Note that half of the spermatids will development into spermatozoa carrying an X chromosome and half will develop into spermatozoa carrying a Y chromosome. During spermiogenesis , the morphology of the spermatid radically changes. The cell develops the acrosome , which covers the sperm head and contains enzymes that assist in penetrating the zona pellucida during fertilization.
The cell becomes elongated forming a neck, connecting the head to the middle piece and tail. The middle piece contains mitochondria for generating energy to propel the cell through the female reproductive tract by action of the flagellum in the tail. The cell loses most of its cytoplasm and must depend on secretions in the semen for sustenance on its journey through the female reproductive tract.
Stages in Spermatogenesis. Spermatogonia Type A spermatogonia serve as a stem cell population in the testis. Meiosis is a part of spermatocytogenesis. In the bull, there is the potential to produce 64 round spermatids from each type A spermatogonium that enters into spermatogenesis. However this amount rarely occurs due to the natural process of apoptosis. Cytoplasmic bridges are a likely explanation for why protein expression on the surface of spermatozoa is not different between X and Y spermatozoa.
Indentify which of the following will increase apoptosis in stallions. Going from April to November. Being exposed to trichamoniasis. Being kicked in the groin by a mare that was not in heat. Swelling did oocur from this incidence. An injection of testosterone. An increase in fat accumilation in the scrotum such that the testis temperature increases.
Testicular torsion. In the bull FSH is involved in the stimulation of mitotic divisions of spermatogonia type A while in the primate it causes the entry of stem cell spermatogonia into the proliferating pool. The golgi phase of spermiogenesis involves which of the following; identify all that apply Proacrosomal granules are formed from the golgi apparatus.
Cells do not divide during spermiogenesis Figure Spermatogenic cycle and wave. If one closely examines serial cross-sections of a seminiferous tubule you will discover that sperm cells differentiate in distinctive associations. Each spermatogenic association has been classified as a stage of the seminiferous epithelial cycle. A spermatogenic cycle is defined as the time it takes for the reappearance of the same stage within a given segment of the tubule.
Each stage of the cycle follows in an orderly sequence along the length of the tubule. The distance between the same stage is called the spermatogenic wave. One tubule can contain numerous complete waves.
Adjacent segments of the tubule evidently communicate in some unknown manner. The number of stages within a spermatogenic cycle and the number of cycles required for the completion of spermatogenesis varies between species. There are 12 different stages of the cycle in the bull of about 14 days each; approximately four cycles within a given region of the tubule occur before an A1 spermatogonia is transformed into a spermatozoa. Six stages have been noted in man; four day cycles are needed to complete spermatogenesis.
The linear pattern of the spermatogenic cycle is less ordered in man than in farm animals or rodents. 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.
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