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

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

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

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

Water in the body Total body water (TBW) - ~42 liters – Compartments: 1.Intracellular Fluid - 75% 2.Extracellular Fluid (ECF) – 25% – Plasma 25% – Interstitial Fluid 75%

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

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

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

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

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 +

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

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

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 CO 2 (and, therefore, H 2 CO 3 ) 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

Acid Base Disturbances Acidosis Alkalosis Metabolic Respiratory

Respiratory Acidosis pH below 7.4 caused by respiratory problems Decreased Ventilation and Increased P CO 2 – Increased H 2 CO 3 and H + concentration, thus resulting in acidosis Conditions that damage the respiratory centers or that decrease the ability of the lungs to eliminate CO 2

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

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

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 HCO 3 - excretion

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

Metabolic Acidosis Renal Tubular Acidosis – defect in renal secretion of H + or in reabsorption of HCO 3 – impairment of renal tubular HCO 3 - reabsorption – inability of the renal tubular H + secretory mechanism – renal failure, insufficient aldosterone secretion (Addison's disease),

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

Metabolic Alkalosis excess retention of HCO 3 - or loss of H + from the body Administration of Diuretics Excess Aldosterone Vomiting of Gastric Contents Ingestion of Alkaline Drugs