The breast Flashcards
What are mammary glands?
Modified sweat glands.
They are derived from tissues that comes from the mammary crests during development, which is a line that runs between the axilla and the groin.
Abnormal brest development is likely to occur along the lines of the mammary crests.
How does breast development occur?
They form on a structure called the mammary (milk) crests during development, which is a line that runs between the axilla and the groin.
Breasts development begins at about week 6 with the formation of mammary buds.
The first developmet 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.
As gestation develops the buds develop lumens (become canalised)
Canalisation is induced by placental steroids (estrogen and progesterone). By birth 15-20 lactiferous ducts are present.
By birth the breasts are fully developed and could potentially make milk.
What is the structure of the breasts?
External
Nipple - raised (usually) cylindrical pigmented structure. The lactiferous ducts join the skin at the nipple.
Areola - pigmented circle of tissue, contains sebaceous glands which give a granular textre (no hair follicles with the sebaceous glands)
Internal structures-
Adipose tissue of the pectoral fat pad - texture and shape.
Cooper’s ligaments - suspensory ligaments that support the breasts, affected by age.
15-20 lobes each made up of milk secreting lobules.
Each of the lobules connects to a single lactiferous duct, which all connect the lactiferous sinus and to the nipple.
At puberty the breast ducts develop alveoli in response to estrogen. The estrogen induces growth of the epithelial cells that make up the milk producing alveoli.
During the menstrual cycle estrogen and progesterone promote the growth of alveolar buds - successive cycles cause increased growth -> tenderness
How does the breast change from birth to puberty to pregnancy?
Initially it is mainly just a duct system with no fat.
After puberty and during each menstral cycle the alveolar system begins to develop.
This alveolar development increases during pregnancy
What are the hormones involved in pregnancy?
Estrogen - essential for breast growth (alveoar epithelial cells)
Progesterone - induces the branching of ducts
Prolactin - necessary for alveolar development and production of milk protein
Insulin and cortisol - stimulate alveolar epithelial cell division.
Do pregnant women lactate?
No. Because the steroids, particularly progesterone seem to prevent major milk production.
Progesterone is a smooth muscle relaxant and prevents milk ejection.
It comes from the placenta and corpus leuteum and prevents milk ejection.
After birth, the placenta is gone and so the progesterone levels drop and so does the prolactin levels. Prolactin is then produced in response to suckling (neuroendocrine reflex).
Is lactational amenorrhoea effective?
Only in some women.
How is milk production stimulated?
Prolactin is produced in response to suckling (neuroendocrine reflex). Suckling also causes reduced secretion of dopamine (prolactin inhibiting factor) from the hypothalamus into the portal blood. Vasoactive intestinal peptide secretion is increased.
The increase in vasoactive intestinal peptide secretion and decrease in dopamine cause the production of prolactin from the anterior pituitary.
Prolactin then induces the production of milk proteins in the alveoli. The duration of suckling correlates with prolactin secretion. Prolactin production correlates with the level of milk produced -> baby orders the next meal.
Prolactin meets the alveolar epithelial cells in the breast and induces the production of milk proteins.
What is the milk ejection response?
Milk ejected.
Suckling also causes the synthesis and secretion of oxytocin by the anterior pituitary.
Oxytocin induces the contraction of the myoepithelial cells of surrounding the alveoli causing ejection of the milk into the ducts.
Sex, baby crying, smells can cause the milk let down response.
What does prolactin do to FSH and LH production?
It reduces it. Thought to be through suppression of the kisspeptin neuron. This causes no or irregular menstrual cycles.
Contraceptive effect.
What are supernumeroury nipples/breasts?
Additional breasts usually along the mammary crests.
