The testes in humans are two round shape structures that are located within the scrotum. The scrotum provides protection for the testes against trauma. In addition, due to its presence outside the pelvic cavity, the testes are maintained within the scrotum at a lower temperature than that of the whole body by a 2 degrees Celsius.
Each testes contains two important structures. These are : the leydig cells and the seminiferous tubules. Each of these structures has a unique function in the body. Leydig cells are also called interstitial cells. They are the major endocrine part of the testes. They secrete the steroid hormone testosterone in response to a stimulation from the anterior pituitary gland which secretes the luteinizing hormone LH.
The secretion of LH is regulated by a negative feedback from the hormone testosterone. Therefore, low level of circulating testosterone stimulates the secretionof LH and vice versa. LH is under a positive feed back control from the hormone gonadotropin releasing hormone that is secreted by the hypothalamus.
The importance of the secretion of testosterone is due to its role in the embryonic genesis of male sexual organs. In addition, it has a role in the descending of the testes to the scrotum from the body. Also testosterone is important for maintaining the secondary sexual characteristics in males such as the development of pubic hair and axillar hair.
The other important structure of the testes is the seminiferous tubules. These structures are important for its role in sperm genesis. The seminiferous tubules contain two types of cells that both participate in the process of spermatogenesis. These cells are sertoli cells and germ cells.
The sertoli cells form tight junctions with each other. Thus forming a blood-testes barrier that prevents proteins from entering into the lumen of the seminiferous tubules from the blood. The sertoli cells secrete a protein which is called androgen binding protein. This protein functions by binding to testosterone. Thus making high concentration of this steroid available to the developing germ cells in the process of spermatogenesis.
Sertoli cells secrete androgen binding protein in response to a stimulus by the follicle stimulating hormone that is secreted by the anterior pituitary gland. Germ cells are responsible for the process of spermatogenesis. There are different types of germ cells depending on the state of cell differentiation.
Spermatozoa are the most mature form of germ cells and they are the type of cells that fertilize the ovum of the female. The testes secrete usually several types of androgens. The most important of which is testosterone. More that 90% of testosterone in the blood of males is secreted by the leydig cells of the testes. The remainder is derived from cells of the adrenal cortex.
In addition to testosterone the testes also secrete small amounts of the potent androgen dihydrotesotosterone. The secretion of follicle stimulating hormone and luteinizing hormone is under the control of the hypothalamic hormone gonadotropin releasing hormone. The blood supply to the testes is derived from the testicular artery which is a branch of the internal spermatic artery.
The right testicular vein empties into the spermatic vein whch in turn empties in the vena cava. The left spermatic artery on the other hand empties into the vena cava directly.
The seminiferous tubules empty its content into the epididymis. From the epididymis which functions as a reservoir and passageway for sperm, the sperm is passed to the ejaculatory duct.
Sperm that is formed in the testes is manipulated along its way to the ejaculatory duct by the addition of fluids that are secreted by several glands. These are: the prostate gland which adds fluid to the sperm. Also the seminal vesicles provide the sperm with fluid that is rich with fructose.