Testicles are two slightly flat ellipsoids with smooth surface and free front end, followed by mesangium, which hangs in the scrotum on both sides, and the left testicle is slightly lower than the right. Adult testicles are about 4-5 cm long, 2.5 cm wide and 3 cm in front and back diameter. The weight is about 10.5- 14g.
There are two layers of tunica vaginalis on the surface of testis. The tunica vaginalis covers the surface of testis, and the tunica vaginalis is attached to the inner side wall of scrotum. There is a cavity between the two layers, called tunica vaginalis, which contains a small amount of liquid, which can reduce the resistance of testis when it moves in scrotum. Under the tunica vaginalis, there is a dense fibrous membrane (white membrane) around the testis parenchyma, and the upper part of the white membrane (testicular hilum) is particularly thickened, which is called testicular mediastinum. As a result, many fibrous tissues extend into the testis parenchyma, and the testis is divided into more than 200 lobules, which are composed of seminiferous tubules and interstitial cells, and each lobule can have 3-4 circuitous seminiferous tubules. These curved seminiferous tubules converge to form straight curved seminiferous tubules, and the straight curved seminiferous tubules of each lobule converge back to the upper side to form testicular reticulation. There are 10- 15 testicular output tubules passing through the white membrane and entering the epididymal head.
Testicular spermatogenesis
Epithelial cells of seminiferous tubules are the basis of sperm production, which are composed of multilayer germ cells and supporting cells (supporting cells). Spermatogenesis refers to the evolution of male germ cells, that is, undifferentiated stem cells or spermatogonia grow into spermatocytes through multiple mitosis, then into spermatocytes through meiosis, and finally form sperm through morphological changes. The process of human spermatogenesis is very regular, accompanied by obvious cell change order. The whole period from spermatogonia to sperm is called spermatogenesis cycle, which is about 60 days after determination. During spermatogenesis, spermatogenic cells at all levels in seminiferous tubules can be divided into different developmental stages according to their cell structure, size and location. Generally speaking, spermatogenic cells can be divided into the following levels from basement membrane to lumen:
1. Spermatogonial cell: It is pointed out that the most primitive male germ cell in mitotic stage after birth is usually attached directly to the basement membrane of seminiferous tubules. After spermatogonia divides, except primary spermatocytes, there are still some undifferentiated stem cells.
2. Primary spermatocyte: Located in the inner layer of spermatogonia, the cell is usually in a state of division.
3. Secondary spermatocytes: After meiosis (the first mature division), the primary spermatocytes become two secondary spermatocytes with half chromosomes. Abnormal chromosome combination and distribution in meiosis can lead to infertility or deformity. According to statistics, 3-5 boys in 1000 may have chromosomal abnormalities. The secondary spermatocyte immediately undergoes the second maturation and divides into two spermatocytes. During the maturation and division of spermatocytes, under normal circumstances, some cells will degenerate, so the actual number of spermatocytes produced is less than the theoretical value.
4. Sperm cells refer to cells that are in the process of metamorphosis and sperm formation and do not divide at this stage. Located on the surface of the lumen, it usually gathers at the top of supporting cells. Metamorphosis is a long and complicated period, which is the main stage of sperm abnormality.
5. Sperm: It is a mature male germ cell released from the seminiferous tubule wall. Sertoli cells have a certain effect on sperm release.
Sertoli cells: tall and irregular columnar cells, whose bases often attach to the top of basement membrane and reach the lumen. Spermatogenic cells at all levels are embedded in cytoplasm. They are the only cells in seminiferous tubules that have no reproductive function, but they have the function of supporting, nourishing and protecting seminiferous cells. In recent years, it has been found that sertoli cells can also synthesize androgen.
There are a series of special biochemical changes during spermatogenesis: 1, glycogen, lipid and ribonucleic acid in cells are excreted from cells; 2. There are two unique isozymes: lactate dehydrogenase (LDH-X) and hexokinase, which are unique to testis; 3. Changes of deoxyribonucleoprotein, and protein phosphokinase plays an important role in this process.
The diameter of seminiferous tubules is 300-400 microns, and the length of each seminiferous tubule is 30-70 cm. If you add up the length of the endogenous seminiferous tubules in the testis, the total length can reach 250 meters. In such a long tube, spermatogenic cells keep producing sperm in an orderly way. According to research, a spermatogonia can produce nearly 100 sperm after a spermatogenesis cycle, and one gram of testicular tissue can produce about 10000000 sperm a day. It is not difficult to understand why there are hundreds of millions of sperm at a time.
Testicular endocrine function
In the lobule of testis, there are loose connective tissues around seminiferous tubules, among which there are groups or single interstitial cells (Reddy cells), which have the function of secreting androgen. In embryos, the development of interstitial cells begins at the eighth week, reaches its peak at the sixth month, and then declines. After birth, there are almost no interstitial cells in the testis, mainly fibroblasts. Since puberty, fibroblasts have gradually evolved into mesenchymal cells. With the increase of age, the number of interstitial cells in human testis decreases. At the age of 20, there are about 700 million interstitial cells in bilateral testicles, which will decrease by 8 million every year. However, the concentration of testosterone in plasma did not change until the age of 40 ~ 50.
The physiological functions of testosterone mainly include the following aspects: ① Effects on physiological system: The growth and function of penis, epididymis, seminal vesicle, prostate, Cobb gland and Park Jung Su gland depend on testosterone, which can promote scrotum growth and scrotum skin pigmentation and increase fructose, citric acid and acid phosphatase in semen; Promote testicular seminiferous tubule development and spermatogenesis, and ensure the completion of sexual desire and sexual function. ② Effect on secondary sexual characteristics: Testosterone can thicken skin, increase skin circulation and pigmentation, promote pubic hair growth, and promote the development of male secondary sexual characteristics, including beard, Adam's apple development, exuberant sebaceous gland secretion, deep voice, muscular bones, pelvic stenosis, etc. ③ Effects on metabolism: increase protein synthesis, promote water and sodium retention, increase plasma low density lipoprotein concentration, promote hematopoietic function of bone marrow, and increase the number of red blood cells and hemoglobin.
Androgen can not only directly enter the seminiferous tubule to regulate the spermatogenesis process, but also be transported to the whole body through blood circulation. Normal men can measure about 7 mg of testosterone secretion in testicular vein every day, with an average of 0.6 μ g per ml of blood.
Fluid secretion of testis
The fluid secreted by testis, also called testicular fluid, is isotonic with plasma. The concentration of sperm is usually about 1x 108/ml, and protein in testicular fluid is mainly composed of albumin. Testosterone concentration is higher than that of blood, potassium ion concentration is three times that of venous blood, inositol is more than 100 times that of plasma, and the flow rate of testicular fluid is 0. 1- 1 ml/65433. Testicular fluid is secreted by seminiferous tubules, and its secretion is similar to cerebrospinal fluid and aqueous humor secreted by ciliary body.
Hormone regulation of testicular function and its influencing factors
Testicular function is regulated and controlled by gonadotropins in the anterior pituitary gland. The anterior pituitary gland secretes two gonadotropins:
1, follicle stimulating hormone (FSH), also known as follicle stimulating hormone: promotes spermatogenesis in seminiferous tubules of testis.
FSH acts on spermatogenic cells and sertoli cells, which can start spermatogenesis. FSH can stimulate sertoli cells to secrete ABP, which can combine with testosterone and dihydrotestosterone, thus increasing its local concentration in testicular microenvironment, which is beneficial to spermatogenesis. In addition, FS H can also convert testosterone in sertoli cells into estradiol through aromatase, and estrogen may have a feedback regulation effect on testosterone secretion, so that testosterone secretion can be controlled at a certain level. Direct injection of testosterone can not control FSH secretion in a feedback way. The feedback control of FSH mainly depends on inhibin secreted by testis, which can make pituitary unresponsive to GnRH secreted by hypothalamus, thus inhibiting the secretion of FSH in pituitary in a feedback way.
2. Luteinizing hormone (LH), also known as interstitial cell stimulator (ICSH): Adenylate cyclase system mainly acts on interstitial cells and promotes the secretion of androgen by testicular interstitial cells.
LH secreted by pituitary gland reaches testis through blood circulation, and then combines with LH receptor on interstitial cell membrane, thus triggering interstitial cells to synthesize testosterone. After testosterone is secreted into the blood circulation, it mainly plays a role in three aspects: first, it directly binds to the testosterone receptor of the target organ to promote protein synthesis; Second, it is converted into dihydrotestosterone by 52- reductase; Thirdly, it is converted into estrogen by aromatase. There are other ways of doing things. If the pituitary gland secretes insufficient LH, leydig cells of testis atrophy and testosterone synthesis decreases. On the contrary, the levels of testosterone and estrogen in blood can feedback and control the ability of pituitary gland to secrete LH and hypothalamus to secrete GnRH.
Therefore, there are two regulatory mechanisms: pituitary-mesenchymal cell axis and pituitary-seminiferous tubule axis. When the pituitary gland is diseased, or inhibited by drugs, or there is no gonadotropin after pituitary resection, it will affect the spermatogenic and endocrine functions of testis and shrink seminiferous tubules and interstitial cells. In recent years, it has been confirmed that the activity of the anterior pituitary gland is controlled by hypothalamic nerve cells. Neurons in hypothalamus can also secrete some special chemical transmitters to control the activities of anterior pituitary cells. These chemical transmitters are called release factors (RF). Of course, the activity of the testis itself also has a feedback effect on the pituitary and hypothalamus, which achieve dynamic balance in peacetime.
Other factors affecting testicular function
The normal development of testis still needs certain temperature conditions. The temperature in the scrotum is generally 2-4 degrees Celsius lower than that in the abdominal cavity, which is suitable for the production and development of sperm. If the testis does not fall into the scrotum, some people call it cryptorchidism. Cryptorchidism can shrink due to the influence of hyperthermia in groin or abdominal cavity, and lose the ability of spermatogenesis. In addition, in the early adolescence, when parotitis causes orchitis, it can also make the epithelial cells of testicular seminiferous tubules atrophy, affecting the spermatogenic function. According to statistics, 20% of boys aged 12- 18 have orchitis when they get mumps. Testicular dystrophy in adulthood; Lack of vitamins a and e; Be exposed to radiation; The operation of scrotum and inguinal region affects the blood supply of testis; As well as the influence of some drugs, will cause the decline of testicular spermatogenesis function.
Blood-testis barrier
General drugs are not easy to enter seminiferous tubules, which is because of the blood-testis barrier.
Blood-testis barrier is located between interstitial capillary lumen and seminiferous tubule lumen, and there are capillary and lymphatic endothelial cells and basement membrane, myoid cells, seminiferous tubule basement membrane and supporting cells between the two lumens.
The blood-testis barrier mainly has the following functions: ① forming an immune barrier. Because sperm is antigen, the blood-testis barrier can block the antigenicity of sperm, prevent the body from producing anti-sperm antibodies and avoid autoimmune reactions. ② Prevent harmful substances from interfering with spermatogenesis and damaging the formed sperm. ③ Create a good environment for spermatogenesis and ensure the normal microenvironment for spermatogenesis.
Electron microscope observation showed that the basement membrane of seminiferous tubule was closely combined with its surrounding connective tissue cells and supporting cells, which was the main structure of blood-testis barrier. Sertoli cells are important structures that constitute the blood-testis barrier. Sertoli cells of testis are distributed among spermatogenic cells in different periods, and are conical, with a wide bottom, attached to basement membrane and a narrow top, extending into the cavity. Many depressions are formed on the top and side walls of cells, and spermatogenic cells are embedded in them. The nucleus is irregular, lightly stained and has obvious nucleoli. The basal lateral processes of adjacent supporting cells are connected, and the cell membranes on both sides form a close connection. This junction is located above the spermatogonia, which can prevent some macromolecular substances in the stroma from entering the lumen through the gap between the epithelial cells of seminiferous tubules, thus playing a barrier role.
Some substances, such as cadmium, can selectively destroy the blood-testis barrier, leading to spermatogenesis disorders.
Related Reference: Physical Diagram of Testicular Anatomy
Congenital testicular abnormality cryptorchidism
Testicular testicles
[Keywords:] sexual physiology
A male gonad that produces sperm and gonadal hormones. It is the main sex organ of men. If you remove your testicles before puberty (such as eunuchs in feudal times), you will lose your sexual function and fertility after puberty.
Structural anatomy The testicles are oval, one on the left and one on the right, weighing about 20-30g, with a longitudinal diameter of 4.3-5. 1cm, a width of 2.6-3. 1cm and a thickness of 2-3cm. Its normal volume is 15-25ml, which is about 20ml for most normal people. Testis is the retroperitoneal organ during embryonic development. For a normal boy, the testicles have descended from the inguinal canal into the scrotum at birth. In the descending process, two layers of peritoneum are used as the capsule that wraps the testis, which is called the tunica vaginalis. A small amount of fluid accumulates in the space between them, which is called testicular sheath. The tunica vaginalis and tunica propria of testis form a dense and thick white membrane. Observe the testicular section with the naked eye, and the needle tip can pick out the essence. Microscopically, the testis parenchyma is divided into 100-200 conical lobules, and each lobule contains 2-4 tubules with a length of about 30-80 cm and a diameter of 150-250 microns, which are called seminiferous tubules. It is estimated that if the seminiferous tubules of a testis are connected, the total length can reach 255 meters. The loose connective tissue between seminiferous tubules is called stroma. The curved seminiferous tubules of each leaf converge into straight curved seminiferous tubules to the posterior margin of testis, then anastomose to form testicular reticulation, and then converge into 8- 15 output tubules, which pass through the posterior upper margin of testis and connect with epididymal head. There are three kinds of cells with special functions in testis, including spermatogenic cells, supporting cells on the wall of seminiferous tubules and leydig cells of testis.
Spermatogenesis of spermatogenic cells begins with spermatogenic cells, and sperm is formed through complex processes such as cell division, gene exchange of half chromosomes, formation of sex chromosomes (X and Y chromosomes), and cell metamorphosis (appearance of sperm tail). Spermatogenic cells can be divided into five generations according to their developmental stages, namely spermatogonia, primary spermatocytes, secondary spermatocytes, spermatocytes and sperm.
Sertoli cells The functions of Sertoli cells are numerous and complex, and have not been fully understood so far. However, it plays an important role in maintaining the differentiation and development of spermatogenic cells, so some people call sertoli cells the preservation cells of sperm. Sertoli cells can divide seminiferous tubules into two isolated areas with different internal and external environments to ensure the development and differentiation of seminiferous cells in the best internal environment. On the other hand, sperm is a haploid cell (only 23 chromosomes) which is different from somatic cells, and has a specific antigenic component. However, due to the isolation barrier function of sertoli cells, the immunocompetent substances in blood are prevented from contacting with sperm, so it will not cause any individual's autoimmune reaction. The role of sertoli cells in distinguishing seminiferous tubule lumen from blood environment is called blood-testis barrier. At present, it is also recognized that sertoli cells can secrete a variety of substances to improve the utilization level of androgen in seminiferous tubules and participate in the feedback regulation of hypothalamus-pituitary-testis axis.
Interstitial cell Interstitial cell is one of the cells with the most special function in testis. It accounts for almost 12% of the testicular volume. It can accept the regulation, synthesis and secretion of androgen by pituitary sex hormones, and is an important cell to maintain male sexual function.
Among the above three functional cells of testis, spermatogenic cells are the most sensitive to the changes of internal and external environmental conditions, and their flexibility to adapt to environmental factors is relatively narrow, such as temperature, ultrasound, microwave, ionizing radiation, magnetic field, drugs, systemic diseases, endocrine, vitamins, trace elements, cigarettes, alcohol and other biochemical factors will interfere with the occurrence and production of sperm to varying degrees. Sertoli cells and interstitial cells have high tolerance to these factors and little influence. According to these theoretical foundations, the current reproductive physiology researchers are trying to explore the effects of spermatogenic cells on some physical, chemical, pharmaceutical and immune factors, and provide a new way for men to regulate their fertility.
testicle
The surface of testis is covered with serosa, that is, the dirty layer of tunica vaginalis, and the deep part is white membrane composed of dense nodular tissue, which thickens at the posterior margin of testis to form testis mediastinum. The connective tissue of the mediastinum extends into the testis parenchyma in a xie shape, which divides the testis parenchyma into about 250 pyramidal lobules, and each lobule has 1 ~ 4 curved and slender seminiferous tubules, which are short and straight seminiferous tubules near the testis mediastinum. The seminiferous tubules enter the testis mediastinum and anastomose with each other to form the testis net. The loose connective tissue between seminiferous tubules is called testicular stroma (figure 16- 1).
Fig. 16- 1 morphology of testis and epididymis
(1) seminiferous tubule
Adult seminiferous tubules are 30 ~ 70 cm long, with a diameter of 150 ~ 250 microns, a lumen in the center and a wall thickness of 60 ~ 80 microns, and are mainly composed of seminiferous epithelium. Spermatogenic epithelium consists of sertoli cells and 5 ~ 8 layers of spermatogenic cells. The basement membrane under the epidermis is obvious, and there are collagen fibers and some spindle-like cells outside the basement membrane. Myoid cells contribute to sperm excretion when contracting (figure 16-2).
Figure 16-2 SEM image of human seminiferous tubules × 180
Seminiferous tubule lumen seminiferous epithelium stroma
1. Spermatogenic cells include spermatogonia, primary spermatocytes, secondary spermatocytes, spermatocytes and sperm. Before puberty, the lumen of seminiferous tubule is small or no lumen, and the wall of seminiferous tubule only has supporting cells and spermatogonia. From puberty, under the action of pituitary gonadotropins, spermatogenic cells proliferate and differentiate to form sperm, and spermatogenic cells at different development stages can be seen on the wall of seminiferous tubules (Figure16-3; 16-4)。 The process from spermatogonia to sperm formation is called spermatogenesis.
Fig. 16-3 seminiferous tubules and leydig of testis
Fig. 16-4 semithin sections of seminiferous tubules were stained with toluidine blue-pyrroline × 320.
Keywords spermatogonia, spermatogonia, primary spermatocyte,
Keywords Sp sperm cells, Se sertoli cells, road cavity
(1) spermatogonia: spermatogonia is close to the basement membrane of seminiferous epithelium, round or oval, with a diameter of about 12 μ m, and the organelles in cytoplasm are underdeveloped except ribosomes. Spermatogonial cells are divided into type A and type B (Figure 16-5). The nucleus of type A spermatogonia is oval, with dark chromatin and light stained vesicles in the center of the nucleus. Or the nuclear chromatin is fine and 1 ~ 2 nucleoli are attached to the nuclear membrane. Type A spermatogonia are stem cells in spermatogenic cells. After continuous division and proliferation, some type A spermatogonia continue to act as stem cells. The other part differentiated into type B spermatogonia. The nucleus of type B spermatogonia is round, with thick chromatin particles attached to the nuclear membrane and nucleoli in the center. After several divisions, type B spermatogonia differentiated into primary spermatocytes.
Fig 16-5 toluidine blue-pyrroline staining× 520 semithin section of human seminiferous tubule epithelium.
Keywords spermatogonia, spermatogonia, primary spermatocyte,
Sp sperm cells, RB residual cytoplasm Se supporting cells
(2) Primary spermatocyte: The primary spermatocyte is located near the cavity of spermatogonia, with a large volume, a diameter of about 65,438 0.8 microns, a large and round nucleus and a chromosome karyotype of 46, XY. After DNA replication (4n, DNA), the cells undergo the first mature division, forming two secondary spermatocytes. Because the prophase of the first mature division lasts for a long time, primary spermatocytes in different stages of proliferation can often be seen on the section of seminiferous tubules (Figure 16-5).
(3) Secondary spermatocyte: The secondary spermatocyte is located near the lumen, with a diameter of about 65,438 0.2 microns, a round nucleus and deep staining, with a chromosome karyotype of 23, x or 23, Y(2n, DNA). Each chromosome consists of two chromatids, which are connected by centromeres. Secondary spermatocytes do not copy DNA, that is, they enter the second mature division, centromere separation, chromatid separation and move to the two poles of the cell, forming two sperm cells, the karyotype of which is 23, x or 23, Y( 1N DNA). Because of the short existence time of secondary spermatocytes, it is not easy to see them in the section of seminiferous tubules.
Mature division, also known as meiosis, only occurs in germ cells. The characteristics of mature division are as follows: ① After mature division, the chromosome number of germ cells is halved, from diploid cells to haploid cells, and after fertilization (hermaphroditic germ cells are combined), the zygote (fertilized egg) regains the same chromosome number as the parent cells, ensuring that the chromosome number of species remains unchanged; ② At the early stage of the first mature division, homologous chromosomes are added and hybridized to exchange genetic genes, so that gametes (sperm or eggs) have different gene combinations (Figure 16-6). In the process of mature division, if homologous chromosomes don't divide or there is a problem in gene exchange, it will lead to abnormal chromosome number and genetic composition of gametes, and abnormal gametes will lead to abnormal offspring after fertilization.
Fig. 16-6 schematic diagram of maturation and division of germ cells
Fig. 16-7 sperm formation pattern diagram
(4) Sperm cells: Sperm cells are located near the lumen, with a diameter of about 8μm, a round nucleus and dense chromatin. Sperm cells are haploid, and they no longer divide. After complicated changes, they gradually differentiated from round to tadpole-shaped sperm. This process is called spermatogenesis (figure 16-7). The main changes of sperm formation are as follows: ① the chromatin in the nucleus is extremely concentrated, the nucleus becomes longer and moves to one side of the cell, forming the sperm head; (2) Golgi complex formed acrosome vesicles, which gradually increased, and the depression was a double-layer hat covering the head end of the nucleus, which became acrosome; ③ Centrosome migrates to the caudal side of nucleus (opposite to acrosome) and sends out axoneme. With the growth of axoneme, sperm cells become longer and form tails (or flagella). (4) Mitochondria gather around the proximal axoneme from the periphery of the cell and coil into a spiral mitochondrial sheath; ⑤ The surface of nucleus, acrosome and axoneme is only covered with cell membrane and thin cytoplasm, and the surplus cytoplasm gradually gathers to the caudal side to form residual cytoplasm, and finally falls off.
(5) Sperm: Sperm is tadpole-shaped, about 60μm long and divided into two parts (Figure 16-8). The front view of the head is oval and the side view is pear-shaped. The head mainly has a nucleus with a high concentration of chromatin, and the first two thirds of the nucleus is covered by acrosome. Acrosome contains a variety of hydrolases, such as acrosin, hyaluronidase, acid phosphatase and so on. During fertilization, sperm releases acrosin, which decomposes the radial crown and zona pellucida around the egg and enters the egg. The tail is the movement device of sperm, which is divided into four parts: neck segment, middle segment, main segment and tail segment. The neck segment is short, mainly centriole, and the centriole emits 9+2 microtubules, which constitute the axoneme of the flagella center. In the middle section, there are 9 longitudinal peripheral dense fibers on the outer side of the axoneme, and the outer side is wrapped with a circle of mitochondrial sheath, which provides energy for flagella to swing and makes sperm move forward quickly. The main node is the longest, and there is no mitochondrial sheath around the axoneme, which is replaced by fiber sheath. The end segment is short, with only axoneme.
Figure 16-8 sperm ultrastructure pattern diagram
The tail cross section is shown in the middle, and the three-dimensional structure is shown on the right.
It takes about 64 4.5 days for human beings to develop from spermatogonia to sperm. The cytoplasm of spermatogenic cells at all levels produced by the proliferation and differentiation of a spermatogenic cell is not completely separated, and there are always cytoplasmic bridges between cells, forming a synchronous cell group. Spermatogenesis in different segments of the seminiferous tubule is not synchronous, and the spermatogenesis in the latter segment is a little later than that in the previous segment, so the seminiferous tubule can continuously produce sperm in batches. Therefore, in testicular tissue sections, we can see that different sections of seminiferous tubules have different combinations of seminiferous cells at different developmental stages (Figure 16-5).
Spermatogenic cells with active proliferation are easily affected by many physical and chemical factors, such as radiation, microwave, high temperature, drugs, toxins, sex hormones, vitamins and so on. For example, in patients with cryptorchidism, the testis is located in the abdominal cavity or inguinal canal, and the humidity affects spermatogenesis. Taking cottonseed oil (including gossypol) or tripterygium wilfordii can cause spermatogenesis disorder. At present, some safe and effective factors inhibiting spermatogenesis are being studied in order to be applied to male antifertility.
2. Sertoli cells are also called Sertoli cells. Under the light microscope, the outline of sertoli cells is unclear, the nucleus is often irregular, the nuclear chromatin is sparse, the staining is harmonious and the nucleoli is obvious. Observed by electron microscope, Sertoli cells are irregular conical, with the base close to the basement membrane and the top extending into the lumen. There are many irregular depressions on the lateral surface and lumen surface, which are embedded with spermatogenic cells at all levels (Figure 16-9). Golgi complex in cytoplasm is well developed, with abundant rough endoplasmic reticulum, smooth endoplasmic reticulum, mitochondria, lysosomes and glycogen granules, as well as many microfilaments and microtubules. The cell membranes near the basement of supporting cells are closely connected, and the spermatogenic epithelium is divided into two parts: basal compartment and proximal compartment. The basal chamber is located between the basement membrane of spermatogenic epithelium and the tight junction of supporting cells, and there are spermatogonia in it. The proximal lumen is located above the tight junction and communicates with the lumen of seminiferous tubule, which contains spermatocytes, sperm cells and sperm. There is a blood-seminiferous tubule barrier between seminiferous tubule and blood, which consists of interstitial vascular endothelium and its basement membrane, connective tissue, seminiferous epithelial basement membrane and supporting cells. Tight junction is the main structure that constitutes the barrier between blood and seminiferous tubules.
Sertoli cells have many functions. It supports and nourishes spermatogenic cells. The contraction of microfilaments and microtubules can make mature spermatogenic cells move to the cavity surface and promote the release of sperm into the cavity. The residual cytoplasm shed during sperm formation can be swallowed and digested by sertoli cells. A small amount of fluid secreted by Sertoli cells is helpful for sperm transport, and the secretion contains an inhibin, which can inhibit the synthesis and secretion of FSH in the anterior pituitary gland. Sertoli cells combined with androgen and androgen binding protein (ABP) in FSH can maintain androgen level in seminiferous tubules and promote spermatogenesis. The blood-seminiferous tubule barrier formed by the close connection of supporting cells can prevent some substances from entering seminiferous epithelium, form and maintain a microenvironment conducive to spermatogenesis, and also prevent sperm antigen substances from escaping outside seminiferous tubules, causing autoimmune reactions.
Fig. 16-9 spermatogenic cells and sertoli cells
Left: schematic diagram of the relationship between spermatogenic cells and sertoli cells at all levels
Right: Electrical mirror image ×3600 supporting cell tight junction.
Lanthanum nitrate was perfused and fixed, and Sg spermatogonia (located in basal chamber) supported the tight connection between cells.
(2) Leydig testis
The interstitium between seminiferous tubules is loose connective tissue, which is rich in blood vessels and lymphatic vessels. In the stroma, in addition to the usual connective tissue cells, there is also a kind of interstitial cells, also known as interstitial cells. The cells are distributed in groups, with large volume, round or polygonal nucleus and strong eosinophilic cytoplasm, which has the ultrastructural characteristics of steroid hormone secreting cells (Figure 16- 10). Androgen secreted by mesenchymal cells can promote spermatogenesis, promote the development and differentiation of male reproductive organs, and maintain secondary sexual characteristics and sexual function.
Figure 16- 10 Electron microscopic image of leydig cells in rat testis × 10800
M mitochondria, rough endoplasmic reticulum; Plum fat drops; endoplasmic reticulum
(3) seminiferous tubules and testicular reticulation
The seminiferous tubule becomes a short and straight tube near the testis mediastinum, with a smaller diameter, which is a straight curved seminiferous tubule. The epithelium of the tube wall is single cubic or short columnar, and there are no spermatogenic cells. Seminiferous tubules enter the mediastinum of testis and anastomose into reticular duct, which is testis reticular and consists of single cubic epithelium. The lumen is large and irregular. Sperm produced by seminiferous tubules leave the testis through seminiferous tubules and testicular reticulation (Figure 16- 1 1).
Fig. 16- 1 1 schematic diagram of seminiferous tubules, seminiferous tubules and testicular reticulation.
Endocrine regulation of testicular function
The neuroendocrine cells in hypothalamus secrete gonadotropin releasing hormone (GnRH), which can promote the gonadotropin cells in the distal pituitary gland to secrete gonadotropin (FSH) and luteinizing hormone (LH). In men, FSH promotes the synthesis of ABP; Through supporting cells; LH, also known as interstitial cell stimulator (ICSH), can stimulate interstitial cells to synthesize and secrete androgen. ABP can bind with androgen, so as to keep the seminiferous tubule containing high concentration of androgen and promote spermatogenesis. Inhibin secreted by supporting cells and androgen secreted by interstitial cells can also inhibit the secretion of GnRH in hypothalamus and FSH and LH in adenohypophysis (figure 16- 12). Under normal circumstances, the secretion of various hormones is relatively constant, and the increase or decrease of a certain hormone secretion or the change of a certain hormone receptor will affect spermatogenesis, causing changes in secondary sexual characteristics and sexual dysfunction.