Penis erection

Question 1

Which nerve stimulations cause an erection?

Answer 1

Parasympathetic stimulation and sympathetic inhibition to produce vasodilation of penile arteries.

Question 2

8 steps of maintaining an erection

Answer 2

1. Parasympathetic nerve fibres in cavernosa spaces release acetylcholine (in response to nerve impulse
2. This binds to muscarinic receptors on epithelial cells which activates nitric oxide synthase
3. Nitric oxide synthase converts Arginine into Nitric oxide and Citrulline
4. The NO diffuses into nearby smooth muscle cells and activates guanylate cyclase
5. Guanylate cyclase converts GTP to cGMP
6. cGMP causes calcium release from smooth muscle cells which leads to fall in intracellular calcium causing smooth muscle cells to relax.
7. As smooth muscle cells of corpora cavernosa relax the cavernosa spaces expand and fill with blood which passively compress the veins (trapping the blood inside the corpora)
8. The erectile tissue becomes engorged resulting in the stiffening of penis

Question 3

How is an erection lost?

Answer 3

cGMP is converted to GMP via PDE-5 which restores intracellular calcium levels in smooth muscle (this stops smooth muscle relaxation)

Question 4

Describe emission

Answer 4

Movement of sperm from distal epididymis through the vas deferent and into the ejaculatory duct

Question 5

Which sphincter prevents retrograde flow of sperm?

Answer 5

Internal urethral sphincter

Question 6

What is retrograde ejaculation?

Answer 6

When internal urethral sphincter doesn’t contract properly so sperm travels into bladder

Question 7

What role do the accessory glands play in ejaculation?

Answer 7

As the sperm travels through the ejaculatory duct and urethra it is combined with secretions from the accessory glands to make semen

Question 8

Define anejaculation

Answer 8

Inability to ejaculate

Question 9

Define aspermia

Answer 9

Failure to produce semen or abscence of sperm in semen

Question 10

Define priapism

Answer 10

A persistent erection lasting >4hrs with risk of causing ischaemic injury.

Question 11

Define erectile dysfunction

Answer 11

Persistent inability to initiate or sustain a penile erection

Question 12

Describe how atherosclerosis cause ED

Answer 12

Build up of atheromatous plaques harden the arteries supplying the penis, making it harder for them to dilate.

Question 13

Describe how hypertension causes ED

Answer 13

Hypertension damages endothelial cells, causing a decrease in their ability to produce nitric oxide.

Question 14

Describe how Diabetes causes ED

Answer 14

The hyperglycaemic state seen in DM causes deposition of hyaline deposits in arteriale walls, making it harder for them to dilate. These hyaline deposits also build up in capillaries, increasing the diffusion distance of O2 to enter tissues. Eventually this leads to hypoxia and death of smooth muscle cells and parasympathetic fibres. Damaged para fibres are unable to release acetylcholine to there is a reduced amount of NO produced.

Question 15

First-line medical treatment for ED

Answer 15

PDE-5 enzyme inhibitors. lead to increased levels of cGMP

Question 16

Side effects and Contraindications of PDE-5 enzyme inhibitors

Answer 16

Headache, facial flushing, impaired colour vision.

Contraindicated by nitrate medication due to risk of hypotension.

Question 17

Second line medical treatment for ED

Answer 17

Prostaglandin E1 intracavernosal injections