Test 1 (Body Fluids Compartments Lecture) Flashcards
Total Body Water (TBW)
= 0.6 x Body Weight
Extracellular Fluid (ECF)
= 0.2 x Body Weight
- Can be broken up into Interstitial Fluid (3/4 of ECF) and Plasma (1/4 of ECF)
Intracellular Fluid (ICF)
= 0.4 x Body Weight
Effective Circulating Volume (ECV)
- Is the volume of the Arterial Blood EFFECTIVELY PERFUSING TISSUE
- 20%!!!!!
Transcellular Fluid
- Included in the ECF
- It normally contains only a small amount of water such as Epithelial Secretions, Synovial, CSF, etc
- It is said to occupy a “THIRD SPACE”
**The Venous side is the COMPLIANT SIDE!!!!!
Hypovolemia due to Vomiting
1) Effective Circulating Volume:
- DECREASES
2) Extracellular Fluid Volume:
- DECREASES
3) Plasma Volume:
- DECREASES
4) Cardiac Output:
- DECREASES
Heart Failure
1) Effective Circulating Volume:
- DECREASES
2) Extracellular Fluid Volume:
- INCREASES
3) Plasma Volume:
- INCREASES
4) Cardiac Output:
- DECREASES
Clinical Relevance of Body Fluid Compartments
Pharmacology: Volume of Distribution (Vd) of a drug
- Apparent volume of Body Fluid in which the TOTAL DOSE of the drug is distributed at the same concentration as in the Plasma. USEFUL IN CALCULATING LOADING DOSES
Volume of Distribution Assumptions:
1) Vd
1) Vd 45L
- Drug widely distributed and body in BODY TISSUES
Body Fluid Compartments- Intake and Output are Balanced
***The Main OUTPUT of Body Fluids is from URINE!!!!!!!
Constituents of Body Fluids
Extracellular:
- Na+ as the MAIN CATION
- Cl- as the main ANION
Intracellular:
- K+ as the MAIN CATION
- HPO4-, and H2PO4- are the main ANIONS
**At ALL TIMES, the OSMOLARITY is the same between the Intracellular and Extracellular Compartments!!!!!
Non- Electrolytes
- HIGHER PROTEIN levels in ICF and Intravascular compartments (Primarily Albumin); LOWER in Interstitial Fluid
- Proteins normally DO NOT MOVE (Membranes are IMPERMEABLE to Proteins), therefore they DO NOT normally impact OSMOLARITY but do exert ONCOTIC PRESSURE
Oncotic Pressure
- Osmotic pressure generated by LARGE MOLECULES (Proteins) in solution which are IMPERMEABLE to Membranes
Measurements of Body Fluid Compartment Volumes- Indicator/ Dilution Methods
1) Total Body Water
2) Extracellular Fluid
3) INTRACELLULAR FLUID
4) Plasma Volume
5) INTERSTITIAL FLUID
1) H2O, H2O, ANTOPYRINE
2) Na, I- Iothalamate, THIOSULFATE, INULIN
3) (Calculated as TOTAL BODY WATER - Extracellular Fluid Volume)
4) I-Albumin, Evans Blue Dye
5) (Calculated as EXTRACELLULAR FLUID VOLUME - Plasma Volume)
Balance of Ions
Normally, Osmolarity is balanced between:
1) Interstitial and Intravascular Fluids (ECF Compartments)
2) ECF and ICF
**Na and K Concentration is slightly HIGHER in Vascular Space than expected fur to DONNAN EFFECT
Donnan Effect
- Negative charge of Proteins with Vasculature attracts POSITIVELY Charged Na and K Ions
Osmolarity of Body Fluid Compartments
1) ECF Osmolarity id due to:
- [Na + Cl]
- Concentration of Na in Vasculature > Interstitial Fluid > ICF
( Due to Na- K ATPase pump on Cell Membranes working Normally) - Disruption of Pump Activity (HYPOXIA) results in INCREASED ICF Na
- Water follows Na+ into cell and Cellular Swelling occurs
2) ICF Osmolarity is due to:
- [K+]
Osmolarity of Body Fluid Compartments
Plasma Osmolarity can be estimated by:
1) 2 x [Na+]
2) 2 x [Na+] + Glucose/ 18 + Urea/ 2.8
Movement of Water between compartments
1) Cell membrane between ECF and ICF is HIGHLY WATER- PERMEABLE
- NOT Permeable to most electrolytes
- Fluid distribution between two compartments in dependent on Osmolar Gradient
2) Capillary membrane between ECF compartments is highly permeable to SMALL IONS - Fluid distribution is due to a Balance of STARLING FORCES:
A) CAPILLARY HYDROSTATIC PRESSURE (Favoring Filtration)
B) COLLOID ONCOTIC PRESSURE (Primarily due to PLASMA PROTEINS which OPPOSES FILTRATION)
- The primary protein is Albumin
Fluid Shifts- Osmotic Equilibrium
- ECF Osmolarity controls ICF Volume
- Water enters or leaves ECF Rapidly to Balance Osmolarity of ECF and ICF
“OSMOTIC EQUILIBRIUM”
- Movement of water across Cell Membranes from Higher to Lower Concentration as a result of an OSMOTIC PRESSURE DIFFERENCE (Difference in number of Solute Particles in Solution) across the Membrane
- Osmotic Pressure exerted across a Membrane by a substance is also due to that membrane been IMPERMEABLE to that SOLUTE!!!
Osmotic Equilibrium
- 1) Initially ECF and ICF have same SOLUTE CONCENTRATIONS
2) Withdraw 3 Liters Pure H2O from ECF: Osmotic Gradient is created
OSMOTIC EQUILIBRATION:
- H2O RAPIDLY diffuses from ICF to ECF to re-establish OSMOTIC EQUILIBRIUM. Note Proportional changes in each Compartment’s VOlume
Think changes in ECF FIRST!!!!!!
- All water and Solutes must pass through ECF (Acts as a reservoir)
- Evaluate changes in ECF First, the ICF
**Equilibration of ICF and ECF Osmolarity occurs primarily by SHIFT in WATER and not Shifts in Solute
Factors Affectin Osmolarity and Volume of ECF/ ICF
- Water Ingestion
- Dehydration
- Intravenous Infusions
- Diarrhea or Vomiting
- Sweating
- Diuresis
- Disease
Fluid Shifts
1) Excessive NaCL Intake, Hyperaldosteronism (Conn’s Disease)
A) ECF Volume:
- INCREASE
B) ICF Volume:
- DECREASE
C) ECF mOsm:
- INCREASE
D) ICF mOsm:
- INCREASE
2a) Water Gain Initially (SIADH, Psychogenic Polydypsia)
A) ECF Volume:
- INCREASE
B) ICF Volume:
- INCREASE
C) ECF mOsm:
- DECREASE
D) ICF mOsm:
- DECREASE
2b) Later on with Water Gain:
A) ECF Volume:
- DECREASE
B) ICF Volume:
- DECREASE
C) ECF mOsm:
- DECREASE
D) ICF mOsm:
- DECREASE
3) Water Loss (Dehydration)
A) ECF Volume:
- DECREASE
B) ICF Volume:
- DECREASE
C) ECF mOsm:
- INCREASE
D) ICF mOsm:
- INCREASE
4) NaCl Loss (Adrenal Insufficiency)
A) ECF Volume:
- DECREASE
B) ICF Volume:
- INCREASE
C) ECF mOsm:
- DECREASE
D) ICF mOsm:
- DECREASE
