Urophysiology introduction

Question 1

At what level do the kidneys lie?

Answer 1

T12-L3 - protected by ribs 11+12

Question 2

Which kidney lies slightly lower? Why?

Answer 2

Right kidney due to the presence of the liver

Question 3

Blood supply to the kidneys?

Answer 3

Renal artery from the aorta at level L1

Question 4

How many nephrons does each kidney contain

Answer 4

1 million

Question 5

What gland rests on top of each kidney?

Answer 5

Adrenal glands

Question 6

How long are the ureters?

Answer 6

25-30cm long

Question 7

How is reflux of urine back into the ureters prevented?

Answer 7

Ureters enter the bladder at an angle and there is a valvular mechanism at the vesicoureteric junction to prevent backflow

Question 8

What is the internal sphincter of the bladder?

Answer 8

Involuntary muscle which keeps the bladder closed when the bladder is empty

Question 9

What is the external sphincter of the bladder?

Answer 9

Located on the floor of the pelvis and is under voluntary control to stop urination voluntarily.

Question 10

Why are women more prone to incontinence?

Answer 10

Weaker external sphincter

Question 11

Where does the parasympathetic innervation to the bladder come from?
What effect does it have on the detrusor muscle and sphincter?

Answer 11

Pelvic nerve (s2-s4)
Detrusor muscle contracts and smooth muscle sphincter relaxes to urinate.

Question 12

Where does sympathetic innervation to the bladder. come from? What effect does it have on the detrusor and sphincters?

Answer 12

Hypogastric nerve (T11-L2)
Causes smooth muscle sphincter contraction and detrusor relaxation.

Question 13

What is onuf’s nucleus involved in?

Answer 13

The guarding reflex

Question 14

Describe the steps in micturition

Answer 14

1. Specialised nerves in the bladder wall sense that the bladder is about half full & sends impulses to the spinal cord at levels S2 and S3, known as the micturition center, and the pons of the brain.
2. The spinal cord response is part of the micturition reflex and causes an increase in parasympathetic stimulation and a decrease in sympathetic stimulation which makes the detrusor muscle contract and the internal sphincter relax.
3. It also decreases motor nerve stimulation to the external sphincter allowing it to relax as well.
4. At this point, urination would occur. The pons is the region that we train to voluntarily control urination.
5. If we want to delay urination, the pons overrides the micturition reflex
   
   • The sympathetic nervous system communicates with the bladder via the hypogastric nerve(T12 – L2). It causes relaxation of the detrusor muscle. These functions promote urine retention.
6. When we want to urinate, the pons allows for the micturition reflex to happen.
   
   • The parasympathetic nervous system communicates with the bladder via the pelvic nerve (S2-S4). Increased signals from this nerve causes contraction of the detrusor muscle. This stimulates micturition.

Question 15

If parasympathetic innervation is inhibited and sympathetic innervation is stimulated, will a person urinate or retain urine?

Answer 15

Retain urine - detrusor relaxation.