Body Fluids Flashcards
Homeostasis
The relative constancy of the Milieu Interieur
All functional activities are directed at maintaining homeostasis
Milieu Interieur
Internal environment remains relatively constant under conditions of health
Body water
-most abundant constituent of the body
- large variance of water content person to person (45-75 %)
-where solutes are dissolved and metabolic reactions take place
% of Water in Various Tissues
Skin - 70%
Muscle 0 75 %
Heart, Liver, Brain, Kidney - 70-80 %
Bone - 25 %
Fat - 10 %
Body Water proportion of Total body mass
Physiological reference individual: 60% water
More adipose tissue: Less than 60 % (45%)
Less adipose tissue: Over 60 % (75%)
If body water content is computed as a fraction of LEAN BODY MASS (excluding FAT) the differences between individuals become…
insignificant
Variations in body water with age and sex
-Decreases with age
-Male is greater than female
Infants ~ 75% (same in male and female)
Woman ~ 50% (more adipose tissue)
Man ~ 60%
Elderly ~ Less than 50% / 60%
Calculations of Body Water
Weight (kg) * % Water (%) = Water content (L)
For standard male: 42 L
Calculations for medication dosing
Water-soluble medications
Weight (kg) * % Water (%) = Water content (L)
mg medication (mg) / Water content (mL) = dose
Body water is in “Dynamic Steady State”
Between the individual and external environment and internally between compartments
Water Balance Intake
Intake (2.7 L)
-Oral Fluid 1.2 L
-Oral intake in food 1.1 L
-Oxidative water from metabolism 0.4 L
Water Balance Output
Output (2.7L)
Insensible (Obligatory)
-Lungs 0.4 L
-Skin (passive evaporation) 0.5 L
Sensible (Obligatory)
-Kidneys 0.5 L
-Stool 0.1 L
Facultative: losses vary with intake
-maintain balance with urine
-1.2 L
Sweat
Insensible Perspiration
-pure water
-passive evaporation
-from entire skin surface
-continuous and obligatory
Sweating
NEITHER OBLIGATORY NOR FACULTATIVE
(but still an output)
-Electrolyte solution
-Active secretion
-Sweat glands
-Activated by heavy work / high temp
Water turnover
Adult: 3-4% a day
Infant: ~10% a day
Infant- greater surface area : volume ratio = more passive evaporation
Negative Water Balance
Water loss > Water intake
1. Reduced Intake
2. Excessive Loss from Gut
3. Excessive Sweating
4. Excessive Loss in Expired Air
5. Excessive Loss in Urine
Water Intoxication
Water loss < Water intake
1. Excessive intake
2. Renal system failure
Body Water Compartment
ICF (Intracellular Fluid):
-2/3
-40% of body mass
~28 L
ECF (Extracellular Fluid)
-1/3
-20% of body mass
~14 L
ECF compartment divisions
2 Major subcompartments
- Plasma
- ISF (Interstitial fluid)
2 Minor subcompartments
-Lymph
-Transcellular Fluid
Water moves into capillaries becomes plasma and moves out becomes ISF
Plasma
the fluid medium, in which blood cells are suspended
- 1/3 of the ECF
-5% of body mass
~3.5 L
Centrifuged Blood
-Plasma ~55%
-Buffy Layer (WBCs and platelets) ~1%
-RBCs ~45%
Hematocrit
(height of erythrocyte column / height of whole blood column)
Percent of blood occupied by RBCs
Normal value ~45%
Interstitial Fluid (ISF)
The fluid which percolates between individual cells
- 2/3 of the ECF
-15% of the body mass
~10.5 L
Lymphatic System
~1-2% of ECF
Compartment % of Body Weight
Total H20 - 60%
ICF - 40%
ECF -20%
ISF - 15%
Plasma -5%
Transcellular fluid
Aggregate of small fluid volumes secreted by specific epithelial cells that line some body cavities
Have specialized functions in part of body
~ < 1-2% of ECF
Does not contribute to overall water exchange
Methods to Determine Compartment Volumes
Direct: volume measurement
Indirect: Indicator dilution method
Indicator dilution method
V = Q / c
- Total quantity of test substance introduced (Q)
- Concentration of substance / unit volume of plasma (c)
(IDM): Total Body Water measurement
-Antipyrine, D2O, or T2OQ
-Can pass through cell membrane and capillary wall
(IDM): ECF measurement
-inulin, sucrose, mannitol
-Can pass through capillary wall but not cell membrane
-Stays within the ECF (does not pass into cells)
(IDM): Plasma measurement
-Evans’ Blue (T1824) or I131-Albumin
-Can not pass through capillary wall
-Remains within the capillaries
(IDM): ICF and ISF calculations
Total Body Water - ECF = ICF
ECF - Plasma = ISF
Ionic composition
ICF
-High in K+ (and Mg++)
-Low in Na+and Cl-
ECF
-High in Na+and Cl- (0.9 % NaCl)
-Low in in K+
IN ECF
-plasma has proteins anions
-ISF has no proteins
(GRADIENT)
Artificial Physiological Solutions
substitute for ECF fluids (plasma/ISF)
Physiological Saline = 0.9% NaCl
Barriers” to Transport
Cell membrane : between ICF and ECF
Capillary wall: between ECF/ISF and plasma
Body Fluid Ionic Composition
ECF approximated by 0.9 % NaCl
300 mOsm = 6.7 atm ~ 5100 mmHg
