Fluid compartments L9

Question 1

What percentage of the body is water in a typical adult?

Answer 1

About 60%.

Question 2

What is the 60-40-20 rule in fluid compartments?

Answer 2

Total body water = 60% of body weight.
Intracellular fluid (ICF) = 40% of body weight.
Extracellular fluid (ECF) = 20% of body weight.

Question 3

How does fat content affect body water percentage?

Answer 3

Higher fat content reduces body water percentage because fat does not store water.

Question 4

Why do females typically have a lower body water percentage than males?

Answer 4

Females have more fat tissue, which stores less water than muscle tissue.

Question 5

Name the two major fluid compartments in the body.

Answer 5

Intracellular Fluid (ICF).
Extracellular Fluid (ECF).

Question 6

What are the subdivisions of extracellular fluid?

Answer 6

Plasma (~3 L).
Interstitial fluid (~10 L).
Transcellular fluid (~1 L).

Question 7

What is transcellular fluid? Give examples.

Answer 7

Specialised fluid separated by membranes, including cerebrospinal fluid (CSF), synovial fluid, peritoneal fluid, and aqueous humour.

Question 9

What proportion of total body water is in the ICF?

Answer 9

Approximately two-thirds, or 40% of body weight.

Question 10

hat are the major cations and anions in intracellular fluid (ICF)?

Answer 10

Cations: Potassium (K⁺) and Magnesium (Mg²⁺).
Anions: Proteins and organic phosphates (e.g., ATP).

Question 11

What are the major cations and anions in extracellular fluid (ECF)?

Answer 11

Cations: Sodium (Na⁺).
Anions: Chloride (Cl⁻) and bicarbonate (HCO₃⁻).

Question 12

How do sodium-potassium ATPase pumps maintain ion gradients?

Answer 12

They pump Na⁺ out of the cell and K⁺ into the cell, maintaining high intracellular K⁺ and high extracellular Na⁺.

Question 13

What is the main difference between plasma and interstitial fluid?

Answer 13

Plasma contains large proteins like albumin, while interstitial fluid has fewer proteins.

Question 14

What is the Gibbs-Donnan effect?

Answer 14

Plasma proteins attract cations (like Na⁺) and repel anions (like Cl⁻), creating slight differences in ion concentrations between plasma and interstitial fluid.

Question 15

What percentage of blood is plasma?

Answer 15

Plasma makes up about 55% of blood volume.

Question 16

What is the dilution method used for?

Answer 16

Measuring the volumes of different fluid compartments using specific markers.

Question 17

What marker is used to measure plasma volume?

Answer 17

Radiolabeled albumin, which stays confined to plasma.

Question 18

What markers are used to measure extracellular fluid volume?

Answer 18

Mannitol and inulin, which diffuse into the interstitial fluid but not the intracellular fluid.

Question 19

How is intracellular fluid volume calculated?

Answer 19

By subtracting extracellular fluid volume from total body water.

Question 20

Write the formula for calculating volume using the dilution method.

Answer 20

Volume = Amount Injected ÷ Concentration Measured.

Question 21

What can cause reduced plasma albumin levels?

Answer 21

Liver failure, protein malnutrition, or renal disease.

Question 22

What is a common consequence of low plasma albumin?

Answer 22

Edema, due to reduced oncotic pressure.

Question 23

Why is maintaining ion gradients essential?

Answer 23

For cellular functions such as neuronal action potentials, muscle contractions, and osmoregulation.

Question 24

What is osmosis?

Answer 24

The movement of water across a semipermeable membrane from an area of lower solute concentration to higher solute concentration.

Question 25

What is osmotic pressure?

Answer 25

The pressure required to prevent the movement of water across a semipermeable membrane due to osmosis.

Question 26

What is oncotic pressure?

Answer 26

The osmotic pressure exerted by plasma proteins, particularly albumin, to retain water in the vascular space.

Question 27

What happens if a solution is isosmotic but not isotonic?

Answer 27

Water movement may still occur; for example, urea can cross the membrane, causing intracellular osmolarity to rise and water to enter the cell, potentially leading to swelling.

Question 28

What is the dilution method used for measuring total body water?

Answer 28

Heavy water isotopes (e.g., D₂O) are used because they freely diffuse across all compartments.

Question 29

What is pulmonary edema?

Answer 29

Fluid accumulation in the lungs, often caused by left-sided heart failure or low plasma oncotic pressure.

Question 30

What is osmolality?

Answer 30

Osmolality is the number of osmoles of solute per kilogram of solvent, measured in Osm/kg.

Question 31

What is osmolarity?

Answer 31

Osmolarity is the number of osmoles of solute per liter of solution, measured in Osm/L.

Question 32

What is the key difference between osmolality and osmolarity?

Answer 32

Osmolality measures solutes per mass of solvent (kg).
Osmolarity measures solutes per volume of solution (L).

Question 33

Why is osmolality preferred in physiological contexts?

Answer 33

Osmolality is less affected by temperature and pressure changes because it is based on solvent mass, making it more stable in biological systems.

Question 34

What is the normal range of plasma osmolality in humans?

Answer 34

Approximately 275-295 mOsm/kg.

Question 35

What is the difference between an isosmotic solution and an isotonic solution?

Answer 35

Isosmotic: Two solutions have the same osmolality.
Isotonic: A solution does not cause net water movement across a semipermeable membrane when applied to cells.

Question 36

Can a solution be isosmotic but not isotonic? Give an example.

Answer 36

Yes.
Example: Urea is isosmotic with intracellular fluid but not isotonic because urea freely diffuses into cells, increasing intracellular osmolality and causing water influx.

Question 37

How do you calculate osmolarity for a solute that dissociates in water?

Answer 37

Osmolarity = Molar concentration × Number of particles per molecule.
For example:

NaCl: 1 mol/L dissociates into Na⁺ and Cl⁻, so osmolarity = 2 Osm/L.
CaCl₂: 1 mol/L dissociates into Ca²⁺ and 2 Cl⁻, so osmolarity = 3 Osm/L.

Question 38

What is the relationship between osmotic pressure and osmolality?

Answer 38

Osmotic pressure is directly proportional to osmolality and is calculated using the van’t Hoff equation:
Osmotic Pressure = nCRT, where:

nC is the osmolality.
R is the gas constant.
T is the temperature in Kelvin.

Question 39

What happens to cells in a hypertonic solution?

Answer 39

Water leaves the cells, causing them to shrink (crenation).

Question 40

What happens to cells in a hypotonic solution?

Answer 40

Water enters the cells, causing them to swell and potentially burst (lysis).

Question 41

What is the role of osmotic pressure in capillary exchange?

Answer 41

It opposes hydrostatic pressure to prevent excessive water loss from capillaries.

Question 42

How does osmolality affect fluid movement across the blood-brain barrier?

Answer 42

The blood-brain barrier tightly regulates osmolality to prevent swelling or shrinking of brain cells, which could disrupt neurological function.

Question 43

What does a high plasma osmolality indicate?

Answer 43

Dehydration or hypernatremia (excessive sodium).

Question 44

What does a low plasma osmolality indicate?

Answer 44

Overhydration or hyponatremia (low sodium).

Question 45

What is the osmolality of an isotonic saline solution?

Answer 45

~285 mOsm/kg, matching plasma osmolality.