fluids and acid base physiology dr. meg-angela christi amores
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Fluids and Acid Base Physiology
Dr. Meg-angela Christi Amores
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• maintenance of a relatively constant volume and a stable composition of the body fluids is essential for homeostasis
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• 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
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• 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
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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%
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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
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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
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Hyponatremia
• Causes:– Loss of NaCl – diarrhea and vomiting, diuretics• Addison's disease
– excess water retention• excessive secretion of antidiuretic hormone
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Hypernatremia
• Causes:– loss of water• Dehydration due to prolonged sweating or exercise
– excess sodium in the extracellular fluid
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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+
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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
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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
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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
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Acid Base Disturbances
• Acidosis • Alkalosis
• Metabolic• Respiratory
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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
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• What are possible causes of decreased ventilatory rate?
• Central area of respiratory control• Peripheral• Voluntary
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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
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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
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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
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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),
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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
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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