Spermatogenesis Flashcards
Male Reproductive anatomy - sperm production POV (7)
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1) produced in Testis
2) stored in Epididymis
3) During ejac: contractions in epidid + vas deferens = propel out sperm from vas deferens
4) sperm mixes w/ epidermal fluid
5) sperm in seminal vesicle - sec. from here are added to the mixture
6) makes way to ejac. duct - sec. from prostate + calpas? gland are added
7) ejaculated - using the corpus spongiosum’s flexibility - keeping urethra open
Testes (7)
- Produce sperm + store it.
- Produce hormones (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
Testicular structure (4)
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Tubules lead to an area on one side called rete.
Rete leads to epididymis and vas deferens.
Testis is 90% seminiferous tubules, site of spermatogenesis.
600m of seminiferous tubule in each testis. Tubules are tightly coiled. (the shard=306m)
Seminiferous Epithelium: (4)
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1) brown layer = basal lamina
2) germ cells- undergoing somatic genesis going towards lumen in each stage
3) b/w each cluster of germ cells = sertoli cells ( respond to T and regulate spermatogenesis + provides sustenance for spermatogenic cells)
4) opening that the fluid comes out of
How does regulation of Spermatogenesis take place?
Seminiferous epithelium- zoomed in - sertoli cells junctions (4)
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-Tight Junctions exist between Sertoli cells forming seal around each of the germ cells = blood-testis barrier.
=Protects spermatogonia from immune attack.
-Open = allows passage of spermatogonia prior to completion of meiosis
-Allows specific enclosed environment (filled with secretions from Sertoli cells i.e. T) for spermatogenesis
- Divides into basal and adluminal compartments
Stages of spermatogenesis (named) - (5)
1)spermatogonia ( a -> b)
2)primary spermatocyte
3)secondary spermatocyte
4)spermatids
5)spermatozoa
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Spermatogonia (5)
Germ cell on basement membrane, capable of mitotic or meiotic division to produce primary spermatocytes or more spermatogonia by mitosis.
-They are diploid.
-2 types - Type Ad (dark) and Type Ap (pale)
- Type Ad: either gives rise to copy of itself or diff. into Type Ap
-Type Ap only gives rise to b spermatogonia (committed to spermatogenesis)
Primary spermatocyte (3)
- B spermatogonia differs. into 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 spermatocytes
Secondary spermatocyctes have undergone meiosis I to give 23X + 23Y haploid number of chromosomes arranged as sister chromatids. (2 haploids formed)
Spermatids (2)
-Meiosis II occurs (using sister chromatids) to give 4 haploid spermatids.
-Round spermatid to elongated spermatid differentiation.
Spermatozoa (2)
-Differs. confers maturity to these 4 haploid cells (removing extra cytoplasm, formation of acrosome + tail)
SPERMEOGENESIS
-mature sperm extruded into the lumen.
Spermatogenesis facts (7)
-New 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.
HPG and spermatogenesis - hormonal control men vs women
(2)
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females = cyclical (-ve and +ve feedback)
males = constant (always -ve)
Androgen production in the testis (LH and FSH): (8)
1) LH acts on Leydig cells (containing LHr)
2) primarily convert cholesterol into androgens.
3) T makes its way into sertoli: to regulate spermatogenesis
1) FSH acts directly on sertoli cells (containing FSHr) -reg.s sertoli pop., sustenance role + triggers prod. of Androgen binding protein (ABP)
2) ABP binds to T = conc’s T in seminiferous epithelium to aid reg of spermato.
-Intra-testicular testosterone levels are 100x those in plasma.
-Androgens cross over to and stimulate Sertoli cell function and thereby control spermatogenesis.
-FSH establishes a quantitatively normal Sertoli cell population, whereas androgen initiates and maintains sperm production.
Inhibin production in the testis (4)
1) InhibinB is produced primarily by Sertoli cells in response to FSH
2) 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.
