Acid-Base Balance Chapter 22 PDF

Acid-Base Balance Chapter 22  Learning Objectives Lesson 22.1: Acid-Base Balance (1 of 2) 1. Define the term acid-base balance. 2. Describe how to use the pH scale. 3. Discuss the pH unit. 4. Define the term base. 5. Explain the difference between strong and...

Acid-Base Balance Chapter 22  Learning Objectives Lesson 22.1: Acid-Base Balance (1 of 2) 1. Define the term acid-base balance. 2. Describe how to use the pH scale. 3. Discuss the pH unit. 4. Define the term base. 5. Explain the difference between strong and weak acids. 6. List the three chemical mechanisms that control pH of body fluids. 7. Define the terms buffer and buffer pair and discuss buffers as a compensatory mechanism.  Learning Objectives Lesson 22.1: Acid-Base Balance (2 of 2) 8. Compare and contrast respiratory and urinary mechanisms of pH control. 9. Define acidosis and alkalosis. 10.Discuss the two types of metabolic and respiratory disturbances. 11.Discuss compensatory mechanisms that may help return blood pH to near healthy levels in cases of pH imbalances.  pH of Body Fluids  pH: A number that indicates the relative hydrogen ion (H+) concentration (compared with OH−) of a fluid  pH 7.0 indicates neutrality (neutral solution)  pH higher than 7.0 indicates alkalinity (alkaline or basic solution; base)  pH less than 7.0 indicates acidity (acid solution)  pH Scale  Normal range of blood pH is approximately 7.35 to 7.45  Arterial blood pH: About 7.45  Venous blood pH: About 7.35  pH scale based on multiples of 10  H+ concentration changes by 10 times for each pH unit  Large pH fluctuations may appear small pH Range  Mechanisms That Control pH of Body Fluids  pH homeostatic mechanism: Three coordinated homeostatic mechanisms act to maintain the normal pH of body fluids and prevent pH swings when excess acids or bases are present  Chemical/buffer mechanism  Respiratory mechanism  Urinary mechanism  Removal of Carbonic Acid  Once carbonic acid is formed in the blood, it needs to be removed  Lungs remove over 30 L of carbonic acid each day by eliminating carbon dioxide (CO2)  This acid is buffered well to keep the pH of venous blood close to that of arterial blood Integration of pH Control Mechanisms  Chemical and Physiological Control Mechanisms  Chemical pH control mechanism  Based on buffers in blood/RBCs and body fluids: Act immediately  Physiological pH control mechanisms  Changes in pH regulated by changes in respiratory rate that result in changes in blood CO2: Act within minutes  Changes in pH regulated by altered renal activity: Act within hours  Buffers  Definition: Substances that prevent a sharp change in the pH of a fluid when an acid or base is added to it  “Fixed” acids are buffered mainly by sodium bicarbonate (NaHCO3)  More acids than bases are added to body fluids because of catabolism  Buffer salts weaken these acids when they enter the blood  Buffer Pairs  Buffers consist of two kinds of substances: Sodium bicarbonate (NaHCO3) and carbonic acid (H2CO3)  Amount of carbonic acid (H2CO3) in blood increases slightly  Amount of NaHCO3 in blood decreases; ratio of amount of NaHCO3 to the amount of H2CO3 does not normally change; normal ratio is 20:1  H+ concentration of blood increases slightly  Blood pH decreases slightly below arterial level Buffering Action of Carbonic Acid Buffering Action of Sodium Bicarbonate  Lactic Acid Buffered by Sodium Bicarbonate Respiratory Mechanism of pH Control  Respirations remove some CO2 from blood as blood flows through lung capillaries  Amount of H2CO3 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  Respiratory control centers in brainstem react to dropping pH and promote increased respirations; when pH increases, then breathing slows Urinary Mechanism of pH Control  Kidneys are the body’s most effective regulator of blood pH  Usually urine is acidified by way of the distal tubules secreting hydrogen ions and ammonia (NH3) into the urine from blood in exchange for NaHCO3 being reabsorbed into the blood  pH Imbalances  Acidosis and alkalosis are the two kinds of pH, or acid-base, imbalances  Disturbances in acid-base balance depend on relative quantities of NaHCO3 and H2CO3 in the blood  Body can regulate both of the components of the NaHCO3–H2CO3 buffer system Blood levels of NaHCO3 regulated by kidneys H2CO3 levels regulated by lungs  Alkalosis and Acidosis  When holding your breath too long, the brainstem detects the dropping pH and rising CO2; this forces you to inhale as a survival mechanism  Acidosis results from anything that causes decreased respirations over time  Alkalosis results from anything that causes increased respirations over time  Metabolic and Respiratory Disturbances  Both can alter the normal 20:1 ratio of NaHCO3 to H2CO3 in blood  Metabolic disturbances affect the NaHCO3 levels in blood Metabolic acidosis: Bicarbonate (NaHCO3) deficit Metabolic alkalosis: Bicarbonate (NaHCO3) excess; complication of severe vomiting  Respiratory Disturbances  Affect the H2CO3 levels in blood  Respiratory acidosis (H2CO3 excess)  Respiratory alkalosis (H2CO3 deficit)  In uncompensated metabolic acidosis, the normal ratio of NaHCO3 to H2CO3 is changed  In compensated metabolic acidosis, the ratio remains at 20:1, but the total amount of NaHCO3 and H2CO3 changes Questions?