Lecture 2: Body Fluids and Clearance Concepts Flashcards
What average percentage of body weight is water?
60% body weight
What does water percentage of body weight vary upon?
Gender and adipose tissue
Changes in body weight can reflect what?
Changes in water content
What % of body weight is intracellular fluid?
40% BW
What % of body weight is extracellular fluid?
20% BW
What does extracellular fluid consist of?
Interstitial fluid and plasma
What % of body weight is interstitial fluid?
~16% BW
What % of body weight is plasma?
~4% BW
What is intracellular fluid?
Water inside cells where intracellular solutes dissolve
What are the major cations of intracellular fluid?
K+; Mg+
What are the major anions of intracellular fluid?
Proteins and organic phosphates
What is extracellular fluid?
Water outside cells
What is the major cation(s) of extracellular fluid?
Na+
What is the major anion(s) of extracellular fluid?
Cl- and HCO3-
What is interstitial fluid (in basic terms)?
Ultrafiltrate of plasma
What does it mean when it is said that interstitial fluid is the ultrafiltrate of plasma?
No free proteins or blood cells, pores in capillaries allow small solutes to filter, but no protein or blood cells
What is the composition of interstitial fluid?
Similar to plasma (minus proteins and blood cells)
What do you multiply by to get mL?
1000
What can alter solute or water balance, causing water to shift between fluid compartments?
Physiological disturbances can alter solute or water balance
What does volume of a compartment depend on?
Total solute in compartment
What is osmolarity? (Include units)
Concentration of osmotically active particles (mOsm/L)
What is the osmolarity of a normal cell?
290 mOsm/L - 300mOsm/L
In steady state, what could be said about ICF osmolarity and ECF osmolarity?
Equal to one another, water shifts freely across membrane
If a disturbance occurs to change ECF osmolarity
Water shifts across cell membranes (depends on what change to determine direction)
What are considered to be confined to ECF as they cannot readily cross cell membranes
Large solutes/Na (ingestion of large amount of NaCl)
Any loss or gain of water and/or electrolytes initially occurs where?
ECF
Volume contraction
Decrease in ECF volume
Volume expansion
Increase in ECF volume
Isosmotic disturbance
No change in ECF osmolarity
Hyperosmotic disturbance
Increase in ECF osmolarity
Hypo-osmotic disturbance
Decrease in ECF osmolarity
If water is added, what can be said about the change in ECF?
Volume expansion
If isotonic saline is added, what can be said about the change in ECF?
Simply expanded (no solute added)
If salt is added, what can be said about the change in ECF?
More osmotic particles in ECF
What is the 3 step approach to predict changes in response to ECF disturbance?
- Identify change occuring in ECF (was solute added to ECF or water lost from ECF?)
- Will the change in ECF produce an increase, decrease, or no change in ECF osmolarity?
- If there is a change in ECF osmolarity, will water shift into or out of cells to reestablish equality between ECF and ICF osmolarity?
If there is no change in ECF osmolarity then
No water shifts occur
What is the affect of diarrhea on the ECF?
Lose large volume of iso-osmotic fluid from ECF
ECF volume decreases, but no change in osmolarity
Overall: ECF volume decreases, blood volume decreases, decrease in arterial pressure
No need for shift across membranes due to no change in osmolarity
What is the affect of water deprivation on ECF?
Lack of drinking water + sweating
Loss of volume in ECF; ECF osmolarity increases
Sweat contains more ___, than what?
More water than solutes
How does ICF react to water deprivation?
Water is going to move from ICF To ECF because ECF osmolarity is greater than the ICF osmolarity
What is the affect of adrenal insufficiency on ECF?
ECF osmolarity decreases since Na reabsorption not occuring as normal, Na being excreted in urine.
ECF osmolarity lower than ICF, so water (and some Cl-might come along) moves into ICF
What hormone is deficient in adrenal insufficiency, and which electrolytes are excreted in excess in urine?
Aldosterone; sodium reabsorption
What hormone regulates sodium reabsorption?
Aldosterone
What happens when there is an infusion of isotonic NaCl to ECF?
ECF volume increases, ECF osmolarity does not change
What happens when there is high NaCl intake?
NaCl added to ECF, ECF osmolarity decreases, water moves from ICF to ECF, which will decrease ICF volume
What happens to ECF and ICF volume and osmolarity with a syndrome of inappropriate anti-diuretic hormone?
Too much water reabsorption (ADH too high), volume of ECF increases, osmolarity in ECF decreases, water shifts into the ICF (ICF volume increases)
What is the importance of renal clearance?
Uses the rate at which a compound is “cleared” from the body (excreted in urine) to determine aspects of renal function
Renal clearance definition
Volume of plasma completely cleared of a substance by the kidneys per unit time
High renal clearance =
More plasma cleared of substance within a unit of time
Substance may be completely removed in single pass through kidneys
Low renal clearance =
Substance may not be removed at all (or very little amount removed)
Clearance can be calculated for
Any substance
Clearance for some substances has
Clinical significance
Inulin or creatinine are used to
Estimate glomerular filtration rate
Glomerular filtration rate (GFR)
Process by which kidneys filter blood
Goes down if kidney function decreases, way to estimate kidney function
Inulin and creatinine are
Exogenously given
Para-aminohippurate (PAH) is
Endogenous
Para-aminohippurate (PAH) is used to
Estimate renal plasma flow (RPF)
Renal plasma flow (RPF) is
The volume of blood plasma delivered to kidneys per unit time
Renal clearance can vary from
0-600 mL/min
PAH (RPF gold standard) is
Filtered and secreted
Inulin (GFR gold standard) is
Filtered ONLY – nothing happens to it besides filtration
Sodium, calcium, magnesium, phosphate are
Filtered and reabsorbed
Potassium is
Filtered + reabsorbed, secreted
Albumin is
Should be zero filtration
Glucose is
Filtered and completely reabsorbed, very little to NONE in urine
Clearance ratios are
Clearance of any substance that might be coming through the kidney can be compared with the clearance of a gold standard such as inulin to express a clearance ration
CR = 1.0
Filtered, but no net secretion or reabsorption
CR > 1.0
Filtered and secreted, amount in urine > what was filtered by glomerular
CR < 1.0
Either substance is not filtered or is filtered and reabsorbed
What makes inulin perfect for clearance ratio calculation?
- Only substance whose clearance is exactly equal to GFR, it is freely filtered, and either reabsorbed or secreted
- Amount of inulin filtered is amount excreted