Unit Five: The Body Fluids and Kidneys

1. Unit Five: The Body Fluids and Kidneys Chapter 30: Acid-Base Regulation Guyton and Hall, Textbook of Medical Physiology, 12th edition

2. Acid-Base Regulation • Hydrogen Ion Concentration is Precisely Regulated • Acid- molecules that release H+ in solution • Base- ion or molecule that can accept an H+ • Alkali- formed by the combination of one or more • of the alkali metals (i.e. Na) with a highly basic • ion (i.e. OH); the base portion reacts quickly • with hydrogen ions and remove them from • solution---therefore they act as bases

3. Acid-Base Regulation • Strong Acid- one that rapidly dissociates and • releases large amounts of H+ in solution • Strong Base- one that reacts rapidly and strongly • with H+ and quickly removes them from • solution

4. Acid-Base Regulation The normal H+ concentration is 40nEq/L (0.00000004); therefore, the normal pH is

5. Acid-Base Regulation Table 30.1 pH and Hydrogen Ion Concentration of Body Fluids

6. Defending Against Changes in H+ • Three primary systems regulate H+ concentration • to prevent acidosis or alkalosis • Chemical acid-base buffer systems of body fluids • (1st line of defense) • The respiratory center which regulates the • removal of CO2 and therefore H2CO3 (2nd line • of defense) • The kidneys which can excrete either acid or • alkaline urine

7. Bicarbonate Buffer System • Consists of (1) a weak acid and (2) a bicarbonate salt

8. Bicarbonate Buffer System Fig. 30.1 Titration curve for bicarbonate buffer system

9. Phosphate Buffer System • Addition of a Strong Acid • Addition of a Strong Base

10. Phosphate Buffer System • Role of Phosphate Buffer • Relatively insignificant as an extracellular buffer • Important in the tubular fluids of the kidney • Phosphate becomes greatly concentrated in • the tubules • Tubular fluid usually has a considerably • lower pH than extracellular fluid • Important in intracellular fluid because of the • phosphate concentration

11. Proteins As Important Intracellular Buffers • Proteins are the most plentiful buffer due to high • concentrations inside cells • In the rbc, hemoglobin is an important buffer • Approximately 60-70% of the total chemical • buffering of body fluids is inside the cells, • and most of this comes from intracellular • proteins

12. Respiratory Regulation of Acid-Base Balance • Pulmonary Expiration of CO2 Balances Metabolic • Formation of CO2 • Increasing Alveolar Ventilation Decreases • Extracellular Fluid H+ Concentration and • Raises pH

13. Fig. 30.2 Change in ECF pH caused by increased or decreased rate of alveolar ventilation, expressed as times normal

14. Respiratory Regulation (cont.) • Increased H+ Concentration Stimulates • Alveolar Ventilation Fig. 30.3 Effect of blood pH on the rate of alveolar ventilation

15. Respiratory Regulation (cont.) • Feedback Control of H+ Concentration By the • Respiratory System (Negative Feedback) • Increased H+ concentration stimulates respiration • Increased alveolar ventilation decreases H+ • concentration • Efficiency of Respiratory Control of H+ Concentration- cannot return the concentration • back to normal when a disturbance outside • the respiratory system has altered the pH

16. Respiratory Regulation (cont.) • Buffering Power of the Respiratory System • a. Acts as a physiologic type of buffering system • Impairment of Lung Function Can Cause • Respiratory Acidosis

17. Renal Control of Acid-Base Balance • Secretion of H+ and Reabsorption of HCO3- By • the Renal Tubules 30.4 Reabsorption of bicarbonate in different segments of the renal tubule

18. Renal Control of Acid-Base Balance • H+ is Secreted by Secondary Active Transport in • the Early Tubular Segments 30.5 Cellular mechanisms for (1)active secretion of hydrogen ions into the renal tubule, (2) tubular reabsorption of bicarbonate by formation of carbonic acid, and (3) sodium ion reabsorption in exchange for hydrogen ion secretion

19. Renal Control of Acid-Base Balance • Filtered HCO3 is Reabsorbed by Interaction with • H+ in the Tubules • Each time an hydrogen ion is formed in the • tubular epithelium, an HCO3 is also formed • and released back into the blood • b. HCO3 is “titrated” against H+ in the tubules

20. Renal Control of Acid-Base Balance • Primary Active Secretion of H+ in the Intercalated • Cells of Late Distal and Collecting Tubules Fig. 30.6 Primary active secretion of H ion through the membrane of the intercalated cells

21. Renal Control of Acid-Base Balance • Phosphate Buffer System Carries Excess H+ into • the Urine and Generates New HCO3 Fig. 30.7

22. Renal Control of Acid-Base Balance • Excretion of Excess H+ and Generation of New • HCO3 by the Ammonia Buffer System Fig. 30.9 Buffering of the hydrogen ion secretion by ammonia in the collecting tubules Fig. 30.8 Production and secretion of ammonium ion by the proximal tubular cells

23. Quantifying Renal Acid-Base Excretion • Bicarbonate excretion is calculate as the urine • flow rate multiplied by urinary HCO3 concentration • The amount of new HCO3 contributed to the blood • at any given time is equal to the amount of H+ • secreted that ends up in the tubular lumen • The rest of the non-bicarbonate, non-ammmonia • buffer excreted is measured by determining a • value known as titratable acid

24. Quantifying Renal Acid-Base Excretion • Regulation of Renal Tubular H+ Secretion

25. Renal Correction of Acidosis • Acidosis Decreases the ration of HCO3/H+ • in Renal Tubular Fluid • In metabolic acidosis, an excess of H+ over • HCO3 occurs in the tubular fluid primarily • because of decreased filtration of HCO3 • There is also a decrease in pH and a rise in • ECF H+ concentration

26. Renal Correction of Alkalosis • Alkalosis Increases the Ratio of HCO3/H+ in • Renal Tubular Fluid Table. 30.3 Characteristics of Primary Acid-Base Disturbance The primary event is indicated by the double arrows. Respiratory acid-base disorders are initiated By an increase or decrease in PCO2; metabolic disorders are initiated by an increase or decrease in HCO3