Body fluids can be discussed in terms of their specific fluid compartment, a location that is largely separate from another compartment by some form of a physical barrier.
The intracellular fluid (ICF) compartment is the system that includes all fluid enclosed in cells by their plasma membranes.
Extracellular fluid (ECF) surrounds all cells in the body.
Extracellular fluid has two primary constituents: the fluid component of the blood (called plasma) and the interstitial fluid (IF) that surrounds all cells not in the blood
Hydrostatic pressure, the force exerted by a fluid against a wall, causes movement of fluid between compartments.
Water Balance: Plasma osmolality is thus the ratio of solutes to water in blood plasma.
Role of ADH: Antidiuretic hormone (ADH), also known as vasopressin, controls the amount of water reabsorbed from the collecting ducts and tubules in the kidney.
Electrolyte Balance
Sodium
Potassium
Chloride
Chloride is the predominant extracellular anion.
Hypochloremia, or lower-than-normal blood chloride levels, can occur because of defective renal tubular absorption.
Bicarbonate: Bicarbonate is the second most abundant anion in the blood.
Calcium
Phosphate
Hypophosphatemia, or abnormally low phosphate blood levels, occurs with heavy use of antacids, during alcohol withdrawal, and during malnourishment.
Hyperphosphatemia, or abnormally increased levels of phosphates in the blood, occurs if there is decreased renal function or in cases of acute lymphocytic leukemia.
Angiotensin II: Angiotensin II causes vasoconstriction and an increase in systemic blood pressure.
Buffer Systems in the Body
The buffer systems in the human body are extremely efficient, and different systems work at different rates.
Hemoglobin as a Buffer: Hemoglobin is the principal protein inside of red blood cells and accounts for one-third of the mass of the cell.
Bicarbonate-Carbonic Acid Buffer
Respiratory Regulation of Acid-Base Balance
Disorders of Acid-Base Balance
Metabolic acidosis occurs when the blood is too acidic (pH below 7.35) due to too little bicarbonate, a condition called primary bicarbonate deficiency.
Metabolic alkalosis is the opposite of metabolic acidosis.
Respiratory acidosis occurs when the blood is overly acidic due to an excess of carbonic acid, resulting from too much CO2 in the blood.
Respiratory alkalosis occurs when the blood is overly alkaline due to a deficiency in carbonic acid and CO2 levels in the blood.
Respiratory Compensation: Respiratory compensation for metabolic acidosis increases the respiratory rate to drive off CO2 and readjust the bicarbonate to carbonic acid ratio to the 20:1 level.
Metabolic Compensation: Metabolic and renal compensation for respiratory diseases that can create acidosis revolves around the conservation of bicarbonate ions.
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