Micturition + assessing renal function

Question 1

What happens to plasma conc. of a drug if GFR falls

Answer 1

increases which can –> toxicity

Question 2

Plasma clearance tests determine what

Answer 2

ability of the kidney to clear the plasma of various substances (note: relates to clearance of a volume of plasma, NOT clearance of a specific substance in plasma) i.e. renal function

Question 3

Gold standard measurement of GFR (i.e. excretory renal function) is (although this actually isn’t used much despite being gold standard)

Answer 3

Inulin clearance

Question 4

Inulin is not reabsorbed or secreted in the nephron once filtered into it so would a substance that IS reabsorbed have a higher or lower clearance than insulin

Answer 4

lower as urine concentration of this substance would be less since plasma concentration of it rises as it’s being reabsorbed

Question 5

Despite being gold standard, inulin clearance as a measurement of GFR/renal function is too complex so clearance of what is more routinely measured to ESTIMATE GFR

Answer 5

creatinine (breakdown product of muscle) clearance

Question 6

Why is creatinine clearance only an estimate go GFR

Answer 6

because creatine clearance actually exceeds GFR as peritubular capillaries secrete small amounts of creatinine

Question 7

Factors affecting serum creatinine levels (3)

Answer 7

Muscle mass
Dietary intake
Medication

Question 8

With a higher muscle mass, serum creatinine will be lower or higher

Answer 8

higher

Question 9

A common mistake made when assessing renal function by just looking at serum creatinine to is the failure to account for

Answer 9

muscle mass
-as the same serum creatinine level may indicate renal dysfunction in an old lady but actually be normal for a young muscular person

Question 10

Normal GFR per min

Answer 10

> 90

Question 11

Is clearance of urea more or less than inulin + why

Answer 11

less because some urea is reabsorbed, inulin is not

Question 12

PAH (para-amino hippuric) acid clearance, an anion (-vely charged), is a measurement of what

Answer 12

renal plasma flow, i.e. the amount of plasma flowing through the kidneys at any given time

Question 13

Urine flows from kidneys to ureters via what action of the ureters

Answer 13

peristalsis

Question 14

Name the smooth muscle of the bladder

Answer 14

detrusor

Question 15

Internal urethral sphincter is not a

Answer 15

true sphincter - just refers to smooth muscle at the start of the urethra which acts as a sphincter when it relaxes

Question 16

External urethral sphincter composed of what muscle type + under what control

Answer 16

skeletal muscle

somatic voluntary

Question 17

Bladder line day what epithelium

Answer 17

transitional

Question 18

What is the trigone of the bladder

Answer 18

triangular area of the floor of the bladder formed by the 3 openings - two ureteric orifices coming from kidney and the internal urethral orifice

Question 19

Describe the shape of the volume-pressure curve of the bladder

Answer 19

Intravesical pressure rises slightly when there’s a first urge to void

Then there’s a long flat line of the curve as urine volume increases

When 350ml urine reached, sudden sharp rise of the curve as detrusor contraction stimulated causing big increase in intravesical pressure –> initiating micturition

Question 20

Bladder volume for initiation of micturition reflex in adults is about

Answer 20

350mls

Question 21

What nerve innervates the external urethral sphincter and allows voluntary control to keep it closed

Answer 21

Motor fibres of the pudenal nerve (S2-S4 origin)

Question 22

List the 3 motor innervations of the bladder that control micturition

Answer 22

Parasympathetic - pelvic nerve (S2-S4) - contracts detrusor muscle to stimulate micturition

Sympathetic - hypogastric nerve (T12-L1) - relaxes detrusor muscle, closes internal sphincter - to retain urine

Somatic motor - pudenal nerve (S2-S4) - innervates the external sphincter to allow voluntary control

Question 23

Micturition is a … reflex

Answer 23

spinal reflex

Question 24

Micturition is stimulated in response to

Answer 24

stretch of bladder

Question 25

Describe how the micturition reflex is stimulated (hints: distension, stretch receptor afferents, interneurons, parasympathetic/sympathetic/ somatic outflow to bladder)

Answer 25

Distension of bladder detected by stretch receptors in bladder wall –> increased discharge in the afferents from these receptors to spinal cord –> synapse on interneurons which cause:

• excitation of parasympathetic outflow –> detrusor contraction
• inhibit sympathetic outflow –> opens internal sphincter
• inhibit somatic control to external sphincter

Question 26

How do we voluntarily delay micturition (2)

Answer 26

By descending pathways from brain which

• inhibit parasympathetic motor activity to the detrusor
• stimulate somatic motor activity to the external sphincter

therefore over-riding input from stretch receptors

Question 27

How do we voluntarily initiate micturition (3)

Answer 27

By summation of descending input with afferent input (stretch receptors)

Descending pathways from brain which

• stimulate parasympathetic activity to detrusor
• inhibit somatic motor activity to external sphincter

Question 28

Where is the micturition centre in the brain

Answer 28

pons

Question 29

Serum creatinine will not be raised above normal range until what % of kidney function is lost

Answer 29

60%

Question 30

Inulin is not reabsorbed or secreted in the tubules so if a drug has greater clearance than inulin, what does this mean

Answer 30

net secretion of the drug

Question 31

Inulin is not reabsorbed or secreted in the tubules so if a drug has less clearance than inulin, what does this mean

Answer 31

net reabsorption