Lecture 13 Physiology of Micturition & Assessment of Renal Function, Urea, Creatinine and GFR

Question 1

Why is the assessment t of renal function important

Answer 1

Assess progression of the underlying disease

When GFR falls, excretion falls so drug dose may. need to be adjusted

Question 2

How is GFR measured

Answer 2

Plasma clearance test

Question 3

What is the equation for the calculation of plasma clearance

Answer 3

Plasma Clearance = Urine concentration X Urine flow rate/Plasma Concentration

Question 4

What is the gold standard for measuring plasma clearance

Answer 4

Inulin

Question 5

Why is inulin used to measure plasma clearance

Answer 5

Freely filtered at the glomerulus and isn’t reabsorbed nor secreted

Question 6

At what rate does the GFR decline

Answer 6

1ml/min/year after 30

Question 7

What is used instead of inulin in clinical practice to measure plasma clearance

Answer 7

51Cr-EDTA

Question 8

Name factors that affect serum creatinine

Answer 8

Muscle mass
Dietary intake
Drugs

Question 9

What is the clearance of glucose and why

Answer 9

Zero clearance because all is normally absorbed

Question 10

Is the clearance of urea less than inulin and why?

Answer 10

Yes, because some urea is reabsorbed

Question 11

What is used to measure real plasma flow

Answer 11

Para-amino-hippuric acid (PAH)

Question 12

How does urine flow from the kidneys to the bladder

Answer 12

Through the ureters via peristaltic contractions of the smooth muscle of the ureters

Question 13

At what angle doe the ureters enter the bladder and why

Answer 13

Oblique angles

Prevent reflux

Question 14

What muscle surrounds the bladder

Answer 14

Detrusor muscle

Question 15

Contraction of what muscle is responsible for the emptying of the bladder during micturition

Answer 15

Detrusor muscle

Question 16

What is the internal urethra made up of

Answer 16

Smooth muscle

Question 17

What is the external urethra made up of

Answer 17

Skeletal muscle

Question 18

What type of epithelium lines the bladder

Answer 18

Transitional epithelium

Question 19

What are the openings in the bladder

Answer 19

2 vesicoureteric openings

Question 20

What is the normal daily urine production

Answer 20

Varies between 730ml to 2500mls

Question 21

Describe the sphincters of the bladder at rest

Answer 21

Internal sphincter- passively contracted

External sphincter- stays contracted

Question 22

What is the parasympathetic motor innervation of micturition

Answer 22

Pelvic nerve
S2-S4
Increase in activity- detrusor muscle contraction

Question 23

What is the sympathetic motor innervation of micturition

Answer 23

Hypogastric nerve
L1-L3
Inhibit bladder contraction 
Closes internal urethral sphincter 
Prevents reflux of semen into bladder during ejaculation

Question 24

What is the somatic motor innervation of micturition

Answer 24

Pudendal nerves
S2-S4
Innervate skeletal muscle of external urethral sphincter

Question 25

Describe the sensory innervation of the bladder

Answer 25

Stretch receptor in bladder wall as bladder fills sends a discharge in afferent nerves to spinal cord
Excitation of parasympathetic
Inhibition of sympathetic and somatic

Question 26

In an adult what is the volume of urine in the bladder required to initiate the spinal reflex

Answer 26

300-350 mls

Question 27

How is the delay in micturition achieved

Answer 27

Inhibit the parasympathetic and stimulate the somatic

Question 28

After urination, how dies female urethras empty

Answer 28

By gravity

Question 29

How can urine flow be interrupted once it begins

Answer 29

Perineal muscles and external sphincter muscles being contracted voluntarily

Question 30

How is urine remaining in the male urethra expelled

Answer 30

Contractions of the bulbocavernous muscle

Question 31

Name 3 abnormalities of the micturition

Answer 31

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