Spermatogenesis PDF

Assisted prof.Dr. Sumeya Gametogenesis Slide 1  Obgectives This lecture discuss the steps of sperm formation from primordial germ cells to mature spermatozoa, hormonal control and abnormality of spermatogenesis...

Assisted prof.Dr. Sumeya Gametogenesis Slide 1  Obgectives This lecture discuss the steps of sperm formation from primordial germ cells to mature spermatozoa, hormonal control and abnormality of spermatogenesis Slide 2 Gametogenesis – gamete formation by meiosis. Spermatogenesis – Sperm formation (1N) Oogenesis – Egg formation (1N) Slide 3  Primordial germ cells (PGCs)  Gametes are derived from (PGCs) that are formed in epiblast during 2nd week & that move to wall of yolk sac.  During 4th week, these cells begin to migrate by amoeboid movement from yolk sac toward developing gonads, where they arrive by end of 5th week Slide 4 Slide 5  Spermatogenesis 2N Primary spermatocyte Meiosis 1N Secondary 1N spermatocytes, 2N 1N 1N 1N 1N Spermatids, 1N morphogenesis 1N 1N 1N Sperm, 1N 1N Slide 6  Spermatogenesis Maturation of Sperm Begins at Puberty Spermatogenesis, which begins at puberty, includes all of the events by which spermatogonia are transformed into spermatozoa. It can be divided into 3 phases : a. spermatocytosis b. meiosis C. spermiogenesis At birth, germ cells in the male infant can be recognized in the sex cords of the testis as large, pale cells surrounded by supporting cells. Supporting cells, which are derived from the surface epithelium of the testis become sustentacular cells, or Sertoli cells Slide 7 Spermatogenesis occurs in testes Slide 8  Cross section through testes’ tubes Slide 9 sperm Slide 10  Shortly before puberty, the sex cords acquire a lumen and become the seminiferous tubules. At about the same time, PGCs give rise to spermatogonial stem cells. At regular intervals, cells emerge from this stem cell population to form type A spermatogonia, and their production marks the initiation of spermatogenesis. Type A cells undergo a limited number of mitotic divisions to form clones of cells. The last cell division produces type B spermatogonia, which then divide to form primary spermatocytes Slide 11  spermatocytes then enter a prolonged prophase (22 days) followed by rapid completion of meiosis I and formation of secondary spermatocytes. During the second meiotic division, these cells immediately begin to form haploid spermatids. Throughout this series of events, from the time type A cells leave the stem cell population to formation of spermatids, cytokinesis is incomplete, so that successive cell generations are joined by cytoplasmic bridges. Slide 12  Furthermore, spermatogonia and spermatids remain embedded in deep recesses of Sertoli cells throughout their development). In this manner, Sertoli cells support and protect the germ cells, participate in their nutrition, and assist in the release of mature spermatozoa. Spermatogenesis is regulated by LH production by the pituitary gland. LH binds to receptors on Leydig cells and stimulates testosterone production, which in turn binds to Sertoli cells to promote spermatogenesis. Follicle-stimulating hormone (FSH) is also essential because its binding to Sertoli cells stimulates testicular fluid production and synthesis of intracellular androgen receptor proteins. Slide 13  flagella Primary Spermatocyte 2N Secondary Spermatocyte 1N Spermatid 1N Sperm 1N Slide 14  Sperm morphogenesis (change of shape) Golgi complex nucleus mitochondrion Slide 15  Spermiogenesis The series of changes resulting in the transformation of spermatids into spermatozoa is spermiogenesis. These changes include (1) formation of the acrosome, which covers half of the nuclear surface and contains enzymes to assist in penetration of the egg and its surrounding layers during fertilization (2) condensation of the nucleus; (3) formation of neck, middle piece, and tail (4) shedding of most of the cytoplasm as residual bodies that are phagocytized by Sertoli cells. In humans, the time required for a spermatogonium to develop into a mature spermatozoon is approximately 74 days, and approximately 300 million sperm cells are produced daily. Slide 16  When fully formed, spermatozoa enter the lumen of seminiferous tubules. From there, they are pushed toward the epididymis by contractile elements in the wall of the seminiferous tubules. Although initially only slightly motile, spermatozoa obtain full motility in the epididymis. Slide 17 Spermatogenesis is regulated by LH production by the pituitary gland. LH binds to receptors on Leydig cells and stimulates testosterone production, which in turn binds to Sertoli cells to promote spermatogenesis. Follicle-stimulating hormone (FSH) is also essential because its binding to Sertoli cells stimulates testicular fluid production and synthesis of intracellular androgen receptor proteins. Slide 18 Slide 19  Acrosome Head with digestive enzymes nucleus Middle piece with mitochondria tail Slide 20 Mitochondria Slide 21 THANK YOU Slide 22