Renal Assessment and Micturition

Question 1

When is the measurement of GFR useful?

Answer 1

Assessment of renal disease in nephron damage/disease Awareness when giving renal excreted drugs

Question 2

What is total GFR?

Answer 2

Sum of all filtration by function of nephrons

Question 3

What is the plasma plasma clearance formula (for substance x)?

Answer 3

Clearance_x = [Urine_x] x Urine flow rate/[plasma_x]

Question 4

What is the gold standard for clearance measurement?

Answer 4

Inulin clearance - loading dose given

Give time for equilibrium to be reached

Simultaneous plasma and (timed) urine measurement

Question 5

What is plasma clearance?

Answer 5

The amount of plasma free of substance

Question 6

Why is inulin used for true GFR measurement?

Answer 6

O% reabsorbed = 100% excreted

Question 7

What clearance do substances filtered and reabsorbed have, relative to inulin?

Answer 7

Lower clearance because some will be taken back into the plasma

Question 8

What clearance do substances filtered and secreted have, relative to inulin?

Answer 8

Higher clearance because the concentration in the urine will be lower

Question 9

What is the change in GFR through life?

Answer 9

Decrease by 1ml/min/year after 30

Question 10

What substance is used instead of inulin?

Answer 10

51Cr-EDTA

Question 11

How is creatinine produced?

Answer 11

Endogenous breakdown of Creatine by muscles

Question 12

eGFR is taken as what?

Answer 12

(estimate)GFR = 1/[P_CR]

Question 13

Why does eGFR lack accuracy?

Answer 13

GFR can be halved before PCR is elevated

Question 14

What factors affect serum creatinine?

Answer 14

Muscle mass

Dietary intake

Drugs

Ketoacidosis

Question 15

What is the normal clearance of glucose?

Answer 15

Zero - as it is all reabsorbed

Question 16

What is the normal clearance of urea?

Answer 16

50mL/min as 50% is excreted

Question 17

What is the use of PAH clearance?

Answer 17

Measure of real plasma flow

Measure of all plasma flowing through kidneys at any one time

Question 18

What is PAH?

Answer 18

Para-amino-hippuric acid

Question 19

What is PAH clearance used for?

Answer 19

Measure real plasma flow

Measure of all plasma flowing through kidneys at any one time

Question 20

Why is PAH clearance used?

Answer 20

PAH is freely filtered at glomerulus

Remainder is actively secreted into tubule

90% of plasma PAH is cleared

Question 21

What is a normal real plasma flow?

Answer 21

660mls/min

Question 22

Why does penicillin has a greated clearance than inulin?

Answer 22

Because its filtered AND excreted

Question 23

How does urine flow from kidneys to bladder?

Answer 23

Peristaltic contraction of smooth muscles of the ureters

Question 24

How does urine enter the bladder? Why is this important?

Answer 24

Enters at an oblique angle

Prevents reflux of urine into the ureters

Question 25

What is the name of the muscles of bladder contraction

Answer 25

Detrusor muscles

Question 26

What is the structure of the internal urethral sphincter?

Answer 26

NOT true sphincter Smooth muscle acts as sphincter when relaxed

Question 27

What is the structure of the external urethral sphincter?

Answer 27

True sphincter Skeletal muscle under voluntary somatic control

Question 28

What epithelium lines the bladder?

Answer 28

Transitional of ureter

Question 29

The three openings of the bladder make up which structure?

Answer 29

Trigone of bladder

Question 30

What openings make up the trigone of bladder?

Answer 30

2 Vesicoureteric openings Urethral opening

Question 31

What is the structure of the pressure-volume curve of the bladder?

Answer 31

Long flat segment as initial increments of urine enter bladder Sharp rise as micturition reflex is triggered

Question 32

What is a typical, temperate climate normal daily urine production?

Answer 32

750-2500mls

Question 33

What is the passive state of the internal urethral sphincter?

Answer 33

Passively contracted

Question 34

How is the bladder innervated?

Answer 34

Parasympathetic - Pelvic nerves S2-S4 Sympathetic supply - inhibit bladder contraction, close internal sphincter (L1-L3) Somatic motorneurones (pudendal nerves) innervate skeletal muscle

Question 35

What is the role of parasympathetic innervation of the bladder?

Answer 35

Increased activity = increased contraction of the detrusor muscle Increases pressure within the bladder

Question 36

What is the role of sympathetic innervation of the bladder?

Answer 36

Prevent reflux of semen back into the bladder during ejaculation Inhibit bladder contraction Close internal urethral sphincter

Question 37

What is the role of somatic innervation of the bladder?

Answer 37

Motor control - contraction of the external urethral sphincter against bladder contractions

Question 38

What is the sensory innervation of the bladder?

Answer 38

Stretch receptor afferents (↑ discharge as bladder fills)

Question 39

↑ sensory discharge as bladder fills triggers what?

Answer 39

Via interneurones: - Excitation of parasympathetic outflow - Inhibition of sympathetic outflow - Inhibition of somatic motorneurones to external sphincter - Pathways to sensory cortex = sensation of fullness

Question 40

Why do babies pee themselves?

Answer 40

Sensory interneurones causing excitation of parasympathetic bladder innervation, and inhibition of somatic motorneurones to external sphincter causes micturition But the little fucker hasnt learned to control it yet

Question 41

What volume of urine is required to initiate the spinal reflex in adults?

Answer 41

300 - 350mls

Question 42

Micturition delay is accomplished how?

Answer 42

Descending pathways (from cortex, brainstem) Inhibit parasympathetic Stimulate somatic nerves of external sphincter and override stretch receptor input

Question 43

Voluntary initiation of micturition involves which descending pathways?

Answer 43

Stimulation of parasympathetic contraction of the detrusor muscles Inhibition of somatic motorneurones controlling external sphincters

Question 44

Which muscles are used to initiate contraction of detrusor muscles in voluntary urination?

Answer 44

Contraction of pelvic floor muscles tugging on detrustor muscles

Question 45

What muscles are used in interrupting urine flow through the urethra?

Answer 45

Perineal muscles External sphincter muscles

Question 46

How do females empty the urethra in urination?

Answer 46

Gravity

Question 47

How do males empty the urethra after urination?

Answer 47

Contractions of the bulbocavernosus muscle

Question 48

Which types of neural lesions cause abnormalities in micturition?

Answer 48

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

Question 49

How do paraplegic patients "learn" to initiate voiding?

Answer 49

Mild mass reflex - pinch/stroking thigh