What is spermatogenesis

Hormonal regulation. Spermatogonia continue to divide, but in reduced numbers, after hypophysectomy. Spermatocytogenesis is completely arrested at the primary spermatocyte stage in hypophysectomized animals; this step is restored by testosterone. Androgen-binding protein the testicular counterpart of SHBG sequesters testosterone within the seminiferous tubule and caput epididymis. Meiosis II is hormonally-independent.

Follicle-stimulating hormone participates in spermiogenesis. Estradiol and DHT are also involved in the spermatogenic process. Hormonal effects on sperm cells are not direct, but are mediated through Sertoli cells. Biochemical and biophysical facets of sperm-Sertoli interactions in spermatogenesis are largely unknown.

Rate of production of spermatozoa is not influenced by endocrine therapy. Blood-testis barrier. As sperm cells mature they move between Sertoli cells from the basal toward the adluminal compartment of the seminiferous tubule. Because nucleotide recombinations can occur during meiosis I, the genetic code of chromosomes of gametes can differ from that of somatic parent cells ie.

Occluding junctions that interconnect adjacent Sertoli cells shield secondary spermatocytes, spermatids, and spermatozoa from autoimmune recognition Figure The blood-testis barrier also acts to conserve certain products of Sertoli cells within the seminiferous tubule, such as ABP. The epithelial syncytium of this barrier extends through the epididymis. Vasectomy can lead to a breakdown in the blood-testis barrier in laboratory animals and subhuman primates; as a result, an autoimmune response is mounted against sperm antigens released into the periphery.

Immune complexes can lodge within the kidneys and adhere to walls of blood vessels causing renal damage and atherosclerosis; possible complications of this nature, although not detected thusfar, need to be monitored closely in long-term vasectomized men. Effect of temperature. Sperm cells will not mature at core body temperature in most mammals spermatogenic DNA polymerase b and recombinase activities exhibit unique temperature optima ; to adapt, the testes assume an external position.

Testicular descent from the abdomen normally transpires during fetal or neonatal life. If the testes fail to descend into the scrotum, a condition called cryptorchidism, the male will be sterile; gone uncorrected by surgery or androgen treatment spermatogonia will eventually degenerate. Cryptorchidism does not have a major effect on testicular output of testosterone.

Testicular descent is permanent in many mammals eg. Sometimes high ambient temperatures are associated with infertility. A transient condition of "summer sterility" is common in rams. In other species eg. The testes of hibernating mammals often descend when body temperature begins to rise after awakening.

A few mammals do not have scrotal sacs eg. Notwithstanding, the internal testes of birds produce viable gametes in spite of very high abdominal body temperatures. From an evolutionary perspective it is difficult to reconcile the hazardous location of pendulous testes.

Scrotal temperature is a few degrees lower than internal body temperature. Several compensatory mechanisms aid in maintaining testicular temperature within defined limits. For efficient dissipation of heat, the scrotum lacks subcutaneous fat and is rich in sweat glands. A two-muscle system lowers and lifts the testis. The Golgi apparatus surrounds the now condensed nucleus, becoming the acrosome. One of the centrioles of the cell elongates to become the tail of the sperm.

The non-motile spermatozoa are transported to the epididymis in testicular fluid secreted by the Sertoli cells with the aid of peristaltic contraction. While in the epididymis, the spermatozoa gain motility and become capable of fertilization. Seminiferous Tubule: Micrograph showing seminiferous tubule with maturing sperm. Maturation takes place under the influence of testosterone, which removes the remaining unnecessary cytoplasm and organelles. The excess cytoplasm, known as residual bodies, is phagocytosed by surrounding Sertoli cells in the testes.

The resulting spermatozoa are now mature but lack motility, rendering them sterile. The mature spermatozoa are released from the protective Sertoli cells into the lumen of the seminiferous tubule in a process called spermiation. Spermatogenesis is highly sensitive to fluctuations in the environment, particularly hormones and temperature. Seminiferous epithelium is sensitive to elevated temperature in humans and is adversely affected by temperatures as high as normal body temperature.

Consequently, the testes are located outside the body in a sack of skin called the scrotum. This is achieved by regulation of blood flow and positioning towards and away from the heat of the body by the cremaster muscle and the dartos smooth muscle in the scrotum. Dietary deficiencies such as vitamins B, E, and A , anabolic steroids, metals cadmium and lead , x-ray exposure, dioxin, alcohol, and infectious diseases will also adversely affect the rate of spermatogenesis.

Spermatozoon: Diagram of parts of a spermatozoon, including the acrosome, plasma membrane, nucleus, centriole, mitochondria, terminal disc, axial filament, tail, endpiece, midpiece, and head. Key Takeaways. Key Points Spermatogenesis begins with a diploid spermatogonium in the seminiferous tubules, which divides mitotically to produce two diploid primary spermatocytes.

The primary spermatocyte then undergoes meiosis I to produce two haploid secondary spermatocytes. Accessed 12 Nov. More Definitions for spermatogenesis. Subscribe to America's largest dictionary and get thousands more definitions and advanced search—ad free!

Log in Sign Up. Save Word. Definition of spermatogenesis. Examples of spermatogenesis in a Sentence Recent Examples on the Web Vibliome will develop a drug that will impair spermatogenesis by building on work already done by researchers at Stamford University.

First Known Use of spermatogenesis , in the meaning defined above. History and Etymology for spermatogenesis New Latin. Learn More About spermatogenesis. Share spermatogenesis Post the Definition of spermatogenesis to Facebook Share the Definition of spermatogenesis on Twitter.