Lecture 23: Lactation I Flashcards
What is the purpose of the breast/mammary glands?
- For breast milk production to feed young
- Lactational Amenorrhea
The mammary Glands are acutally modified __________!
They are derived from what tissue?
The mammary Glands are acutally modified Sweat glands!
From tissue first found of the mammary/milk crests of embryo
(arise between axilla armpit and groin)
So abnormal breast development will v. likely occur along the lines of these crests.
Breast development begins with?
Descrbe the following stages?
The formation of mammary buds at ~6weeks
From mammary crest → localised breast buds
- First development is a down-growth (infolding) of the dermis → Primary Breast Bud
- Secondary Buds develop: start to branch
- Lactiferous Ducts develop: carry milk from alveoli to nipple
As gestation progresses, buds develop lumens (become canalised)
By birth, the breasts are _____ developed, and could potentially make _____.
What does milk production require to begin and what is ‘witches milk’
By birth, the breasts are fully developed, and could potentially make milk.
This requires a hormonal stimulus.
Witches Milk: a colostrum-like secretion from the fetus breast, as it’s been exposed to the placental steroids and maternal hormones at birth.
Canalisation of breast buds is induced by what?
And by birth how many lactiferous ducts are present in the women?
Canalisation of breast buds is induced by Oestrogen and progesterone placental steroids which leads to formation of lectiferoous ducts
15-20 lactiferous ducts are present at birth per breast
External structures of the Breast are?
Remember they come in many shapes and sizes!
Nipple:
- Raised (usually) cylinderical pigmented structure
- Can be inverted (v common)
- The lactiferous ducts join to the skin here
Areola:
- pigmented circle of tissue around nipple
- Contains sebaceous glands which give a granular texture to the surface; but they don’t have hairs!!!
Internal Structures of the Breast are?
- Adipose tissue of the Pectoral Fat pad: gives the breast its texture and shape.
-
Suspensory ligaments of Cooper or Cooper’s Ligaments: support the breast
- can be affected by age and hormones and become less supportive
-
15-20 Lobes: made of milk-secreting lobules
- these connect to a single lactiferous duct
- Look like a bunch of grapes
Lactiferous sinus is?
The lactiferous duct runs towards the nipple and expands into a lactiferous sinus
15-20 lactifferous sinuses open into the nipple to allow extraction of the milk
although a babyb has all the tissue required to produce milk, the milk producing structures don’t start developing until?
Develop during puberty, eg alveoli formation, particularly under the influence of oestrogen (and progesterone) in the cyclic fashion of each mensstrual cycle. Many mammals only develop boobs during pregnancy!!
Successive cycles cause increased growth of alveolar buds and the smaller branches of the lactiferous ducts that connect the lobes. (increased branching to alveolar tissue and already present L.ducts)
Noticeable premenstrual increases in breast volume and tenderness
These hormones all affect breast development, in what way?
Oestrogen:
Progesterone:
Prolactin:
Growth Hormone:
Insulin and cortisol:
Oestrogen: essential for breast growth, a ‘mitogen’
Progesterone: induces side branching of ducts
Prolactin: Neccessary for alveolar development (milk prod.) but also stimulates casein and alpha-lactalbumin mRNAs
Growth Hormone: (related to PRL) important in some species
Insulin and cortisol: stimulate alveolar epithelial divsion/cell growth
What are the different birth weights in women when non-pregnant, near-term pregnant and lactating?
Non-pregnant: 200g
Near term: 400-600g
Lactating: 600-800g
Prolactin in theory should promote milk production, but lactation doesn’t occur until after birth (and PRL is present during birth!).
This is due to inhibition by progesterone to the production of milk; is a smooth muscle relaxant and prevents milk ejection
What’s the endocrine control via prolactin, on pregnancy?
- Produced in large amounts in pregnancy; falls at birth as placenta is gone
- Infant nipple suckling → secretion of PRL by anterior pituitary
- via a neuroendocrine reflex
- Cutting the nerves to the nipple stops this reflex!
- Suckling → reduced secretion of dopamine (Prolactin Inhibiting Factor) into portal blood
- At the same time vasoactive intestinal peptide (VIP) secretion from the paraventricular nuclei is increased
- The changes in balance of these act on the lactotrophs to secrete prolactin
- Prolactin then induces the production of milk proteins
The level of _______ correlates with the level of milk produced, as well as the duration and extent!
The level of Prolactin correlates with the level of milk produced, as well as the duration and extent (suckling harder means baby is hungry, and it can order up it’s next meal!!)
This is why 2 infants suckling induces more prolactin → more milk is needed!
Therefore milk productional is proportional to the amount the baby wants; this cannot be achieved by bottling feeding!
Whats the secondary Milk Ejection Response?
- Can also be stimulated in response to suckling → secretion of oxytocin by the posterior pituitary
- Oxytocin: induced the contraction of the myoepithelial SM cells (have lots of oxytocin receptors) of the alveoli. Causes ejection from milk into the ducts (can even be ejected from the nipple) so baby doesn’t have to suck so hard
- Stimulation of the Female reproduction tract → incuded oxytocin release
- milk let down during sex
- blowing into a cows vagina → ket down
- Also Baby crying and smell
How do we have lactational amenorrhea?
Prolactin (produced via suckling/feeding) can suppress secretion of gonadotropins LH **and FSH
- Thought to be via an effect on kisspeptin neurons in the hypothalamus (that sit above and trigger GnRH neurons)
- Means lactating women breastfeeding have no/irregular
- menstrual cycles
- Lactation is therefore an (unreliable) contraception!!
- Evolutionary as we can’t handle to many babies! Spaces them out in the days before contraception
