CHAPTER TWENTY-SIX
Fluid, Electrolyte, and Acid-Base Balance
26.1 Body Fluids and Compartments A. Body water content 1. Water is the largest single component of the body. Males are 60% water and 40% solid materials while women are 50% water and 50% solid materials. 2. Since fat is essentially free of water tihydrophobic), the less fat present corresponds to greater percentage of body weight due to water. Adipose tissue is 20% hydrated while skeletal muscle is 65% water. a. Early embryo = 97% water b. Newborn infant = 77% water C. Adult male = 60% water d. Adult female = 50% water e. Elderly adult = 45% water 3. Fluid compartments a. Intracellular fluid compartment tilCF) = fluid within the body cells such as cytosol, nucleoplasm, matrix of mitochondria, etc. ti33% in males and 27% in females) b. Extracellular fluid compartment tiEcF) = fluid found outside of cells:
i. Interstitial fluid = the fluid in the microscopic spaces between cells ti21.5% in males and 18% in females) ii. Intravascular = fluid portion of blood tiplasma) and located within blood vessels ti4.5% in males and females) iii. Other = lymph, cerebrospinal fluid, humors of the eye, synovial fluid, serous fluids, and secretions of the gastrointestinal tracts tiless than 1%). B. Composition of body fluids 1. Solutes can be classified as being electrolytes or non-electrolytes. 2. Electrolytes=molecules that dissociate in solution to form charged particles, called ions, rendering the solution capable of conducting an electrical current. Examples are salts, acids, and bases. Two types of ions can be produced from electrolytes: a. Cations = an ion carrying a positive charge: Na*, H*, K*, Ca2*, and Mg2* b. Anions = an ion carrying a negative charge: CI, HCO3, HPO42-, SO42 3. Non-electrolytes=molecules that have covalent bonds that prevent them from dissociating in solution: proteins, carbohydrates, lipids, creatinine, and urea. Non-electrolytes are far more abundant than the electrolytes. 4. Electrolyte concentrations are usually expressed in milliequivalents per liter timEq/L) 5. Comparison of extracellular and intracellular fluids: a. Blood plasma and interstitial fluids tiboth components of the ECF) are very similar except that protein levels are higher in blood because they are too large to diffuse into and out of capillary vessels. b. Blood plasma and interstitial fluids tiECF) have: i. Increased Na+ cations ii. Increased Cl- anions c. Intracellular fluids tiiCF) have: i. Increased K+ cations ii. Increased HPO42- anions
C. Fluid movement occurs between compartments 1. Blood plasma circulates throughout the body and links the external and internal environments as well as the ICF and ECF. 2. Recall exchanges at the capillary beds from Chapter 20. a. Increased hydrostatic pressure at the arteriole end of the capillary bed forces fluid and substances out of the blood vessels and into the interstitial spaces. b. Increased colloid osmotic pressure at the venous end of the capillary bed tidue to impassable plasma proteins) creates a suction of fluids into the blood vessel and out of the interstitial spaces. 3. Movements from interstitial spaces to intracellular compartments