glandular to fatty tissue?
2:1
65% of parenchyma is within how many millimetres of the nipple?
30mm
List the five developmental stages of breast function.
- Embryogenesis
- Mammogenesis
- Lactogenesis
- Lactation
- Involution
Breasts start to develop on the ventral surface of the body from what week of gestation?
4th week
Mammogenesis occurs in two phases, when do these occur?
Puberty and pregnancy.
Mammogenesis is not complete until after parturition: true or false?
True.
The ovulatory cycle enhances breast growth up until what age?
30
Which hormones stimulate the growth of mammary ducts during puberty
Oestrogen and growth hormone.
When do the lactiferous ducts and alveoli develop during mammogenesis?
In the second half of the menstrual cycle.
What hormone stimulates development of the lactiferous ducts and alveoli in mammogenesis?
Progesterone
What are the three stages of lactogenesis?
Priming, initiation and maintenance.
When does stage 1 (priming) of lactogenesis occur?
During pregnancy.
At how many weeks’ gestation is the breast capable of synthesising milk components?
16 weeks
Which hormones contribute to accelerated breast growth in pregnancy?
Human placental lactogen, prolactin, human chorionic gonadotrophin, oestrogen and progesterone.
During stage 1 of lactogenesis, which hormone contributes to the development of differentiated secretory alveolar cells?
Prolactin
During stage 1 of lactogenesis, which hormone contributes to ductal growth?
Oestrogen
During stage 1 of lactogenesis, which hormone contributes to lobular formation and alveolar growth?
Progesterone
During stage 1 of lactogenesis, what two things are responsible for suppressing secretory activity?
Progesterone and prolactin-inhibiting factor.
Lactogenesis 1 can be considered the transitional milk stage: true or false?
False. Walker (2015) defines Lactogenesis 1 as the colostrum stage.
How many millilitres of colostrum is available to the infant on day 0 postpartum?
100ml
In the first trimester, what is the percentage increase in blood flow to the breasts?
50%.
Stage 2 of lactogenesis involves which two maternal reflexes?
The milk production reflex and the milk ejection reflex.
Stage 2 of lactogenesis is dependent on which three neonatal reflexes?
The rooting reflex, the sucking reflex and the swallowing reflex.
What three hormones are necessary for initiation of lactation?
Prolactin, insulin and hydrocortisone.
Why is the anterior pituitary gland no longer inhibited after the birth of the placenta?
Because there is an abrupt drop in progesterone, oestrogen and human placental lactogen.
Nipple stimulation causes the hypothalamus to inhibit the release of what?
Dopamine
Why are lower levels of dopamine necessary for stage 2 of lactogenesis?
Lower levels of dopamine stimulate the release of prolactin from the anterior pituitary gland.
How many hours after birth does the composition of milk rapidly change from colostrum to transitional milk?
30-72 hours.
When does stage 3 of lactogenesis occur?
Approximately 10 days after birth.
When is a mature milk supply established?
Approximately 10 days after birth.
When is lactation the earliest lactation is said to be established?
4 weeks after birth.
Stage 3 of lactogenesis is reliant on an intact hypothalamic-pituitary axis regulating what?
Oxytocin and prolactin
Stage 3 of lactogenesis is dependent on what neonatal behaviours?
Frequent suckling and removal of milk.
Lactation involves two concepts: milk ____ and milk _____.
synthesis
production
What is milk synthesis?
The accumulation of milk within the breast.
What is milk production?
The volume of milk removed from the breast.
When is there an increased synthesis of milk?
In the morning, peaking between 8am and midday.
Approximately how much milk can an infant remove from the breast?
76%
List four factors influencing milk synthesis.
Frequency of feeds, the time of day, the amount of milk removed, and the storage capacity of each breast.
How long is the average period of involution?
3 months.
Is re-establishment of full lactation possible during involution?
Yes.
During involution, accumulation of milk in the alveoli and ducts causes what to happen to the epithelial cells?
Distension and mechanical atrophy.
During involution, accumulation of milk in the alveoli eventually causes what to happen to the alveoli?
The alveolar walls rupture.
During involution, what happens to the waste cells and glandular debris?
Phagocytosis
During involution, what happens to the alveolar lining?
Alveolar lining changes from a single secretory, to double non-secretory layer.
Breasts often remain larger after lactation due to deposition of fat and connective tissue: true or false?
True.
Describe the changes in milk composition whilst weaning.
There are higher levels of fat, sodium and immunoglobulins. There are lower levels of lactose.
Why are the breasts vulnerable to infection with abrupt weaning?
Because it takes 2 days for immunoglobulin and lactoferrin levels to rise.
Feedback Inhibitor of Lactation is found in which component of milk?
Whey.
Where is Feedback Inhibitor of Lactation produced?
It is secreted by the alveolar cells.
It is thought that the Feedback Inhibitor of Lactation inhibits secretion of lactose by blocking what?
Prolactin
If milk accumulates in the breast, the concentration of Feedback Inhibitor of Lactation increases. What effect does this have?
It inhibits lactation by reducing the rate of milk synthesis.
Where is prolactin produced?
In the anterior pituitary gland.
Secretion of prolactin is modified by which hormones?
Oestrogen and Thyroid Stimulating Hormone
What are the prolactin levels at term?
150-400ng/ml
Prolactin levels are not reliant on infant suckling until when?
Approximately day 3 after birth.
Describe what happens to prolactin levels during a feed.
Prolactin levels rise within 10 minutes of suckling. They peak at 30 minutes. Levels return to base levels within 4 hours of the start of the feed.
Prolactin circadian rhythms exist throughout lactation. When are levels highest?
At night.
In non-breastfeeding mothers, when should their prolactin levels return to normal?
Within two weeks of giving birth.
Prolactin concentrations are highest in which type of breastmilk?
Transitional breastmilk.
When absorbed by the neonate, what effect does prolactin have on the intestine?
It influences fluid, sodium, potassium and calcium transport.
What is dopamine also known as?
Prolactin-inhibiting factor.
Where is prolactin-inhibiting produced?
The hypothalamus
What determines whether the hypothalamus produces prolactin-inhibiting factor?
Catecholamine levels
List three factors that affect prolactin release.
Physiological stimuli, pharmacological stimuli, and pharmacological suppressors.
According to the prolactin receptor theory, when are the specialised prolactin receptor sites most sensitive?
Immediately after the birth of the placenta.
According to the prolactin receptor theory, where can the specialised prolactin receptor sites be found?
Surrounding the acini cells.
According to the prolactin receptor theory, receptor sites that are not primed shut down. What effect does this have?
The receptor sites lose their sensitivity to prolactin. If insufficient sites are primed, the resultant milk supply will be lower for the duration of that lactation.
When a baby suckles at the breast, _____ impulses pass from the nipple via the ______ to the _____.
sensory
spinal cord
brain
Sensory impulses from the newborn suckling at the breast stimulates the hypothalamus to produce what?
Prolactin-releasing factor.
Prolactin-releasing factor stimulates the _____________ to produce ________.
anterior pituitary gland
prolactin
Prolactin is transported via the _____ to the ______, where it directs _____ cells to produce milk.
blood
breast
acini
Suckling (possibly via prolactin release) suppresses which three hormones implicated in menstruation and ovulation?
Gonadotrophin releasing hormone, luteinising hormone and follicle-stimulating hormone
If a mother is exclusively breastfeeding (including at least once at night) and her baby is less than 6 months old, how effective is lactation amenorrhoea as a method of contraception?
98% effective.
Where is oxytocin produced?
The posterior pituitary gland
Oxytocin binds to receptors on _____________ cells and to __________ cells in the duct walls, causing ________.
myoepithelial
longitudinal
contractions
Does the milk ejection reflex increase or decreases intraductal mammary pressure?
Increase
Describe what happens to oxytocin levels during a feed.
Levels rise within one minute of breast stimulation. Levels remain elevated during stimulation due to pulsatile release at one minute intervals. Levels return to baseline within 6 minutes of cessation of stimulation.
