Males make sperm continuously from pu-
berty onward, in a process called
s p e r m a t o g e n -
e s i s
(
F ig u r e 1 6 . 3
). Spermatogenesis involves
a process first introduced in Chapter 3 called
m e io s is
. In this process of gamete production,
gametes receive a single set of 23 chromosomes,
symbolized as
n .
In this way, the new individual
receives the proper number of chromosomes
when the male and female gametes join.
Meiosis is followed by
s p e r m i o g e n e s i s
, in
which the sperm are reshaped to form the clas-
sical ovoid cell with the tail that we refer to as the sperm.
Sperm are produced at the rate of 300 million per
day. Once ejaculated, they do not survive more than 48
hours in the female reproductive tract. The
major parts of a sperm cell are the head and
tail. The head contains the nuclear material
(DNA) and an acrosome. An
a c r o s o m e
is a
vesicle containing enzymes that aid penetra-
tion into the egg (or oocyte) by the sperm cell.
The tail of a sperm cell is divided into four
parts: neck, middle piece, principal piece,
and end piece. The
neck
is the constricted
region just behind the head. The
m id d le p iece
contains mitochondria that provide ATP for
locomotion. The
p r in c ip a l p iece
is the longest portion of
the tail, and the
e n d p iece
is the terminal, tapering por-
tion of the tail.
m e io s is
(me-O-sis)
A type of cell division
that occurs during pro-
duction of gametes,
involving two succes-
sive nuclear divisions
that result in cells with
a haploid (n)—one half
the normal—number
of chromosomes.
S p e r m a t o g e n e s i s a n d t h e s t r u c t u r e o f s p e r m
F i g u r e 1 6 . 3
a.
Sperm atogenesis
b. Anatomy of
a
sperm
The Reproductive Organs Make, Deliver, and Receive the Sex Cells
473
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