CHAPTER 18
Male Reproductive System
355
J. Naftel
J. Naftel
1. Spermatogonium
2. Prepachytene primary
spermatocyte
3. Pachytene primary
spermatocyte
4. Metaphase primary or
secondary spermatocyte
5. Early spermatid
6. Intermediate
spermatocyte
7. Late spermatid
8. Detaching spermatozoan
Figure 18-9.
Overview of readily identi± able spermatogenic cells in the seminiferous epithelium.
H&E,
3
1,496
Spermatogenesis
involves an orderly sequence of changes as cells proceed through
mitosis
(
spermatogonia
),
meiosis
(
spermatocytes
),
and
spermiogenesis
(
spermatids
). Only the eight most readily identiF
able stages are illustrated here owing to their distinctiveness
and adequate abundance in ordinary sections.
Spermatogonia
can be identiF
ed by their position (in contact with the basement mem-
brane) and their oval interphase nuclei with the long axis parallel to the basement membrane.
Primary spermatocytes
undergo
several substages of prophase I, but, here, the earlier substages are denoted as
prepachytene
. The condensing chromosomes in
prepachytene primary spermatocytes
tend to be clumped at one edge of the nuclear envelope. By contrast, the paired chromosomes
of
pachytene primary spermatocytes
form broad bands that F
ll the nucleus.
Pachytene primary spermatocytes
are abundant in
sections, because this is the phase of meiosis with the longest duration. After a primary spermatocyte completes pachytene, the
remaining steps of meiosis I and meiosis II (by the daughter secondary spermatocytes) are completed very rapidly, so examples of
cells in these stages of meiosis are more difF cult to F nd in sections. Cells in either metaphase I or metaphase II are most conspicuous
and easiest to locate. The products of meiosis II are
spermatids
. These haploid cells begin as
early spermatids
, recognizable by their
small spherical interphase nuclei. The F rst clear evidence that spermiogenesis is underway is a change in shape of the nucleus from
spherical to a broad diamond shape; a cell with such a nucleus can be designated an
intermediate spermatid
. When the nucleus has
assumed the sharply pointed shape and dense appearance of a spermatozoan but remains inserted deeply into the epithelium, the
cell can be denoted a
late spermatid
. ±inally, nuclei of
detaching spermatozoa
can readily be recognized, because they form a row at
the surface of the epithelium and overlie a layer of residual bodies.
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