862
UNIT SIX
called
breasts.
The breasts overlie the
pectoralis major
mus-
cles and extend from the second to the sixth ribs and from
the sternum to the axillae
(f
g. 22.34
a
)
.
A
nipple
is located near the tip of each breast at about the
level of the fourth intercostal space. It is surrounded by a cir-
cular area of pigmented skin called the
areola
(F g. 22.34
b
).
Structure of the Glands
A mammary gland is composed of F fteen to twenty irreg-
ularly shaped lobes. Each lobe contains glands (alveolar
glands), drained by alveolar ducts, which drain into a lactif-
erous duct that leads to the nipple and opens to the outside.
Dense connective and adipose tissues separate the lobes.
These tissues also support the glands and attach them to the
fascia of the underlying pectoral muscles. Other connective
tissue, which forms dense strands called
suspensory liga-
ments,
extends inward from the dermis of the breast to the
fascia, helping support the breast. Clinical Application 22.4
discusses breast cancer.
Development of the Breasts
The mammary glands of males and females are similar. As
children reach
puberty,
the glands in males do not develop,
whereas ovarian hormones stimulate development of the
glands in females. The alveolar glands and ducts enlarge, and
fat is deposited so that each breast becomes surrounded by
Nipple
Areola
Alveolar
duct
Ampulla
Rib
Clavicle
Intercostal
muscles
Adipose
tissue
Pectoralis
major m.
Pectoralis
minor m.
Lactiferous
duct
Alveolar
duct
Alveolar
glands
(a)
(b)
FIGURE 22.34
Structure of the female breast and mammary glands. (
a
) Sagittal section. (
b
) Anterior view. (
m.
stands for
muscle.
)
adipose tissue, except for the region of the areola. Chapter 23
(pp. 902–903) describes the hormonal mechanism that stim-
ulates mammary glands to produce and secrete milk.
PRACTICE
55
Describe the structure of a mammary gland.
56
How does ovarian hormone secretion change the mammary glands?
22.7
BIRTH CONTROL
Birth control
is the voluntary regulation of the number of off-
spring produced and the time they are conceived. This con-
trol requires a method of
contraception
(kon
trah-sep
shun)
designed to avoid fertilization of an egg cell following sexual
intercourse or to prevent implantation of a hollow ball of
cells (a
blastocyst
) that will develop into an embryo.
Coitus Interruptus
Coitus interruptus
is the practice of withdrawing the penis
from the vagina before ejaculation, preventing entry of
sperm cells into the female reproductive tract. This method
of contraception often proves unsatisfactory and may result
in pregnancy, because a male may F
nd it difF
cult to with-
draw just prior to ejaculation. Also, some semen containing
sperm cells may reach the vagina before ejaculation occurs.
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