Renal Physiology: Body fluid compartments Flashcards
(43 cards)
what is the 60 40 20 rule
60 percent of body weight is total water
40 percent of body weight or 2/3 of total body water is intracellular fluid (ICF)
20 percent of body weight or 1/3 of total body water is extracellular fluid (ECF)
these are divided by a cell membrane
of the extra cellular fluid what are the components that make it up
3/4 of the ECF is interstistial fluid
1/4 is the plasma of the ECF
these are divided by a capillary wall
what is the only fluid that can be acted on directly to control its volume and composition, how does it effect the other spaces
Plasma
If the volume and composition of the plasma are regulated the volume and composition of the interstitial fluid bathing the cells are also regulated
any control mechanism that operates on plasma in effect regulates the entire ECF
what is the significance of the ECF
it is the intermediary between the cells and the external environment
all exchanges of H2O and other constitutents between the ICF and the external world must occur through the ECF
water added to the body fluids always enters the ECF compartment first, and fluid always leaves the body via the ECF
what is the third spacing?
it is part of the ECF
its where too much fluid shifts from the blood vessels (intravascular) into the nonfunctional area of cells (fluid trapped between tissues and organs of the abdomen)
-pulmonary edema
this is problematic and represents fluid lost from the intravascular space
how are fluid compartments seperated
Fluid compartments are seperated by a semipermeable membrane
utilizing osmosis, mater moves from an area of higher concentration of water to an area of lower concentration of water
how is the ECF and the ICF different in composition
ICF has proteins that cant permeate the plasma membrane to leave the cell, Plasma has proteins that cant penetrate the capillary wall
as a result of the membrane bound Na+/K+ ATPase
- ICF has high K+ but low Na+, also has high PO4-
- ECF has low K+ and high Na+, has high Cl-
difference between an electrolye and a nonelectrolyte
nonelectrolyte: contain covalent bonds that prevent them from dissociating in solution and therefore have no electrical charge (glucose, lipids, urea)
electrolyte: dissociate into ions in water (Mg+, Na+, Cl-, K+)
- have a higher osmotic power because they can dissociate into at least two ions
- greater abillity to cause a shift
Osmolality vs osmolarity
Osmolality is a measure of the number of osmotically active particles per kilogram of H2O
Osmolarity is the number of osmotically active particles per liter of total solution
all body fluid compartments have approximately the same osmolality (290mOsm)
how to measure the fluid compartments
Volume of B = (Vol A x Conc A)/ (Conc of B)
Indication-dilution method: use a tracer dye and enter into a substance
- know the concentrations of both once the dye mixes
- calculate volume
requirements:
- the indicator disperses evenly throughout the compartment
- the indicator disperses only in the compartment that is being measured
- indicator is not metabolized or excreted
what indicators to use for specific volumes and how to find them:
Total body of water: H2O and antipyrine
Extracellular fluid: Na, I-iothalamate, thiosulfate, inuliin
Intracellular fluid: calculated as total body water -extracellular fluid voluume
Plasma volume: I-albumin, evens blue die
Blood volume: Cr labeled red blood cells or calculated as blood volume=plasma volume
Interstitial volume: (calculated as extracellular fluid volume-plasma volume)
what are the main solutes of the plasma and how do we calculate its osmolarity
Sodium, glucose, urea
2(Na+) + glucose/18 = BUN/2.8 = mOsm/kg
what is the eyeball way to calculate plasma osmolality
2(plasma[Na+])
Gibbs-Donnan Effect
Cell membranes are impermeable to proteins (negative charge)
Presence of negatively charge proteins (anions) creates two events
-protein particles create an oncotic gradient facoring the movement of water into the cell
-negative charges on proteins creates an electrical environment favoring the movement of charges into the cell
leads to membrane permeable to ions but impermeable to large proteins
How is the the Gibbs-Donnan effect couteracted
Na/K ATPase pump counter acts the inward force created by the gibbs-Donnan effect
- 3 Na+ out for 2K+ in
- Net balance prevents excessive inward movement of water
if did not have this the intracellular proteins would result in an influx of water into the cell (causing death
what are the forces of the starling forces
Osmotic pressure: pull of pressure of large proteins that cant pass through the membrane i.e. albumin
-albumin would be plasma colloid osmotic pressure
also have hydrostatic pressure
- pressure for water to leave the area
- BP is the capillary hydrostatic pressure
What is Edema and two causes
Palpable swelling produced by expansion of interstitial fluid volume
Causes:
1) alteration in capillary hemodynamics (altered starling forces with increased net filtration pressure)
-fluid moves from vascular space into the interstitum
-need a 2.5 - 3 L increase
-compensatory renal retention of Na+ and water to maintain plasma volume
2) Renal retention of dietary Na+ and water expansion of ECF volume
- Inapporopriate renal fluid retention
- usually results in elevated blood pressre, expanded plasma and interstitial volumes
- renal disease (glomerulonephritis, nephortic syndrome)
- non pitting edema: swolen cells due to increased ICF volume
- Pitting edema: increased interstitial fluid volume
- Dema often treated with diuretics
What is the Tonicity of a solution, isotonic, hypertonic, and hypotonic
is the effect the solution has on cell volume whether the cell remains the same size, swells, or shrinks when the solution surrounds the cell
-cells have a NaCl concentration equal to 0.85
Isotonic: concentration of the environment is equal to the cell, there is equal movement of water in and out
Hypertonic: cells placed in environment with higher concentration of solute
-water will leave cell to go into the environment and cause the cell to shrink
Hypotonic: cells environment has a lower concentration of solute
-net movement of water into the cell which will cause the cell to swell
if their is an increase or decrease in the ECF how does it affect the total protein plasma
ECF volume loss will result in an increase total plasma protein concentration
ECF volume gain will result in decreased total plasma protein dilution
what is the average blood volume of adults and what is it made up of
7 percent of body weight or about 5 liters of blood
about 60 percent of blood is plasma and 40 percent is red blood cells
how does ECF and ICF decreases and increases affect the Hematocrit
ECF volume loss will result in increased in hematocrit concentration
ECF volume gain will result in decreased hematocrit (dilution)
ICF volume loss will result in decreased hematocrit (shrinkage of red blood cells)
ICF volume gain will result in increased hematocrit (swelling of red blood cells
what are the two types of replacement therapy for fluid and their characteristics
crystalloids and colloid
crystalloids:
- contain organic or inorganic salts dissolved in water
- Do not cross plasma membranes and remains in ECF
- will difuse across capillary walls
- most common is NaCl and glucose
Colloid:
- contain large molecules that dont pass through semipermeable membranes
- when infused they remain in intravascular compartment and expand intravascular volume by drawing fluid from extravasular spaces
- albumin, hydroxyethy starches (HES)
Dextrose 5% IV uses
FLuid loss
dehydration
hypernatraemia
0.9% sodium choride IV uses
Shock Hyponatraemia Blood transfusions Resusitation fluid challenges Diabetic Keto acidosis (DKA)
