Water Balance
What organ controls water output?
Kidneys
Name the most abundant cation in extracellular fluid.
Na⁺
What percentage of body water is intracellular?
63%
What is the normal blood pH range?
7.35–7.45
What is dehydration?
Loss of more water than intake
What percentage of daily water intake comes from food?
30%
Which hormone regulates Na⁺ and K⁺ levels?
Aldosterone
Name one transcellular fluid.
Cerebrospinal fluid, Synovial fluid, etc.
What buffer system uses bicarbonate?
Bicarbonate buffer system
Name a symptom of alkalosis.
Agitation, dizziness, light-headedness
What hormone helps conserve water during dehydration?
ADH
What does hypoproteinemia lead to?
Edema
What two pressures control movement between compartments?
Hydrostatic and Osmotic pressure
What happens during respiratory acidosis?
CO₂ and H₂CO₃ build up in the blood
What causes metabolic acidosis in diabetes?
Ketone buildup
What physiological mechanisms are triggered when 1% of body water is lost, and how do they help restore homeostasis?
Osmoreceptors in the hypothalamus detect increased osmotic pressure and stimulate the thirst center. Stretch receptors in blood vessels detect decreased volume, triggering the renin-angiotensin system, where angiotensin II stimulates thirst. Drinking water distends the stomach and inhibits the thirst center, helping restore fluid balance.
Explain how aldosterone regulates both sodium and potassium levels, and describe the consequences of its dysfunction.
Aldosterone increases reabsorption of Na⁺ and secretion of K⁺ in the renal tubules. If aldosterone is deficient, sodium is lost in urine and potassium accumulates, which can lead to hyponatremia, hypotension, and hyperkalemia—potentially resulting in cardiac dysfunction.
Compare the ionic composition of intracellular and extracellular fluids and explain how osmotic gradients drive water movement.
Intracellular fluid is rich in K⁺, Mg²⁺, PO₄³⁻, and SO₄²⁻, while extracellular fluid is rich in Na⁺, Cl⁻, Ca²⁺, and HCO₃⁻. Water moves via osmosis toward areas with higher impermeant solute concentration, creating osmotic gradients that regulate hydration status across compartments.
How does the body compensate for metabolic alkalosis using all three regulatory mechanisms?
Chemical buffers release H⁺ to lower pH. The respiratory system decreases ventilation to retain CO₂, forming carbonic acid and lowering pH. The kidneys reduce secretion of H⁺ and increase bicarbonate excretion to correct the base excess.
Explain how edema can result from low plasma protein levels and describe at least two other contributing factors.
Low plasma proteins reduce oncotic pressure, leading to fluid leakage into interstitial spaces. Other factors include increased capillary permeability (e.g., from inflammation), lymphatic obstruction (reducing drainage), or increased venous pressure (e.g., from heart failure), all contributing to fluid accumulation.