Under electron microscope, two adjacent supporting cells are closely connected near the basal part, and the basal part is closely attached to the basement membrane of seminiferous tubules, which is the main structural basis of BTB (vascular endothelial cells, myoid cells, basement membrane, etc.). It is also involved in the formation of blood-testis barrier). The existence of tight junction divides seminiferous tubule epithelium into basal part and cavity part. The spermatogenic cells at the base are immature and their nutrition is provided by interstitial blood vessels. Various nutrients in interstitial blood vessels can be directly supplied to spermatogenic cells at the base through the basement membrane, but not all of them can reach the lumen through tight connection, such as albumin and cholesterol. Gonadotropins and sex hormones can pass; Sugar, fatty acids, amino acids, etc. It is easy to pass. Therefore, tight junction plays the role of blood-testis barrier.

① Make the proximal lumen in a microenvironment conducive to the differentiation and development of spermatogenic cells;

② Avoid spermatogenic cells from autoimmune reaction.

BTB is an effective immune barrier, which can prevent spermatocytes and sperm antigens from contacting with the immune system in vivo, so there is no immune response. At the same time, once anti-sperm antibodies appear, BTB can also prevent anti-sperm antibodies in the blood circulation from entering the seminiferous tubules and having an immune reaction with sperm.

Spermatogenic cells can produce some specific protein, such as lactate dehydrogenase X, which is considered to be a tetramer of C subunit, so it is named LDH-C4. It can bind with immunoglobulin IgG in blood, which makes sperm agglutinate and lose fertilization ability. BTB does not allow IgG to enter the seminiferous tubule cavity, which can avoid the occurrence of autoimmune reaction of spermatogenic cells. Therefore, BTB prevents the passage of IgG in the blood. ① inhibin

1923, the research interest in this substance is rising again. Originally purified from bovine testis solution, it is a substance with molecular weight of 100000, which can inhibit the secretion of FSH in adenohypophysis and is called inhibin. Ovarian granulosa cells are also known to secrete inhibin. In vitro experiments show that inhibin secreted by Sertoli cells can be secreted from the top of Sertoli cells into the seminiferous tubule cavity, and then enter the testicular reticulum where it is absorbed into the blood. It can also be absorbed into the blood after entering the matrix from the substrate. However, 96% of inhibin in mature testis is secreted into the lumen, which may be related to the increase of BTB in mature testis.

α -rays destroyed spermatogenic epithelium, and androgen secretion was not affected, but FSH secretion increased obviously. Inhibin is believed to be secreted by Sertoli cells.

In vitro culture: support cell culture, and add its culture solution to pituitary cell culture solution. It was found that LH production was not affected, but FSH secretion was significantly reduced. Clinically, some people use inhibin to inhibit fertility, but it does not affect fertility, which is considered as an idea of contraception.

② The study of androgen binding protein (ABP) shows that androgen can enhance the function of FSH in maintaining spermatogenesis. If antiandrogen preparation is used, this effect of FSH will be inhibited, indicating that the effect of FSH on sperm may be through androgen. Sertoli cells can secrete ABP, which is a carrier protein with high affinity for androgen. A small part of ABP secreted by supporting cells enters the blood through the basement membrane; Most of them enter the lumen of seminiferous tubule, and then reach epididymis through the output tubule. Therefore, the ABP level in epididymis is higher than that in testis. ABP is secreted by sertoli cells under the action of FSH and T, and has strong affinity with dihydrotestosterone or testosterone, and its dissociation rate is fast. The development and maturation of spermatogenic cells need a certain concentration of T, which is a primary testicular disease. ABP can be used as an index to detect testicular function.

Because of ABP's high affinity for androgen, the amount of testosterone secreted by interstitial cells fluctuates to some extent (day and night, the highest in the morning), and the existence of ABP can keep the androgen in seminiferous tubules at a stable level.

A, the fluctuation of androgen concentration in the buffer tube makes androgen continuously released, which reduces the fluctuation and is beneficial to sperm production;

B, ABP binding T can reach epididymis with testicular fluid and promote sperm maturation.

③ Testicular fluid

It is a watery liquid with little protein content, in which K+ and HCO 3- are more. Sperm produced by seminiferous tubules flows to epididymis, and 99% of the liquid is reabsorbed by epididymal epithelium after reaching epididymis. Sertoli cells can devour and digest the residual cytoplasm that falls off the lumen during sperm formation and the spermatogenic cells that partially degenerate during development. There are a large number of polymorphic lysosomes in sertoli cells to digest substances swallowed into cells.

Experiments show that retrograde injection of carbon dye into testis can make sertoli cells have phagocytosis function. If E2 pill is implanted into male mice, it will cause a lot of damage, degeneration and shedding of spermatogenic cells, and the phagocytosis of sertoli cells is active, and the degenerated spermatogenic cells can be quickly removed by sertoli cells. Significance: It is of certain significance to maintain the stability of the internal environment of seminiferous tubules. Some people have observed the sperm release process of frogs in detail. When male frogs are injected with gonadotropin, the top of sertoli cells first undergo vacuolar degeneration, and then disintegrate, releasing trapped sperm. It is believed that sperm release is related to sertoli cell activity. But the exact mechanism is still unclear.

Morphological observation showed that the sperm head was buried at the top of sertoli cells. It is assumed that the release mechanism may be:

(1), under the action of LH, the Na+ pump on sertoli cell membrane was inhibited, the intracellular Na+ and water were equal, sertoli cells swelled, the apical depression flattened, and sperm entered the lumen;

(2) Microfilaments and microtubules in supporting cells contract, and spermatogenic cells embedded in supporting cells are pushed into the lumen.