Fluids and Acid Base Physiology Dr Megangela Christi
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 m. L/day • cannot be precisely regulated • continuous loss of water by evaporation from the respiratory tract and diffusion through the skin – Sweating – 100 m. L/day – Feces – 100 m. L/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 m. Eq/L – Hypernatremia
Hyponatremia • Causes: – Loss of Na. Cl – 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
p. H • 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+
p. H • 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 • p. H is inversely related to the H+ concentration
p. H • normal p. H of arterial blood is 7. 4 • The lower limit of p. H 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 • p. H below 7. 4 caused by respiratory problems • Decreased Ventilation and Increased PCO 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 feces • • 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
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