Renal Assessment and Micturition

Question 1

Why is GFR a useful assessment in those with renal disease?

Answer 1

A decrease in GFR shows how much nephron is deteriorating

Question 2

Why is GFR useful in drug metabolism monitoring?

Answer 2

Many drugs are removed by excretion via filtration. If GFR falls, filtration decreases and drug concentration increases = toxicity

Dose may need to be adjusted

Question 3

What factors affect serum creatinine?

Answer 3

Muscle mass, dietary intake, drugs

Question 4

What is normal GFR?

Answer 4

100ml/min/1.73m2

Question 5

What is used to measure renal plasma flow?

Answer 5

Para-amino Hippuric Acid (PAH)

Question 6

Where is PAH diltered?

Answer 6

The glomerulus

Question 7

What is PAH a measure of?

Answer 7

All the plasma flowing through the kidneys at any given time

Question 8

How does urine flow through the kidneys?

Answer 8

Via peristaltic contraction of smooth muscle of ureter

Question 9

What kind of muscle is within the internal sphincter?

Answer 9

Smooth Muscle

Question 10

What kind of muscle is within the external sphincter?

Answer 10

Skeletal muscle

Question 11

What kind of problems arise from urethral obstructions?

Answer 11

Bilateral renal problems

Question 12

What kind of problems arise from ureter obstruction?

Answer 12

Unilateral renal problems

Question 13

What is the normal daily urine production volume?

Answer 13

750ml-2500ml

Question 14

How is the detrusor muscle inervated?

Answer 14

via pelvic nerves (s2-4)

Increase nerve activity, increase contraction of detrusor muscle, Increase pressure within the bladder

Question 15

What inhibits bladder contraction?

Answer 15

sympathetic supply by hypogastric nerves which closes the internal urethra sphincter

Question 16

What nerves innervate the external urethral sphincter?

Answer 16

Pudendal nerves of s2-s4

Question 17

How does the stretch reflector reflex affect micturition?

Answer 17

As bladder fills, there is an increase in afferent nerves to spinal cord via interneurones. Excitation of parasympathetic outflow occurs, there is inhibition of sympathetic outflow, there is inhibition of somatic motorneurones to external sphincter

the pathways to sensory cortex = sensation of fullness

Question 18

How does the local spinal reflex operate?

Answer 18

As bladder fills, stretch receptors are stimulated until their output becomes great enough to cause bladder contraction via

stimulation of parasympathetic nerves and relaxation of external sphincter (inhibition of somatic motorneurones)

Question 19

What is the volume of urine in an adult that initiates the spinal reflex?

Answer 19

300-350mls

Question 20

How is delay of the spinal reflex accomplished?

Answer 20

Accomplished via descending pathways in brain centres. They inhibit parasympathetic reflex, stimulate somatic nerves of external sphincter.

Question 21

How does voluntary initiation of the delay reflex occur?

Answer 21

Parasympathetic nerves are stimulated and somatic motor neurones are inhibited = summation with stretch reflex

Question 22

How does relaxation of the pelvic floor muscles aid in urination?

Answer 22

Causes a downward tug on the detrusor muscle to initiate contraction

Question 23

What muscles can prevent urine flow?

Answer 23

Perineal muscles and external sphincter

Question 24

How does the male urethra empty?

Answer 24

via contractions of the bulbocavernous muscles

Question 25

How does the female urethra empty/

Answer 25

Via gravity

Question 26

How do abnormalities of micturation arise?

Answer 26

Neural lesions

• Interruption of afferent nerves
• Interruption of both afferent and efferent nerves
• Interruption of facilitatory and inhibitory descending pathways from the brain