| Seminiferous tubule | |
|---|---|
 | |
 1: Testicular septa 2: Convoluted seminiferous tubules 3: Testicular lobules 4: Straight seminiferous tubules 5: Efferent ductules 6: Rete testis | |
| Details | |
| Identifiers | |
| Latin | tubuli seminiferi |
| MeSH | D012671 |
| TA98 | A09.3.01.022 |
| TA2 | 3599 |
| FMA | 19825 |
| Anatomical terminology | |
Seminiferous tubules are located within the testicles, and are the specific location of meiosis, and the subsequent creation of male gametes, namely spermatozoa.
The epithelium of the tubule consists of a type of sustentacular cells known as Sertoli cells, which are tall, columnar type cells that line the tubule.
In between the Sertoli cells are spermatogenic cells, which differentiate through meiosis to sperm cells. Sertoli cells function to nourish the developing sperm cells. They secrete androgen-binding protein, a binding protein which increases the concentration of testosterone.
There are two types: convoluted and straight, convoluted toward the lateral side, and straight as the tubule comes medially to form ducts that will exit the testis.
The seminiferous tubules are formed from the testis cords that develop from the primitive gonadal cords, formed from the gonadal ridge.
Spermatogenesis, the process for producing spermatozoa, takes place in the seminiferous tubules. During spermatogenesis, the DNA of spermatogenic cells in the seminiferous tubules is subject to damage from such sources as reactive oxygen species. [1] The genomic integrity of spermatogenic cells is protected by DNA repair processes. [2] Deficiencies in the enzymes employed in these repair processes may lead to infertility. [2]
A spermatozoon is a motile sperm cell, or moving form of the haploid cell that is the male gamete. A spermatozoon joins an ovum to form a zygote.
A testicle or testis is the male gonad in all bilaterians, including humans. It is homologous to the female ovary. The functions of the testicles are to produce both sperm and androgens, primarily testosterone. Testosterone release is controlled by the anterior pituitary luteinizing hormone, whereas sperm production is controlled both by the anterior pituitary follicle-stimulating hormone and gonadal testosterone.
A gonad, sex gland, or reproductive gland is a mixed gland and sex organ that produces the gametes and sex hormones of an organism. Female reproductive cells are egg cells, and male reproductive cells are sperm. The male gonad, the testicle, produces sperm in the form of spermatozoa. The female gonad, the ovary, produces egg cells. Both of these gametes are haploid cells. Some hermaphroditic animals have a type of gonad called an ovotestis.
A germ cell is any cell that gives rise to the gametes of an organism that reproduces sexually. In many animals, the germ cells originate in the primitive streak and migrate via the gut of an embryo to the developing gonads. There, they undergo meiosis, followed by cellular differentiation into mature gametes, either eggs or sperm. Unlike animals, plants do not have germ cells designated in early development. Instead, germ cells can arise from somatic cells in the adult, such as the floral meristem of flowering plants.
Spermatogenesis is the process by which haploid spermatozoa develop from germ cells in the seminiferous tubules of the testicle. This process starts with the mitotic division of the stem cells located close to the basement membrane of the tubules. These cells are called spermatogonial stem cells. The mitotic division of these produces two types of cells. Type A cells replenish the stem cells, and type B cells differentiate into primary spermatocytes. The primary spermatocyte divides meiotically into two secondary spermatocytes; each secondary spermatocyte divides into two equal haploid spermatids by Meiosis II. The spermatids are transformed into spermatozoa (sperm) by the process of spermiogenesis. These develop into mature spermatozoa, also known as sperm cells. Thus, the primary spermatocyte gives rise to two cells, the secondary spermatocytes, and the two secondary spermatocytes by their subdivision produce four spermatozoa and four haploid cells.
Sertoli cells are a type of sustentacular "nurse" cell found in human testes which contribute to the process of spermatogenesis as a structural component of the seminiferous tubules. They are activated by follicle-stimulating hormone (FSH) secreted by the adenohypophysis and express FSH receptor on their membranes.
The rete testis is an anastomosing network of delicate tubules located in the hilum of the testicle that carries sperm from the seminiferous tubules to the efferent ducts. It is the homologue of the rete ovarii in females. Its function is to provide a site for fluid reabsorption.
Spermatocytes are a type of male gametocyte in animals. They derive from immature germ cells called spermatogonia. They are found in the testis, in a structure known as the seminiferous tubules. There are two types of spermatocytes, primary and secondary spermatocytes. Primary and secondary spermatocytes are formed through the process of spermatocytogenesis.
The male reproductive system consists of a number of sex organs that play a role in the process of human reproduction. These organs are located on the outside of the body, and within the pelvis.
Spermiogenesis is the final stage of spermatogenesis, during which the spermatids develop into mature spermatozoa. At the beginning of the stage, the spermatid is a more or less circular cell containing a nucleus, Golgi apparatus, centriole and mitochondria; by the end of the process, it has radically transformed into an elongated spermatozoon, complete with a head, midpiece, and tail.
The blood–testis barrier is a physical barrier between the blood vessels and the seminiferous tubules of the animal testes. The name "blood-testis barrier" is misleading as it is not a blood-organ barrier in a strict sense, but is formed between Sertoli cells of the seminiferous tubule and isolates the further developed stages of germ cells from the blood. A more correct term is the Sertoli cell barrier (SCB).
Spermatogenesis arrest is known as the interruption of germinal cells of specific cellular type, which elicits an altered spermatozoa formation. Spermatogenic arrest is usually due to genetic factors resulting in irreversible azoospermia. However some cases may be consecutive to hormonal, thermic, or toxic factors and may be reversible either spontaneously or after a specific treatment. Spermatogenic arrest results in either oligospermia or azoospermia in men. It is quite a difficult condition to proactively diagnose as it tends to affect those who have normal testicular volumes; a diagnosis can be made however through a testicular biopsy.
The germinal epithelium is the epithelial layer of the seminiferous tubules of the testicles. It is also known as the wall of the seminiferous tubules. The cells in the epithelium are connected via tight junctions.
Sertoli cell-only syndrome (SCOS), also known as germ cell aplasia, is defined by azoospermia where the testicular seminiferous tubules are lined solely with sertoli cells. Sertoli cells contribute to the formation of the blood-testis barrier and aid in sperm generation. These cells respond to follicle-stimulating hormone, which is secreted by the hypothalamus and aids in spermatogenesis.
Gonocytes are the precursors of spermatogonia that differentiate in the testis from primordial germ cells around week 7 of embryonic development and exist up until the postnatal period, when they become spermatogonia. Despite some uses of the term to refer to the precursors of oogonia, it was generally restricted to male germ cells. Germ cells operate as vehicles of inheritance by transferring genetic and epigenetic information from one generation to the next. Male fertility is centered around continual spermatogonia which is dependent upon a high stem cell population. Thus, the function and quality of a differentiated sperm cell is dependent upon the capacity of its originating spermatogonial stem cell (SSC).
Spermatozoa develop in the seminiferous tubules of the testes. During their development, the spermatogonia proceed through meiosis to become spermatozoa. Many changes occur during this process: the DNA in nuclei becomes condensed; the acrosome develops as a structure close to the nucleus. The acrosome is derived from the Golgi apparatus and contains hydrolytic enzymes important for fusion of the spermatozoon with an egg cell. During spermiogenesis, the nucleus condenses and changes shape. Abnormal shape change is a feature of sperm in male infertility. The acroplaxome is a structure found between the acrosomal membrane and the nuclear membrane. The acroplaxome contains structural proteins including keratin 5, F-actin and profilin IV.
FNA mapping is an application of fine-needle aspiration (FNA) to the testis for the diagnosis of male infertility. FNA cytology has been used to examine pathological human tissue from various organs for over 100 years. As an alternative to open testicular biopsy for the last 40 years, FNA mapping has helped to characterize states of human male infertility due to defective spermatogenesis. Although recognized as a reliable, and informative technique, testis FNA has not been widely used in U.S. to evaluate male infertility. Recently, however, testicular FNA has gained popularity as both a diagnostic and therapeutic tool for the management of clinical male infertility for several reasons:
A spermatogonial stem cell (SSC), also known as a type A spermatogonium, is a spermatogonium that does not differentiate into a spermatocyte, a precursor of sperm cells. Instead, they continue dividing into other spermatogonia or remain dormant to maintain a reserve of spermatogonia. Type B spermatogonia, on the other hand, differentiate into spermatocytes, which in turn undergo meiosis to eventually form mature sperm cells.
A peritubular myoid (PTM) cell is one of the smooth muscle cells which surround the seminiferous tubules in the testis. These cells are present in all mammals but their organization and abundance varies between species. The exact role of PTM cells is still somewhat uncertain and further work into this is needed. However, a number of functions of these cells have been established. They are contractile cells which contain actin filaments and are primarily involved in transport of spermatozoa through the tubules. They provide structural integrity to the tubules through their involvement in laying down the basement membrane. This has also been shown to affect Sertoli cell function and PTM cells also communicate with Sertoli cells through the secretion of growth factors and ECM components. Studies have shown PTM cells to be critical in achieving normal spermatogenesis. Overall, PTM cells have a role in both maintaining the structure of the tubules and regulating spermatogenesis through cellular interaction.
In vitro spermatogenesis is the process of creating male gametes (spermatozoa) outside of the body in a culture system. The process could be useful for fertility preservation, infertility treatment and may further develop the understanding of spermatogenesis at the cellular and molecular level.
