13. Renal Physiology Session 1

Question 1

What is the 60-40-20 rule?

Answer 1

60% of body weight is total body water

40% of body weight is intracellular fluid

20% of body weight is extracellular fluid

Question 2

What is third spacing?

Answer 2

When fluid shifts from vessels into nonfunctional areas

Examples: between tissues and organs, pulmonary edema, ascites

Question 3

What is the normal range for serum osmolality?

Answer 3

285-295 mOsm/Kg H20

Question 4

What is the normal urine output in a day?

Answer 4

1-2 L

Question 5

What is water diuresis? What can cause it?

Answer 5

Increased water excretion without corresponding increase in salt excretion.

Examples: diabetes insipidus, polydipsiam increased intake of water

Question 6

What is solute (osmotic) diuresis? What can cause it?

Answer 6

Increased water excretion concurrent with increased salt excretion.

Examples: IV NaCl, high protein intake, hyperglycemia, recovering from AKI

Question 7

How does a a urine osmolarity greater than plasma osmolarity effect free water clearance?

Answer 7

Free water clearance will be negative, indicating water conservation.

Question 8

What is the ‘eyeball’ way to calculate plasma osmolality?

Answer 8

2 (plasma [Na+])

Question 9

What is the Gibbs-Donnan effect?

Answer 9

Describes how negatively charged protein on one side of a semipermeable membrane generates both osmotic and electrochemical gradients across the membrane, favoring movement of water into the cell.

Question 10

How is the Gibbs-Donnan effect countered?

Answer 10

Na/K ATPase moving 3 Na+ out and 2 K+ in the cells

Question 11

What is is the main driving force behind plasma colloid osmotic pressure?

Answer 11

Large proteins such as albumin that can’t pass through capillary membranes. They attract water into the intravascular space.

Question 12

What is the NaCl concentration in a isotonic-cell environment?

Answer 12

0.85%

Question 13

What is the difference between crystalloid and colloid replacement therapy?

Answer 13

Crystalloid: organic/inorganic salts dissolved in water (e.g. NaCl, glucose)

Colloid: large molecules that don’t pass through semipermeable membranes (e.g. albumin, hydroxyethyl starches)

Question 14

How does high Na+ and fluid retention contribute to CHF?

Answer 14

Fluid is being stored in areas it shouldn’t. The heart senses this as low blood pressure. This leads to increased RAAS, ADH, and fluid retention.