CMQ S

The extracellular fluid is called the internal environment of the body; it surrounds cells and transports substances to and from them. This compartment contains plasma, interstitial fluid, and transcellular fluids:

Plasma is the liquid part of whole blood;

Interstitial fluid surrounds the cells; and

Transcellular fluids include lymph; joint fluids; cerebrospinal fluid; and eye humors.

Intracellular fluid is the largest fluid compartment.

Intracellular means it is located inside of the cells.

This fluid serves as solvent to facilitate intracellular chemical reactions.

Fluid balance is maintained between fluid intake and fluid output.

Sources of fluid intake include the liquids we drink, water in food that we eat, and metabolic water from cellular respiration.

Sources of fluid output include water vapor lost during respiration, sweating from the skin, urine from the kidneys, and water lost in the feces. The organs responsible for fluid output are the lungs, skin, kidneys, and large intestine.

Three main factors affect plasma, interstitial fluid, and intracellular fluid volumes:

Regulating fluid output;

Regulating fluid intake; and

Exchanging fluid among compartments and around the body.

Fluid output, mainly urine volume, adjusts to fluid intake.

Antidiuretic hormone (ADH) serves to decrease fluid output.

ADH is released from the posterior pituitary gland when extracellular fluid volume is low.

ADH promotes water reabsorption from the kidney tubules into the blood.

Water is thus retained by the body and less fluid is lost in urine.

An aldosterone mechanism decreases fluid output.

Aldosterone is released from the adrenal cortex.

It increases kidney tubule reabsorption of sodium.

Water follows sodium from the kidney tubules into the blood.

Water is retained by the extracellular fluid (and total body fluid) by decreasing urine volume.

Atrial natriuretic hormone (ANH) increases fluid output.

ANH is released from the heart’s atrial wall in response to high blood volume.

ANH promotes sodium loss from the blood into the kidney tubules.

Water follows sodium from the blood, thus increasing loss of water in urine.

Fluid intake is regulated by sensory receptors that detect change in volume and extracellular fluid concentration and send signals to the hypothalamus.

Signals from the hypothalamus cause the feeling of thirst, which triggers drinking of fluids to restore balance.

The constancy of internal fluid balance is also maintained by exchanging fluids between fluid compartments.

Increased capillary blood pressure transfers fluid from blood plasma to interstitial fluid—a fluid shift.

Blood plasma protein concentration contributes to osmotic pressure, thus attracting water and holding it in the plasma.

Fluid imbalances include dehydration, overhydration, and water intoxication.

In dehydration, the total volume of body fluids is below healthy levels.

Interstitial fluid volume shrinks first, and then if treatment is not given, intracellular volume and plasma volume decrease.

Dehydration occurs when fluid output exceeds intake for an extended period.

In overhydration, the total volume of body fluids is larger than needed for healthy survival.

Fluid intake exceeds output, and excess volume burdens the pumping action of the heart.

Water intoxication is a possibly life-threatening neurological impairment caused by severe overhydration and associated electrolyte imbalance.

It is important for you to understand the roles of electrolytes in body fluids.

First realize that nonelectrolytes are organic substances that do not break up or dissociate when placed in water solution (e.g., glucose).

Electrolytes are compounds that break up or dissociate in water solution into separate particles called ions. (An example is ordinary table salt or sodium chloride.)

Ions are the dissociated particles of an electrolyte that carry an electrical charge.

Cations are positively charged ions (such as, potassium and sodium ions that each carry one positive charge)

Anions are negatively charged ions (such as chloride and bicarbonate that each carry one negative charge, and anionic proteins).

Electrolytes are found within body fluids.

The extracellular fluid is dominated by sodium ions (which are positive) and chloride ions (which are negative).

Intracellular fluid is dominated by potassium ions (positive) and anionic proteins (which are negative)

Edema is swelling caused by high interstitial fluid volume.

Large volumes of sodium-containing internal secretions are produced daily.

Electrolyte imbalances include sodium imbalances, potassium imbalances, and calcium imbalances. Homeostasis of electrolytes is related to “intake” and “output” of electrolytes and also absorption and distribution of electrolytes in body fluids and availability for use by body cells.

Sodium imbalances are hypernatremia (high blood sodium) or hyponatremia (low blood sodium).

Hypernatremia is blood sodium more than 145 mEq/L.

It is characterized by relative deficit of water to salt in extracellular fluid.

Causes include overuse of salt tablets; dehydration; and prolonged diarrhea.

Hyponatremia is a blood sodium less than 136 mEq/L.

It results when there is relatively too much water in the extracellular fluid for the amount of sodium present.

Causes of hyponatremia include excessive secretion of antidiuretic hormone, massive infusion of sodium-free intravenous solution, burns, and prolonged use of certain diuretics.

Symptoms of both hypernatremia and hyponatremia are related to central nervous system malfunction and include headache, confusion, seizures, and coma.

Potassium imbalances are hyperkalemia (high blood potassium) or hypokalemia (low blood potassium).

Hyperkalemia is blood potassium more than 5.1 mEq/L.

Causes include increased intake, shift of potassium from intracellular fluid to blood caused by tissue trauma and burns, and renal failure.

Clinical signs of hyperkalemia are related to muscle malfunction and include skeletal muscle weakness, paralysis, and cardiac arrest.

Hypokalemia is blood potassium less than 3.5 mEq/L.

Causes include fasting, diets low in potassium, abuse of laxatives and certain diuretics, diarrhea, vomiting, and gastric suction.

Clinical signs include skeletal muscle and cardiac problems; smooth muscle weakness causing abdominal distention, and slow rate of passage of gastrointestinal contents.

Calcium imbalances are hypercalcemia (high blood calcium) or hypocalcemia (low blood calcium).

Hypercalcemia is a blood calcium level more than 10.5 mg/dL.

It is caused by excessive intake, increased absorption, shifts of calcium from bone to extracellular fluid, Paget disease and other bone tumors, and hyperparathyroidism.

Clinical signs are related to decreased neuromuscular activity, and include fatigue, muscle weakness, diminished reflexes, and cardiac problems.

Hypocalcemia is a blood calcium level less than 8.4 mg/dL.

It is caused by dietary deficiency, decreased absorption or availability, increased excretion, pancreatitis, hypoparathyroidism, rickets, osteomalacia, and renal insufficiency.

Clinical signs of hypocalcemia are related to increased neuromuscular irritability, such as cramping, muscle twitching, hyperactive reflexes, and abnormal cardiac rhythms.

This concludes the audio review of Chapter 19.