CHAPTER 18
Male Reproductive System
353
Seminiferous
Seminiferous
tubule
tubule
Seminiferous
tubule
Leydig
Leydig
cells
cells
Leydig
cells
Seminiferous
Seminiferous
tubule
tubule
Seminiferous
tubule
A
Lipid
vacuoles
Lipid vacuoles
of Leydig cell
of Leydig cell
Lipid
vacuoles
of Leydig cell
Leydig cell
Leydig cell
Leydig cell
Fibroblast
Fibroblast
Fibroblast
Lumen of
Lumen of
capillary
capillary
Lumen of
capillary
B
Basement membrane
Basement membrane
of the
of the
seminiferous tubule
seminiferous tubule
Basement membrane
of the
seminiferous tubule
Leydig
Leydig
cells
cells
Leydig
cells
C
Figure 18-7.
Interstitial cells of Leydig.
H&E,
left
3
263;
right
3
2,016; iron hematoxylin stain,
3
237
The
interstitial cells of Leydig
are located in the interstitial (connec-
tive) tissue near the blood capillaries and between the seminiferous
tubules. These cells have round nuclei and pale-stained cytoplasm with
lipid drops (lipid vacuoles) in the peripheral region of the cytoplasm,
which give them a bubbly appearance (like many steroid-producing
cells). These cells contain abundant smooth endoplasmic reticulum,
which contributes to steroid hormone production. The interstitial cells
of Leydig derive from the mesoderm and are usually large in size (about
20
μ
m in diameter) compared with other cells in the connective tissue.
They are the endocrine cells that produce the important male sex
hormone,
testosterone
. Testosterone plays important roles in develop-
ing and maintaining male sex characteristics, stimulating muscle and
bone growth, and increasing bone density. A small amount of testoster-
one is also produced by the adrenal glands and ovaries in the female.
SYNOPSIS 18-1
Functions of Sertoli Cells
Support
: Provide physical support and nutrition for the different stages of spermatogenic cells.
Protection
: Form
blood-testis barrier
by tight junctions between adjacent Sertoli cells that protect spermatogenic cells
from autoimmune destruction; also control hormones, nutrients, and other substances being transported in and out of the
seminiferous tubules.
Phagocytosis
: Remove
residual bodies
after excess cytoplasm is shed from the spermatids during maturation of the
spermatozoa.
Secretion
: (1) Secrete and release fructose-rich fl
uids (testicular fl
uid) to help nourish and move sperm from the seminifer-
ous tubules to the epididymis; (2) secrete
anti-Müllerian hormone
to prevent oviducts from developing from the Müllerian
duct in the early stages of the male embryo; (3) secrete
androgen-binding protein
(
ABP
) to maintain the concentration of
testosterone in the seminiferous tubules, thereby promoting spermatogenesis; (4) secrete
glial cell–derived neurotrophic
factor (GDNF)
to promote survival and differentiation of the spermatids (GDNF is better known for promoting development
of neurons); and (5) produce
inhibin
and
activin
hormones to provide negative and positive feedback to the hypothalamus,
thereby regulating follicle-stimulating hormone (FSH) secretion by the pituitary gland.
SYNOPSIS 18-2
Functions of Testosterone
The
interstitial cells of Leydig
secrete
testosterone
, which is the major male sex hormone. Its functions include:
Promoting development of male sex organs in early fetal development.
Promoting male sexual characteristics, such as growth of beard and axillary hair, enlargement of the larynx, and deepening
the voice.
Increasing muscle growth, thickness of the skin, and sebaceous gland secretion.
Promoting bone growth and increasing bone density.
Increasing basal metabolism and physical energy.
Promoting spermatogenesis.
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