Fluid, Electrolyte and Acid-Base Homeostasis

Twenty question-and-answer flashcards covering the key points of fluid, electrolyte, and acid-base homeostasis.

What fraction of total body water is found inside cells (intracellular fluid)?

Approximately two-thirds of total body water.

Which two major subdivisions make up the extracellular fluid compartment?

Interstitial fluid and plasma.

Name three smaller ECF fluids that are grouped with interstitial fluid.

Lymph, cerebrospinal fluid (CSF), and synovial, serous, and other transcellular fluids.

Which three routes account for the largest daily water loss in an average adult?

Urine via the kidneys, evaporation through the skin, and water vapor from the lungs.

Which physiological changes collectively trigger the thirst center during dehydration?

Decreased saliva flow, increased blood osmolarity stimulating hypothalamic osmoreceptors, and decreased blood pressure activating the renin-angiotensin pathway.

What is water intoxication and what two conditions commonly precipitate it?

A dangerous dilution of body fluids caused by rapid excessive water intake or poor renal function combined with sodium and water loss replaced only by plain water.

List four key functions of electrolytes in the body.

They control osmosis between compartments, help maintain acid-base balance, carry electrical currents, and act as enzyme cofactors.

Which hormone increases renal reabsorption of sodium (Na+)?

Aldosterone.

When plasma sodium is low (hyponatremia), what happens to ADH release and why?

ADH secretion is stopped so that excess water is excreted, preventing further dilution of sodium.

Which hormone promotes sodium excretion during hypernatremia?

Atrial natriuretic peptide (ANP).

What hormone controls potassium secretion by the kidneys?

Aldosterone increases K+ secretion.

Which two hormones work together to raise blood calcium levels, and by what mechanisms?

Parathyroid hormone (PTH) releases calcium from bone and increases renal reabsorption and calcitriol production; Calcitriol then increases calcium absorption from the gastrointestinal tract.

Name the three principal chemical buffer systems in the body.

Protein buffer system, phosphate buffer system, and carbonic acid–bicarbonate buffer system.

In the bicarbonate buffer system, what happens when H+ concentration rises?

H+ combines with bicarbonate (HCO3−) to form carbonic acid, which then dissociates into CO2 and H2O, removing free hydrogen ions.

Define acidosis and give the blood pH threshold.

Acidosis is a systemic arterial blood pH below 7.35.

A patient with PCO2 greater than 45 mm Hg is experiencing which acid–base disorder?

Respiratory acidosis.

Give three possible causes of metabolic acidosis.

Loss of bicarbonate (e.g., diarrhea), accumulation of acids (e.g., ketosis), or failure of the kidneys to excrete H+.

Define alkalosis and give its pH threshold.

Alkalosis is a systemic arterial blood pH above 7.45.

Hyperventilation leading to PCO2 below 35 mm Hg produces which disorder?

Respiratory alkalosis.

How do the kidneys compensate for respiratory acid–base imbalances?

By secreting or retaining H+ and reabsorbing or excreting bicarbonate; maximal effect takes several days.