Body Fluids PDF

Body Fluids Prof. Noha Mohsen Abogresha M.D.,Ph.D.,DHPME  By the end of the lecture, Each student should be able to: 1.Describe the distribution of body fluids in different body compartments. 2.Discuss how to determine the volumes of water in different body compartments 3.Explain the differ...

Body Fluids Prof. Noha Mohsen Abogresha M.D.,Ph.D.,DHPME  By the end of the lecture, Each student should be able to: 1.Describe the distribution of body fluids in different body compartments. 2.Discuss how to determine the volumes of water in different body compartments 3.Explain the difference in ionic composition between the extracellular and intracellular body fluids. 4.Assess the mechanisms involved in regulation of body fluid volumes and electrolytes 5.Define terms used to describe concentration of substance and osmolarity in physiology Body fluids 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. 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. Percentage of water in body 5 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 Body Water The Total Body Water (TBW) represents about 60% of the total body weight. TBW is variable: infant: 73% male adult: 60% female adult: 40-50% Old age 45% Percentage of the water in the body Jj Functions of Body Water  FLUID COMPARTMENTS EXTRA CELLUAR INTRA CELLULAR FLUID FLUID INTERSTITIAL TRANSCELLULAR PLASMA FLUID FLUID CSF Intra ocular Pleural Peritoneal Synovial Digestive Secretions Body Water Distribution TBW = 0.6 x 70 Kg (Body Weight in adult male) = 42 L 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 What is the distribution of water in the body Compartments The total body water is divided into : - 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 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. 13 A 30-years-old male with body weight is 74 kgs, calculate his total body fluids volume, extracellular fluid volume, intracellular fluid volume, interstitial fluid volume & plasma volume in liters 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. Composition of intracellular and extracellular fluids 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. Composition of intracellular and extracellular fluids COMPOSITION OF BODY FLUIDS CATIONS (mmol/l) Plasma Interstitial Intracellular Na 142 139 14 K 4.2 4.0 140 Ca 1.3 1.2 0 Mg 0.8 0.7 20 ANIONS (mmol/l) Cl 108 108 4.0 HCO3 24.0 28.3 10 Protein 1.2 0.2 4.0 HPO4 2.0 2.0 11 - Regulation of total body water and also the movement of fluids between different body compartments greatly influence the volume of fluid compartments. -Ingestion and excretion of fluids and electrolytes affect total body water (TBW) and total body osmolarity (TBO) while the movement of fluids between compartments is also affected by osmolarity created by solutes and by hydrostatic pressures of fluids within that compartment In the next few slides, we will discuss the concept of regulation of total body water and also the effect of osmolarity and hydrostatic pressure on changes on the volume of different fluid compartments.  Water input and output Naturally, any increase in water output must be compensated for by an increase in intake. Someone who exercises strenuously, for example, may lose 1 to 2 liters of water in sweat and must replace that water by drinking more fluids. In a healthy individual, water intake equals water output, even though the amounts of each may vary greatly from the averages just mentioned 22 Water Balance Water balance: Input = output Dehydration is an abnormal reduction of the major fluid volumes Overhydration is an abnormal increase of total body water Osmolarity Osmolarity is defined as the number of particles per liter of fluid 24 (Osmolarity is the osmolar concentration expressed as osmoles per liter of solution ). Blood plasma osmolarity is approximately 286- 300 mOsmoles /L. Any fluid with a value less than this is described as hypoosmotic to plasma , and greater is hyperosmotic. 24  Osmolarity Molarity is the mass in molecular weight dissolved in one litre (one Kg)  Choose the correct answer? Q1.The osmolarity of a solution containing a 1M NaCl solution is ____. a.) 1 b.) 2 c.) 3 d.) None of the above Correct Answer– (b.) 2.. The osmolarity of a solution containing a 1M CaCl 2 solution is ____. a.) 1 b.) 2 c.) 3 d.) None of the above Correct Answer– (c.) 3. a) At the cellular level The ECF and ICF are osmotically equal and any change in plasma osmolarity causes cells to shrink or swell Why Intravenous fluids must be isotonic to blood ? In order to: maintain the correct osmotic pressure prevent cells from either expanding or shrinking Common fluids used for this purpose are normal saline have about the same osmolality as normal plasma 29 b) At the capillary level Plasma proteins account for about 1.2 mosml/L of the total plasma osmolarity (290 mosm/L) create an osmotic pressure about 25 mmHg, called the colloid oncotic pressure, which draws water from interstitial fluid to the capillaries This oncotic pressure is balanced by the hydrostatic pressure of the capillaries which causes filtration of 30 The solution’s tonicity is determined by the concentrations of only those solutes that do not enter (“penetrate”) the cell *Hypertonic solution: Solution in which there is high non-penetrating solute concentration (>300mosm./L in ECF), and hence low water concentration. *Hypotonic solution: Solution in which there is low non-penetrating solute concentration (