Ganong's Review of Medical Physiology, 23rd Edition

CHAPTER 25The Gonads: Development & Function of the Reproductive System 403

cytoplasmic bridges. Tight junctions between adjacent Sertoli

cells near the basal lamina form a blood–testis barrier that

prevents many large molecules from passing from the intersti-

tial tissue and the part of the tubule near the basal lamina (basal

compartment) to the region near the tubular lumen (adluminal

compartment) and the lumen. However, steroids penetrate this

barrier with ease, and evidence suggests that some proteins

pass from the Sertoli cells to the Leydig cells and vice versa in a

paracrine fashion. In addition, maturing germ cells must pass

through the barrier as they move to the lumen. This appears to

occur without disruption of the barrier by progressive break-

down of the tight junctions above the germ cells, with concom-

itant formation of new tight junctions below them.

The fluid in the lumen of the seminiferous tubules is quite

different from plasma; it contains very little protein and glu-

cose but is rich in androgens, estrogens, K+, inositol, and

glutamic and aspartic acids. Maintenance of its composition

presumably depends on the blood–testis barrier. The barrier

also protects the germ cells from bloodborne noxious agents,

prevents antigenic products of germ cell division and matura-

tion from entering the circulation and generating an autoim-

mune response, and may help establish an osmotic gradient

that facilitates movement of fluid into the tubular lumen.

Spermatogenesis

Spermatogonia, the primitive germ cells next to the basal lami-

na of the seminiferous tubules, mature into primary spermato-

cytes (Figure 25–13). This process begins during adolescence.

FIGURE 25–12 Section of human testis.

Seminiferous

tubules

Primary

spermatocyte

Spermato-

gonium

Interstitial

cell

FIGURE 25–13 Seminiferous epithelium. Note that maturing germ cells remain connected by cytoplasmic bridges through the early sper-
matid stage and that these cells are closely invested by Sertoli cell cytoplasm as they move from the basal lamina to the lumen. (Reproduced with
permission from Junqueira LC, Carneiro J: Basic Histology: Text & Atlas, 10th ed. McGraw-Hill, 2003.)

Late spermatids

Spermiogenesis

Meiosis

Basal lamina

Fibroblast

Capillary Capillary

Myoid cells

Interstitial cells

Spermatogonium

Primary spermatocyte

Secondary spermatocytes

Early spermatids

Cytoplasmic

bridges

Sertoli

cell

Sertoli

cell

[Low resolution, for proofing only]