11.1 Flashcards
Draw the structure of a breast and label: Lactiferous ducts Lactiferous sinus Lobules of mammary gland Alveolus Pec major and minot Suspensory ligaments
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What does the breast consist of?
Glandular and supporting fibrous tissue embedded within a fatty matrix, together with blood vessels, lymphatics and nerves.
Where are mammary glands located? What do they consist of?
In subcutaneous tissue overlying the pec major and minor.
They consist of 15-20 lobulated masses of tissues, with fibrous tissue connecting the lobes and adipose tissue between them.
What makes up the lobes of mammary glands?
Alveoli
Surrounded by blood vessels and lactiferous ducts that carry the secretions away.
What happens in the alveoli? What cells allow milk let down? Where are they located?
Alveoli are the site of milk synthesis
Myoepithelial SMCs responsible for milk let down surround the alveoli.
What determines the size of non-lactating breasts?
he amount of fat surrounding the glandular tissue.
Where does the breast extend from to? (surface markings?)
Lateral sternal edge –> Midaxillary line
2nd Rib –> 6th Rib
What do the mammary glands secret in the first week after birth? How much? What does this contain?
Colostrum
40ml/day
Contains less water soluble vitamins, fat and sugar than later milk but more protein, fat soluble vitamins and immunoglobulins
Particularly IgA that coat intestinal mucosa and prevent bacteria entering intestinal cells.
White cells that kill microorganisms
What happens to mammary gland secretion2-3 weeks after birth?
IgG and total protein content declines in colostrum, whilst fat and sugar rise to produce mature milk.
What are the constituents of mature milk? Proteins? How long is it produced for? Energy value? pH?
Composition
90% water
7% lactose
3% fat
Proteins: Lactoglobulin (IgG) Lactalbumin Minerals Vitamins
Produced as long as the baby suckles.
27MJ/liter energy
pH 7.0
Where does synthesis of breast milk take place? Components?
Alveolar cells
Fats:
Synthesised in SER
Passes in membrane bound droplets towards the lumen
Protein:
Passes through the Golgi apparatus
Secreted by exocytosis
Sugar:
Synthesised and secreted
Describe how the breast is before puberty and how hormones lead to its growth and development.
At birth, only a few lactiferous ducts are present.
At puberty, oestrogens cause the ducts to sprout and branch and ends from the masses of cells that later become alveoli.
With each menstrual cycle, changes in breast tissue occur with changes in O and P.
Describe how hormones lead the breast to develop during pregnancy?
During pregnancy high P:O ratio favours development of alveoli but not secretion.
Substantial hypertrophy of ducular-lobular-alveolar system and prominent lobules form.
When are alveolar cells capable of milk production?
Mid gestation.
Describe the hormonal changes after birth and how they change the breast.
Progesterone level falls sharply along with less sharp fall in oestrogen.
These lead to breast becoming more responsive to prolactin.
What is the function on infant suckling?
Suckling initiates and maintains secretion by a neuroendocrine reflex by mechanically stimulating receptors in the nipple.
Impulses pass up to the brain stem and to hypothalamus to reduce secretion of dopamine and faso-active intestinal peptide to promote prolactin secretion.
What is prolactin
Polypeptide hormone
From ant pit
Controlled by dopamine (PIH) from the hypothalamus
What happens if the infant does not suckle?
Prolactin levels fall?
What is the key to maintaining milk production?
The amount of milk produced before the next feed depends on the suckling stimulus.
Thus, sufficient suckling stimulus is required each feed.
Milk is produced continually between feeds and accumulates in ducts increasing the turgor of the breasts.
What is milk let down? What causes it?
Babies do not suck milk out of breast, it is ejected by let-down reflex.
Caused by a dramatic increase in secretion of oxytocin from the post pit due to stimulation of mechanoreceptors in the nipple or anticipation of feed.
How does oxytocin result in let down of milk?
Oxtocin causes the myoepithelial cells surrounding the alveoli to contract, ejecting the milk.
Infants do not suck milk out of the breast and so have to learn how to suck milk from a bottle.
The let down reflex can be conditioned and often begins before the baby reaches for the nipple.
What effect does suckling reflex have on the uterus?
Release of oxytocin keeps the uterus clamped down on open placenta blood vessels.
What produces cessation of lactation?
If suckling stops, the production of milk also stops.
Pain: increased turgor from non-suckling intact or infection.
This is in part due to lower prolactin levels and in part due to turgor induced damage to the breast.
Why is it less likely for pregnancy to occur while an infant is suckling?
Prolactin reduces fertility by inhibiting ovulation.
