Page 471 - Anatomy and Physiology of Farm Animals, 8th Edition

456 / Anatomy and Physiology of Farm Animals

Seminiferous Tubules fluid, androgen‐binding protein, trans-
and Spermatogenesis
ports androgens from their site of synthe-
VetBooks.ir sis in the testis to the epididymis, where
they are required for maturation of the
Seminiferous Tubules
spermatozoa. Interstitial cells (Leydig
The epithelium lining the seminiferous cells) in the connective tissue between
tubules contains two cell types, the susten- seminiferous tubules secrete testoster-
tacular, or Sertoli cells, and the develop- one, the primary androgen originating in
ing spermatozoa and their precursor germ the testicles.
cells (Fig. 25‐1). The composition of the interstitial fluid
The large sustentacular cells extend between sustentacular cells and within the
from the base of the epithelium to the lumen of the seminiferous tubules differs
lumen of the seminiferous tubules. Their from typical interstital fluid. The differ-
shape is highly irregular because they ences are due in part to a selectively
encircle the developing germ cells permeable barrier (blood–testis barrier)
(Fig. 25‐1). Sustentacular cells secrete a between these fluids and fluid outside the
fluid that bathes the developing germ tubules. The cell junctions between adja-
cells and assists with the transport of cent sustentacular cells and between myoid
spermatozoa from the tubules into the cells that surround the tubules contribute
rete testis after their release from the sus- to this barrier (Fig. 25‐1). The luminal con-
tentacular cells. One component of this centrations of cellular secretions, such as

Enlarged
cross-section of
seminiferous tubule

Rete testis
fluid Testicular
fluid
Expanded
portion
Seminiferous
tubules

Germ
cells

Cauda epididymis

Sertoli cells Myoid cells

Figure 25-1. Location and microscopic anatomy of seminiferous tubules. Note the irregular border of
the sustentacular (Sertoli) cells and their relation to the developing germ cells. Source: Reece, 2015.
Reproduced with permission of John Wiley & Sons, Inc.