spermatogenesis bds
DESCRIPTION
TRANSCRIPT
testis
• Normal spermatogenesis can occur only if the testes are at a temperature lower than that of the abdominal cavity.
• When they are located in the scrotum, they are at a temperature about 3°C lower than the abdominal temperature.
epididymis
• The long length of the duct of the epididymis provides storage space for the spermatozoa and allows them to mature.
• A main function of the epididymis is the absorption of fluid.
• Another function may be the addition of substances to the seminal fluid to nourish the maturing sperm
Vas deferens
• conveys mature sperm from the epididymis to the ejaculatory duct and the urethra.
Seminal vesicle
• The function of the seminal vesicles is to produce a secretion that is added to the seminal fluid. The secretions nourish the spermatozoa.
• During ejaculation the seminal vesicles contract and expel their contents into the ejaculatory ducts, thus washing the spermatozoa out of the urethra.
Ejaculatory duct
• their function is to drain the seminal fluid into the prostatic urethra.
prostate
• The prostate produces a thin, milky fluid containing citric acid and acid phosphatase that is added to the seminal fluid at the time of ejaculation
• The prostatic secretion is alkaline and helps neutralize the acidity in the vagina.
Structure of testis
• Gametogenesis (gamete formation) is the process of formation and development of specialized generative cells, gametes.
• Gamete maturation is called spermatogenesis in males and oogenesis in females.
SPERMATOGENESIS
• Spermatogenesis is the sequence of events by which spermatogonia are transformed into mature sperms. This maturation process begins at puberty.
• Spermatogonia, which have been dormant in the seminiferous tubules of the testes since the fetal period, begin to increase in number at puberty.
• After several mitotic divisions, the spermatogonia grow and undergo changes.
• Sertoli cells lining the seminiferous tubules support and nurture the germ cells and may be involved in the regulation of spermatogenesis.
• Spermatogonia are transformed into primary spermatocytes, the largest germ cells in the seminiferous tubules.
• Each primary spermatocyte subsequently undergoes a reduction division-the first meiotic division-to form two haploid secondary spermatocytes, which are approximately half the size of primary spermatocytes.
• Subsequently, the secondary spermatocytes undergo a second meiotic division to form four haploid spermatids, which are approximately half the size of secondary spermatocytes.
spermiogenesis
• The spermatids are gradually transformed into four mature sperm by a process known as spermiogenesis
• The entire process of spermatogenesis, which includes spermiogenesis, takes approximately 2 months.
• When spermiogenesis is complete, the sperms enter the lumina of the seminiferous tubules.
• Sperms are transported passively from the seminiferous tubules to the epididymis, where they are stored and become functionally mature.
• The epididymis is the elongated coiled duct along the posterior border of the testis .
• It is continuous with the ductus deferens (vas deferens), which transports the sperms to the urethra.
• Mature sperms are free-swimming, actively motile cells consisting of a head and a tail .
• The head of the sperm forms most of the bulk of the sperm and contains the haploid nucleus.
• The anterior two thirds of the nucleus is covered by the acrosome, a caplike saccular organelle containing several enzymes.
• When released, these enzymes facilitate dispersion of the follicular cells of the corona radiata and sperm penetration of the zona pellucida during fertilization.
• The neck of the sperm is the junction between the head and tail.
• The tail of the sperm consists of three segments: middle piece, principal piece, and end piece
• The tail provides the motility of the sperm that assists its transport to the site of fertilization.
• The middle piece of the tail contains mitochondria, which provide the adenosine triphosphate necessary for activity.
Laboratory tests for male infertility
• Semen analysis – Gold standard test for infertility – Components of semen
• Spermatozoa derive from the seminiferous tubules.
• Coagulant derives from the seminal vesicles • Enzymes to liquefy semen derive from the
prostate gland.
– Components evaluated in a standard semen analysis • Volume
– Volume does not correlate with the number of sperm.
• Sperm count – Normal is 20 to 150 million sperm/mL.
• Sperm morphology – Morphology is very abnormal in reconnections of a vasectomy.
• Sperm motility
• Serum gonadotropins, testosterone, prolactin