Body fluids compositions, and their measurements By: DR QAZI IMTIAZ RASOOL

OBJECTIVES a)Discuss the distribution of total body H2O (TWB) in the body b) List the ionic composition of different body compartments   c) Explain the principles of measurements

Body as an open sytem Body exchanges materials and energy with its surroundings

Regulatory influences Route Range (l/day) Regulatory influences Insensible - lungs 0.3-0.4 Atmospheric vapor pressure (temperature) Insensible - skin 0.35-0.4 10x increase in burn victims Sweat 0.1-2 (per hour) Temperature, exercise Feces 0.1-0.2 Diarrheal disease Urine 0.5-1.4-20 Body fluid composition

FACTORS AFFECTING Total Body H2O varies depending on body fat: Infant: 73-80% Male adult: 60% Female adult: 40-50% Effects of obesity Old age 45% Climate Level of physical activity

PERCENTAGE OF H2O IN TISSUES

PLASMA INTERSTITIAL TRANSCELLULAR FLUID COMPARTMENTS EXTRA CELLUAR INTRA CELLULAR FLUID (cytosol)FLUID PLASMA INTERSTITIAL TRANSCELLULAR FLUID FLUID CSF Intra ocular Pleural Peritoneal Synovial Digestive Secretions

% is important in fluid therapy PERCENTAGE OF WATER IN TISSUES Average 70 kg person total body weight 42 litres total H2O 60% 28 l. Intracellular fluid (ICF) 40% 14 l. Extracellular fluid (ECF) 20% % is important in fluid therapy divided into ¾ ISF and ¼ plasma water 10.5 l. Interstitial fluid (ISF) 15% 3.5 l. Plasma water 5%

Regulation of H2O Intake The hypothalamic thirst center is stimulated: By a decline in plasma volume of 10%–15% By increases in plasma osmolality of 1–2% Via baroreceptor input, angiotensin II, and other stimuli

Net Osmotic Force Development Semipermeable membrane Movement some solute obstructed H2O (solvent) crosses freely End point: H2O moves until solute concentration on both sides of the membrane is equal OR, an opposing force prevents further movement H2O 34 34

Solutes – dissolved particles Electrolytes – charged particles Cations – positively charged ions Na+, K+ , Ca++, H+ Anions – negatively charged ions Cl-, HCO3- , PO43- Non-electrolytes - Uncharged Proteins, urea, glucose, O2, CO2

APPROXIMATE IONIC COMPOSITION OF THE BODY H2O COMPARTMENTS

Summary of Ionic composition Interstitial H2O Plasma H2O Cell H2O 32 32

Intra-ECF H2O Redistribution Plasma vs. Interstitium Balance of Starling Forces acting across the capillary membrane osmotic forces hydrostatic forces Plasma vs Interstitial Space -Balance between Hydrostatic and Colloid Osmotic forces across the capillary membranes Intracellular vs Extracellular Osmotic effect (e.g. electrolytes) ICFV is NOT altered by: iso-osmotic changes in extracellular fluid volume. 50 50

Plasma Osmolarity Measures ECF Osmolarity Plasma is clinically accessible Dominated by [Na+] and the associated anions Under normal conditions, ECF osmolarity can be roughly estimated as: POSM = 2 [Na+]p 270-290 mOSM 54 54

Net Osmotic Force Development Ionic composition very different -Total ionic concentration very similar -Total osmotic concentrations virtually identical Semipermeable membrane. Movement some solute obstructed. H2O (solvent) crosses freely. End point: H2O moves until solute concentration on both sides of the membrane is equal. OR, an opposing force prevents further movement. 34 34

Disorders of H2O Balance: Dehydration Cells lose H2O to ECF by osmosis; cells shrink 1 Excessive loss of H2O from ECF 2 ECF osmotic pressure rises 3 (a) Mechanism of dehydration

Primary Disturbance: H2O moves out of cells ECF Osmolarity ? ECF Osmolarity ? H2O moves out of cells ICF Volume decreases (Cells shrink) ICF Osmolarity increases Total body osmolarity remains higher than normal H2O moves into the cells ICF Volume increases (Cells swell) ICF Osmolarity decreases Total body osmolarity remains lower than normal 52 52

CRITERIA FOR A SUITABEL DYE. BODY FLUID MARKER Must mix evenly throughout the compartment Non toxic, no physiological activity Even mixing Must have no effect of its own on the distribution of H2O or other substances in the body Either it must be unchanged during the experiment or if it changes , the amount changed must be known. The material should be relatively easy to measure.

Inject x gm of marker into compartment DILUTION PRINCIPLE Principle of mass conservation Based on using a marker whose concentration can be measured. Inject x gm of marker into compartment measure concentration at equilibrium (y gm/L) Since concentration = mass/ volume Volume = mass / concentration = x/y L C1V1=C2V2

Measuring Compartment Size Indirect METHOD – INDICATOR (DYE) DILUTION TECHNIQUE (Law of Mass Conservation) Based on concentration in a well-mixed substance that distributes itself only in the compartment of interest. Compartment Amount of Tracer Lost From Compartment (E) Volume (V) Amount of Tracer Added (A) Tracer Concentration (C) Concentration = Amount Injected Volume of Distribution Amount of Tracer Remained in Compartment = A - E Compartment Volume = (A – E)/C

Indicators used for measuring plasma volume, ECF volume and total body H2O Compartment Criterion Indicators Plasma Substance should not cross capillaries Evans blue dye; radioiodinated fibrinogen; radioiodinated albumin ECF volume Substance should cross capillaries but not cross cell membranes Isotonic solutions of sucrose, inulin, mannitol, NaCl Total body H2O (TBW) Substance distributes evenly in ICF & ECF Heavy H2O, tritiated H2O, aminopyrine, antipyrine

Total Body H2O (TBW) Deuterated H2O (D2O) Tritiated H2O (THO) Antipyrine 44 44

Blood volume /Markers used Obtained from plasma volume and hematocrit Total blood volume = Plasma volume/1- Hematocrit Example: If the plasma volume is 4 liters and the hematocrit is 0.45, total blood volume is ? =PLASME VOL X 100 100 -HCT 1.T-1824 (Evans blue dye) attaches to plasma proteins and is removed by the liver. Measures plasma volume 2. Radioactive labeled 125 i albumin 3. Cr51 (radioactive chromium) is incubated with red blood cells then injected Measures total blood volume

Take this problem: 100 mg of sucrose is injected into a 70 kg man. The plasma sucrose level after mixing is 0.01 mg/ml. If 5 mg has been metabolized during this period, then, what is the ECF volume? 9.5 L 14 L 17.5 L 10 L If 1mL of solution (10mg/mL) of dye is dispersed in chamber B and final concentration is the chamber is 0.01mg/mL. What is the volume in chamber B? 1000ml or 1L

Compartments with no Compartment-Specific Substance Determine by subtraction: How would you measure ICF volume? Cannot be measured; it is calculated (estimated).. ICF volume = Total body H2O – ECF volume Interstitial volume Can not be measured directly Interstitial Fluid Volume (ISFV). ISFV = ECFV - PV 47 47

Measurement of other spaces Extracellular volume Na24 Cl35 Inulin Sucrose Mannitol Sulfate I125 iothalamate Disperse in plasma and interstitial fluid, but not permeable to cell membrane 30-60 min for dispersion to extracellular fluid

Determining body fat: Technique: bioelectric impedance technique Principle: Body fluids conduct electricity well; But fat is anhydrous and therefore is a poor conductor of electricity; The resistance to flow of a small current between points on the body is proportional to fat mass.

Lean body mass (LBM) Definition: LBM is fat free mass Total body mass = fat mass + fat free mass Note: fat is relatively anhydrous Note: the H2O content of LBM is constant H2O content of LBM is constant - 70 ml /100 g tissue

Take this problem: In a healthy adult male weighing 70 kg, total body H2O (TBW) was measured to be 42 L. What is his lean body mass (LBM)? What is his fat mass? Given TBW = 42 L Assume all this H2O is in LBM & that fat is H2O free We know that H2O content of LBM is 70 ml/100 g Thus, if TBW is 42 L, LBM = 60 kg Since he weights 70 kg, his fat mass is 70-60 = 10 kg