follicles. FSH treatment of humans results in development of more than the
usual number of mature follicles and an increased number of mature
gametes. FSH is also critical for sperm production. It supports the function
of Sertoli cells, which serve a nutritive role in sperm cell maturation.
Parathyroid hormone (answer e)is synthesized and released from the prin-
cipal cells of the parathyroid gland.
Sertoli cells (asterisks, *) function in a nutritive and supportive role
somewhat analogous to the glial cells of the CNS. The Sertoli cells produce
inhibin, which feeds back on the anterior pituitary and hypothalamus to
regulate FSH release. Testosterone binds to androgen-binding protein
(ABP), which is synthesized by the Sertoli cells. Testosterone is necessary for
maintenance of spermatogenesis as well as the male ducts and accessory
glands. ABP is regulated by FSH, testosterone, and inhibin. Sertoli cells have
extensive tight (occluding) junctions between them that form the blood-
testis barrier. Sertoli cells communicate with adjacent cells through gap
junctions and extend from outside the blood-testis barrier (basal portion) to
luminal (apical portion). During spermatogenesis, preleptotene spermato-
cytes cross from the basal to the adluminal compartment across the zonula
occludens between adjacent Sertoli cells. Each Sertoli cell is, therefore, asso-
ciated with multiple spermatogenic cells.
The testis is composed of seminiferous tubules containing a number
of spermatogenic cells undergoing spermatogenesis and spermiogenesis.
The cells labeled with the arrowheads are spermatogonia, the derivatives
of the embryonic primordial germ cells. These cells comprise the basal
layer and undergo mitosis (spermatocytogenesis) to form primary sper-
matocytes, which have distinctive clumped or coarse chromatin (marked
by arrows). Secondary spermatocytes are formed during the first meiotic
division and exist for only a short period of time because there is no lag
period before entry into the second meiotic division that results in the for-
mation of spermatids. The spermatids begin as round structures and elon-
gate with the formation of the flagellum. This last part of seminiferous
tubule function is the differentiation of sperm from spermatids (spermio-
genesis) and is complete with the release of mature sperm into the lumen
of the tubule.
237.The answer is b.(Young, pp 329, 335.)The photomicrograph is taken
from an area that shows the ductuli efferentes (efferent ductules) (B)with
their distinctive wavy epithelium in which adjoining cells are tall (ciliated)
374 Anatomy, Histology, and Cell Biology