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Chapter 17 Fluid and Electrolyte Balance Copyright © 2012 Wolters Kluwer Health | Lippincott Williams & Wilkins Homeostasis • Homeostasis – Dynamic process through which the body maintains balance by constantly adjusting to internal and external stimuli. – Fluids move into and out of cells, bringing with them enzymes, hormones, and nutrients, as well as removing waste products. – Continual movement of fluids is necessary to maintain homeostasis. Copyright © 2012 Wolters Kluwer Health | Lippincott Williams & Wilkins Homeostasis and Feedback • Negative feedback – When the body reverses an original stimulus to regain homeostasis • Positive feedback – When the body enhances or intensifies an original stimulus • The major systems involved in feedback are the nervous and endocrine systems. Copyright © 2012 Wolters Kluwer Health | Lippincott Williams & Wilkins Body Fluids Copyright © 2012 Wolters Kluwer Health | Lippincott Williams & Wilkins Fluids and Body Weight • Fluids constitute 50% to 60% of total body weight. • They are composed of water and electrolytes. • Intracellular fluid constitutes about one-half to two-thirds of the total body fluid in an adult. • Extracellular fluid constitutes about one-third of the total body fluid in an adult. Copyright © 2012 Wolters Kluwer Health | Lippincott Williams & Wilkins Question Is the following statement true or false? Extracellular fluid is the most important fluid in fluid balance. Copyright © 2012 Wolters Kluwer Health | Lippincott Williams & Wilkins Answer True Without adequate ECF, the body cannot maintain normal blood pressure. A significant loss of ECF volume can drop blood pressure to a life-threatening point where cells can no longer function, due to a lack of oxygen and nutrients. Copyright © 2012 Wolters Kluwer Health | Lippincott Williams & Wilkins Regulation of ECF • Primary mechanisms – Actions of the thirst center in the hypothalamus – Release of antidiuretic hormone (vasopressin—ADH) from the pituitary gland – Effects of the renin–angiotensin–aldosterone (RAA) system – Release of the atrial natriuretic peptide (ANP) hormone by the heart Copyright © 2012 Wolters Kluwer Health | Lippincott Williams & Wilkins Overhydration and Edema • Daily output should approximately equal intake. • Overhydration – Excess of water in the body • Edema – Excess accumulation of fluid in interstitial (tissue) spaces also called third-space fluid Copyright © 2012 Wolters Kluwer Health | Lippincott Williams & Wilkins Overhydration and Edema (cont’d) • Causes of edema – Increased capillary pressure – Decreased colloidal osmotic pressure – Increased capillary permeability – Obstruction of lymphatic flow Copyright © 2012 Wolters Kluwer Health | Lippincott Williams & Wilkins Prevention of Edema • Monitor the client’s sodium intake and blood pressure. • Encourage intake of foods with potassium. • Administer medications as ordered. Copyright © 2012 Wolters Kluwer Health | Lippincott Williams & Wilkins Dehydration • Fluid volume deficit • Water output is greater than intake. • Causes include: – Disturbance of electrolytes – Prolonged sun exposure, excessive exercise, diarrhea, vomiting, and burns – Inappropriate use of diuretics, malnutrition, excessive fasting, anorexia, or bulimia Copyright © 2012 Wolters Kluwer Health | Lippincott Williams & Wilkins Functions of Water • Primary solvent within the body • Primary compound in all body fluids • Suspension agent • Helps regulate body temperature, body pH, and fluid pressures inside and outside cells • Assists or participates in chemical reactions • May be end product of chemical reactions Copyright © 2012 Wolters Kluwer Health | Lippincott Williams & Wilkins Electrolytes and Ions • An electrolyte is a substance that dissociates into ions when dissolved in water. • An ion is an atom that has acquired an electrical charge and bonding ability. • Cation is a positively charged ion. – Sodium, potassium, calcium, magnesium • Anion is a negatively charged ion. – Chlorine, bicarbonate Copyright © 2012 Wolters Kluwer Health | Lippincott Williams & Wilkins Question Is the following statement true or false? Common table salt is a compound. Copyright © 2012 Wolters Kluwer Health | Lippincott Williams & Wilkins Answer True Common table salt is a compound. A compound combines elements in exact proportions, which are the same each time. Saline solution (salt and water) is a mixture because it can be separated without a chemical reaction. Copyright © 2012 Wolters Kluwer Health | Lippincott Williams & Wilkins Fluid and Electrolyte Transport • Permeability – Ability of a membrane to allow molecules to pass • Freely permeable membranes – Allow easy transfer from intravascular fluid to interstitial fluid • Selectively permeable membranes – Allow only specific substances to pass through Copyright © 2012 Wolters Kluwer Health | Lippincott Williams & Wilkins Factors Affecting Permeability • Size of pores in the membrane • Osmotic pressure • Hydrostatic pressure • Electrical charges of the molecule, the body fluid, or the plasma membrane • Solubility of the molecules • Size of the molecules Copyright © 2012 Wolters Kluwer Health | Lippincott Williams & Wilkins Transportation of Fluids and Molecules • Passive transport processes – Diffusion – Osmosis – Filtration • Active transport processes – Move solutes “uphill,” against the normal rules of concentration and pressure. Copyright © 2012 Wolters Kluwer Health | Lippincott Williams & Wilkins Passive Transport: Diffusion Copyright © 2012 Wolters Kluwer Health | Lippincott Williams & Wilkins Passive Transport: Osmosis Copyright © 2012 Wolters Kluwer Health | Lippincott Williams & Wilkins Passive Transport: Filtration Copyright © 2012 Wolters Kluwer Health | Lippincott Williams & Wilkins Question Which of these is the diffusion of a pure solvent across a semipermeable membrane? a. diffusion b. osmosis c. filtration d. active transport e. crenation Copyright © 2012 Wolters Kluwer Health | Lippincott Williams & Wilkins Answer b. osmosis Osmosis is the diffusion of a pure solvent, such as water, across a semipermeable membrane in response to a concentration gradient, in situations where the molecules of a higher concentration are nondiffusible. Copyright © 2012 Wolters Kluwer Health | Lippincott Williams & Wilkins Fluid and Electrolyte Balance • Dependent on – Cell membrane permeability – Osmolarity—the property of particles in a solution to dissociate into ions – Electroneutrality—the balance of positive and negative charges • Monitor of fluid balance – Intake and output records and daily weights Copyright © 2012 Wolters Kluwer Health | Lippincott Williams & Wilkins Acid–Base Balance • Major mechanisms to control acid–base balance – The kidneys excrete ammonia (NH3) in the form of ammonium (NH4) in an effort to balance hydrogen ions – pH buffers • bicarbonate–base • carbon dioxide–acid – Excretion of CO2 (constantly produced by the cells) – Hydrogen ions are making constant chemical changes Copyright © 2012 Wolters Kluwer Health | Lippincott Williams & Wilkins Significance of Arterial Blood Gas Values • Arterial blood gases (ABGs) are measured in a laboratory test to determine the extent of compensation by the buffer system. • The pH level and amounts of specific gases in the blood indicate if there is more acid or base and their associated values. Copyright © 2012 Wolters Kluwer Health | Lippincott Williams & Wilkins Risk for Fluid and Electrolyte Imbalances • Infants – More body fluid than adults – ECF is lost more easily than ICF – Immature kidney function Copyright © 2012 Wolters Kluwer Health | Lippincott Williams & Wilkins Risk for Fluid and Electrolyte Imbalances (cont’d) • Elders – ICF levels decrease; thirst sensation declines. – Muscle tissue turns to fat. – Many medications cause loss of fluid and electrolytes. – Circulatory and renal disorders may cause fluid retention. Copyright © 2012 Wolters Kluwer Health | Lippincott Williams & Wilkins End of Presentation Copyright © 2012 Wolters Kluwer Health | Lippincott Williams & Wilkins