Fluid and Electrolytes
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Carbonic Acid–Sodium Bicarbonate Buffer System
- -Normal ECF has a ratio of 20 parts bicarbonate (HCO3-) to 1 part carbonic acid (H2CO3)
- -Carbonic acid and bicarbonate must be controlled to maintain the ratio
- -If the ratio changes, so will the pH
- -Lungs assist in regulating the production of carbonic acid
- -Kidneys assist by regulating the production of bicarbonate
Phosphate Buffer System
-Active in the intracellular fluids, particularly the renal tubules
-Converts alkaline sodium phosphate (Na2HPO4), a weak base, to an acid–sodium phosphate (NaJ2PO4) in the kidneys
Protein Buffer System
-Plasma proteins and hemoglobin possess chemical groups that combine or liberate hydrogen ions
-Excess hydrogen ions in the blood cross the plasma membrane and bind to hemoglobin molecules
What is a buffer?
- -A buffer is a substance that prevents body fluids from becoming overly acidic or alkaline.
- -Buffers can:Combine with excess acids or bases to prevent major changes in pH
- -Work like a base and bind with a free hydrogen ion
- -Work like an acid and release hydrogen ions
Acid–Base Balance: Respiratory Regulation
-lungs regulate acid–base balance by eliminating or retaining carbon dioxide
-can change pH rapidly: within minutes
-Blood levels of carbonic acid and carbon dioxide rise as RR increase (to blow off carbon dioxide).
-Blood levels of carbonic acid and carbon dioxide fall as RR decrease (carbon dioxide is retained).
Acid–Base Balance: Renal Regulation
-Acidosis: kidneys excrete hydrogen ions => conserve bicarbonate ions => raises pH to the normal range (7.35–7.45).
-Alkalosis: kidneys retain hydrogen ions => excrete bicarbonate ions => lowers pH to the normal range.
-Acid–base balance by the kidneys occurs slowly. Approx. 3 days to return pH to normal.
What is an Acid?
-a substance that releases hydrogen ions in a solution and has a pH value less than 7.
What is a Base?
-a substance that retains hydrogen ions in a solution and has a pH value greater than 7.
-a condition characterized by an excess of hydrogen ions or loss of base ions (bicarbonate) in the ECF.
-The pH falls below 7.35. Death will occur if the pH falls below 6.80.
-a condition characterized by a lack of hydrogen ions or a gain of base ions (bicarbonate).
-The pH rises above 7.45. Death will occur if the pH rises above 7.80.
Intracellular fluid (ICF)
-fluid found within the cells
-comprises two thirds of the total body fluid.
-ICF contains oxygen, electrolytes, and glucose along with water.
Extracellular fluid (ECF):
- -found outside the cells
- -carries oxygen and nutrients to body cells, and carries waste products away from body cells.
- -comprises one third of the total body fluid.
- -two compartments: intravascular and interstitial.
- -aka plasma
- -accounts for 20% of the ECF.
- -accounts for 75% of the ECF
- -fluid that surrounds the cells.
- -5% of the ECF
- -Ex:Cerebrospinal, pericardial, pancreatic, pleural, intraocular, biliary, peritoneal, and synovial fluids
positively charged ions are called cations
- -Sodium (Na+)
- -Potassium (K+)
- -Calcium (Ca2+)
- -Magnesium (Mg2+)
negatively charged ions are anions
- -Chloride (Cl-)
- -Bicarbonate (HCO3-)
- -Phosphate (HPO42-)
- -Sulfate (SO42-)
- -Substances that dissolve in a liquid
- -carbon dioxide,
- -amino acids,
- -a solution that can dissolve a solute.
- -Water is a solvent.
-The concentration of solutes in body fluids is expressed as osmolality.
- total solute concentration within a fluid compartment
-Sodium is the greatest determinant of osmolality of plasma
-Potassium, glucose, and urea are determinants of osmolality of ICF
- -0.9% NaCl (normal saline)
- -Normal saline is administered with blood products
- -Ringer lactate (balanced electrolyte solution)
- -5% dextrose in water (D5W)
- -Have the same concentration of solutes as blood plasma
- -Used to restore vascular volume
- -Assess clients for signs of hypervolemia (i.e., bounding pulse and dyspnea)
- -5% dextrose in normal saline (D5NS)
- -5% dextrose in 0.45% NaCl (D51/2NS)
- -5% dextrose in Ringer lactate (D5LR)
- -Greater concentration of solutes than plasma
- -Draw fluid out of ICF and interstitial compartments into the vascular compartment
- -Expand vascular volume
- -Do not administer to clients with kidney or heart disease, or if dehydrated
- -Assess for hypervolemia
- -0.45% NaCl (half normal saline)
- -0.33% NaCl (one-third normal saline)
- -Provides free water and treats cellular dehydration
- -Promotes waste elimination by the kidneys
- -Do not administer if client is at risk for increased intracranial pressure or fluid shift
-Osmotic pressure allows the solution to pull water across the semipermeable membrane.
-the solution with the higher solute concentration exerts a higher osmotic pressure.
-water is pulled across the membrane to equalize the concentrations of the solutions.
-Opposes Hydrostatic pressure
-the movement of solutes across a semipermeable membrane from higher to lower concentration.
-the diffusion of water across the cell membrane from lower to higher concentration.
-equalizes water and solute.
-maintains homeostasis and fluid balance
-the movement of fluid and solutes together across a semipermeable membrane from an area of higher pressure to one of lower pressure.
-occurs when fluids and nutrients in the body move from the capillaries to the interstitial fluid around the cells.
-force exerted by the blood against the blood vessel walls is hydrostatic pressure.
-Osmotic pressure opposes hydrostatic pressure, holding fluid in the vascular compartment to maintain vascular volume.
-If the hydrostatic pressure is greater than the osmotic pressure, fluid filters out of the blood vessels.
-The movement of solutes across the cell membrane from a less concentrated solution to a more concentrated one.
-requires metabolic energy.
-A substance combines with a carrier and moves it inside the cell membrane.
-maintains the differences between sodium and potassium concentrations in ECF and ICF.
1 kg (2.2 lb) of weight gain or loss equals?
1 L of fluid gained or lost
- increases with dehydration
- decreases with overhydration
Three hormones assist in controlling the balance of fluid and electrolytes:
- Antidiuretic hormone (ADH):
- Renin-angiotensin-aldosterone system:
- Atrial natriuretic factor (ANF):
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