renal assessment and micturition

Question 1

How is renal function assessed

Answer 1

eGFR

Question 2

What is GFR

Answer 2

Sum of all filtration by all functioning nephrons so the progression of renal disease would show a decreased GFR

Question 3

Why do you need to be careful when prescribing drugs and antibiotics to people with renal disease

Answer 3

The drugs are excreted via filtration and when the GFR falls, so does the excretion of the drug so the drug concentration in the plasma may rise which would cause toxicity

Question 4

How is eGFR measured

Answer 4

Plasma clearance test (not how much is found in the urine) - give a dosage of inulin and give it time to spread within the plasma and equiblirate and then over time period sample simultaneously urine and plasma and then do the equation to find eGFR

Creatinine clearance is routinely used as well

Question 5

Why is inulin used in plasma clearance test for measuring eGFR

Answer 5

100% is excreted - 0% reabsorption and it is not secreted either

Question 6

What substances have highest clearance

Answer 6

Substances which are secreted because their plasma concentration will decrease while their quantity in urine will increase

Question 7

What is the normal GFR

Answer 7

125mls/min

Question 8

Does GFR decline with age

Answer 8

It declines 1ml/min/year after 30

Question 9

What factors affect serum creatinine

Answer 9

Muscle mass
Diet - creatine supplements and meat intake
Drugs - some can lead to increases and so can ketoacidosis

Question 10

What is the clearance of glucose

Answer 10

0 due to it being fully reabsorbed

Question 11

What is the clearance of urea

Answer 11

50% since it is only 50% reabsorbed

Question 12

What is para-amino-hippuric acid (PAH) and what is it used to measure

Answer 12

It is an organic anion which is used to measure real plasma flow (RPF)

Question 13

Why is PAH used to measure renal blood flow

Answer 13

It is freely filtered at the glomerulus and the PAH which isn’t filtered and is in the plasma, gets secreted into the tubule so the clearance is high at 90% in one transit of the kidney

Question 14

What is normal renal plasma flow

Answer 14

660mls/min

Question 15

What is the clearance of penicillin

Answer 15

Very high due to it being secreted from the plasma into the tubule as well

Question 16

What causes urine to flow from the kidney to the ureters and then to the bladder

Answer 16

Peristaltic contraction of the smooth muscle of the ureters

Question 17

Why do ureters enter the bladder at an oblique angle

Answer 17

prevents reflux of urine

Question 18

What is the detrusor muscle

Answer 18

smooth muscle of the bladder which is arranged in spiral, longitudinal and circular bundles

Question 19

What is responsible for the emptying of the bladder during micturition

Answer 19

The detrusor muscle contracting

Question 20

What is the internal urethral sphincter

Answer 20

The smooth muscle at the bladder neck at the start of the urethra where it acts as sphincter when relaxed

Question 21

What is the external urethral sphincter

Answer 21

True sphincter made up of skeletal muscle which is under voluntary control

Question 22

Describe the anatomical position of the bladder

Answer 22

Lies in the midline posterior to the pubic bone
It is anterior to the reproductive system and the rectum
It is superior to the urethra and prostate

Question 23

What epithelium lines the bladder

Answer 23

Transitional epithelium (uroepithelium)

Question 24

does a urethral obstruction cause a bilateral problem or unilateral

Answer 24

bilateral

Question 25

does a ureteric obstruction cause a bilateral problem or unilateral

Answer 25

Unilateral

Question 26

What is the normal range of urine production in a day

Answer 26

750-2500mls

Question 27

At what volume in the bladder is there an increased urgency to urinate

Answer 27

400-500mls

Question 28

What controls micturition (motor innervation specifically)

Answer 28

Parasympathetic supply from the pelvic nerves which causes contraction of detrusor muscle which increases the pressure of the bladder leading to micturition (S2-4)

Scattered sympathetic supply by the hypogastric nerves which inhibits the contraction of the bladder and keeps the internal urethral sphincter closed (main function is to prevent reflux of semen into the bladder during ejaculation (L1-3)

Somatic motor neurons (pudendal nerves) - innervate the skeletal muscle that forms the external urethral sphincter which keeps it closed even against bladder contractions

Question 29

What happens when the hypogastric nerve gets cut with relation to micturition

Answer 29

Increased frequency as the hypogastric nerve inhibits the detrusor muscle and keeps the internal urethral sphincter closed

Question 30

What controls micturition (sensory innervation)

Answer 30

Stretch receptor afferent nerves from the bladder which sense how full the bladder is - as the bladder fills it sends discharges in afferent nerves to the spinal cord and then via interneurons it causes

Excitation of parasympathetic outflow
Inhibition of sympathetic outflow
Inhibition of somatic motor neurons to external sphincter
Tells the sensory cortex that there is a sensation of fullness

Question 31

How is delay in micturition accomplished

Answer 31

Descending pathways from many brain centres like the cortex and brainstem

They inhibit parasympathetic (control over detrusor contraction)
stimulate somatic nerves to the external sphincter

Question 32

How is voluntary initiation done

Answer 32

parasympathetic system is stimulated and somatic motor neurons are inhibited

Question 33

What is the effect of relaxation of pelvic floor muscles during voluntary urination

Answer 33

Creates a downwards tug on the detrusor muscle to initiate contraction

Question 34

After urination what empties the female urethra

Answer 34

gravity

Question 35

After urination what empties the male urethra

Answer 35

Contractions of the bulbocavernosus muscle

Question 36

What is the mild mass reflex

Answer 36

Initiation of voiding by pinching or stroking thighs - this is commonly seen in some paraplegic patients