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Unit Five: The Body Fluids and Kidneys

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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 ( ); therefore, the normal pH is

5 Acid-Base Regulation H+ Concentration pH ECF Arterial Blood 4.0 x 10-5
Table pH and Hydrogen Ion Concentration of Body Fluids H+ Concentration pH ECF Arterial Blood 4.0 x 10-5 7.40 Venous blood 4.5 x 10-5 7.35 Interstitial Fluid Intracellular Fluid 1 x to 4 x 10-5 Urine 3 x 10-2 to 1 x 10-5 Gastric HCl 160 0.8

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 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 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 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 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 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 Production and secretion of ammonium ion by the proximal tubular cells Fig Buffering of the hydrogen ion secretion by ammonia in the collecting tubules

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 Increase H+ Secretion and HCO3 Reabsorption Decrease H+ Secretion and Increase PCO2 Decrease PCO2 Increase H Decrease HCO3 Decrease H Increase HCO3 Decrease ECF volume Increase ECF volume Increase Angiotensin II Decrease Angiotensin II Increase Aldosterone Decrease Aldosterone Hypokalemia Hyperkalemia

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 Characteristics of Primary Acid-Base Disturbance pH H+ PCO2 HCO3 Normal 7.4 40 mEq/L 40 mm Hg 24 mEq/L Respiratory Acidosis Alkalosis Metabolic 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

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