Urinary: Clearance and Electrolyte Balance

Question 1

What are normal adult glomerular filtration rates?

Answer 1

Males 115-125 ml/min

Females 90-100 ml/min

Question 2

How do we calculate renal clearance?

Answer 2

conc in urine x volume of urine / conc in plasma

Question 3

Whats the link between GFR and creatinine clearance?

Answer 3

Creatine clearance gives an estimate of GFR however slightly overestimates it because creatine is secreted by the proximal tubule as well as filtered by the glomerulus

Question 4

What is renal clearance?

Answer 4

The volume of plasma that can be cleared of a certain substance per unit time

Question 5

What are the volumes of fluid in each compartment?

Answer 5

ICF (cytosol) = 28L

ECF = 14L (interstitial fluid is 11L and plasma is 3L)

Question 6

Define osmolarity

Define osmolality

Answer 6

Osmolarity is the solute per kg of solvent
Osmolality is the number of osmoles of solute per litre

We usually measure in osmolality, units: milli-osmoles

Question 7

What are the electrolyte compositions of the ICF and ECF?

Answer 7

The ICF:
Low Na+  10mM
High K+  160mM
Low Cl-  3mM
Many large organic anions

The ECF:
High Na+  145mM
Low K+  4.5mM
High Cl-  114mM
Some HCO3-

Question 8

How are calcium levels regulated?

Answer 8

Parathyroid hormone stimulates calcium reabsorption in the kidney (asc limb and DCT)
, also stimulates synthesis of 1,25(OH)2 (active form of vit D) which stimulates calcium absorption in the small intestine