Lecture 4: Renal Phys. Body Fluid Compartments Flashcards
What’s the 60-40-20 rule; total liters in ECF and ICF?
60% of BW is total body water
40% of BW or 2/3 TBW is ICF (25 L)
20% of BW or 1/3 TBW is ECF (15 L)
The only fluid that can be acted on directly to control is volume and composition is?
Plasma
Any control mechanism that operates on plasma will in effect regulate what?
The entire ECF - since interstitial will also be regulated
Water added to the body fluids and fluid leaving will always go through which compartment?
Water added to the body fluids always enter the ECF compartments first, and fluid always leaves the body via the ECF
When third spacing occurs, fluid is being lost from?
The intravascular space into the “nonfunctional” are of cells
Water moves in which direction based on water concentration/solute concentration?
Areas of higher water concentration (more dilute, lower solute) —> lower concentration (more concentrated, higher solute conc.)
Na+ is the primary cation of, and K+ is the primary cation of?
Na+ is primary ECF cation
K+ is primary ICF cation
What are nonelectrolytes; and their charge?
Contain covalent bonds that prevent them from dissociating in solution and therefore have no electrical charge (i.e., glucose, lipids and urea)
What are electrolytes?
Dissociate into ions (ionize) in water
Each electrolyte dissociates into at least? Gives them which power?
At least two ions; gives them higher osmotic power (ability to cause fluid shift)
What is the osmolality of all body compartments?
290 milliosmoles/kg H2O (290 mOsm)
*Use 300 mOsm
What is the extra 1 mOsm representative of?
Colloid osmotic pressure or oncotic pressure (force of proteins)
ECF of the blood is?
Plasma
ICF of the blood is?
RBC’s
Average blood volume of adults is ___% of BW, or about _____ liters
7% of BW, or about 5 liters
ECF volume loss will result in what change to total plasma protein?
Increased total plasma protein (concentration)
ICF volume gain will result in what change to total plasma protein?
Decreased total plasma protein (dilution)
Hematocrit is the fraction of the blood composed of (equation); normal for men and women?
RBC’s; Height of RBC’s/Total Height (in test tube)
Men: 0.40
Women: 0.36
ICF volume loss will cause what disturbance to hematocrit?
Decreased hematocrit (shrinkage of RBC’s)
ICF volume gain will cause what disturbance to hematocrit?
Increased hematocrit (swelling of RBC’s)
How is intracellular fluid calculated?
TBW volume - ECF volume
How is interstitial fluid volume calculated?
ECF fluid volume - plasma volume
Presence of negatively charge proteins (anions) creates what two events? (Gibbs-Donnan effect)
- Protein particles create oncotic gradient favoring the movement of water into the cell
- Negative charges on proteins create an electrical environment, favoring the movement of charges into the cell
Membrane is permeable to ______ and impermeable to ______?
permeable to ions and impermeable to large proteins
What counters the inward force created by the Gibbs-Donnan effect to prevent cell swelling/death?
Na/K ATPase pump; pumps 3 Na+ out for every K+ in
How does the Na/K ATPase protect the swell?
Pumping out the Na+ maintains a higher concentration of Na+ outside the cell preventing the excessive inward movement of water.
Which 2 factors make the free movement of fluids between compartments possible?
- H2O molecules diffuse thru capillary walls faster than blood
- Pressure difference between the inside and outside of the vessels (capillary filtration pressure)
When hydrostatic pressure builds inside capillary, fluid and solutes are forced where?
Out through the capillary walls into the interstitial fluid
Normally capillary blood pressure (hydrostatic) exceeds plasma colloid osmotic pressure in what end and falls below it in?
Exceeds in the arteriole end and falls below it in the venule end.
The main contributing protein to plasma colloid oncotic pressure is; acts like a magnet how?
Albumin; attracts water and hold it inside the blood vessel
Best indicators for Total body water?
3H2O, 2H2O, antipyrine
Best indicators for Extracellular fluid?
Inulin
Best indicators for Plasma volume?
Albumin, Evans blue dye
Best indicator for Blood volume?
51Cr-labeled RBC’s
How do you solve for the concentration and volume with an indicator?
C1V1 = C2V2 *rearrange for desired value
Isotonic-cell enviornment has a NaCl concentration of; what happens to cells placed here?
- Equal to 0.85%
- Will be equal movement in and out of cell (no net flow)
Hypertonic-cell enviornment has a NaCl concentration of; what happens to cells placed here?
- >0.85%
- Water will rush out of cell causing it to shrink
Hypotonic cell-enviornment has a NaCl concentration of; what happens to cells placed here?
- <0.85%
- Water will rush in causing them to swell
Replacement therapy is divided into 2 general categories, what’s the difference?
1) Crystalloids - organic or inorganic salts dissolved in saline (i.e., 0.9% sodium chloride) and lactated Ringer’s
2) Colloids - Contain large molecules that don’t pass through semipermeable membranes, remain in intravascular compartment
Why do Crystalloid replacement therapies work; mechanism?
DO NOT cross plasma membrane
- remain in ECF
- Can readily diffuse across capillary walls to equilibrate the intravascular (plasma, ECV) and interstitial volume. ECF will be diluted now so we can work towards a balance rather than having water rush out of the cells towards the increased osmolarity of the ECF due to dehyrdration
How does the body sense its osmolality; part of brain; what do they stimulate secretion of?
- Osmoreceptors in brain (organum vasculosum of OVLT)
- OVLT connect to hypothalamus, the source of ADH
- Will cause secretion of ADH when blood osmolality increases.
The two effects of ADH (aka vasopressin)?
- Prevent diuresis = conserves body water
- Vasoconstriction
Increases in osmolality leads to what 2 events, which happens first?
- Changes in osmolality lead to release of ADH and stimulate thirst
- ADH is released at lower osmolarity than thirst *Why by the time you feel thirst you’re already dehydrated
Where is ADH produced, and where is is secreted?
Produced in the Hypothalamus, released by the Posterior Pituitary
Explain the negative feedback mechanism once ADH is released
ADH is released, causing constriction of blood vessels inhibiting the signal of high solute concentration
What are 2 abnormalities of ADH secretion:
1) Syndrome of inappropriate hypersecretion of ADH
2) Diabetes insipidus (lack of ADH)
Equation for Osmolarity
Osmolarity = (2 x Na+) + (glucose/18) + (BUN/2.8)
What are the 3 kinds of dehydration?
Isotonic (isonatremic): Both H2O and Na+ lost in equal amounts —> no net water flow
Hypotonic (hyponatremic): Loss of Na+ > loss of H2O in ECF –> net flow of water into cell
Hypertonic (hypernatremic): Loss of H2O > loss of Na+ in ECF —> net flow of water out of cell
What’s represents on the X and Y axis of a Darrow-Yannet diagram; solid vs. dashed line?
X-axis: Volume (liters)
Y-axis: Osmolality (mOsm/kg H2O)
*Solid line represent normal and dashed is the change
Volume contraction vs Volume expansion; effect on ECF
Volume contraction (depletion) = decreased ECF = decreased blood volume and BP
Volume expansion = increased ECF = increases BP and edema
What is shown here and what causes this?
Iso-osmotic volume contraction
- Hemorrhage
- Diarrhea
- Vomiting
What is shown here and what can cause this?
Hyper-osmotic volume contraction
- Dehydration
- Diabetes insipidus
- Alcoholism
What is shown here and what can cause this?
iso-osmotic volume expansion
- Infusion with saline and NaCl solution
- ECF volume would increase, but no change in osmolality and ICF volume
What is shown here and what causes this?
Hypo-osmotic volume expansion
- Excess water-drinking and SIADH (syndrome inappropriate ADH)
- Increases in ECF and ICF volume, decreases osmolality
