PBL 2- Male reproductive system and ART Flashcards
How long does it take for spermatogenesis to occur
Takes 65-75 days
What are the types of spermatogonia
Type Dark A- reserve spermatogonia
Type Pale A- undergoes mitosis to give Type B spermatogonia
Type B- Divides by mitosis to give primary spermatocytes
Do spermatogonia contain haploid or diploid number of chromosomes
Diploid number of chromosomes
Describe how type dark A spermatogonia are ‘reserve spermatogonia’
they remain near the basement membrane of seminiferous tubules as precursor stem cells for future cell division and subsequent sperm production
describe how Type pale A becomes type B and then primary spermatocytes
Type pale A spermatogonia lose their contact with the basement membrane and squeeze through the tight junction of the blood-testis barrier and differentiate into Type B and then they differentiate into Primary spermatocytes
what happens to primary spermatocytes
They undergo DNA replication and Meiosis I begins which produces Secondary Spermatocytes
What happens to secondary spermatocytes
Enters meiosis II and produces FOUR spermatids
Are spermatids haploid or diploid
they are haploid
What process occurs after 4 spermatids are made
Spermiogenesis
Describe spermiogenesis
No cell division occurs here
Each spermatid becomes a sperm
describe the structural changes a spermatid goes through to become a sperm
- Spherical spermatids transform into elongated, slender sperm
- An acrosome forms atop the nucleus
- tail forms for motility + mitochondira multiply
- sertoli cells phagocytose excess cytoplasm
- midpiece forms- area between head and tail
What is the definition of spermatogenesis
Process by which immature stem cells (spermatogonia) proliferate and differentiate into mature sperm
where does spermatogenesis takes place
Takes place in the seminiferous tubules
how long do men make sperm for
Production from puberty until death
Describe the hormonal regulation of spermatogenesis
All controlled by the brain
At puberty, hypothalamus causes the release of GnRH which acts on the anterior pituitary gland to release LH and FSH
What is the purpose of FSH and LH in spermatogenesis
FSH enters the testes and stimulates sertoli cells to begin spermatogenesis using negative feedback
LH enters the testes and stimulates leydig cells to release testosterone into the testes and blood
–> Testosterone stimulates spermatogenesis
What effect does testosterone and FSH have on sertoli cells
FSH and testosterone stimulate sertoli cells to support the developing germ cells.
What happens once spermatogenesis reaches sufficient levels
sertoli cells produce inhibin, inhibin acts on the anterior pituitary:
- Limits FSH production
- Decreases spermatogenesis
describe how testosterone has an inhibitory effect on GnRH once spermatogenesis reaches sufficient levels
Testosterone inhibits the secretion of GnRH by the hypothalamus
decreased FSH and LH secretion
decreased spermatogenesis
Where does fertilisation take place
occurs in the ampulla of the uterine tubes
what is the 1st step in fertilisation and describe it
Penetration of Corona Radiata:
Acrosome membrane begins to perforate, releasing the enzyme hyaluronidase- this disrupts the cell matrix and enables sperm to push through the remaining granulosa cells.
What is the 2nd step in fertilisation and describe it
Penetration of Zona Pellucida
Receptors on acrosome bind to ZP3 molecules causing the release of acrosin- enzyme that digests glycoprotein chains of the zona pellucida. This allows the sperm to push through the weakened structure
What is the 3rd step in fertilisation and describe it
Fusion of the plasma membranes:
Membranes of the sperm + oocyte bind via integrin receptors and fuse. sperm nucleus enters oocyte cytoplasm (leaving tail, membrane and mitochondria behind)
what occurs after fusion of the plasma membranes (step 4 and 5)
Capacitation- Fast block and Slow block
