843
CHAPTER TWENTY-TWO
Reproductive System
pora cavernosa and bears the urethral opening—the
external
urethral orif
ce.
The skin of the glans is very thin, hairless,
and contains sensory receptors for sexual stimulation. A
loose fold of skin called the
prepuce
(foreskin) begins just
posterior to the glans and extends anteriorly to cover it as
a sheath. The prepuce is sometimes removed by a surgical
procedure called
circumcision.
At the
root
of the penis, the columns of erectile tissue
separate. The corpora cavernosa diverge laterally in the
perineum and are F
rmly attached to the inferior surface of
the pubic arch by connective tissue. These diverging parts
form the
crura
(sing.,
crus
) of the penis. The single corpus
spongiosum is enlarged between the crura as the
bulb
of
the penis, attached to membranes of the perineum (see
F
g. 22.4
b
).
Penis
The
penis
is a cylindrical organ that conveys urine and
semen through the urethra to the outside. It is also special-
ized to enlarge and stiffen, which enables it to enter the
vagina during sexual intercourse.
The
body,
or shaft, of the penis is composed of three
columns of erectile tissue, which include a pair of dorsally
located
corpora cavernosa
and a single, ventral
corpus spon-
giosum.
A tough capsule of white dense connective tissue
called a
tunica albuginea
surrounds each column. Skin, a
thin layer of subcutaneous tissue, and a layer of connective
tissue enclose the penis
(f
g. 22.15)
.
The corpus spongiosum, through which the urethra
extends, enlarges at its distal end to form a sensitive, cone-
shaped
glans penis.
The glans covers the ends of the cor-
clinical setting or at home using a kit
ordered from the Internet, with the
sample mailed to a lab. The CASA sys-
tem captures images with a digital
camera and analyzes and integrates
information on sperm density, motil-
ity, and morphology with details of the
patient’s health and reproductive his-
tory (F
g. 22A). The result is a “spermio-
gram.” ±igure 22B shows the results for
a normal sample.
The first sperm classification sys-
tem, in the 1950s, considered only
sperm head shape. Then World Health
Organization classification evaluated
dimensions of the sperm head, mid-
piece, and tail, adding the require-
ment of analyzing at least 200 moving
sperm to establish fertility. The National
Institutes of Health have more recently
revised the WHO standards, and these
are presented in Table 22B.
TABLE
22B
|
Sperm Cell Analysis
Density
(million cells/milliliter)
% Motile
% Normal morphology
±ertile
>48
>63%
>12%
Borderline fertile
13.5–48
>63%
>12%
Infertile
<13.5
<32%
<9%
(a)
(b)
(c)
(d)
FIGURE 22B
A computer tracks sperm cell movements. In semen, sperm cells swim in a straight line (
a
),
but as they are activated by biochemicals in the woman’s body, their trajectories widen (
b
). The sperm cells
in (
c
) are in the mucus of a woman’s cervix, and the sperm cells in (
d
) are attempting to digest through the
structures surrounding an egg cell.
previous page 873 David Shier Hole's Human Anatomy and Physiology 2010 read online next page 875 David Shier Hole's Human Anatomy and Physiology 2010 read online Home Toggle text on/off