The Mammary Glands
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The
intercostal area | Main Anatomy
Index | The thoracic diaphragm
Last updated 30 March 2006
The Mammary
Glands
- Both men and women have breasts; normally they are well
developed only in women.
- They are situated on the anterior surface of the thorax,
overlying the pectoral muscles
(pectoralis
major and serratus
anterior).
- The mammary glands are accessory organs of the female
reproductive system. They secrete milk for the
nourishment of the infant in a process called lactation.
- They often extend toward the axillae forming axillary tails.
- The amount of fat surrounding the glandular tissue
determines the size of the breasts.
The
Female Breasts
- The lactiferous ducts give rise to buds that form 15 to
20 lobules of glandular tissue, which constitute the mammary gland.
- Each lobule is drained by a lactiferous
duct, which opens on the nipple.
- These ducts extend from the nipple in a manner similar to
spokes of a wheel.
- Deep to the areola, each duct has a dilated portion
called the lactiferous sinus,
in which milk accumulates during lactation.
The Areolae (p.
45)
- These contain numerous sebaceous
glands, which enlarge during pregnancy and
secrete an oily substance that provides a protective
lubricant for the areola and nipple.
- The areolae are variable in size, and are pink in white nulliparous women (who have
not borne children). During the first pregnancy, the
areolae of white women change permanently to brown.
- There is now fat beneath the areolae.
The Nipples (p.
45)
- There are conical or cylindrical prominences that are
located in the centre of the areolae. There is no fat in
the nipples.
- In nulliparous women they are usually located at the
level of the fourth intercostal
space. However, the position of the nipple
varies considerable and cannot be used as a guide to the
fourth intercostal spaces.
- The tip of the nipple is fissured and contains the
openings of the lactiferous ducts.
- The nipples are composed mostly of circularly arranged
smooth muscle that compresses the lactiferous ducts and
erects the nipples when they contract.
Description
(p. 46)
- The mammary gland is a modified
sweat glandthis explains why it has no special capsule or sheath.
- It lies in the superficial fascia,
anterior to the thorax.
- The deep aspect of the breast is separated from the
pectoral muscles by the deep fascia.
- Between the breast and the deep fascia, there is an area
of loose connective tissue that contains little fat.
- This zone is called the retromammary
space (bursa), and allows the breast to move
freely on the deep fascia covering the pectoralis major
muscle.
- Although it is easily separated from the deep fascia, the
mammary gland if firmly bound to the skin of the breast
by suspensory ligaments
(Coopers ligaments).
- These fibrous band which supports the breast, runs
between the skin and deep fascia.
- The rounded contour and most of the bulk of the breasts
are produced by fat lobules.
- The shape of the breast varies considerably in different
persons and races and in the same person at different
ages.
- Although breasts vary in size, their roughly circular
bases are fairly constant and have the following limits
in well-developed females: vertically
from the second to sixth ribs and laterally from the edge of the sternum to
the midaxillary line.
- Two-thirds of the breast rest on the pectoralis major
muscle; one-third covers the serratus anterior muscle.
- Its inferior border overlaps the superior part of the rectus sheath.
Arterial
Supply of the Breast (p. 46)
- There is abundant blood supply to the breast.
- The arteries are mainly from the internal
thoracic artery via its perforating
branches, which pierce the 2nd
to 4th intercostal spaces.
- The breast also receives several branches from the axillary artery, mainly from
its lateral thoracic and
thoracoacromial branches,
and lateral and anterior branches from the intercostal arteries (in the 3rd
to 5th intercostal spaces).
Venous
Drainage of the Breast (p. 46)
- Veins from the breast drain into the axillary, internal
thoracic, lateral thoracic and intercostal veins.
- The chief venous drainage is the axillary
vein.
Lymphatic
Drainage of the Breast (p. 46)
- Most of the lymphatic drainage (about 75%) is to the axillary lymph nodes, mainly
the pectoral group.
- Lymph from the medial part of the breast drains into the parasternal lymph nodes, which
are located within the thorax along the internal thoracic
vessels.