Spermatogenesis Flashcards
Major functional components of the testes?
- Seminiferous Tubules - ~250m total length, has developing germ cells and sertoli cells.
- Interstitial Spaces - have leydig cells (synthesise androgens) and blood & lymph vessels.
- Compartments held by separate by blood-testis barrier which prevents immune response to spermatozoa and separates fluid of different composition.
3 stages of spermatogenesis
- Mitotic proliferation
- Meiotic divisions
- Cell modelling (spermiogenesis)
Spermiation
At the end of differentiation; cytoplasmic links are broken, spermatozoa released into tubule lumen, and sperm are virtually immobile.
Fluid secreted by Sertoli cells flushes spermatozoa from seminiferous tubules, through the Rete Testis into the Epididymis: Capacity for motility by the time they reach the tail of the epididymis, motility is suppressed by epididymal fluid and instead movement through reproductive tract is aided by peristaltic muscle contractions.
Spermiogenesis
Spermatocyte > Spermatid > Spermatozoon
About 200million/day (approx. 2300/second)
Spermatogenic Cycle
Stem Cell > Type A Spermatogonia > Intermediate Spermatogonia > Type B Spermatogonia > Resting Primary Spermatocyte > Stages of meiosis (leptotene, zygotone, pachytene, diplotene) > secondary spermatocyte (formed by first meiotic division) > spermatid (formed by second meiotic division) > Spermatozoon.
Average length of Spermatogenic Cycle?
~74 days from 1st mitotic division to release of spermatozoa.
Spermatogenesis - Rate of each developmental stage?
- Spermatogonium - Primary Spermatocyte - 25 days
- Meiotic Division 1 - Secondary Spermatocyte - 9 days
- Development - Spermatids - 19 days
- Differentiation - Spermatozoa - 21 days
Processes of Sperm Maturation
- Development of motility
- Nuclear maturation
- Water loss
- Acrosome changes shape
- Surface charge changes
- Permeability of membrane changes
- Cytoplasmic droplet is shed
- Cellular lipid reserves are depleted
- Sialic acid glycoprotein coat is gained
Changes made to the Spermatozoa in the Epididymis
- Concentration - 10-fold (10^8/ml entering > 10^9/ml leaving)
- Sperm modelling - nuclear condensation and acrosome shaping completed. Cytoplasmic droplet is shed.
- Metabolism - increased dependent on extracellular fructose for glycolytic energy, little oxidative metabolism, increase intracellular pH (due to Na+/H+ exchange).
- Motility - increased disulphide bridges between proteins in outer dense fibres of tail. increased concentration of cAMP in the tail. Acquires the capacity for forward movement.
- Membrane - composition changes.
Sub-fertility
- Human sperm quality is poor - only 4-14% show normal morphology under the microscope.
- If normal morphology drops below 4% fertilisation rates obtained with IVF are reduced.
- Infertility in men is primarily diagnosed by semen analysis comprising of: determination of sperm concentration/total count, motility, morphology.
Oligozoospermia
Reduced sperm count (<15million/ml)
Azoospermia
Absence of sperm in the ejaculate
Asthenozoospermia
Reduced sperm motility (<40% moving)
Teratozoospermia
Reduced percentage of sperm with normal morphology
Anti-sperm Antibodies
Abnormal immune response to sperm