Test 1 (Body Fluids Compartments Lecture) Flashcards Preview

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1

Total Body Water (TBW)

= 0.6 x Body Weight

2

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)

3

Intracellular Fluid (ICF)

= 0.4 x Body Weight

4

Effective Circulating Volume (ECV)

- Is the volume of the Arterial Blood EFFECTIVELY PERFUSING TISSUE

- 20%!!!!!

5

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!!!!!

6

Hypovolemia due to Vomiting

1) Effective Circulating Volume:
- DECREASES

2) Extracellular Fluid Volume:
- DECREASES

3) Plasma Volume:
- DECREASES

4) Cardiac Output:
- DECREASES

7

Heart Failure

1) Effective Circulating Volume:
- DECREASES

2) Extracellular Fluid Volume:
- INCREASES

3) Plasma Volume:
- INCREASES

4) Cardiac Output:
- DECREASES

8

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

9

Volume of Distribution Assumptions:

1) Vd

1) Vd 45L
- Drug widely distributed and body in BODY TISSUES

10

Body Fluid Compartments- Intake and Output are Balanced

***The Main OUTPUT of Body Fluids is from URINE!!!!!!!

11

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!!!!!

12

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

13

Oncotic Pressure

- Osmotic pressure generated by LARGE MOLECULES (Proteins) in solution which are IMPERMEABLE to Membranes

14

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)

15

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

16

Donnan Effect

- Negative charge of Proteins with Vasculature attracts POSITIVELY Charged Na and K Ions

17

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+]

18

Osmolarity of Body Fluid Compartments

Plasma Osmolarity can be estimated by:
1) 2 x [Na+]

2) 2 x [Na+] + Glucose/ 18 + Urea/ 2.8

19

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

20

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!!!

21

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

22

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

23

Factors Affectin Osmolarity and Volume of ECF/ ICF

- Water Ingestion

- Dehydration

- Intravenous Infusions

- Diarrhea or Vomiting

- Sweating

- Diuresis

- Disease

24

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

25

Summary- Fluid Exchange and Osmotic Equilibrium

- Many diseases are accompanied by fluid shifts between compartments

- Maintenance of adequate fluids in ICF, ECF, and both is IMPORTANT in Treatment of these patients

- Normallu, fluid i distributed between compartments based on balance of STARLING FORCES across capillaries and distribution of ions across cell membranes:

1) Fluid distribution BETWEEN PLASMA AND INTERSTITIAL FLUID (within ECF) is maintained by balance of Hydrostatic and Osmotic forces across CAPILLARIES

2) Fluid distribution BETWEEN ECF AND ICF is determined by Osmotic effect of Small saluted across CELL MEMBRANE (Highly water permeable, but Impermeable to Ions)

26

Clinical Relevance of Fluid Balance- Hydration Therapy/ Replacement Fluids

- Primary aim is to replace Body Volume and Solute Losses
(Burns, Hemorrhage, Vomiting/ Diarrhea, Dehydration)

- Intravenous replacement fluids used when Oral Rehydration not suitable

- Target compartment which is VOLUME-DEPLETED

- Distribution in compartments depends on Type of Fluid
1) CRYSTALLOID FLUIDS: Contain varying CONCENTRATION of Electrolytes and can stay in ECF or be widely distributed, depending on Composition (Ex: Normal Saline, Lactated RInger's Solution)

2) COLLOID FLUIDS: Contain large Proteins and Molecules which tend to STAY WITHIN THE VASCULAR SPACE (Ex: Dextran, Albumin)

27

Isosmotic, Hyperosmotic, Hyposmotic Solutions

- These terms DO NOT indicate whether the Cell Membrane is permeable to the SOLUTE!!!! Indicates Osmolarity of Solution as compared to that of the ECF

1) ISOSMOTIC: Solutions which have the same Osmolarity as the ECF
- When added to the ECF, does not change Osmolarity, but INCREASES VOLUME ONLY

2) Hyperosmotic: Solutions having an Osmolarity GREATER THAN that of the ECF
- When added to the ECF, Osmolarity INCREASES and causes WATER to move from the CELLS to the ECF Compartment with a resulting INCREASE in ECF VOLUME and DECREASE in ICF VOLUME!!!!!

3) Hyposmotic: Solutions having an Osmolarity less than that of the ECF
0 When added to the ECF, DECREASES Osmolarity and WATER moves into the cells to Equalize Osmolarity. ECF and ICF VOLUMES are BOTH INCREASED!!!

28

Tonicity

- CHANGES in CELL VOLUME due to Osmotic Equilibrium with Water movement across Cell Membranes

- Small changes in concentration of IMPERMEANT Solutes in ECF can cause Large changes in CELL VOLUME

- Water always moves from an area in which it is in HIGHER Concentration to an are of LOWER CONCENTRATION

29

Tonicity Cont.

- Tonicity of a Solution relates to the effect of that Extracellular Solution on Cell Volume

- Depends on the Concentration of IMPERMEANT solutes in the Extracellular vs Intracellular Fluid

1) ISOTONIC SOLUTION: No Change in Cellular Volume

2) HYPOTONIC SOLUTION: Cellular Volume INCREASES (Swelling)

3) HYPERTONIC SOLUTION: Cellular Volume DECREASES (Shrinking)

30

Summary- Fluid Exchange/ Balance

1) Distribution of Fluid between the ECF and ICF compartments is determine primary by:
- Ion Distribution (Na)

- ATPase activity (Keeps Na low and K high)


2) Distribution of ECF between the Plasma and Interstitial compartments is determine primarily by:
- Balance of Hydrostatic vs Oncotic Pressures

- Intravascular Pressure in Capillaries vs Plasma protein and Solution Concentration

31

Edema

- Palpable swelling produced by EXPANSION of Interstitial Fluid Volume

Caused By:
1) Alteration in Capillary hemodynamics (Altered STARLING FORCES with Increased Net filtration Pressure)
- Fluid Moves from VASCULAR SPACE into the INTERSTITIAL

2) Renal RETENTION of dietary Na+ and Water
- Expansion of ECF VOLUME!

32

Edema (Altered Starling Forces- Renal Role)

- Edema does not become apparent until Interstitial Volume is INCREASED by 2.5 to 3.0 L. Normal plasma Volume is only 3L

- Therefore, Edema fluid is not derived only from PLASMA

- Compensatory Renal Retention of Na+ and water to maintain Plasma Volume in response to UNDERFILLING of the Vasculature must occur in this situation to cause EDEMA

- This renal compensation is APPROPRIATE to RESTORE Tissue perfusion although it exacerbates EDEMA (ex: Congestive Heart Failure)

33

Edema (Renal Retention of Na+ and Water)

- Results in OVERFILLING of the Vascular Tree

- INAPPROPRIATE Renal Fluid Retention

- Usually results in ELEVATED BLOOD PRESSURE, Expanded Plasm and Interstitial Volumes!

- Ex: Primary Renal Disease (Glomerulonephritis, Nephrotic Syndrome)

1) NON PITTING EDEMA: Swollen Cells due to INCREASE ICF Volume

2) PITTING EDEMA: INCREASE Interstitial Fluid Volume

***EDEMA often treated with Diuretics!!!