Urology physiology

Question 1

Renal blood flow

Answer 1

25% of cardiac output

~1.25L /min

Question 2

How is the glomerulus in the nephron more selective for positively charged molecules?

Answer 2

Negative charge of glycoproteins in the basement membrane results in greater permeability to positively or neutrally charged molecules than negatively charged molecules

Question 3

Hydrostatic pressure across Bowman’s capsule

Answer 3

Efferent arteriole constriction results in higher hydrostatic pressure than normal ~50mmHg

Pressure in Bowmen’s ~10mmHg

Produces net hydrostatic pressure of 40mmHg

Plasma proteins generate osmotic pressure; they are not filtered and therefore produce an opposing absorption pressure to the hydrostatic pressure.

Osmotic pressure is about 25 mmHg; therefore the net filtration pressure is around 15 mmHg.

Question 4

Proximal convoluted tubule

Answer 4

Absorbs 70% of Na

Sborbs 90% K+

Absorbs water in equal proportions so fluid is isotonic

Question 5

Site of producton of ADH

Answer 5

Supraoptic nucleus in hypothalamus

Released in posterior pituitary

Question 6

Juxtaglomerular cells

Answer 6

Juxtaglomerular cells are specialised smooth muscle
cells that lie in the wall of the afferent arteriole

Secrete renin

Question 7

Clearance

Answer 7

= UV / P

Urinary concentration, multiplied by the volume per unit time

Divided by the plasma concentration

Question 8

Para-aminohippuric acid

Answer 8

Measuring renal plasma flow

Question 9

Inulin

Answer 9

Measuring glomerular filtration rate

Question 10

Parasympathetic innervation to bladder

Answer 10

Sacral outflow S2-S3

and pudendal nerve

Question 11

Sympathetic innervation to bladder

Answer 11

Hypogastric plexus

Question 12

Innervation of the bladder

Answer 12

L1–2: sympathetic outflow

S2–4: parasympathetic

Efferent sensory fibres enter the spinal cord at L1–2 and S2–4.

Question 13

Neurological injuries and the bladder

Answer 13

Atonic

Automatic reflex

Autonomous

Question 14

Atonic bladder

Answer 14

Early phase of spinal cord injury

Atonic bladder, empties by overflow

If injury above L1-L2 –> patient asymptomatic from distension

Question 15

Automatic reflex bladder

Answer 15

Seen once spinal shock has subsided in patient with an injury ABOVE sympathetic outflow L1-L2

Reflex emptying every 3-4 hours

Question 16

Autonomous bladder

Answer 16

Damage to sacral area

–> The bladder is flaccid

Capacity greatly increases; the bladder fills to capacity and then overflows
Partial emptying can be performed by compression of the lower abdomen

Backpressure leading to vesicoureteric reflux and hydronephrosis is unavoidable –> chronic renal failure

Question 17

Erythropoeitin

Answer 17

Majority made in kidney

Some made in liver and spleen

Stimulated by:

• Hypoxia
• Haemorrhage, Respiratory disease, High altitude (all causes of hypoxia)
• Vasoconstriction
• Increase red cell breakdown products in blood

Question 18

Activation of Vitamin D

Answer 18

1α-hydroxylase is secreted by the kidney in reponse
to ↓Ca2+

Converts 25-hydroxycholecalciferol to 1,25-dihydroxycholecalciferol.
–> 25-hydroxylation occurs first in the liver

1,25-dihydroxycholecalciferol promotes Ca2+ reabsorption and decreases urinary loss