Urinary

Question 1

Describe the general location of the kidneys and ureters in the abdominal cavity.

Answer 1

Retroperitoneal

Question 2

Which kidney is lower in the abdominal cavity and why?

Answer 2

Right. Depressed by the liver.

Question 3

Which nerve roots do the two kidneys span each?

Answer 3

Left: T11-L3
Right: T12-L3

Question 4

What are the two types of nephrons? What are their blood supplies like and their relative functions?

Answer 4

Cortical - has peritubular capillaries, primarily reabsorption

Juxtamedullary - has vasa recta, primarily creation of a concentration gradient to control concentration of urine

Question 5

Relative to fluid in the tubule, which direction do the blood flow in the vasa recta and what is the significance of this?

Answer 5

Countercurrent,

Thick ascending limb is impermeable to water and pumps out Na+, K+ and Cl- ions into the intersticium to establish a concentration gradient. The blood in the vasa recta runs down this, becoming increasingly concentrated as water leaves to enter intersticium.
Thin descending limb contains plenty of water which moves out of the tubule, into the intersticium and the ascending vasa recta which have been concentrated by action of the thick ascending limb.

Question 6

Urea is recycled in the nephron. Where, how and why?

Answer 6

The cycle is under ADH influence - this only works if aquaporins are present on the apical membrane of cells of the CD.

Urea leaves the collecting duct down its concentration gradient –> intersticium so water follows through aquaporins –> urea enters the vasa recta (more concentrated blood) –> water follows into vasa recta further concentrating the urine.

Question 7

What does isosmotic reabsorption mean? Where does it happen and what ion is involved?

Answer 7

Reabsorption of solutes from a filtrate in a 1:1 ratio with water which results in no change in the osmolarity of the filtrate.

PCT

Na+

Question 8

What is reabsorbed in the PCT?

Answer 8

Glucose, amino acids, Na+, Some Cl-

Question 9

Give an example of a substance with a 100% clearance rate. What renal value can this give you?

Answer 9

Bile salts, inulin

Is equal to GFR value.

Question 10

PAH (paraaminohippurate) is completely secreted by the kidneys. What can it be used as a direct measure of?

Answer 10

Renal Plasma Flow

Question 11

Equation to calculate renal plasma flow?

Answer 11

RPF = plasma from haematocrit x renal blood flow

Question 12

Equation to calculate filtration fraction?

Answer 12

FF = RPF/GFR

Question 13

Equation to calculate clearance rate?

Answer 13

C = (Concentration of substance in urine x urinary flow rate)/Concentration of substance in plasma

Question 14

Equation to calculate filtered load?

Answer 14

FL = concentration of substance in plasma x GFR

Question 15

What is the typical value for GFR?

Answer 15

125 ml.min-1

Question 16

Name the retroperitoneal organs.

Answer 16

SAD PUCKER

Suprarenal glands
Aorta/IVC
Duodenum

Pancreas
Ureters
Colon (except transverse which is intraperitoneal)
Kidneys
oEosophagus
Rectum

Question 17

What two main cell groups are found in the juxtaglomerular appartus?

Answer 17

Macula Densa cells

Juxtaglomerular cells

Question 18

What do juxtaglomerular cells produce?

Answer 18

Renin in response to a drop in renal perfusion pressure in afferent arteriole of glomerulus (via stretch receptors in vasc walls)

Question 19

How does renin act on the kidney? hint: RAAS

Answer 19

Activates RAAS –> renin cleaves angiotensinogen to angiotensin I. Angiotensin I enters blood and is carried to the lungs where angiotensin converting enzyme (ACE) cleaves to to form Angiotensin II. Angiotensin II is a vasoconstrictor and increases ADH and aldosterone release.

Concluding effect: indirectly increases blood volume via vasoconstriction, sodium retention and hormone-induced water reabsorption to increase renal perfusion and GFR.

Question 20

Aldosterone is a part of the RAAS. Where is secreted from and what is its mechanism of action at its target organ?

Answer 20

Secretion from zona glomerulosa of adrenal cortex (mineralocorticoid secreting portion).
Action in the nephron DCT and CD on the principal cells to increase Na+ reabsorption and therefore water.

Question 21

What ion channels of which cells does aldosterone act on and where are they located?

Answer 21

Action on principal cells of DCT and CD

Ion channels:
3Na+/2K+ antiporter (K+ lost to tubule)
ENaC

NB: it also acts on intercalated cells in cortical CD on the H+/Na+ antiporter (H+ lost)

Question 22

What is one possible danger of hyperaldosteronism (Conn’s syndrome, adenoma)?

Answer 22

Hypokalaemia –> tachycardia and tachyarrhythmias

Question 23

Where is the action of Thiazide diuretics? Give an example.

Answer 23

Inhibit Na+ reabsorption at the Distal Convoluted Tubule

Question 24

Where do carbonic anhydrase inhibitors act? What patient indicator may make them the diuretic of choice?

Answer 24

Proximal Convoluted Tubule. They are potassium preserving and so useful for patients who may be hypokalaemic.

Question 25

Spironolactone is another potassium sparing antidiuretic. What is its mechanism of action and where?

Answer 25

Site of action is distal convoluted tubule. It inhibits the action of aldosterone which otherwise acts on the Na+/H+ antiporter to conserve Na+

Question 26

Where do loop diuretics act? Give an example.

Answer 26

Ascending limb of loop of Henle, on the Na+K+2Cl- symporter preventing establishment of a concentration gradient in the medulla for water to flow out into.

Furosemide

Question 27

Where is the ENaC found and give an example of a diuretic that acts on it.

Answer 27

Distal convoluted tubule.

Amiloride

Question 28

The macula densa is involved in which sensory renal feedback loop?

Answer 28

Tubuloglomerular autoregulatory feedback loop.

Question 29

How do cells of the macula densa regulate GFR?

Answer 29

Detect NaCl concentration in ultrafiltrate. Salt enters cells, water follows and causes swelling.

GFR too high: cells swell too much –> cause vasoconstriction of afferent arteriole to reduce GFR

GFR too low: cells do not swell enough –> cause vasodilation of afferent arteriole to increase GFR AND release prostaglandins that act on the juxtaglomerular cells which then secrete renin –> RAAS to restore blood volume.