Sex

Question 1

Describe the stages in the human sexual response. (4)

Answer 1

Excitement phase - psychogenic or somatic stimuli.
Plateau phase - stimulus maintained
Orgasm phase - threshold released
Resolution phase - haemodynamic norms reaches (following refractory period in men but not women)

Question 2

Describe the excitement phase in a man. (2)

Answer 2

Parasympathetic responses to stimuli dominate via the pelvic nerve, and somatic from pudendal nerve result in erection.

Question 3

Describe how an erection is initiated. (7)

Answer 3

Parasympathetics stimulated by increased intracellular calcium act via M3 receptors to release NO. This causes smooth smuscle relaxation via cGMP. This makes sinusoids within the corpus cavernosum relax and arteries dilate. Venous dilation then occurs due to the increased blood flow against the tunica albuginea.

Question 4

Describe causes of erectile dysfunction. (5)

Answer 4

Inadequate psychological input
Vascular disorders like low bp
Anti-hypertensives
Penile trauma 
Neurological disorders

Question 5

Describe the treatments of erectile dysfunction. (3)

Answer 5

Treat the underlying cause.
Increase NO to increase vasodilation
Increase cGMP to increase the effects of NO.

Question 6

Describe how ejaculation occurs. (2)

Answer 6

Semen moves into prostatic urethra with smooth muscle contraction from prostate, vas Deferens and seminal vesicles caused by sympathetic stimulation.

Question 7

What sphincter must close during ejaculation and why? (2)

Answer 7

The internal urethral sphincter, to prevent retrograde ejaculation.

Question 8

Why is it important that the corpus spongiosum remains patent during an erection despite the increase in pressure in the penis? (1)

Answer 8

So the semen can actually escape.

Question 9

Describe the capacitation of sperm. (2)

Answer 9

Maturation of sperm within the female reproductive tract. Cell membrane and tail movement change.

Question 10

Explain why the acrosome reaction is needed. (3)

Answer 10

The acrosome is a coating on the oocyte containing enzymes that exists to allow the sperm to push through the corona radiata to bind to the zona pellucida. The acrosome reaction then digests the zona pellucida to prevent polyspermy.

Question 11

Which two reactions help to prevent polyspermy? (2)

Answer 11

Acrosome and cortical.

Question 12

Describe the fertile window. (2)

Answer 12

Sperm can survive for 72 hours, ovum for only 24, so sperm often need to be deposited before ovulation.

Question 13

Where does fertilisation normally occur? (1)

Answer 13

Ampulla of the Fallopian tubes.