Copyright © 2012 Wolters Kluwer Health | Lippincott Williams & Wilkins Chapter 17 Fluid and Electrolyte Balance

Copyright © 2012 Wolters Kluwer Health | Lippincott Williams & Wilkins 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 (NH 3 ) in the form of ammonium (NH 4 ) in an effort to balance hydrogen ions –pH buffers bicarbonate–base carbon dioxide–acid –Excretion of CO 2 (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