Pathophysiology: Fluid and Electrolyte Imbalance

Fluid Distribution in the Body, Electrolytes, Electrolyte Deficiency

1. FLUID AND ELECTROLYTE IMBALANCE

2. Fluid Compartments Intracellular Fluid  2/3 Extracellular Fluid  1/3 Interstitial Fluid  1/4 Intravascular Fluid  3/4 Cerebrospinal Fluid  1

3. Hormonal Regulation of Fluid Balance Antidiuretic Hormone (ADH) Prevents fluid loss Promotes conservation of water Aldosterone Regulates blood sodium levels Increases sodium reabsorption in the distal convoluted tubule and collecting duct of the nephron in the kidneys Conserves sodium – may also lead to water retention when ADH is present because “water follows salt”

4. Hormonal Regulation of Fluid Balance Atrial Natriuretic Peptide (ANP) Promotes both fluid and sodium loss by the kidneys Release from the atria and stimulated when blood volume and pressure are elevated Three major effects of ANP: 1) Decreases aldosterone release to decrease sodium reabsorption and increase sodium loss in the urine 2) Decreases ADH release to decrease water reabsorption and increase water loss to lower blood volume and pressure 3) Decreases thirst

5. Physiological Disturbances of Fluid and Electrolyte Imbalance Edema Excess of watery fluid collecting in the cavities or tissues of the body Many different types of Edema Peripheral Edema Pedal Edema Lymphedema Pulmonary Edema Cerebral Edema Macular Edema

6. Physiological Disturbances of Fluid and Electrolyte Imbalance Dehydration Harmful reduction in the amount of water in the body Signs: decreased skin turgor, sunken eyes, low blood pressure, rapid/weak pulse, high temperature Overhydration Excess of water in the body Signs: confusion, muscle spasms, weakness, cramps Cause: disorder that decreases the body’s ability to excrete water or increases the body’s ability to retain water

7. Electrolytes Functions Solutes for maintenance of acid-base equilibrium Maintain proper volume of body fluids Concentration of electrolytes determines their physiologic function Intracellular Electrolytes Potassium, Phosphate, Magnesium Blood Electrolytes Sodium, Calcium, Bicarbonate

8. Intracellular Electrolytes Potassium Major electrolyte inside the cells Regulates heartbeat and muscle function Forms the other half of the electrical pump that keeps electrolytes in balance Allows conductivity between the cells, which makes potassium a critical part of neuron transmission Phosphate Works closely with calcium to strengthen bones and teeth Energy production within cells Necessary for tissue growth and repair Major building block for cell membranes and DNA Magnesium Maintains normal nerve and muscle function Boosts the immune system Maintains stable heart rate Stabilizes blood sugar Promotes formation of bones and teeth

9. Blood Electrolytes Sodium Controls total amount of water in the body Regulates blood volume Maintains muscle and nerve function Calcium Formation of bones and teeth Critical for transmission of nerve impulses Blood clotting Muscle contraction Bicarbonate Lungs regulate CO 2 in the body and combine it with water to be converted to carbonic acid, H 2 CO 3 Carbonic acid is converted to bicarbonate, the key component in the pH buffer The bicarbonate buffer is one of the biggest reasons our body can maintain homeostasis and function properly

10. Acid-Base Balance Pulmonary Mechanism Carbon dioxide is removed from the lungs during respiration The amount of carbon dioxide removed depends on the partial pressure of carbon dioxide in arterial blood. Renal Mechanism H+ ions can be excreted through urine Three ways ions secreted by tubular cells are buffered in the glomerular filtrate: Combining with phosphates to form phosphoric acid Combining with ammonia to form ammonium ions Combining with filtered carbonate ions to form carbonic acid

11. Acid-Base Balance Buffer System Buffers are substances that have weak acids and strong bases Buffers limit the change in H+ ion concentration to the normal range When a strong acid is added, it is neutralized by the conjugate base When a strong base is added, it is neutralized by the conjugate acid The buffer system is the first line of defense for maintaining acid-base balance because they take up H+ ions when pH rises Bicarbonate-Carbonic Acid System regulates blood pH

12. Bicarbonate-Carbonic Acid Buffer System

13. Normal Fluid Pressure Osmotic Pressure The pressure exerted by the chemical constituents of the body Includes: Crystalloid Osmotic Pressure Colloid Osmotic Pressure Effective Oncotic Pressure Hydrostatic Pressure Capillary blood pressure Includes: Tissue Tension Effective Hydrostatic Pressure

14. Osmotic Pressure – the pressure exerted by the chemical constituents of the body Crystalloid Osmotic Pressure Pressure exerted by electrolytes in the extracellular fluid Comprises the major portion of total osmotic pressure Colloid Osmotic Pressure (Oncotic Pressure) Pressure exerted by proteins in the extracellular fluid Constituents a small part of the total osmotic pressure but is more significant physiologically Protein content of plasma is greater than protein content of interstitial fluid, so oncotic pressure of plasma is higher than oncotic pressure of interstitial fluid Effective Oncotic Pressure The difference between the higher oncotic pressure of plasma and the lower oncotic pressure of interstitial fluid Force that draws fluid into the vessels

15. Hydrostatic Pressure – capillary blood pressure A pressure gradient exists at the two ends of the capillary loop. Pressure is higher at the arteriolar end and lower at the venular end Tissue Tension Hydrostatic pressure of interstitial fluid Lower than hydrostatic pressure in the capillary at either end Effective Hydrostatic Pressure Difference between the hydrostatic pressure in the capillary end and the lower tissue tension Force that drives fluid through the capillary wall into the interstitial fluid

16. Normal Fluid Exchange Arteriolar End of the Capillary Balance between hydrostatic pressure and plasma oncotic pressure = hydrostatic pressure Outward-driving force allowing a small quantity of fluids and solutes to leave the vessel and enter the interstitial space Venular End of the Capillary Balance between hydrostatic pressure and plasma oncotic pressure = oncotic pressure Inward-driving force allowing fluids and solutes to re-enter the plasma Tissue Fluid Fluid left after the exchanges across the capillary walls escape into the lymphatics and are drained into venous circulation Tissue Factors Oncotic pressure of interstitial fluid and tissue tension oppose plasma hydrostatic pressure and capillary hydrostatic pressure, respectively

17. Electrolyte Deficiency Sodium Hyponatremia Low blood sodium Hypernatremia High blood sodium Potassium Hypokalemia Low blood potassium Hyperkalemia High blood potassium Calcium Hypocalcemia Low blood calcium Hypercalcemia High blood calcium Magnesium Hypomagnesemia Low blood magnesium Hypermagnesemia High blood magnesium

18. Sodium Deficiency Hyponatremia Causes Excessive vomiting or diarrhea Insufficient aldosterone production Kidney failure Excessive water intake Effects Impaired nerve conduction Fatigue Abdominal pain Decreased osmotic pressure in ECF, so fluid flows into cells Hypernatremia Causes I nsufficient ADH production Lo ss of thirst mechanism R apid respiration W atery diarrhea Effects F luid shifts out of cell and produces weakness Dry tongue or mucous membranes Increased blood pressure

19. Potassium Deficiency Hypokalemia Causes Diarrhea Diuresis Excessive aldosterone Low dietary intake Insulin drives K+ into cells Effects Cardiac dysrhythmias Interference with the neuromuscular junction Decreased digestive tract motility Hyperkalemia Causes Renal failure Aldosterone deficit K+ leakage from ICF to ECF Prolonged acidosis Effects Cardiac dysrhythmias Muscular weakness progressing to paralysis Respiratory arrest

20. Calcium Deficiency Hypocalcemia Causes Hypothyroidism Malabsorption syndrome Deficient serum albumin Increased serum pH Effects Increased permeability and excitability of nerve membranes Spontaneous stimulation of skeletal muscle Weak heart contractions Hypercalcemia Causes Uncontrolled release of calcium from bones Bone de-mineralization from immobility Increased calcium intake Effects Depressed neuromuscular activity Interference with ADH production Increased strength of cardiac muscle contractions

21. Magnesium Deficiency Hypomagnesemia Causes Malabsorption syndrome associated with alcoholism Diuretics usage Effects Neuromuscular hyperirritability Heart arrhythmia Hypermagnesemia Causes Renal Failure Effects Depressed neuromuscular function

22. Acid-Base Imbalance Acidosis Excess in hydrogen ions Alkalosis Deficit in hydrogen ions

23. Acidosis Metabolic Acidosis Drop in blood pH due to metabolic changes is a direct result of decreased bicarbonate levels and excess H+ ions in the blood Excess H+ ions in the blood stimulate the respiratory center so that breathing is deep and rapid Example – chronic renal failure Respiratory Acidosis Drop in blood pH due to raised CO 2 pressure from underventilation of the lungs and CO 2 retention Peripheral vasodilation and raised intracranial pressure Severe cases: confusion, drowsiness, and coma Example – air obstruction in COPD

24. Alkalosis Metabolic Alkalosis Rise in blood pH due to rising bicarbonate levels as a result of losing H+ ions Causes depressed respiration, depressed renal function, uremia, and increased bicarbonate excretion in the urine Example – prolonged vomiting Respiratory Alkalosis Rise in blood pH due to lowered CO 2 pressure as a result of hyperventilation of the lungs and excess removal of CO 2 Causes peripheral vasoconstriction, pallor, lightheadedness, and tetany Example – meningitis, or high altitudes

25. Arterial Blood Gases in Acidosis/Alkalosis