Lecture 25: The breast Flashcards
Whats the purpose of the breast?
1) Nutrition of the young
2) Spacing of pregnancies
What is breast tissue derived from?
- Modified sweat glands
- Derived from tissue that is identified in the mammary crests that arise between the axilla and the groin
(NB: Abnormal breast development is likely to occur along the lines of the mammary crests) - Breast development begins with the formation of mammary buds at about six weeks
Describe the first and secondary bud developments:
The first development takes place as a down growth of the dermis to form the primary breast bud
Secondary buds develop from the primary bud.
- These secondary buds will become the lactiferous ducts
Describe how the secondary buds develop during pregnancy:
- As gestation progresses the buds develop lumens (become canalised)
- Canalisation is induced by placental steroids (estrogen and progesterone)
- By birth 15-20 lactiferous ducts are present
At what point can breast make milk?
- By birth the breasts are fully developed and could potentially make milk
- Milk production would require a hormonal stimulus
- Because the fetus has been exposed to the placental steroids and maternal hormones at birth some babies do make a colostrum-like secretion called witchs milk
Describe the structure of the breast
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Describe the external structures of the breast:
Body of breast - Many different shapes
Nipple: Raised, can be inverted, lacterferous ducts join the skin at the nipple
Areola: Pigmented circle of tissue surrounding the nipple, contains sebaceous glands which give a granular texture to the surface
What are the internal structures of the breast?
- Adipose tissue of the pectoral fat pad
- Suspensory ligaments: Coopers ligaments (affected by age, hormones in pregnancy and can become less supportive)
Describe the lobule divisions of the breast:
- Each human breast contains 15-20 lobules each made up of milk secreting lobules
- Each of the lobules connects to a single lactiferous duct
i.e like a bunch of grapes
Describe the route of the lactiferous duct:
- The lactiferous duct runs towards the nipple and expands into a lactiferous sinus (widenings of the duct)
- THe lactiferous sinuses (15-20) open onto the nipple to allow extraction of the milk
How does the breast develop during puberty?
- Breast ducts dont have alveoli until after puberty - these develop under the influence of estrogen
- The resting (non-pregnant, non-lactating) breast is dominated by the duct system and fat - not alveoli
Describe the relation of the menstural cycle and puberty:
- During the menstrual cycle oestrogen and progesterone promote the growth of alveolar buds - successive cycles cause increased growth
- There can be noticeable premenstrual increases in the volume of the breast (and tenderness)
What hormones develop the breast in pregnancy?
Oestrogen: Essential for growth
Progesterone: Induces side branching of ducts (prevents SM relaxation and milk ejection, as well as preventing milk production)
Prolactin: Necessary for alveolar development but also stimulates casein and alpha lactalbumin mRNAs (causes milk production after birth)
Insulin and cortisol: Stimulate alveolar epithelial cell division
Describe the endocrine control of milk production:
- Prolactin is produced in large amounts in pregnancy and falls at birth
- Sucking induces secretion of prolactin - via reduced secretion of dopamine aka PIH. Concurrently vasoactive intestinal peptide secretion from paraventricular nuclei is increased [Both factors act on the lactotrophs to secrete prolactin] = milk production
- Prolactin secretion is stimulated by a neuroendocrine reflex.
What does the duration of suckling correlate with?
Duration and extent of suckling correlates with prolactin secretion i.e two infants induce more prolactin
The level of prolactin correlates with the level milk production
