Physiology of Micturition and Assessment of Renal Function

Question 1

When would renal function need to be assessed?

Answer 1

-In patients w renal disease
-To check drug level in body*

->*this is because most drugs are removed from the body by excretion by filtration and if there is a fall in GFR, drugs may accumulate causing toxicity

Question 2

What could assessing renal function tell us about someone with renal disease?

Answer 2

Progression of the disease as results in nephron descruction and loss of function

Question 3

What is total GFR?

Answer 3

Sum of all filtration by functioning nephrons

Question 4

Progression of renal disease would be indicated by what GFR?

Answer 4

Decrease in GFR

Question 5

What type of tests are used to measure renal function?

Answer 5

Plasma clearing tests

->show how much of a substance can be cleared from the plasma.

Question 6

What is the gold standard for measuring GFR?

Answer 6

Inulin clearance

This involves polyfructose loaded via IV of inulin, allowing time to equilibrate and then sampling plasma and urine simultaneously

Question 7

To measure GFR, what must the substance used to measure this be?

Answer 7

The substance used must not be one that is secreted or reabsorbed

Question 8

What is the normal GFR is a ‘normal’ healthy man?

Answer 8

125mls/min

->values for women about 10% lower

Question 9

GFR is now not commonly measured in clinical practice- why?

Answer 9

Too complex and expensive
Takes several hours and requires injections of isotope 51Cr EDTA

Question 10

If EFR is taken in clinical practice, inulin is no longer used, what is used instead?

Answer 10

51Cr-EDTA

Question 11

What alternative is used routinely as a replacement for measuring GFR?

Answer 11

Creatinine clearance is used to estimate GFR

Question 12

What is creatinine?

Answer 12

Breakdown product of muscle

Question 13

There is a relationship between GFR and plasma creatinine concentration. However, what % of GFR is lost before there is any change in plasma creatinine concentration?

Answer 13

50% reduction in GFR before seeing any increase in plasma creatinine concentration

->may be worth looking a graph to show this - google like GFR and plasma creatinine rate graph

Question 14

What are some factors which affect serum creatinine?

Answer 14

Muscle mass
Dietary intake e.g. supplements, vegetarians
Drugs

Question 15

What is normal GFR?

Answer 15

100mls/min/1.73 meter squared of body surface area

…duh

Question 16

What is the usual clearance of glucose by the kidneys?

Answer 16

Zero as normally all of it is reabsorbed

Question 17

RECAP- in which part of the system is water reabsorbed?

Answer 17

Proximal tubule

Question 18

What is the clearance of inulin like?

Answer 18

Inulin is completely filtered out at the glomerulus but neither secreted or reabsorbed by the tubules

Question 19

What is the clearance of urea like?

Answer 19

Less than that of inulin as urea is not fully reabsorbed

Question 20

What % of urea is reabsorbed in the proximal tubule?

Answer 20

50%

->if filtration rate is 100mL/min and 50% of urea is reabsorbed, urea clearance is 50mL/min

Question 21

What organic anion can be used to measure renal plasma flow?

Answer 21

PAH- para-amino-hippuric acid

Question 22

How can PAH be used to measure real plasma flow?

Answer 22

PAH is freely filtered at the glomerulus and then the PAH remaining in the plasma is actively secreted into the tubule so that > 90% of plasma is cleared of its PAH content in one transit of the kidney.
PAH clearance is a measure of all the plasma flowing through the kidneys in a given time = renal plasma flow

->idk if this makes sense, imma be honest with you, the next few flashcards might not make a lot of sense cos I’m doing this after having brownies w Oli at Kilau…you’ll remeber

Question 23

What has a greater clearance- inulin or penicillan?

Answer 23

Penicillin

->more penicillin is excreted than was filtered

Question 24

Okay so bear with me;

Let’s use molecule X in these examples. It can be literally whatever you fancy. Molecule X gets freely filtered at the glomerulus.
What happens if filtration of molecule X is greater than the excretion?

Answer 24

There will be a net reabsorption of molecule X

Question 25

Okay so bear with me;

Let’s use molecule X in these examples. It can be literally whatever you fancy. Molecule X gets freely filtered at the glomerulus.
What happens if excretion of molecule X is greater than filtration?

Answer 25

There will be a net secretion of molecule X

Question 26

Okay so bear with me;

Let’s use molecule X in these examples. It can be literally whatever you fancy. Molecule X gets freely filtered at the glomerulus.
What happens if filtration and excretion of molecule X are the same?

Answer 26

No net reabsorption or secretion of molecule X

Question 27

Okay so bear with me;

Let’s use molecule X in these examples. It can be literally whatever you fancy. Molecule X gets freely filtered at the glomerulus.
What happens if clearance of molecule X is less than inulin clearance?

Answer 27

Net reabsorption of molecule X

Question 28

Okay so bear with me;

Let’s use molecule X in these examples. It can be literally whatever you fancy. Molecule X gets freely filtered at the glomerulus.
What happens if clearance of molecule X is equal to inulin clearance?

Answer 28

Molecule X is neither reabsorbed or secreted

->this is the same in inulin clearance, no reabsorption or secretion

Question 29

Okay so bear with me;

Let’s use molecule X in these examples. It can be literally whatever you fancy. Molecule X gets freely filtered at the glomerulus.
What happens if clearance of molecule X is greater than inulin clearance?

Answer 29

Net secretion of molecule X

Question 30

How does urine flow from the kidneys to the ureters?

Answer 30

Via peristaltic contraction of the ureter smooth muscle

Question 31

Why do the ureters enter the bladder at an oblique angle?

Answer 31

Prevents the reflux of urine

Question 32

Does the composition of urine change at all after leaving the kidney?

Answer 32

No

Question 33

What type of muscle is the bladder composed of?

Answer 33

Detrusor muscle

->Smooth muscle arranged in spiral, longitudinal and circular bundles

Question 34

Micturition?

Answer 34

Action of urinating

Question 35

How many sphincters does the bladder have?

Answer 35

Internal urethral sphincter- NOT a true sphincter
External urethral sphincter

Question 36

What type of muscle is the internal urethral ‘sphincter’ made of?

Answer 36

Smooth muscle

->this acts as a sphincter when the smooth muscle is relaxed but is not a true sphincter

Question 37

What type of muscle is the external urethral sphincter made of?

Answer 37

Skeletal muscle

Question 38

What type of control is the external urethral sphincter under?

Answer 38

Voluntary somatic control

Question 39

Where does the bladder in relation to the reproductive system and rectum?

Answer 39

Lies anterior

Question 40

What is the bladder overlain with?

Answer 40

Peritoneum

Question 41

What type of epithelium is the bladder lined with?

Answer 41

Transitional epithelium

Question 42

If there is urethral obstruction, how does this affect the renal system?

Answer 42

Bilateral renal problems

Question 43

If there was ureter obstruction, how would this affect the renal system?

Answer 43

Unilateral renal problems

Question 44

What is normal daily urine production?

Answer 44

Varies between 750ml-2500mls in temperate climates

Question 45

Which sphincter of the bladder stays contracted?

Answer 45

External sphincter

->internal sphincter is passively contracted

Question 46

What is the motor innervation in the control of micturition?

Answer 46

Rich parasympathetic supply from the pelvic nerves

Question 47

What does the rich parasympathetic supply from the pelvic nerves lead to?

Answer 47

Increased contraction of the detrusor muscle leading to increased pressure within the bladder

Question 48

There is sparse sympathetic supply which inhibits the bladder contraction and closes the internal urethral ‘sphincter’. What nerves provide this innervation?

Answer 48

Hypogastric nerves

Question 49

Sympathetic supply is not very important to the bladder. However, what would happen if the hypogastric nerve was cut or damaged?

Answer 49

Increased frequency of micturition

Question 50

What role does the somatic motoneurons have in micturition?

Answer 50

Innervate the skeletal muscle that forms the external urethral sphincter
This keeps the bladder closed even against strong bladder contractions

Question 51

The stretch receptor of the bladder afferents from the bladder wall.
As the bladder fills, there is increased discharge in afferent nerves to the spinal cord.
What happens in terms of different innervation pathways e.g. parasympathetic, sympathetic

Answer 51

Excitation of parasympathetic outflow

Inhibition of sympathetic outflow

Inhibition of somatic motoneurones to external sphincter

Pathways to sensory cortex lead to sensation of fullness

Question 52

What happens to the stretch receptors as the bladder fills?

Answer 52

The stretch receptors become increasingly stimulated until their output becomes great enough to cause bladder contraction

Question 53

In bladder contraction, the external sphincter relaxes to allow urination. What ensures this sphincter relaxes?

Answer 53

Inhibition of somatic motoneurons

Question 54

In an adult, what is the volume of urine required in the bladder to initiate the spinal reflex responsible for urination?

Answer 54

300-350mls

Question 55

How is delay of urination achieved?

Answer 55

Inhibition of parasympathetic
Stimulation of somatic nerves to the external sphincter which overrides the bladder stretch response

Question 56

How does voluntary initiation of urination occur?

Answer 56

Inhibition of the somatic motor neurons thus summating w the stretch receptors

Question 57

One of the initial stages of voluntary urination involves the relaxation of which muscles?

Answer 57

Pelvic floor

->this can cause a sufficient downward tug on the detrusor muscle to trigger contraction

Question 58

Which muscles can be contracted voluntarily to prevent urine flow which can stop flow once urination begins?

Answer 58

Perianal muscles
External sphincter

Question 59

After urination, how does the female urethra empy?

Answer 59

Gravity

Question 60

After urination, how is any urine remaining in the male urethra expelled?

Answer 60

By contractions of the bulbocavernous muscle

Question 61

There are three major abnormalities to urination due to neural lesions.
What do these cause?

Answer 61

1. Interruption of afferent nerves
2. Interruption of both afferent and efferent nerves
3. Interruption of faciliatory and inhibitory descending pathways from the brain

->In all 3 types the bladder contracts but the contractions are generally insufficient to empty the bladder completely and urine is left in the bladder.