356
UNIT 3
Organ Systems
Figure 18-10.
Overview of spermatogenesis and the stages of the seminiferous epithelium.
If small patches of
seminiferous epithelium
are examined, it can be seen that there are six recurring groupings of stages of
developing
gametes that populate the epithelium. These groupings (associations) represent recurring stages that a patch of epithelium cycles
through over time, and their existence indicates that the many steps in
spermatogenesis
proceed with a very rigid timetable. If the
composition of a bit of epithelium could be monitored over time, it would be seen that, as cohorts of germ cells begin and complete
spermatogenesis within the epithelium, the epithelium itself will change in appearance and contain the six different groupings of
developing germ cells. The ability to recognize the stages in the cycle of the epithelium has made it possible to undertake simple
experiments that have revealed some important dynamics of spermatogenesis. Therefore, the time required for a patch of epithelium
to complete the six stages of one cycle is 16 days, and it can be inferred that with each 16-day cycle a single patch of epithelium will
release a group of new
spermatozoa
for only a brief period when it reaches the end of
stage II
. Likewise, the end of stage II is the
only time during the 16-day cycle that a new cohort or generation of primary spermatocytes will enter the
adluminal compartment
to begin
meiosis I
. The time required for a new
type B spermatogonium
to generate completed spermatozoa is 56 days.
II
II III IV V VI
B
B
I
J. Naftel
A
AAA
Interphase primary
Interphase primary
spermatocyte
spermatocyte
Interphase primary
spermatocyte
Prepachytene
primary spermatocyte
Pachytene primary
spermatocyte
Meiotic metaphase
spermatocyte
Early spermatid
Intermediate
spermatid
Late spermatid
Detaching
spermatozoan
with residual
body
4.8 days’
duration
3.1 days’
duration
1.0 days’
duration
1.2 days’
duration
5.0 days’
duration
0.8 days’
duration
type B
spermatogonium
type A
spermatogonium
previous page 371 Dongmei Cui -  Atlas of Histology with Functional and Clinical Correlations 2011 read online next page 373 Dongmei Cui -  Atlas of Histology with Functional and Clinical Correlations 2011 read online Home Toggle text on/off