PHYSIOLOGY - Micturition

Question 1

How do the bladder and urethra prevent urine from escaping while it is filling?

Answer 1

The internal urethral sphincter is passively stretched closed by the elastic tissue in the neck of the bladder as the bladder fills. Voluntary contraction of the urethralis muscle of the external urethral sphincter also prevents urine from escaping

Question 2

List the four adrenoreceptors and whether they have an inhibitory or stimulatory action?

Answer 2

α1: stimulatory
α2: inhibitory
β1: stimulatory
β2: inhibitory

Question 3

What do all nicotinic receptors do?

Answer 3

All nicotinic receptors are stimulatory and increase permeability to Na+ and K+

Question 4

List the five muscarinic receptors and whether they have an inhibitory or stimulatory action?

Answer 4

M1: stimulatory
M2: inhibitory
M3: stimulatory
M4: inhibitory
M5: stimulatory

Question 5

Describe the process of urine storage

Answer 5

The sympathetic nervous system stimulates the hypogastric nerves to innervate the β2 receptors to relax the detrusor muscle and the α1 receptors to occlude the internal urethral sphincter. Furthermore, sympathetic activity inhibits the pelvic nerve from triggering contractions of the detrusor muscle

Question 6

Describe the process of micturition

Answer 6

The parasympathetic nervous system stimulates the pelvic nerve which innervates M3 receptors to stimulate contraction of the detrusor muscle and M2 receptors to relax the internal urethral sphincter, allowing for voiding of the urine from the bladder. Furthermore, parasympathetic activity inhibits the hypogastric nerves from triggering relaxation of the detrusor muscle

Question 7

How often do bitches develop spay incontinence?

Answer 7

80% of bitches develop spay incontinence within their lifetime

Question 8

List two causes of urinary incontinence

Answer 8

Hypercontractile detrusor
Hypocontractile sphincter/urethra

Question 9

List two causes of urinary retention

Answer 9

Hypocontractile detrusor
Hypercontractile sphincter/urethra

Question 10

Which drug can be used to treat urinary incontinence caused by a hypercontractile detrusor?

Answer 10

Atropine

Question 11

Which drugs can be used to treat urinary incontinence caused by a hypocontractile sphincter/urethra?

Answer 11

Phenylpropanolamine
Ephedrine

Question 12

What are some of the side effects of Phenylpropanolamine and Ephedrine due to being non-specific adrenergic agonists?

Answer 12

Hypertension
Restlessness
Increases intra-ocular pressure

Question 13

Which drug can be used to treat urinary retention caused by a hypocontractile detrusor?

Answer 13

Bethanechol

Question 14

What are some of the side effects of Bethanechol due to being a non-specific muscarinic agonist?

Answer 14

Gastrointestinal stimulation
Hypersalvation

Question 15

Which drugs can be used to treat urinary retention caused by a hypercontractile sphincter/urethra?

Answer 15

Phenoxybenzamine
Prozosin
Terazosin

Question 16

What are some of the side effects of Phenoxybenzamine due to being a non-specific adrenergic antagonist?

Answer 16

Hypotension
Tachycardia
Increased intra-ocular pressure

Question 17

Why do Prozosin and Terasozin have less side effects than Phenoxybenzamine when used to treat urinary retention caused by a hypercontractile sphincter/urethra?

Answer 17

Prozosin and Terasozin are selective alpha 1 antagonists so only target the alpha 1 receptors which are causing the hypercontractility