Sex & Fertilisation

Question 1

How does the motility of sperm change in the epididymis?

Answer 1

At Entry: functionally immature and incapable of movement

At the tail: they are capable of movement and have the potential to fertilise

Question 2

What is the function of seminal plasma?

Answer 2

• Transport medium
• Nutrition
• Buffering capacity ready for entrance into female repro tract

Question 3

Which accessory vesicles contribute to seminal plasma and what does each secretion contain?

Answer 3

Seminal Vesicles : alkaline fluid, fructose, prostoglandins and clotting factors

Prostate Gland: milky and slightly acidic, proteolytic enzymes to breakdown clotting proteins

Bulbourethral glands (Cowper’s): alkaline fluid and mucus to lubricate penis

Question 4

Which site in the female reproductive tract does fertilisation normally occur?

Answer 4

Ampulla of the uterine tube

Question 5

What are the 4 phases of the Human Sexual Response?

Answer 5

1. Excitement
2. Plateu Phase
3. Orgasm Phase
4. Resolution Phase

Question 6

What are the 2 stimulants of erection?

Answer 6

1. Psychogenic
2. Tactile (touch)

Question 7

How do the stimulants of erection lead to penis erection?

Answer 7

• Psychostimulus and Tactile information sent to the brain by the spinal reflex
• Pelvic nerve (PNS) and Pudenal Nerve (somatic) signal to the penis causing haemodynamic changes

Question 8

What nerve routes make up the pudenal nerve?

Answer 8

S2-S4

Question 9

Describe the anatomical course of the pudenal nerve

Answer 9

• Branches S2, S3 and S4 form the pudenal nerve
• Leaves the pelvis through the greater sciatic foramen
• Passes under the sacrospinous ligament and re-enters the pelvis through the lesser sciatic foramen
• Passes through the pudenal canal where it gives off branches before continuing to the dorsal nerve or penis or clitoris

Question 10

What 3 haemodynamic changes are required for erection to occur?

Answer 10

1. Sinusoids in corpus cavernosum need to relax
2. Arterial dilation in the corpus cavernosum
3. Venous compression by the tunica albuginea
   
   • (stops blood leaving penis)

Question 11

What is the parasympathetic innervation of erection?

Answer 11

• Pelvic nerve and pelvic plexus
• Cavernous nerve to corpora and vasculature

Question 12

What is the most important neurotransmitter involved in erection? Explain how it is released?

Answer 12

Nitric Oxide (NO)

• Parasympathetic post glanglionic fibres release ACh which binds to M₃ receptors on endothelial cells
• Causes a rise in intracellular [Ca²⁺] which activates NO formation
• NO diffuses into vascular smooth muscle causing vasodilation, mediated by cGMP

Question 13

How does viagra treat erectile dysfunction?

Answer 13

Viagra slows the rate that cGMP is degraded, increasing NO

Question 14

What things can cause erectile dysfunction?

Answer 14

• Drugs (anti-hypertensives mainly)
• Neurological disorders affecting spinal reflex
• Tears in the fibrous tissue of corpus cavernosum
• Vascular problems (arterial and venous)

Question 15

Emission and Ejaculation is under what control?

Answer 15

Sympathetic Control

Question 16

What happens during emission in reproduction?

Answer 16

Semen moves to the prostatic urethra by mucular contractions of smooth muscle in the prostate, vas deferens and seminal vesicles

Question 17

What happens in ejaculation?

Answer 17

Expulsion of semen

Requires contraction of glands and smooth mucle

To prevent retrograde ejaculation the internal sphincter must contract

Question 18

How does cervical mucus change throughout the menstrual cycle under the influence of different hormones?

Answer 18

Pre-ovulation: Oestreogen is high , mucus is thin & stretchy to allow entry of male gametes

Post ovulation: Oestrogen & Progesterone forms a thick, sticky mucus plug to close of the repro tract from further sperm entry

Question 19

What happens in capacitation?

Answer 19

• Occurs 6-8 hours after depostion in reproductive tract
• Tail movement changes to whip like movement
• Undergoes acrosome reaction

Question 20

How long are spermatozoa and oocytes fertile for?

Answer 20

Spermatazoa: 48-72hr

Oocyte: 6-24hr (max)

Question 21

What is the acrosome reaction?

Answer 21

Essentially the loss of the outer membrane of sperm

Sperm pushes through corona radiata and is able to bind to the ZP3 glycoprotein of the zona pellucida

This triggers digestion of the zona pellucida

Question 22

What happens to prevent polyspermy?

Answer 22

Once sperm penetrates and fuses to oocyte plasma membrane, the cortical reaction is triggered

A calcium dependent reaction

Question 23

When does meiosis II complete in the oocyte?

Answer 23

Once oocyte fuses with spermatazoa

Membrane fusion triggers calcium waves which causes meiosis II to occur

Question 24

What is hatching?

Answer 24

Growing blastocyst hatches out of the zona pelliculada allowing growth and interaction with uterine wall

Question 25

In assisted reproductive technology, at what stage is the fertilised egg transferred to the uterus?

Answer 25

When the morula is formed

Question 26

What happens during implantation of the blastocyst?

Answer 26

The trophoblast (outer cells) interact with the endometrial lining and implants within the stroma of endometrium

Question 27

What is placenta previa?

Answer 27

Implantation of fertilised egg in the lower uterine lining to the placenta grows to cover the cervix

Question 28

What is ectopic implantation?

Answer 28

Where the fetilised egg implants at sites other to the endometrium lined uterine cavity