Repro 11.1 Lactation Flashcards
What are the lobes of the mammary gland made up of?
Lobules of alveoli
Blood vessels
Lactiferous ducts
What does the mammary gland consist of?
15-20 lobulated masses of tissue
Fibrous connective tissue and adipose tissue
What type of ducts are the Lactiferous ducts?
Exocrine, blind ended
What is the site of milk synthesis?
Alveoli
What are myoepithelia?
Smooth muscle cells surrounding the alveoli responsible for milk let down
How do mammary glands differ at birth and post-puberty?
Few ducts at birth
At puberty oestrogens cause the ducts to sprout and branch and the ends form masses of cells that later become alveoli. Cyclic changes of the breast under the influence of oestrogen and progesterone during the menstrual cycle - endocrine ducts grow in literal phase and size may grow up to 20%
What happens to the breast during pregnancy?
Rising titres of oestrogen and progesterone stimulate considerable hypertrophy of the ductular-lobular-alveolar system. Prominent lobules form and the lumina of alveoli become dilated. The alveolar cells differentiate in mid-pregnancy. Cells are capable of secretion at this time and contain substantial amounts of secretory material but milk is not secreted in significant quantities.
What is colostrum?
Milk secreted by mammary glands just after giving birth (first week or so). Contains antibodies and is lower in fat but higher in protein than normal milk
Why is IgG from breast milk not digested in the babies GI tract?
Neonatal gut is open so it crosses without digestion
What is the composition of mature human milk?
Water - 90%
Lactose - 7%
Fat - 2%
Proteins including lactalbumin and lactoglobulin
Minerals - Ca Fe Mg K Na P S (can deplete maternal stores)
Vitamins - A B B2 C D E K
pH 7
What is the energy value of mature human milk?
27MJ/L
Where is milk fat synthesised?
Smooth enroll aspic reticulum of alveolar cells and passes in membrane bound droplets towards the lumen
Where is milk protein secreted from?
Passes through Golgi apparatus and is released by exocytosis
What are the benefits of breast feeding?
Fewer infections
Bonding
What favours development of the alveoli in pregnancy?
High progesterone/oestrogen
What causes lactation after birth?
Progesterone levels fall precipitously and oestrogen levels fall less so. This leads to alveolar cells becoming responsive to prolactin.
Where is prolactin secreted from?
Lactotrophs in the anterior pituitary gland
What effect does suckling do?
Initiates and maintains secretion by a neuro-endocrine reflex. Mechanically stimulates receptors in the nipple
Impulses pass to the brainstem and to the hypothalamus to reduce secretion of dopamine and vasoactive intestinal peptide, so promoting prolactin secretion
What determines the amount of milk produced?
Prolactin - determined by the amount of suckling
When is milk produced?
Continuously between feeds and accumulates in the ducts, increasing the turgor of the breast
How does milk let down occur?
Dramatic increase in the secretion of oxytocin from the posterior pituitary gland. This contracts myoepithelia which eject the milk. It is NOT suckled out of the breast
What happens if suckling stops?
Milk production gradually ceases, in part due to lack of prolactin levels, in part due to turgor-induced damage to the breast.
Milk production can also be suppressed by steroids
Why is pregnancy unlikely while breast feeding?
Prolactin reduces fertility
What happens to the breasts after ovulation?
Cell proliferation and stromal oedema increase
With menstruation see decrease in size of lobule
What happens to lobules after cessation of lactation?
Atrophy of lobules but not to former levels
What happens to breast tissue with increasing age?
Terminal lobular units decrease in size and number, interlobular stroma is replaced by adipose (mammograms easier to interpret)
