Breast
Begins to develop in 6th week of fetal life
Breast tissue initially develops along the
lines of the armpits and extends to the groin
By the 9th week of fetal life it regresses to
the chest area leaving two breast buds in the
upper half of the chest
Mammary glands are modified sweat glands
which remain undeveloped until puberty
Usually one breast is smaller, or sometimes
higher than the other one
Contains no muscle tissue
The nipples are constantly erect but to
others is only when touched or cold
The color of the nipple is determined by the
thinness and pigmentation of its skin
Pigmentation surrounding the nipple
contains muscle fibers that respond to
stimulation to make nipple erect
Proliferation of the glandular breast
parenchyma results in an overall increase in
breast size through gestation
during pregnancy, the intralobular ductal
epithelium proliferates and the cells increase
in size; the number and length of the ductal
branches therefore increase. Areola houses
the Montgomery’s gland that may appear
as tiny, raised bumps on the surface of the
areola
Montgomery’s gland helps lubricate the
areola
mammary gland lies in the superficial fascia
covering the anterior chest wall
Each breast consists of 15 to 20 lobes, which
radiate out from the nipple
A space filled by loose connective tissue
called the retromammary space lies deep to
the breast and superficial to the underlying
pectoral muscles.
The lobes of the gland are separated by
fibrous septa that serve as suspensory
ligaments
During pregnancy, the myoepithelial cells,
which are initially spindle-shaped, become
highly branched stellate cells , especially
around the alveoli; Their cytoplasm contains
actin and myosin filaments, and they are
contractile; There is a concomitant reduction
in adipose tissue in the stroma. The numbers
of lymphocytes, including plasma cells, and
eosinophils increase greatly. Blood flow
through the breast increases;
During lactation, true milk secretion begins a
few days after parturition as a result of a
reduction in circulating oestrogen and
progesterone; The alveolar cell cytoplasm
accumulates membrane-bound granules of
casein and other milk proteins, and these are
released from the apical plasma membrane
by membrane fusion; Lipid vacuoles are
formed directly in the apical cytoplasm as
small lipid droplets that fuse with each other
to create large ‘milk vacuoles’ up to 10µm
across; After the onset of lactation, there is a
gradual reduction in the numbers of
lymphocytes and eosinophils in the stroma;
Alveolar cells take up IgA synthesized by
adjacent plasma cells by endocytosis at their
basal surfaces;
lactation ceases, which may be after as long
as 31 2 years, the secretory tissue
undergoes some involution but the ducts and
alveoli never return completely to the pre-
pregnant state
ANATOMY OF BREAST (navarro)
Breast tissue includes small sacs (alveoli)
made of milksecreting cells, and the ducts
that carry the milk to the outside
Myoepithelial cells around the alveoli
contract
Nipple has an average of 9 milk ducts
passing to the outside
Montgomery's gland produces the mother's
unique scent that attracts her baby to her
breast.
HORMONES INVOLVED
PROLACTIN
Prolactin triggers the cells of the alveoli to
secrete milk.
stimulating the growth and development of
breast tissue in preparation for milk
production
Increase in progesterone and estrogen
stimulated during pregnancy block milk
secretion
This "supply-and-demand" feedback
mechanism is particularly important in the
early weeks of lactation
More prolactin is produced at night
prolactin induces relaxation in mothers and
promotes sleep, she will eventually rest well
enough to handle the nighttime
breastfeeding routines
Suckling also affects the release of other
pituitary hormones such as gonadotrophin
