Chapter 3: The Cellular Environment — Fluids and Electrolytes

A set of Q&A flashcards covering key concepts from Chapter 3: Fluids and Electrolytes, including body fluid compartments, fluid balance, edema, and major electrolyte disorders.

What are the major body fluid compartments?

Intracellular fluid (ICF) inside cells; Extracellular fluid (ECF) outside cells, including interstitial fluid, intravascular (plasma), and cerebrospinal fluid (CSF).

How is total body water distributed by age and sex?

Newborn: 70–80% body weight; Children: 60–65%; Adults: 50–60%; Older adults decline with age; Men typically have higher TBW than women due to more muscle mass.

Define hypovolemia.

ECF volume deficit due to abnormal fluid loss, inadequate intake, or plasma-to-interstitial fluid shift; cells become dehydrated.

Name the two main pressures that govern fluid movement when correcting deficits.

Osmotic pressure (solutes like sodium) and oncotic pressure (plasma proteins like albumin); rapid correction can cause edema or fluid overload.

What are the four primary causes of edema?

Increased capillary hydrostatic pressure; decreased plasma oncotic pressure; increased capillary permeability; lymphatic obstruction.

What is edema?

Accumulation of fluid in the interstitial spaces.

Differentiate 1st, 2nd, and 3rd space shifting.

1st space: normal ECF; 2nd space: edema in interstitial space; 3rd space: fluid in areas normally with little/no fluid (e.g., ascites, pleural effusions).

Which hormone regulates water balance and where is it released?

Antidiuretic hormone (ADH, vasopressin) released from the posterior pituitary in response to increased plasma osmolality or decreased blood volume.

What triggers aldosterone release?

Low blood pressure/volume, hyponatremia, and hyperkalemia.

What do natriuretic peptides do in fluid balance?

ANP and BNP oppose the RAAS, promoting sodium and water excretion in the kidneys.

What is the primary extracellular fluid (ECF) cation?

Sodium (Na+).

What is the primary extracellular fluid (ECF) anion?

Chloride (Cl−).

Which hormonal system regulates sodium and water balance through signaling?

Renin-angiotensin-aldosterone system (RAAS).

What is aldosterone’s main function?

Sodium and water retention with loss of potassium (and hydrogen) ions.

What is the normal serum potassium range?

3.5–5.0 mEq/L.

What are the causes and signs of hypokalemia?

Causes: reduced intake, increased cellular entry, increased loss. Signs: ECG changes and dysrhythmias.

What are the causes of hyperkalemia?

Increased intake; shift of K+ from ICF to ECF; decreased renal excretion; hypoxia; acidosis.

Which hormones regulate calcium and phosphate?

Parathyroid hormone (PTH), Vitamin D, and Calcitonin.

What are calcium’s key roles in the body?

Bone/teeth structure, blood clotting, and muscle contractions.

What are the features of hypocalcemia (causes and signs)?

Causes: inadequate intake/absorption; decreases in PTH and vitamin D; blood transfusions. Signs: increased neuromuscular excitability; muscle spasms; Chvostek and Trousseau signs; convulsions; tetany.

What are the features of hypercalcemia (causes and signs)?

Causes: hyperparathyroidism, excess vitamin D, immobilization, hypophosphatemia, malignancy, acidosis. Signs: decreased neuromuscular excitability; weakness; kidney stones; heart block.

What is the normal phosphate range for adults?

2.5–4.5 mg/dL.

What causes hypophosphatemia and what are its manifestations?

Causes: intestinal malabsorption/renal excretion, vitamin D deficiency, alcohol. Manifestations: osteomalacia and muscle weakness.

What causes hyperphosphatemia and what are its manifestations?

Causes: chemotherapy, long-term use of phosphate laxatives/enemas, renal failure; may cause calcifications and symptoms similar to hypocalcemia.

Explain the calcium–phosphate relationship and its clinical significance.

Calcium and phosphate have a reciprocal relationship; imbalances affect muscles and other systems; monitoring both is important.

What is the normal magnesium range and where is it stored?

1.5–3.0 mg/dL; stored mostly in muscle and bone; interacts with calcium and affects neuromuscular excitability.

What are the signs of hypomagnesemia and hypermagnesemia?

Hypomagnesemia: increased reflexes, tetany, tachycardia. Hypermagnesemia: muscle weakness, decreased deep tendon reflexes, hypotension, respiratory depression.

Why is sodium imbalance especially concerning for the brain?

Sodium imbalances strongly affect brain function; signs include headaches, altered level of consciousness, seizures.

What are the three tonicity categories for IV fluids?

Hypertonic, hypotonic, and isotonic solutions.

What happens in hypernatremia at the cellular level?

Water moves from the intracellular fluid (ICF) to the extracellular fluid (ECF), causing intracellular dehydration and potential neurologic symptoms.

What are the clinical manifestations and initial treatment considerations for edema?

Manifestations: edema, weight gain, JVD, pulmonary congestion; Treatment: elevate limbs, compression, limit salt, diuretics, avoid prolonged standing.

What is filtration and reabsorption in capillary fluid movement?

Filtration: water moves from capillary to interstitial space; Reabsorption: water moves from interstitial space back into capillary.

What pressures influence capillary fluid exchange and edema formation?

Capillary hydrostatic pressure pushes water out; capillary oncotic pressure pulls water in; interstitial hydrostatic and oncotic pressures also influence movement.

What is the role of ADH in water balance?

ADH increases water reabsorption in the renal collecting ducts, reducing urine volume.

What triggers aldosterone release and what does it do in the kidney?

Triggered by low BP/volume, hyponatremia, hyperkalemia; increases sodium and water reabsorption and promotes potassium excretion in the kidneys.

What is the function of natriuretic peptides in fluid balance?

ANP and BNP oppose RAAS; decrease tubular sodium reabsorption and promote excretion of sodium and water.

Which space shift is most associated with ascites and pleural effusions?

2nd space shifting (interstitial edema) involves fluid in areas normally having little fluid; ascites is a classic example.

Identify a key signs and symptom pair for hyponatremia’s CNS impact.

Headache, changes in level of consciousness, seizures due to brain swelling from hypo-osmolality.