Lactation Flashcards
Describe the structure of mammary and breast tissue?
15-24 lobulated masses of tissue embedded in breasts. Fibrous and adipose tissue in between. Lobes containing alveoli, blood vessels and lactiferous ducts which coalesce on the lactiferous sinus/lacunae/ampullae. These sinuses converge onto 4/5 nipple pores. Note: Mammary tissue and breast tissue are not the same.
Describe the development of breast tissue pre-birth?
Mammary tissue develops in utero as an invagination of the epithelium taking with it some melanin, this branches into many ducts. Development stops at birth due to drop in oestrogen and progesterone (was being produced by the placenta).
How do breasts develop after birth?
At birth only few ducts present but at puberty these ducts sprout (oestrogen receptors alpha) and branch and alveoli begin development (oestrogen receptor b and progesterone receptor b and switching off the receptors for prolactin). With each menstrual cycle, there are changes in breast tissue associated with changes in oestrogen & progesterone.
What prevents breast development in men?
In men testosterone and other androgens prevent this development.
What happens to mammary tissue during pregnancy?
During pregnancy, high levels of oestrogen and progesterone stimulate more breast development developing ducts and alveoli further. Also stimulate the myoepithelial cells to send out processes to each other connecting themselves to each other.
What is mammogenesis, describe how this happens?
Preparation of breasts (mammogenesis) – During pregnancy
Hypertrophy of the ductularlobular-alveolar system, prominent lobules form, alveolar cells differentiate and become capable of milk production from mid gestation (2nd trimester). Towards the end of pregnancy, the nipple becomes erect, areola enlarges, montgomery tubercules form (bumps in the areolar from fusion of sebaceous glands and mammary lobules) producing oil lubricating the breast and preventing cracking during feeding and pheromones specific to the mum allowing the baby to tell where the mother is. The breast becomes more sensitive due to growth of neurones from intercostal nerves III, IV and V.
Is milk produced during pregnancy and why?
During pregnancy, little milk is secreted early on because the high progesterone vs oestrogen ratio which favours growth and not secretion, after the 2nd half of the 2nd trimester there is a switch to oestrogen domination – causing prolactin receptors to be switched on, invagination of blood vessels to bring the resources needed for milk production and adipose tissue proliferation and growth.
Describe lactogenesis
Lactogenesis in alveolar cells. The fat is made in smooth endoplasmic reticulum, protein in RER and secreted via Golgi apparatus and Sugars synthesised and secreted. Hemidesmasomes look after the epithelial cells and moves out of the way allowing white blood cells (neutrophils and macrophages) into the lumen of the alveoli.
What is the milk first produced after birth called and how does it change?
Soon after birth (0-3 days) about 40 ml per day of Colostrum is produced this contains less water, fat & sugar than milk produced later. More proteins (making it smell), particularly immunoglobulins (IgA, IgM, IgG) that coat intestinal mucosa preventing bacteria from entering intestinal cells and white cells that kill microorganisms. Over the next two weeks the composition gradually changes to mature milk, Intermediate milk with large amounts of lactose and endocannabinoids making the neonate sleepy and sated.
How is milk production controlled?
High progesterone and oestrogen in pregnancy stimulates breast tissue growth, secretion is allowed by fall in steroids and promoted by prolactin. Prolactin is a polypeptide hormone secreted by anterior pituitary gland controlled by dopamine from hypothalamus (inhibits). Factors promoting secretion of prolactin reduce dopamine secretion.
How is the pituitary prolactin stimulated to be released?
Stimulation of pituitary prolactin secretion is promoted by suckling – potent neuro-endocrine reflex. Suckling at one feed promotes prolactin by inhibiting dopamine release which causes production of the next feed, which accumulates in alveoli and ducts so there must be sufficient suckling stimulus at each feed.
Why does lactation cause menses to cease?
Prolactin inhibits GnRH preventing LH and FSH stopping the menstrual cycle whilst breast feeding is occurring.
How is colostrum produced?
Colostrum is produced because of release of prolactin from the decidual cells in the endometrium which is pumped into the amnion, into the umbilical cord, chorion and then out into maternal circulation.
What is the role of oestrogen from the placenta in lactation and what hormones need to be released to stimulate secretion?
Oestrogen from the placenta stimulate the lactotrophs to undergo hyperplasia meaning the cells can now produce large amounts of prolactin but can’t yet secrete it. They need thyrotropin releasing hormone stimulating the release of prolactin. TRH also inhibits Dopamine by down regulating the number of dopamine receptors in the brain.
What is galactokinesis?
Ejection of milk (galactokinesis).
Babies do not suck milk out of the breast it is ejected by a let-down reflex. Myoepithelial cells surround alveoli and are contracted by oxytocin which is released from posterior pituitary when the breast is stimulated by suckling. Babies don’t suck – they can’t until they can walk
