Chapter 25 Fluid Electrolyte and Acid Base Homeostasis Overview of Fluid Electrolyte and Acid Base Homeostasis Expected Learning Outcomes Explain the concept of balance with respect to fluids and electrolytes and acids and bases Define the terms body fluid electrolyte acid base pH scale and buffer Introduction to Body Fluid Body Fluids term used to encompass all of the body s water based liquids Blood plasma interstitial fluid cytosol cerebrospinal fluid lymph and exocrine secretions etc Fluid Balance study of maintaining appropriate volume and concentration of body s intracellular and extracellular fluids Mostly a study of water balance Introduction to Body Fluid Functions of water in the body include Polar Solvent Allows water to transport and deliver a large number of solutes throughout the body Distribution of heat Cushioning of organs and tissues Lubrication of organs and tissues as the move Principle of Mass Balance What is gained by the body must equal what is lost by the body Imbalances of water in the body can have serious consequences on homeostasis Electrolytes Electrolytes Substances that dissociate into ions when placed in water Conduct electricity in a solution of water Found in large quantities throughout the body Nonelectolytes Substances that generally have covalent bonds Do not dissociate into charged particles Electrolytes Figure 25 1 Comparison of electrical conduction in electrolytes and nonelectrolytes Electrolytes Ion Differentiates electrolyte form of an element such as sodium or potassium from its atomic metal form In atomic form sodium and potassium metals explode when placed in water In atomic form calcium metal emits hydrogen gas in In ionic form electrolytes simple dissolve into water of water body s fluids Electrolytes Electrolyte balance is also maintained by the principle of mass balance Amount of electrolytes obtained in the diet equals those lost from a variety of routes from the body Balance is maintained by several mechanisms Mostly hormonal Ion concentration is dependent not only on the number of ions in a body fluid but also on the amount of water in that body fluid Fluid balance is therefore a critical factor in determining electrolyte balance Acids Bases and pH Acid a chemical that dissociates in water to release a hydrogen ion Common acids in the body include hydrochloric acid stomach and carbonic acid blood Hydrogen ions play a variety of roles in physiological functions Digestion of food inactivation of microbes digestion in lysosomes Maintenance of a hydrogen ion gradient is also a critical component of ATP synthesis via the electron transport chain in the mitochondria Acids Bases and pH Base a chemical that accepts a hydrogen ion in a solution Results in the formation of a salt and molecule of water Bicarbonate Ion HCO3 is the most common base in the body Bicarbonate and other bases are components of buffer systems Resist dramatic swings in hydrogen ion concentration of body fluids Acids Bases and pH pH Scale used to measure hydrogen ion concentration of a solution An increase in hydrogen ion concentration results in a solution with a lower pH A solution with a low hydrogen ion concentration has a higher pH Solutions with a pH less than 7 are considered acidic while those with a pH greater than 7 are considered basic or alkaline Solutions with a pH of 7 are neutral Fluid Homeostasis Expected Learning Outcomes Describe the fluid compartments and explain how each contributes to the total body water Compare and contrast the relative concentrations of major electrolytes in intracellular and extracellular fluids Explain how osmotic pressure is generated and compare and contrast the roles that hydrostatic and osmotic pressures play in the movement of water between fluid compartments Describe the routes of water gain and loss from the body Describe the mechanisms that regulate water intake and output and explain how dehydration and overhydration develop Total Body Water Total Body Water Reference volume that uses a standard man of 70 kg 154 lbs Amount of water in body is about 60 of total body weight 42 kg 92 5 lbs One kilogram of water is equal to one liter 42 liters 11 gal of total body water in our standard Actual total body water varies between individuals based on a variety of factors Gender body mass age amount of adipose tissue man etc Fluid Compartments Body fluids are found within two compartments Intracellular compartment Composed of trillions of cells and their cytosol or intracellular fluid ICF Accounts for about 60 26 L of body s fluids Extracellular compartment filled with extracellular fluid ECF composed of a variety of body fluids Blood Plasma About 8 3 L of total body water Interstitial Fluid About 32 13 L of total body water Fluid Compartments Figure 25 2 The distribution of water in the body Fluid Compartments Solute composition of plasma and interstitial fluid is similar Main difference is in protein content Plasma has a much higher protein content than interstitial fluid Solute composition of ECF and cytosol varies dramatically Concentrations of sodium chloride calcium and bicarbonate ions are much higher in ECF than in cytosol Proteins and potassium magnesium sulfate and monohydrogen phosphate HPO42 ions have a much higher concentration in cytosol than in ECF Fluid Compartments Figure 25 3 The solute composition of extracellular fluid and cytosol Osmotic Movement of Water Between Compartments Solute movement between compartments is restricted while water is usually free to move Direction of water movement between compartments is influenced by two gradients Hydrostatic pressure gradient Force that fluid exerts on cells Tends to push water away from area of higher hydrostatic pressure to one with lower hydrostatic pressure Osmotic pressure gradient Force of solutes in a solution Tends to pull water toward solution with higher osmotic Determined by the number of solute particles present in pressure by osmosis the solution Osmotic Movement of Water Between Compartments Direction of water movement between plasma and interstitial fluid is determined by force exerted on water by these pressure gradients High hydrostatic pressure dominates arteriolar end of most blood vessels Pushes water out into surrounding interstitial fluid High osmotic pressure dominates at venular end of most blood vessels Pulls most of water lost to interstitial fluid at arteriolar end back into vessel Any water lost in interstitial fluid is returned to