Renal Physiology: Body fluid compartments Flashcards
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)
Lactated Ringers (hartmanns) IV uses
Dehydration Burns Lower GI fluid loss Acute blood loss Hypovolaemia due to third spacing
what is dehydration and how does it affect the body, and what are the two types
Decreased water intake, increased fluid loss or both
-elderly people, impaired thirst sensation, chronic illness, fever, and sickness are common reasons for a decreased water intake
common causes are vomiting, diarrhea, diuresis, and sweating
can be hypernatremic (hypertonic):
- loss of water is greater than loss of sodium in ECF
- serium sodium concentrationin the ECF is greater than in the ICF so water shifts from the ICF to the ECF
- serum osmolality: will exceed 300 mOsm/kg
- serum sodium will be more than 140
- shrinkage of cells
- hyperactive reflexes muscular weakness
can be hyponaetremic (hypotonic):
- loss of sodium is greater than the loss of water in ECF
- Serum sodium concentration in the ICF is greater than that of the ECF
- water shifts from the ECF to the ICF to establish osmotic equilibrium
- serum sodium and serum osmolality will be less than the normal range
- cells swell
- brain swelling, irritability, depression, confusion, weakness
what does volume expansion and contraction mean
Volume contraction: means a decrease in ECF volume and also called a volume depletion
-causes decreased blood volume and decreased blood pressure
Volume Expansion: means an increase in ECF volume
-volume expansion can cause increased blood pressure and edema
Example, ECF volume, ICF volume, Osmolarity, Hct, and plasma protein when there is: Isosomotic volume contraction
Example: Diarrhea, burn, hemorrhage, vomiting
loss of isomotic fluid
ECF volume: Decrease
ICF volume: no change
Osmolarity: NC
Hct: Increase
Plasma protein: Increase
Example, ECF volume, ICF volume, Osmolarity, Hct, and plasma protein when there is: Hyperosmotic volume contraction
Example: Sweating, fever, diabetes insipdus, alcoholism
hypotonic fluid loss
ECF volume: Decrease
ICF volume: Decrease
Osmolarity: Increase
Hct: NC
Plasma protein: Increase
Example, ECF volume, ICF volume, Osmolarity, Hct, and plasma protein when there is: Hyposmotic volume contraction
Example: Adrenal insufficiency
ECF volume: Decrease
ICF volume: Increase
Osmolarity: Decrease
Hct: Increase
Plasma protein: Increase
Example, ECF volume, ICF volume, Osmolarity, Hct, and plasma protein when there is: Isosmotic volume expansion
Example: Infusion of isotonic NaCl
ECF volume: increase
ICF volume: NC
Osmolarity: NC
Hct: Decrease
Plasma protein: Decrease
Example, ECF volume, ICF volume, Osmolarity, Hct, and plasma protein when there is: Hypertonic volume expansion
Example: High NaCl intake
ECF volume: increase
ICF volume: Decrease
Osmolarity: Increase
Hct: Decrease
Plasma protein: Decrease
Example, ECF volume, ICF volume, Osmolarity, Hct, and plasma protein when there is: Hypotonic Volume expansion
Example: SAIDH, excess water drinking
Gain of hypotonic fluid
ECF volume: increase
ICF volume: increase
Osmolarity: Decrease
Hct: NC
Plasma protein: Decrease
what is a Darrow-Yannet Diagram
study the effect of various clinical conditions on osmolality and volume of extracellular and intracellular fluid
Osmolality on the Y-axis is represented by mOsm/kg H2O
while volume (on the X-axis) is represented in liters
solid line signifies normal values and dashed lines signify a change in the volume and osmolality
Effects of congestive Heart Failure
low effective circulating volume due to decreased cardiac output
- low pressure
- less carrying capacity
Na+ and fluid retention resulting in edema causing venous and paillary hydrostatic pressures to increase:
- activation of RAAS
- stimulation of SNS
- increased ADH
- increased renal fluid retention
Volume sensors and what they are looking for
Detect changes in the ECFV, signals to kidneys, which they adjust by the NaCl and water excretion
- ECFV expanded then renal NaCl and water excretion is increased
- ECFV in contracted then renal NaCL and water excretion is reduced
how does renin affect the body
secreted by kidney via stimulation from drop in BP or a B1 adrenergic activation
converts angiotensinogen to angiotensin I
- then converted to angiotensin II via the ACE in the lungs
- then leads to the release of Aldosterone
angiotensin II will increase thirst, vasoconstriction, increase TPR, increaase aldosterone
all increasing Pa and increasing ECFV
How does ADH/Vasopressin affect arterial pressure
secreted in response to angiotensin II, atrial receptors in presences of low preload, increassed osmolality of blood, or SNS
acts via V1 on blood vessels to increase (increase TPR)
acts via V2 on the kidneys to increase fluid resorption (H2O)
all lead to increase in arterial pressure
How does ANP affect the arterial pressure
Increased secretion by excessive preload of atria and ventricles
causes:
- arteriolar dilation to decrease TPR
- Increase fluid loss to decrease preload
- Inhibits renin to decrese both TPR and Preload
all decrease arterial BP
How much does an individual normally pee and what is polyuria, oliguria, and anuria and causes
typically an individuual pees 1-2 L/day
Polyuria: excessive urine production >2.5 L/day
-DM, DI, excessive caffeine or alcohol, kidney disease, drugs, anemia, excessive water intake
OLiguria: output below the minimum volume 300-500mL
-dehydration, blood loss, diarrhea, shock, kidney disease, enlarge prostate
Anuria: virtul absence of urine, less than 50mL
-kidney failure, obstruction via tumor or stone
what are the 4 mechanisms that can cause polyuria and the two different diuresis
1) increased intake of fluids as in psycogenic causes via stress and anxiety
2) increased GFR as in hyperthyroidism, fever, hypermetabolic states
3) increased output of solutes as occurs in DM, hyperthyroidism, hyperparathyroidism, diuretics
4) inabillity of the kidney to reabsorb water in DCT as in CDI, NDI, drugs and chronic renal failure
Water diuresis: increased water excretion without corresponding increase in salt excretion
- increase water intake
- polydipsia
- DI
SOlute (osmotic) diuresis: Increased water excretion concurrent with increased salt excretion -increased salt in tubular fluid -hyperglycemia -high protein intake -recovery from AKI P
what is the free water clearance equation
C(H2O) = V-Cosm = V- (Uosm x V)/Posm
Uosm = urine osmolarity V = urine flow rate P = plasma osmolarity
represents the rate at which solute free water is excreted by the kidneys
if it is positive there is excess water being excreted (diluted)
if negative then the excess of solutes are being removed from the blood by the kidneys and water is being conserved
if urine osmolarity is greater than plasma osmolarity, free water clearance will be negative indicating water conservation
Obligatory urine volume
minimal amount of solutes that a completely bedridden human must excrete in a day is about 700 mOsm or 1000 mOsm a day that is active
the kidney concentrate urine up to a maximal 1200 mOsm/L
i.e
70 kg must excrete 600 mOsm of solutes a day and if we think of the max urine concentrating ability to be 1200 mOsm/L
then 600/1200 = 0.5 L/day = oliguria
