Lecture 12: Renal Physiology (Rogers) Flashcards
In the body, how is water distributed?
⅔ of water in ICF
⅓ of water in ECF
In the ECF how, is water distributed?
80% interstitial fluid
20% plasma (capillary wall)
What is the 60-40-20 rule?
60% of body weight is body water
40% of body weight is body water in ICF
20% of body weight is body water in ECF
How do constituents between the ICF and external world interact with each other?
Through ECF
-water always enters ECF compartment first and fluid leaves body via ECF
Describe “third spacing”
Most fluids should be in intravascular, intracellular, or interstitial spaces
- However, fluid can shift into nonfunctional areas of cells: b/t tissues and organs of abdomen, ascites, areas around pulmonary edema
- problematic
Why must ECF volume be closely regulated?
To maintain blood pressure
- salt balance
- prevent shrinking and swelling of cells
What ions are in higher concentration in the ECF?
Sodium
Chloride
Bicarbonate
What ions are in higher concentration in the ICF?
Potassium
Phosphate
What is an electrolyte?
Solutes that dissociate into ions
- have higher osmotic power
- greater ability to cause fluid shift
What can cause polyuria?
Increased intake of fluids
Increased GFR
Increased output of solutes
Inability of kidney to reabsorb water
Regarding polyuria, what is the difference between water and solute diuresis?
Water diuresis: increased water excretion w/o corresponding increase in salt excretion
Solute diuresis: increased water excretion with corresponding increase in salt excretion
What can cause oliguria?
Dehydration
Blood loss
Diarrhea
Kidney disease
What can cause anuria?
Kidney failure
Obstruction
How do you calculate free water clearance?
Clearance = Urine Flow Rate - [(Urine Osmolarity x Urine Flow Rate) / Plasma Osmolarity]
What does it mean if free water clearance is positive?
Dilute urine
What does it mean if free water clearance is negative?
Concentrated urine
How is plasma (serum) osmolarity measured?
Osmolarity = (Sodium x 2) + (Glucose/18) + (BUN/2.8)
Rough Calculation: 2 x plasma Sodium
Describe the Gibbs-Donnan Effect.
Unequal distribution of permeant charged ions on either side of a semipermeable membrane
- favors movement of water into cell
- only ions can move into cell not proteins
What counteracts the Gibbs-Donnan Effect?
Na/K+ ATPase pumps
What promotes plasma colloid osmotic pressure?
Albumin in blood vessels
What causes edema?
1) Increased net filtration: fluid moving from vascular space to interstitium)
2) Expansion of ECF volume
What happens to cells placed in hypertonic solution?
Cells will shrink
-water moves out of cell into concentrated solution
What happens to cells placed in hypotonic solution?
Cells will swell
-water moves into cell from dilute solution
Describe crystalloid replacement therapy.
Does not cross plasma membrane (in ECF)
- distributed evenly in ECF
- common solutes: glucose and NaCl
