1 - Renal Flashcards
(38 cards)
What are the functions of the kidney?
- Excretion of metabolic waste
- Regulation of water and electrolytes
- Regulation of body fluid osmolality and electrolyte concentrations
- Regulation of art BP
- Reg of acid-base balance
- Secretion, metabolism, and excretion of hormones
- Gluconeogenesis
Essentially control volume and composition of body fluids.
How is fluid lost? What is the way that is controlled?
Through the skin, lungs, sweat and feces.
Urinary excretion of water tightly controlled.
How much of our body weight is composed of water? What is the average man we consider for our calculations and how much of his body volume is water?
Typically 50-70%. Greater in lean individuals.
Avg 70 kg man - would have ~42 L of total body water (70 x .6)
How is the water in the body distributed?
How does this divide out for the 70 kg man?
Intracellular fluid (ICF) - 2/3 of total body water (40% of body weight)
Extracellular fluid (ECF) - 1/3 total body water (20% weight)
70kg man would have ~28 liters (42 x 2/3) in the ICF and ~14 L in the ECF.
What is extracellular fluid composed of?
How does this pertain to the 70kg man?
Interstitial fluid: ~3/4 of ECF
Plasma (non-cellular, liquid): ~1/4 of ECF
70kg man: ~11 L in the interstitium and ~3 of plasma.
How do you calculate blood volume? What is the blood volume of a normal individual?
Plasma volume / (1-Hct)
3/ (1-.40) = ~5 L
What separates the ECF and ICF?
What separates the plasma and interstitial fluid?
ECF and ICF: cell membrane
Plasma and interstitial fluid: capillary membrane
How does the composition of plasma differ from that of interstitial fluid? Why isthis?
They are approx the same except that plasma has a higher concentration of protein.
This is because the capillary wall is highly permeable to water, electrolytes, and other small molecules but not to proteins.
Explain the differences between the ECF and ICF?
Cell membrane is highly permeable to water, but not most electrolytes.
ECF is relatively high in Na+, Cl-, and HCO3-.
ICF is relatively high in K+, PO43-, organic anions, and protein.
How do you measure body fluid volumes using the indicator dilution method?
Indicator Mass A = Volume A x Concentration A
Indicator mass A = Indicator mass B
Indicator mass B = Vol B x concentration B
Volume B = indicator mass B/Concentration B
How do you calculate body fluid volume?
Volume = quantity remaining in body (amount) / Concentration (amt/vol)
A 70 kg man is injected with 4x10^6 cpm H2O, 15 minutes later the sample is measured at 100 cpm/ml. Calculate the total body water?
total body water = Q/C = 4x10^6 cpm / 100 cpm/ml = 40,000 ml = 40 L
What governs the distribution of water between the ECF and ICF?
Osmotic forces, the barrier being the cell membrane.
Define osmolarity
Function of the total number of proteins in solution, independent of mass, charge, or chemical composition.
Concentration of osmotically active particles in the total solution.
Expressed in terms of milliosmoles (mOsm)/L
For substances that do not dissociate into smaller ones, how many osmoles are in one mole? What does this mean in terms of miliosmoles?
1mmol = 1milliosmole
It’s a one to one ratio when they do not dissociate.
What is the ratio of mmoles to miliosmoles for NaCl?
The miliosmoles is 2x the mmolarity.
1mmol NaCl = 2 mOsm
What is the osmolarity of the ECF and ICF typically? How does this change throughout the body?
280 - 300 mOsm/L
Nearly identical in all major body compartments.
Define osmolality?
When does osmolarity ~= osmolality?
mOsm/Kg solvent (water)
In relatively dilute solutions such as those found in the body.
What is osmotic pressure?
When can dissolved particles exert osmotic pressure?
The force that dissolved particles (osmolytes) exert., which tends to pull water across a semiperm membrane.
Only can exert osmotic pressure if it is not permeable to the membrane,
How do you calculate osmotic pressure?
What is the osmotic pressure of plasma at 37 degrees C?
p = CRT
C=concentration
R=constant
T=temp
At 37 degrees C, osmotic pressure = 19.3 X 282 mOsm/L = 5443 mmHg
Define osmosis
Movement of water across a semi-perm membrane due to differences in osmolarity (osmotic pressure gradient)
What is tonicity?
A term used in reference to the influence of the solution on the volume of a cell.
Define isotonic, hypertonic, and hypotonic?
Solutions that do not change the cell are isotonic.
Hypertonic solns make the cell shrink.
Hypotonic solns make the cell swell.
How does the distribution of fluid between the plasma and interstitial fluid change?
Barrier is capillary membrane, and the distribution is governed by starling forces.
