spermatogenesis Flashcards
Describe testes
Produce sperm and store it.
Produce hormones which regulate spermatogenesis.
Lie in scrotum outside body cavity….optimum temperature for sperm production 1.5-2.5oC below body. Overheating of testes reduces sperm count.
Well-vascularised, well-innervated.
Normal volume of testes approximately 15-25ml.
measured by orchidometer…
Describe testes
Produce sperm and store it.
Produce hormones which regulate spermatogenesis.
Lie in scrotum outside body cavity….optimum temperature for sperm production 1.5-2.5oC below body. Overheating of testes reduces sperm count.
Well-vascularised, well-innervated.
Normal volume of testes approximately 15-25ml.
measured by orchidometer…
Cell division to create sperm
Germinal diploid cell
becomes primary spermatocyte
undergoes meiosis 1 to become secondary spermatocytes
undergoes meiosis 2 to become spermatids which are haploid
develop into spermatozoa
Describe tight junctions
Exist between Sertoli cells forming blood-testis barrier.
Open to allow passage of spermatogonia prior to completion of meiosis.
Divides into basal and adluminal compartments.
Protects the spermatogonia from immune attack.
Allows specific enclosed environment for spermatogenesis which is filled with secretions from Sertoli cells.
Stages of spermatogenesis
Spermatogonia- Germ cell on basement membrane, capable of mitotic or meiotic division to produce primary spermatocytes or more spermatogonia by mitosis. They are diploid.
Primary spermatocyte- Cell committed to differentiative pathway, primary spematocyctes are 46XY diploid. They move into the adluminal compartment and duplicate their DNA to produce sister chromatids which exchange genetic material and enter meiosis I.
Secondary spermatocyte-Secondary spermatocyctes have undergone meiosis I to give 23X + 23Y haploid number of chromosomes arranged as sister chromatids.
Spermatid-Meiosis II occurs to give 4 haploid spermatids. Round spermatid to elongated spermatid differentiation.
Spermatozoa- Mature sperm extruded into the lumen.
Stages of spermatogenesis
Spermatogonia- Germ cell on basement membrane, capable of mitotic or meiotic division to produce primary spermatocytes or more spermatogonia by mitosis. They are diploid.
Primary spermatocyte- Cell committed to differentiative pathway, primary spematocyctes are 46XY diploid. They move into the adluminal compartment and duplicate their DNA to produce sister chromatids which exchange genetic material and enter meiosis I.
Secondary spermatocyte-Secondary spermatocyctes have undergone meiosis I to give 23X + 23Y haploid number of chromosomes arranged as sister chromatids.
Spermatid-Meiosis II occurs to give 4 haploid spermatids. Round spermatid to elongated spermatid differentiation.
Spermatozoa- Mature sperm extruded into the lumen.
ew cycle every 16 days, entire process takes approximately 74 days.
- Mitotic proliferation of spermatogonia.
- Meiosis and development of spermatocytes.
- Spermiogenesis, elongation, loss of cytoplasm, movement of cellular contents.
Movement into lumen controlled by Sertoli cell secretions. Factors produced by sertoli cells are required for development.
Describe androgen production in the testis
Leydig cells contain LH receptors and primarily convert cholesterol into androgens. Intra-testicular testosterone levels are 100x those in plasma.
Androgens cross over to and stimulate Sertoli cell function and thereby control spermatogenesis.
Sertoli cells contain FSH receptors and convert androgens to oestrogen.
FSH establishes a quantitatively normal Sertoli cell population, whereas androgen initiates and maintains sperm production.
Inhibin production in the testis
Inhibin B is produced primarily by Sertoli cells in response to FSH
Inhibin B reduces FSH production by the anterior pituitary.
Germ cells appear to be required for Inhibin B production.
FSH and Inhibin B in combination have been correlated with testicular volume and spermatogenic activity but this hasn’t proved clinically useful as yet.
Semen analysis remains the gold standard.
Describe ejaculation and seminal components
300 million sperm produced per day on average.
3,500 per second so 9 million during this lecture
approximately 120 million in average ejaculate
Normal ejaculate volume is 1.5ml - 6ml.
Spermatozoa account for 1-5% of an ejaculate
Initial portion of the ejaculate is most sperm rich.
99.9% lost before reaching ampulla of the uterine tube
around 120,000 sperm get near to egg, only one enters
Seminal fluid consists of secretions from:
seminal vesicles, prostate, bulbo-urethral gland combined with epididymal fluid
Role of seminal fluid
Transport of sperm through the male reproductive tract.
Coagulation of the ejaculate and creating a sperm deposit in the vagina.
Creation of a neutral to slightly alkaline buffered milieu in the vagina to protect spermatozoa from the acidic vaginal milieu.
Activation and augmenting the motility of the sperm cells.
Coating the sperm cells with capacitation inhibitors.
Supplying nutrients for the sperm cells.
Testicular structure
Testis is 90% seminiferous tubules, site of spermatogenesis.
600m of seminiferous tubule in each testis. Tubules are tightly coiled.
Tubules lead to an area on one side called rete.
Rete leads to epididymis and vas deferens.
Outer layer is tunica albuginea and outermost is tunica vaginalis
Cell division to produce sperm
Meiosis I
Homologous chromosomes group together in pairs.
Homologous chromosomes exchange genetic material…
which gives rise to new chromosomes containing a mixture of maternal and paternal genes.
At the end of meiosis I sister chromatids remain attached and may differ from one another if crossing-over occurred.
Cell division occurs creating two haploid daughter cells, but each chromosome is two sister chromatids; and these are no longer identical due to crossing-over.
Meiosis II
Sister chromatids separate as cell divides giving haploid gametes.
