Fertilisation

Question 1

What occurs in sperm capacitation?

Answer 1

Removal of adherent plasma proteins.
Re-organisation of plasma membrane lipids and proteins.
Increase in cyclic AMP, influx of extracellular calcium and decrease in intracellular pH.

Question 2

Why and where does sperm capacitation occur?

Answer 2

To make sperm more effect at fertilisation. Occurs in female reproduction tract.

Question 3

What is the acrosomal reaction?

Answer 3

Sperm fuses with membrane of zona pellucida and vesiculation occurs.

Huge modified lysosome packed with zone-digesting enzymes is released and destroys the membrane, allowing penetration.

Question 4

What occurs once the sperm and oocyte bind?

Answer 4

Cortical reaction - cortical granules released which contain several proteases.

Question 5

What is the fast block mechanism to prevent polyspermy? How long does it last and what else happens during this time?

Answer 5

First sperm binds, leading to an instantaneous change in sodium ion permeability.
This depolarises the membrane and prevents fusion of additional sperm cells.

This lasts for around 1 minute and during this time, a slow influx of calcium ions triggers the slow block mechanism.

Question 6

What is the slow block mechanism to prevent polyspermy?

Answer 6

Calcium influx causes cortical granules to release their proteases.

These proteases then cause the zona pellucida to harden, sperm receptors to be destroyed and any sperm still fused to the membrane to be released.

Question 7

What barriers must sperm overcome from ejaculation to fertilisation?

Answer 7

Acidity of vagina.
Thickness of mucus.
Phagocytic uterine leukocytes.
Distance from vagina to uterine tubes.

Question 8

Define infertility.

Answer 8

A disease of the reproductive system defined by failure to achieve a clinical pregnancy after 12 months or more of unprotected sexual intercourse.

Question 9

What is primary infertility?

Answer 9

Inability to ever bear a child (no previous birth).

Question 10

What is secondary infertility?

Answer 10

Inability to bear a child following a previous pregnancy or previous ability to carry a child to a live birth.

Question 11

List 6 reasons for female infertility.

Answer 11

PCOS - no ovulation due to FSH /LH balance and androgen production.

Anorexia or excess emotional stress.

Premature ovarian failure - autoimmune or trauma meaning ovaries lose eggs.

Hyperprolactinaemia - reduced oestrogen.

Turner’s - genetic XO.

Endometriosis - blockage of fallopian tubes.

Question 12

List 6 reasons for male infertility.

Answer 12

Sperm production problems

• Genetic
• Varicocele
• Cryptorchidism

Blockage of sperm transport
- Kartagener’s syndrome - cilia motility issue.

Sexual problems

• Retrograde or failure to ejaculate.
• Erectile dysfunction
• Spinal cord injury

Hormonal problems

• Pituitary tumour
• Anabolic steroid use

Sperm antibodies

Question 13

What is the criteria for someone under 40 to be eligible for IVF under the NHS?

Answer 13

• Reasonable expectation of birth.
• Non-smoking for at least 3 months prior and throughout treatment.
• Methadone free for at least one year prior.
• No alcohol.
• BMI 18.5-30.
• No voluntary sterilisation
• Couples must be co-haiting in a stable relationship for a minimum of 2 years.