Body Fluids II
In severe hyperglycemia, glucose acts as an effective osmole and can induce hyponatremia and cell shrinkage. What should the physician focus on treating?
The cell shrinkage, not the hyponatremia needs correcting.
What does the osmotic concentration depend on?
The gram molecular weight of the solute and its dissociablility.
Access to all cells of the body, except the red cells, is via what space?
The interstitial space.
If a primary disturbance causes extracellular fluid (ECF) osmolarity to decrease, what will happen to Intracellular fluid volume (ICFV)?
(ECF) osmolarity decrease = ICFV increase water moves into the cells and the cells swell
If a primary disturbance causes extracellular fluid (ECF) osmolarity to increase, what will happen to Intracellular fluid volume (ICFV)?
(ECF) osmolarity increase = ICFV decreases water moves out of cells and cells shrink
IF 1.0 mole of NaCl is completely dissociated in 1 L, How many osmolar solution does it form? IF One mole of CaCl2 is completely dissociated in 1 L, How many osmolar solution does it form? WHY?
1.0 mole of NaCl, if completely dissociated in 1 L, forms a 2.0 osmolar solution. One mole of CaCl2, if completely dissociated in 1 L, forms a 3.0 osmolar solution. YOU KNOW WHY!
What is the approximate "Total Body Water in adult males? What about in adult females? How many Liters is this for the "average" adult male weighing 70kg?
55 to 60% of body weight in adult males 50 to 55%, in adult females 42L
What effect will a decrease in plasma protein concentration have on water between the interstitium and the plasma?
A decrease in plasma protein concentration causes water to move from the plasma into the interstitium.
What equation can be used to estimate the plasma osmolarity measured by the clinical laboratory?
BUN signifies blood urea nitrogen, and the numbers 18 and 2.8 change from the normal clinical concentration units (mg/dl) to milliosmolar units (mOsm/L).
What affects do Hypertonic Solutions have on intracellular volume?
Administration will tend to contract intracellular volume.
What affects do Hypotonic Solutions have on intracellular volume?
Administration will tend to expand intracellular volume.
What affects do Isotonic Solutions have on intracellular volume?
Administration won't alter intracellular volume.
How does the total osmotic concentrations of extracellular and intracellular fluids compare?
Although ionic composition of extracellular and intracellular compartments is different, the total osmotic concentrations are similar
What effect will an increase in plasma protein concentration have on water between the interstitium and the plasma?
An increase in plasma protein concentration causes water to move from the interstitium into the plasma.
Because membrane pumps effectively keep Na from entering cells, what effect does the osmotic force generated when there is a decrease in extracellular sodium concentration?
Causes extracellular water to move into cells.
How do you measure the concentration of a body fluid in a well-mixed compartment?
Concentration = Amount Injected / Volume of Distribution
What information does a Hematocrit give?
Gives the fraction of blood that is cells.
What is Hypernatremia? What is it generally indicative of? What cells are of particular significance?
High blood sodium concentration Decreased intracellular fluid volume (cell shrinkage) Brain cells being of particular significance!
How does intracellular fluid volume change in response to changes in extracellular fluid osmolarity?
Intracellular fluid volume Changes in response to changes in extracellular fluid osmolarity, but *not* in response to *isosmotic* / *isotonic* changes in extracellular fluid volume.
Approximately, what percent of your body weight is Intracellular fluid? What percent is Extracellular fluid? What percent is Plasma?
Intracellular fluid- Approximately 36% of body weight. Extracellular fluid- Approximately 24% of body weight. Plasma- 4.5% of body weight.
What is the principle intracellular cation?
K+
What is Hyponatremia? What is it generally indicative of? What is it necessary to rule out?
Low blood sodium concentration Generally indicative of increased intracellular fluid volume (cell swelling). Necessary to rule out hyperproteinemia and hyperlipidemia
How do you measure Intracellular Fluid Volume (ICFV)?
Measured by subtraction: ICFV = TBW - ECFV
How do you measure Interstitial Fluid Volume (ISFV)?
Measured by subtraction: ISFV = ECFV - PV
What is the principle extracellular cation?
Na+
What is Osmotic Concentration?
Particles that dissociate to form ions exert an osmotic force in proportion to the number of osmotic particles formed.
What is the equation that relates Plasma volume with blood volume and the Hematocrit?
Plasma volume = Blood volume x (1-Hct). If Hematocrit is given in percentage i.e. 52% then you take 1-0.52
What is the exit point for the body's waste products?
Plasma water
What is the initial body access point for ingested nutrients?
Plasma water
Under normal conditions, what equation can be used to roughly estimated ECF osmolarity?
Posm is plasma osmolarity.
When measuring body fluid compartments, how do you correct for any substance that is excreted during the time it takes for the injected substance to distribute itself in the compartment of interest?
Solving the corrected version of the equation for volume of distribution yields:
IF given plasma osmolarity measured by the clinical laboratory, why calculate Effective Osmolarity?
Urea (BUN) crosses cell membranes just as easily as water, so it does not contribute to redistribution of water between ECF and ICF.
Because membrane pumps effectively keep Na from entering cells, what effect does the osmotic force generated when there is an increase in extracellular sodium concentration?
Water moves out of cells into the extracellular space.
What cation is ECF osmolarity is dominated by?
[Na+] and the associated anions which are necessary to maintain electroneutrality.
What are the principle extracellular anions?
chloride and bicarbonate.
What is the force generated by water movement across a semipermeable membrane?
osmotic pressure
What are the principle intracellular anions?
phosphates [both inorganic (HPO42-, H2PO4-) and organic (ATP, etc.)] and proteins.
Since all ions can cross the capillary endothelial cell membranes that separate the plasma water from the interstitial what is needed to exert important net osmotic forces across the capillary barrier?
plasma proteins
What is the difference between an ineffective osmole and an effective osmoles?
the anions ability to determine the distribution of water between ECF and ICF
