Week 1: Sperm transport and fertilization

Question 1

Sperm transport in male reproductive tract

Answer 1

1. maturation:
   - spermatozoa made in seminiferous tubules of testes and move to epididymis
   - in epididymis, spermatozoa acquire capacity for movement and a membrane coat to prevent premature activation of motility
2. seminal fluid
   - formed by secretion of accessory sex glands: ampullarf glands, seminal vesicles (60%), prostate (30%), bulbourethral glands, urethral glands
   - ~40 mil sperm/mL semen
3. Erection and Ejaculation
   - erection: parasymp., ejac: symp

Question 2

Sperm transport in female tract

Answer 2

1. Cervix
   - barrier and site of storage in cervical crypts
   - most penetrable to sperm mid cycle 11-15 days
2. Uterus
   - not major barrier to sperm, suspended in uterine fluid
3. Oviduct
   - utero-tubal junction is major barrier to sperm, prevents passage of defective or non motile sperm
   - sperm stored in isthmus
   - ampulla is where fertilization occurs mostly
   - after ovulation (day 14), oocyte viable for only 24 hrs.

Question 3

Sperm maturation in female tract

Answer 3

1. Capacitation
   - 4-8 hrs after being in female tract
   - destablization of plasma membrane of sperm head-removal or alteration of protective coat
2. hyper activated motility
   - must occur after UTJ
3. Acrosome reaction
   - acrosome surrounding head of sperm contains hyaluronidase and across, which aid in penetration of zone pellucida and fusion with egg plasma membrane
   - receptors on sperm surface bind to zona pellucida protein (ZP3)
   - acrosome reaction takes ~3mins, after run, ZP2 on ovum binds to zone receptors on sperm plasma membrane for fusion

Question 4

Fertilization: fusion and polyspermy block

Answer 4

1. Zona penetration
   - combo of sperm motility and acrosome reaction
2. sperm egg fusion
   - sperms equatorial segment fuses first
   - not species specific
3. Polyspermy block
   - to prevent fusion with more than 1 sperm
   - 1 min after fusion, oolemma block, but not sufficient
   - release of cortical granules made by golgi under egg plasma membrane (oolemma), causes changes in zone pellucida to prevent polyspermy. Occurs 2-7mins after fusion

Question 5

Fertilization: pronuclei and syngamy

Answer 5

1. Pronuclei formation
   - sperm: breakdown of nuclear envelop, nuclear decondensation, and formation of pronucleus with nuclear envelop from oocyte
   - egg: germinal vesicle breakdown, completion of meiosis, pronuclear formation
2. Syngamy: joining of egg and sperm pronuclei
   - pronuclear membranes interdigitate and breakdown
   - zygote is formed