386
UNIT 3
Organ Systems
Figure 19-15A.
Overview of the mammary gland.
In humans, there are two multilobed
mammary glands
,
one located within the connective tissue of each breast.
These exocrine glands produce milk after a pregnancy.
Each gland is composed of 15 to 25 lobes of
compound
tubuloalveolar glands
. Each lobe is separated from others
by dense connective tissue and adipose tissue and opens
into a
lactiferous duct
. The secretory alveoli produce
milk and drain it into the
intralobular ducts
and then to
the
interlobular ducts
. The interlobular ducts merge into
lactiferous sinuses
from which the milk empties into the
lactiferous ducts
(15–25). The female mammary glands
begin to enlarge during puberty and undergo changes at
different times based on hormone (
estrogen
,
progester-
one
,
prolactin
, and
human placental lactogen
) levels.
Mammary Glands
Lobule of
mammary gland
Interlobular
duct
Lactiferous
duct
Lactiferous
sinus
Nipple
Openings
Lobe of
mammary
gland
Pectoralis
muscles
Rib
Skin
A
Cuboidal
epithelial cell
Myoepithelial
cell
Lobules of
Lobules of
gland
gland
Lobules of
gland
Adipose tissue
Adipose tissue
Adipose tissue
Adipocytes
Adipocytes
Adipocytes
Dense irregular
Dense irregular
connective
connective
tissue
tissue
Dense irregular
connective
tissue
B
Intralobular
Intralobular
ducts
ducts
Intralobular
ducts
Alveolus
Alveolus
Lobule of
Lobule of
gland
gland
Lobule of
gland
Alveoli
Alveoli
Alveoli
Interlobular
Interlobular
duct
duct
Interlobular
duct
Connective tissue
Connective tissue
Connective tissue
C
Figure 19-15B.
Inactive (resting) mammary gland.
H&E,
3
41; inset
3
359
An example of a
resting mammary gland
shows a large
amount of dense irregular connective tissue and adipose
tissue with small mammary gland lobules. The glandu-
lar tissue contains mainly
intralobular ducts
, which are
lined by
cuboidal epithelial cells
and underlying
myo-
epithelial cells
(
inset
). The resting mammary gland has
only a few secretory alveoli, some undeveloped intral-
obular ducts, interlobular ducts, lactiferous sinuses, and
lactiferous ducts.
Figure 19-15C.
Active (during pregnancy) mammary
gland.
H&E,
3
41
An example of a
mammary gland
during pregnancy
shows large lobules and a relatively small amount of
interlobular connective tissue. The glandular tissue con-
tains many proliferated
alveoli
and
intralobular ducts
.
A large interlobular duct is located within the connective
tissue shown here. When the mammary glands begin to
secrete milk (
lactation)
, the lumina of the alveoli and the
ducts are dilated and F
lled with milk. The milk contains
many lipid droplets and proteins (caseins, lactalbumin,
and immunoglobulin A) as well as lactose, ions, vita-
mins, and water. Secretion of milk is initiated by hor-
monal changes: decrease of
estrogen
and
progesterone
and increase of
prolactin
after delivery and the loss of
the placenta. The milk is released by the
milk ejection
refl
ex
when stimulated by suckling (±ig. 19-16A).
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