6. Sex And Fertilisation

Question 1

What is semen made up of?

Answer 1

Spermatozoa

Seminal plasma

Question 2

What is the function of seminal plasma?

Answer 2

Transport medium
Nutrition
Buffering capacity
Role for prostaglandins in stimulating muscular activity in female tract

Question 3

What is seminal plasma made up of?

Answer 3

Alkaline fluid, fructose, prostaglandins, clotting factors - seminal vesicles
Milky, slightly acidic fluid, proteolytic enzymes - prostate gland
Alkaline fluid, mucous - bulbourethral glands

Question 4

Where is the fertilisation site usually?

Answer 4

Ampulla of uterine tube

Question 5

What are the stimulants in male sexual response?

Answer 5

Psychogenic

Tactile - sensory afferent of penis and perineum

Question 6

What are the efferent in male sexual response?

Answer 6

Somatic and autonomic efferent
Pelvic nerve (PNS)
Pudendal nerve (somatic)

Question 7

What does erection require?

Answer 7

Sinusoidal relaxation
Arterial dilation
Venous compression

Question 8

What is the parasympathetic innervation of the penis?

Answer 8

Fibres - lumbar and sacral spinal levels
Pelvic nerve and pelvic plexus
Cavernous nerve to corpora and vasculature

Question 9

What is the neurophysiology of erection?

Answer 9

Inhibition of sympathetic arterial vasoconstrictor nerves
Activation of PNS
Activation of non-adrenergic, non-cholinergic, autonomic nerves to arteries, releasing nitric oxide

Question 10

What is the role of nitric oxide in an erection?

Answer 10

Post-ganglionic fibres release ACh
ACh binds to M3 receptor on endothelial cells
A rise in [Ca2+], activation of NOS and formation of NO
NO diffuses into vascular smooth muscle and causes relaxation (vasodilation)
NO also released directly from nerves

Question 11

What are the causes of erectile dysfunction?

Answer 11

Psychological (descending inhibition of spinal reflexes)
Tears in fibrous tissue of corpora cavernosa
Vascular (arterial and venous)
Drugs

Question 12

How does viagra work?

Answer 12

Slows rate at which cGMP degrades

Question 13

Describe the emission phase of male sexual response?

Answer 13

Under sympathetic control
Emission - movement of semen into prostatic urethra, contraction of SM in prostate, vas deferens and seminal vesicles
Ejaculation - expulsion of semen

Question 14

Describe the ejaculation phase

Answer 14

Contraction of glands and ducts (smooth muscle)
Bladder internal sphincter contracts - preventing retrograde ejaculation
Rhythmic striatal muscle contractions

Question 15

What muscles perform the rhythmic striatal muscle contractions?

Answer 15

Pelvic floor

Perineal muscles - ischiocavernosus, bulbospongiosus

Question 16

How does oestrogen on its own affect cervical mucus?

Answer 16

Thin, stretchy

Question 17

How does oestrogen and progesterone together change cervical mucus?

Answer 17

Thick, sticky, forms a plug

Question 18

What is capacitation?

Answer 18

Further maturation of sperm in female reproductive tract (6-8 hrs)
Sperm cell membrane changes to allow fusion with oocyte cell surface
Tail movement changes from beat to whip-like action
Now capable of undergoing acrosome reaction

Question 19

What is the acrosome?

Answer 19

Derived form Golgi region of developing spermatid
Contains enzymes
Cap like structure

Question 20

What happens in the acrosome reaction?

Answer 20

Sperm pushes through corona radiata
Binding of sperm surface receptor to ZP3 glycoprotein of zona pellucida
Triggers acrosome reaction
Digestion of zona pellucida

Question 21

What happens during the completion of meiosis II after fertilisation?

Answer 21

Series of calcium waves are activated following fusion of oocyte and sperm membranes
Resumption of meiosis II occurs
Pronuclei move together
Mitotic spindle forms leading to cleavage