1. Fluids and Acid Base Physiology Dr. Meg-angela Christi Amores

2. maintenance of a relatively constant volume and a stable composition of the body fluids is essential for homeostasis

3. Daily Intake of Water: • (1) it is ingested in the form of liquids or water in the food, which together normally add about 2100 ml/day to the body fluids • (2) it is synthesized in the body as a result of oxidation of carbohydrates, adding about 200 ml/day • variable

4. Daily Loss of water • Insensible water loss – 700 mL/day • cannot be precisely regulated • continuous loss of water by evaporation from the respiratory tract and diffusion through the skin • Sweating – 100 mL/day • Feces – 100 mL/day • Urine - variable

5. Water in the body • Total body water (TBW) - ~42 liters • Compartments: • Intracellular Fluid - 75% • Extracellular Fluid (ECF) – 25% • Plasma 25% • Interstitial Fluid 75%

6. Body Fluid Compartments • extracellular fluid compartment is balanced between the principal cation—sodium and the principal anions—chloride and bicarbonate • intracellular fluid compartment is comprised primarily of the cations, potassium and magnesium, and of the anions, phosphate and proteins

7. Fluid Electrolyte • primary measurement that is readily available to the clinician for evaluating a patient's fluid status is the plasma sodium concentration • Na (Sodium) • Hyponatremia – when plasma Na concentration falls below 142 mEq/L • Hypernatremia

8. Hyponatremia • Causes: • Loss of NaCl – diarrhea and vomiting, diuretics • Addison's disease • excess water retention • excessive secretion of antidiuretic hormone

9. Hypernatremia • Causes: • loss of water • Dehydration due to prolonged sweating or exercise • excess sodium in the extracellular fluid

10. pH • Precise H+ regulation is essential because the activities of almost all enzyme systems in the body are influenced by H+ concentration • Acids - molecules containing hydrogen atoms that can release hydrogen ions in solutions • Bases - molecules that can accept an H+

11. pH • alkalosis refers to excess removal of H+ from the body fluids • in contrast to the excess addition of H+, which is referred to as acidosis • pH is inversely related to the H+ concentration

12. pH • normal pH of arterial blood is 7.4 • The lower limit of pH at which a person can live more than a few hours is about 6.8, and the upper limit is about 8.0

13. Regulators of H concentration • 1) the chemical acid-base buffer systems of the body fluids, which immediately combine with acid or base to prevent excessive changes in H+ concentration; • (2) the respiratory center, which regulates the removal of CO2 (and, therefore, H2CO3) from the extracellular fluid; and • (3) the kidneys, which can excrete either acid or alkaline urine, thereby readjusting the extracellular fluid H+ concentration toward normal during acidosis or alkalosis

14. Acid Base Disturbances • Acidosis • Alkalosis • Metabolic • Respiratory

15. Respiratory Acidosis • pH below 7.4 caused by respiratory problems • Decreased Ventilation and Increased Pco2 • Increased H2CO3 and H+ concentration, thus resulting in acidosis • Conditions that damage the respiratory centers or that decrease the ability of the lungs to eliminate CO2

16. What are possible causes of decreased ventilatory rate? • Central area of respiratory control • Peripheral • Voluntary

17. Respiratory Acidosis • damage to the respiratory center in the medulla oblongata • obstruction of the passageways of the respiratory tract • pneumonia, emphysema, or decreased pulmonary membrane surface area • compensatory responses: • (1) the buffers of the body fluids and • (2) the kidneys

18. Respiratory Alkalosis • caused by overventilation by the lungs • major means for compensation are the chemical buffers of the body fluids and the ability of the kidneys to increase HCO3- excretion

19. Metabolic Acidosis • (1) failure of the kidneys to excrete metabolic acids • (2) formation of excess quantities of metabolic acids in the body • (3) addition of metabolic acids to the body by ingestion or infusion of acids • (4) loss of base from the body fluids

20. Metabolic Acidosis • Renal Tubular Acidosis • defect in renal secretion of H+ or in reabsorption of HCO3 • impairment of renal tubular HCO3-reabsorption • inability of the renal tubular H+secretory mechanism • renal failure, insufficient aldosterone secretion (Addison's disease),

21. Metabolic Acidosis • Severe diarrhea • loss of large amounts of sodium bicarbonate into the feces • Vomiting of intestinal contents • Diabetes Mellitus • Ingestion of Acids • Chronic Renal Failure

22. Metabolic Alkalosis • excess retention of HCO3- or loss of H+ from the body • Administration of Diuretics • Excess Aldosterone • Vomiting of Gastric Contents • Ingestion of Alkaline Drugs