Lecture 1 physiology body fluid compartments.pdf

1 Body fluid compartments Prof. Dr. Moshira Rateb,MD,MBA [email protected] Medicine and Surgery programme BMS 131 gu.edu.eg  Intended learning outcomes 2 By the end of th...

1 Body fluid compartments Prof. Dr. Moshira Rateb,MD,MBA [email protected] Medicine and Surgery programme BMS 131 gu.edu.eg  Intended learning outcomes 2 By the end of the lecture, Each student should be able to: 1. Describe the distribution of body fluids in different body By the end of the lecture, Each students will be able to: compartments. By the end of the lecture, Each students will be able to: 2. Discuss how to determine the volumes of water in 1. Describe the distribution of total body fluids different body compartments 3. 2.Explain Identify the percentage of water in the body. the difference in ionic composition between the 3.extracellular Discuss how to determine the volumes of and intracellular waterfluids. body in the body 4. Describe the distribution of total body fluids 5. body. 6. Discuss how to determine the volumes of water in the body  Introduction 3 In unicellular organisms, all vital processes occur in a single cell. As the evolution of multicellular organisms progressed, various cell groups organized into tissues, organs and systems. The human body is made up of 75-100 trillion cells Collection of cells with similar properties will form tissues (e.g. Connective tissues). Different tissues combine to form organs (e.g heart, brain, lung) Organs sharing in performing one main function combine to form systems  Introduction 4 Examples of systems include: 1. Gastrointestinal system to digest and absorb food; 2. Respiratory system to take up O2 and eliminate CO2; 3. Urinary system to remove soluble wastes; 4. Cardiovascular system to distribute nutrients, O2, and the products of metabolism to different cells of the body. Body systems 5 5  What is Physiology 6 - Physiology is the study of the normal function of organs and systems of living things. - Human physiology is concerned with the way the human body works and different functions are integrated.  Body fluids 7 The maintenance of a relatively constant volume and a stable composition of the body fluids is essential for a healthy performance of cellular functions. Some of the most common and important problems in clinical medicine arise because of abnormalities in the control systems that maintain this relative constancy of the body fluids.  8 Percentage of water in body In a 70-kilogram adult man, the total body water (TBW) is about 60 percent of the body weight, or about 42 liters. This percentage depends on age, gender, and degree of obesity. o As a person grows older, the TBW gradually decreases o Aging is usually associated with an increased percentage of body fat, which decreases the percentage of water in the body.  9 Percentage of water in body Because women normally have a greater percentage of body fat compared with men, their total body water averages about 50-55 percent of the body weight. In premature and newborn babies, the total body water ranges from 70 to 75 percent of body weight. It is important to notice that variations in total body water percentage exist, depending on age, gender, and percentage of body fat Percentage of water in body 10 10  11 Body fluid compartments The total body fluid is distributed mainly between two compartments: 1. The extracellular fluid (ECF) 2. and the intracellular fluid (ICF). The extracellular fluid is divided into 1. Interstitial fluid ( ISF) 2. Intravascular fluid IVF (blood plasma ). 11  12 What is the distribution of water in the body Compartments The total body water is divided into the following: - Intracellular fluid compartment (lCF): it is the water inside the cells. It accounts for 2/3 of the TBW or 40 % of TB weight. In a 70Kg male, this forms 70x40/100= 28 L. - Extracellular fluid compartment (ECF): it is the water outside the cells and is 1/3 of TBW or 20% of TB weight. In a 70 Kg male, this forms 70x20/100= 14 L. Body fluid compartments 13 Body fluid compartments 14 ECF is distributed as: a) 5 % inside vessels called intravascular fluid (IVF) which is the plasma in the circulatory vessels, arteries, capillaries, veins and lymphatics. In a 70 Kg male, this forms 70x5/100= 3.5 L b) 15 % extracellular are outside the vessels bathing the cells called interstitial fluid (ISF). In a 70 Kg male, this forms 70x15/100= 10.5L N.B. The total blood volume is about 8 % of body weight, which includes the plasma, and the cellular elements of the blood. 14  15 Determination of volumes of water in the body The volume of a fluid compartment in the body can be measured by placing an indicator substance in the compartment, allowing it to disperse evenly throughout the compartment’s fluid, and then analyzing the extent to which the substance becomes diluted. This method is called “ the Fick’s indicator-dilution” method of measuring the volume of a fluid compartment.  16 Determination of volumes of water in the body This is done by using Fick's principle. 1. A known amount of an indicator substance is injected intravenously. 2. The indicator is inert, non- toxic , not utilized by the tissues, will distribute only in the compartment investigated and can be easily measured. 3. Time is allowed for the indicator to diffuse uniformly in water. 4. A sample of blood is then withdrawn and the concentration of the indicator is determined in plasma. 5. The volume of water in which the indicator was distributed can be calculated from the following formula: Volume of compartment = the amount of the indicator injected /concentration of indicator in plasma. 6. This volume is called "The volume of distribution" of the indicator Determination of volumes of water in a 17 compartment A small amount of the indicator contained in the syringe is injected into a chamber and the substance is allowed to disperse throughout the chamber. A sample of fluid containing the dispersed substance is removed and the concentration is analyzed. The total mass of substance in the compartment (Volume B × Concentration B) will equal the total mass of the substance injected (Volume A × Concentration A). 17 Determination of volumes of water in a 18 compartment By simple rearrangement of the equation, one can calculate the unknown volume of chamber B as: Volume B = Volume A X Concentration A/ Concentration B Note that all one needs to know for this calculation is: (1) The total amount of substance injected into the chamber (the numerator of the equation) (2) the concentration of the fluid in the chamber after the substance has been dispersed (the denominator). 18 Determination of volumes of water in body 19 compartments Several substances can be used to measure and or calculate the volume of each of the different body fluid compartments (as long as they distribute in that compartment only). Examples are presented in the table  Applications for the Fick’s principle 20 3- Determination of plasma 1 - Determination of total body volume: water TBW by the use of Evan's blue dye or - by the use of tritium, deuterium (heavy plasma proteins labelled with water (D20)) or antipyrine, which radioactive iodine. distribute themselves in water in all compartments of the body. 4 - Determination of ICF volume: 2- Determination of ECF volume: - Cannot be measured directly. - by use of inulin, sucrose, mannitol , - It is calculated by: TBW – ECF. sulfate or labeled sodium iothalamate, 5 - Determination of ISF volume: which do not enter the cells but are - Cannot be measured directly. distributed in extracellular water only. - it is calculated by: ECF – plasma volume PV  21 Determination of volumes of water in the body 6.. Measurement of blood volume: If one measures plasma volume using the methods described earlier, blood volume can also be calculated if one knows the hematocrit (the fraction of the total blood volume composed of cells), using the following equation:  22 Determination of blood volume 6. Another way to measure blood volume is to inject into the circulation red blood cells that have been labeled with radioactive material. After these mix in the circulation, the radioactivity of a mixed blood sample can be measured and the total blood volume can be calculated using the indicator-dilution principle. A substance frequently used to label the red blood cells is radioactive chromium (51Cr), which binds tightly with the red blood cells. 𝑅𝐵𝐶 𝑣𝑜𝑙𝑢𝑚𝑒 𝑥 100 ○ Total blood volume = 𝐻𝑒𝑚𝑎𝑡𝑜𝑐𝑟𝑖𝑡  23 Do not worry!!! Many examples will be calculated during the lab.!! Please bring a calculator with you!!!!!  24 Composition of intracellular and extracellular fluids The intracellular fluid (ICF) is separated from the extracellular fluid (ECF) by a cell membrane that is highly permeable to water but is far less permeable to most of the electrolytes in the body.  25 Composition of intracellular and extracellular fluids Extracellular fluid (ECF), including the plasma and the interstitial fluid, contains large amounts of sodium and chloride ions, reasonably large amounts of bicarbonate ions. ECF contains small quantities of potassium, calcium, magnesium, phosphate, and organic acid ions.  26 Composition of intracellular and extracellular fluids Because the plasma and interstitial fluid are separated only by the highly permeable capillary membranes, their ionic composition is similar. The most important difference between these two compartments is the higher concentration of proteins in the plasma. This difference because the capillaries have a low permeability to the plasma proteins, so only small amounts of proteins are leaked into the interstitial spaces in most tissues.  27 Composition of intracellular and extracellular fluids In contrast to the ECF, the intracellular fluid contains only small quantities of sodium and chloride ions and almost no calcium ions. Instead, it contains large amounts of potassium and phosphate ions plus moderate quantities of magnesium and sulfate ions, all of which have low concentrations in the ECF. Also, cells contain large amounts of protein—almost four times as much as in the plasma.  What is the difference in composition 28 between ICF & ECF? ECF ICF Plasma Cations (mmol / L) + Na 10 145 + K 155 4.5 ++ Ca 0.001 2.5 ++ Mg 13 1.0 Anions (mmol / L) - Cl 3 115 - HCO3 10 28 - HPO3 50 1 Glucose 1 4-6 Protein ratio 4 1 Osmolarity (mOsm/L) 300 300  29 Summary The total body fluid is distributed between two compartments: the extracellular fluid (ECF) and the intracellular fluid (ICF). The extracellular fluid is divided into the interstitial fluid and the intravascular fluid (blood plasma). The total body water (TBW) is about 60 percent of the body weight. The volume of a fluid compartment in the body can be measured by “ the indicator- dilution” method. The ECF is rich in sodium, chloride and bicarbonate ions while the intracellular fluid compartment is rich in potassium, phosphate and proteins.  30 Test your knowledge: choose the single best answer In an average, healthy, adult male, approximately what is the percentage of body weight that is formed of water? A) 20% (B) 25% (C) 40% (D) 60% (E) 75%  31 Mark true T or False F 1. As human beings age, the percentage of body weight that is formed of water increases 2. The body of neonates if formed of 70% water 3. Intracellular fluid forms 10% of total body weight 4. Extracellular fluid forms 1/3 of total body water 5. Inulin can be used to measure total body water 6. Blood volume forms 25% of total body weight 7. Radioactive iodine labelled proteins can be used to measure plasma volume.  32 Enumerate a. 2 ions that are abundant in the extracellular fluid compartment b. 2 ions that are abundant in the intracellular fluid compartment c. 2 substances that can be used to measure total body water d. 2 substances that can be used to measure extracelluar fluid volume e. 3 characters of a substance that can be used in the applications of Fick’s principle f. 3 variables that affect total body water Reference Ganong's Review of Medical Physiology, 26e. By Kim E. Barrett (Editor), Susan M. Barman (Editor), Jason X.-J. Yuan (Editor), Heddwen Brooks (Editor). eBook. McGraw-Hill Education LLC. 2019 ! 33 Thank You gu.edu.eg 34