Lecture 19: Breast Flashcards
The breasts are? purpose?
They are the mammary glands
- Nutrition of the young
- spacing of the pregnancies (survival advantage)
Derivation of the breast?
Mammry glands are modified sweat glands
- They are derived from tissue that first identified in the mammary (or milk) crest that arises between the axilla and the groin
- Breast development begins with the formation of the mammary buds at about 6 weeks
- The first development takes place as a down growth of the dermis to form the primary breast bud
- Secondary buds develop from the primary buds (these will become the lactiferous ducts)
- These buds become canalised induced by placental steroids
- by birth 15-20 lactiferous ducts are present
Gynaecomastia?
Men having breasts
400 or so die per 2000 from malignancy
men do have the tissue required to produce milk but just don’t (normally) have the required hormones
Structure of the breast?
External structures:
- Body of the breast (many different shapes)
- Nipple - Raised (usually) exit of lactiferous ducts
- Areola - Pigmented circle of tissue surrounding the nipple containing sebaceuos glands which give a granular texture (no hair follicles)
Internal structures:
- Major component is pectoral fat pad
- Supported by the suspensory ligaments of cooper (these are affected by age anf hormones and become less supportive)
Lobular structure of the breast?
- The human breast contains 15-20 lobes each made up of milk secreting lobules
- Each of th lobules connects to a single lactiferous duct
- These structures look like a little bunch of grapes
- The lactiferous ducts run towards the lactiferous sinus
Development of the breasts from birth? How do humans differ?
Until puberty the breast ducts don’t have alveoli - these start to develop during puberty, particulary under the influence of Oestrogen.
the resting (non-preg, non-lactating) breast is dominated by the duct system and fat - not alveoli
During the menstrual cycle oestrogen and progesterone promote the growth of alveolar buds - successive cycles cause increase growth. There can be noticable premenstrual increases in the volume of the breasts (and tenderness)
Hormonal influence of breast development and growth?
Oestrogen - Essential for breast growth
Progesterone - Induces side branching of ducts
Prolactin - Necessary for alveolar development but also stimulates casein and a lactalbumin mRNAs (milk proteins)
Growth hormone - (related to PRL) is important in some species
Insulin and cortisol - Stimulate alveolar epithelial cell division
(breast weight can be 2 or even 4 times the non-pregnant weight when lactating)
Why do we not lactate during pregancy? Post birth?
Prolactin should in theory promote milk production but lactation doesn’t occur until after birth. This is likely due to high levels of steroids, particularly progesterone - prevents major milk production and relaxes smooth muscle preventing ejection
Post birth prolactin levels drop rapidly and recover once the baby begins to suckle on the nipple. This is a neuroendocrine reflex
Suckling causes a reduced secretion of dopamine (prolactin inhibiting factor) into the portal blood. Concurrently vasoactive intestinal peptide (VIP) secretion by the paraventricular nuclei is increased. = BOTH act on lactotrophs to secrete prolactin.
Endocrine control of lactation?
Prolactin induces the production of milk proteins and the duration and extent of suckling correlates with prolactin secretion.
(The level of prolactin correlates with the level of milk production- the infant orders their next meal)
MER? Stimulations for this?
Milk ejection response
Suckling of the nipple stimulates synthesis and secretion of oxytocin by the posterior pituitary. Oxytocin induces the contraction of the myoepithelial cells of the alveoli causing ejection of milk into the ducts.
- Stimulation of the female reproductive tract can induce oxytocin release (may have let down during sex)
- Crying of the baby
- Smell of the baby
Lactations effect on fertility?
Prolactin can supress the secretion of gonadotrphins FSH and particularly LH. (Thought to be via an effect on kisspeptin neuron in the hypothalamus)
Therefore lactating women often have no or irregular menstrual cycles. This therefore has a contraceptive effect (not reliable)
Supernumeroury nipples/breasts?
Usually it is found along the line of the embryonic milk ridge. Additional nipples can occur on the breasts of along the milk ridge and lactiferous ducts can exit the breasts at sites outside of the niple.
