Slide 1 Mosby items and derived items © 2012 by Mosby, Inc., an affiliate of Elsevier Inc. Chapter 19 Acid-Base Balance

Slide 2 Mosby items and derived items © 2012 by Mosby, Inc., an affiliate of Elsevier Inc. pH OF BODY FLUIDS  Definition of pH—a number that indicates the hydrogen ion (H + ) concentration of a fluid; pH 7.0 indicates neutrality, pH higher than 7.0 indicates alkalinity, and pH less than 7.0 indicates acidity— see Figure 19-1  Normal arterial blood pH—about 7.45  Normal venous blood pH—about 7.35

Slide 3 Mosby items and derived items © 2012 by Mosby, Inc., an affiliate of Elsevier Inc.

Slide 4 Mosby items and derived items © 2012 by Mosby, Inc., an affiliate of Elsevier Inc. MECHANISMS THAT CONTROL pH of BODY FLUIDS  Buffers  Definition—substances that prevent a sharp change in the pH of a fluid when an acid or base is added to it—see Figures 19-2 and 19-3  “Fixed” acids are buffered mainly by sodium bicarbonate (NaHCO 3 )  Changes in blood produced by buffering of “fixed” acids in the tissue capillaries Amount of carbonic acid (H 2 CO 3 ) in blood increases slightly Amount of carbonic acid (H 2 CO 3 ) in blood increases slightly Amount of NaHCO 3 in blood decreases; ratio of amount of NaHCO 3 to the amount of H 2 CO 3 does not normally change; normal ratio is 20:1 Amount of NaHCO 3 in blood decreases; ratio of amount of NaHCO 3 to the amount of H 2 CO 3 does not normally change; normal ratio is 20:1 H + concentration of blood increases slightly H + concentration of blood increases slightly Blood pH decreases slightly below arterial level Blood pH decreases slightly below arterial level

Slide 5 Mosby items and derived items © 2012 by Mosby, Inc., an affiliate of Elsevier Inc.

Slide 6 Mosby items and derived items © 2012 by Mosby, Inc., an affiliate of Elsevier Inc.

Slide 7 Mosby items and derived items © 2012 by Mosby, Inc., an affiliate of Elsevier Inc. MECHANISMS THAT CONTROL pH of BODY FLUIDS (cont.)  Respiratory mechanism of pH control—respirations remove some CO 2 from blood as blood flows through lung capillaries, the amount of H 2 CO 3 in blood is decreased and thereby its H + concentration is decreased, and this in turn increases blood pH from its venous to its arterial level  Urinary mechanism of pH control—being the body’s most effective regulator of blood pH, kidneys usually acidify urine by the distal tubules secreting hydrogen ions and ammonia (NH 3 ) into the urine from blood in exchange for NaHCO 3 being reabsorbed into the blood

Slide 8 Mosby items and derived items © 2012 by Mosby, Inc., an affiliate of Elsevier Inc. pH IMBALANCES  Acidosis and alkalosis—pH or acid-base imbalances  Disturbances in acid-base balance depend on relative quantities of NaHCO 3 and H 2 CO 3 in the blood  Body can regulate both of the components of the NaHCO 3 – H 2 CO 3 buffer system  Blood levels of NaHCO 3 regulated by kidneys  H 2 CO 3 levels regulated by lungs  Metabolic and respiratory disturbances—pH disturbances— can alter the normal 20:1 ratio of NaHCO 3 to H 2 CO 3 in blood  Metabolic disturbances affect the NaHCO 3 levels in blood  Respiratory disturbances affect the H 2 CO 3 levels in blood

Slide 9 Mosby items and derived items © 2012 by Mosby, Inc., an affiliate of Elsevier Inc. pH IMBALANCES (cont.)  Metabolic disturbances  Metabolic acidosis—bicarbonate (NaHCO 3 ) deficit  Metabolic alkalosis—bicarbonate (NaHCO 3 ) excess; complication of severe vomiting  Respiratory disturbances  Respiratory acidosis (H 2 CO 3 excess)  Respiratory alkalosis (H 2 CO 3 deficit)  In uncompensated metabolic acidosis, the normal ratio of NaHCO 3 to H 2 CO 3 is changed; in compensated metabolic acidosis, the ratio remains close to 20:1, but the total amount of NaHCO 3 and H 2 CO 3 changes  Cardiac arrest and respiratory acidosis