Fertilization

Question 1

Stages of sperm maturation in male reproductive tract

Answer 1

• Sperm are made in testes and stored in epididymis for maturation
• In epididymis sperm acquire capacity to move (requires androgen) and a glycoprotein coat to prevent premature activation of motility
• 65-70% of seminal fluid from seminal vesicles, 25-30% from prostate

Question 2

Stages of sperm maturation in female reproductive tract 1

Answer 2

• After ovulation (day 14) the oocyte is viable for 1 day
• The optimal time for intercourse would be btwn days 11-15 of the cycle
• Sperm are stored in isthmus of fallopian tubes and cervical glands (can be there for many days)
• Capacitation (sperm maturation in female): hyper activation of tail and acrosome reaction
• Sperm do not reach egg from swimming but from fluid flow, tail activity used to penetrate egg’s thick glycoprotein coat
• Hyperactivation occurs after UTJ (hyper activated sperm cannot pass thru UTJ), and requires Ca

Question 3

Stages of sperm maturation in female reproductive tract 2

Answer 3

• For sperm to penetrate zona pellucida it must undergo acrosome reaction
• In this reaction there is partial breakdown of the sperm head, releasing hydrolytic nzs that will break down the zona pellucida
• This process also exposes the IAM (interacrosomal membrane) on the sperm head, allowing the sperm to fuse w/ the oocyte
• Capacitation is essential for sperm to be able to fertilize the egg (also makes sperm more responsive to Ca), happens 4-8 hrs after intercourse

Question 4

Neural and vascular control of erection, emission, and ejaculation

Answer 4

• Erection is mediated by PsNS, ejaculation is mediated by SNS
• The neurons controlling erection are NO-producing (lead to vasodilation via activation of cGMP within blood vessels of corpus cavernosum)
• Emission is controlled by a-adrenergic neurons
• Ejaculation occurs via contraction of vas deferens and other muscles

Question 5

Changes in egg in sperm during fertilization

Answer 5

• First the oocyte must make sure polyspermy doesn’t occur by releasing cortical granules to change the zona pellucida to make it impermeable to more sperm
• At the same time the oocytes completes meiosis (second division), and creates another polar body, in preparation for syngamy
• The sperm decondenses in preparation for syngamy
• The oocyte and sperm both individually form a pro-nucleus and then they fuse (syngamy) to make a zygote
• First cleavage happens 12 hrs after syngamy