Urinary: Micturation

Question 1

When is the bladder absolutely full? At what volume can urine be felt in the bladder?

Answer 1

Bladder absolutely full at 500ml

Feel urine in baldder at ~150ml

Question 2

What is the trigone?

Answer 2

A smooth triangle made up of the 2 ureteric orifices and the internal urethral orifice

Question 3

What are the layers of the detrusor muscle?

Answer 3

Inner longitudinal
Middle circular
Outer longitudina
This arrangement gives the bladder strength in all direction

Question 4

What is the role of the internal urethral sphincter?

Answer 4

It is the primary muscle of continence

In men it prevents seminal regurgitation back during ejaculation

Question 5

What is the role of the external urethral sphincter?

Answer 5

Under somatic voluntary control - acts to constrict urethra to hold in urine

Question 6

What is the innervation of the detrusor muscle?

Answer 6

Parasympathetic: supplied by the pelvic nerve (S234)
Ach acts via M3 receptors to cause contraction
Sympathetic: supplied by the hypogastric nerve (T10-L2) NA acts via B3 receptors to cause relaxation

Question 7

What is the innervation of the internal urethral sphincter?

Answer 7

Sympathetic: supplied by the hypogastric nerve (T10-L2) NA acts via A1 receptors to cause contraction

Question 8

What is the innervation of the external urethral sphincter?

Answer 8

Somatic: supplied by the pudendal nerve (S234)

Ach acts via a nicotinic receptors to cause contraction

Question 9

Describe the normal voiding reflex

Answer 9

The brain micturation centre signals to the parasympathetic neurones to cause the detrusor to contract (via the pelvic nerve)
The ceerbral cortex then makes the conscious decision to urinate and removes somatic stimulation to the external urethral sphincter so it relaxes.

Question 10

Describe the storage of urine in the bladder

Answer 10

When the bladder fills the intravesicular pressure hardly changes due to distension of the bladder folds.
At around 400mls the afferent nerves of the bladder wall start to signal to the brain L centre.
The cerebral cortex makes the conscious decision not to urinate and increases somatic stimulation to the external urethral sphincter to cause it to contract.

Question 11

What is the blood supply of the bladder?

Answer 11

Receives vasculature from the internal iliac vessels