Principles of Water and Solute Movement

Question 1

What is Interstitial Water, Plasma and Intracellular Fluid bound by?

Answer 1

Interstitial Water - Epithelial Cells
Plasma - Capillary Endothelium
Intracellular Fluid - Plasma Membrane

Question 2

What ions are dominant inside and outside of the cell?

Answer 2

Na+ dominates outside of the cell

K+ dominates inside the cell

Question 3

Why is osmolality the same in all body fluid compartments?

Answer 3

To maintain water ratio

Question 4

What is the normal range of osmolality?

Answer 4

280-310 mOsm/kg

Question 5

What moves easily and what doesn’t move easily through the phospholipid bilayer?

Answer 5

Easily - hydrophobic molecules, lipids, small uncharged polar molecules

Difficult - large uncharged polar molecules, ions and charged polar molecules

Question 6

What is the capillary wall permeable and non-permeable to?

Answer 6

Permeable - Water, urea, Na+, K+

Non-Permeable- Plasma proteins

Question 7

Give 3 examples of passive transport

Answer 7

• Diffusion
• Facilitated Diffusion
• Osmosis
• Osmotic Pressure
• Hydrostatic Pressure

Question 8

What factors influence diffusion?

Answer 8

• Membrane width

- Concentration gradient

Question 9

Define Facilitated Diffusion and 2 of its characteristics

Answer 9

• Movement from a high to low concentration through a protein channel
• Quicker than diffusion
• Not affected by membrane width

Question 10

How are large molecules moved in and out of a cell?

Answer 10

• Through vesicles and vacuoles
• Requires ATP
• Can be phagocytosis, pinocytosis or receptor-mediated

Question 11

What is osmolality? Give an example of this in relation to NaCl

Answer 11

• Measure of solute concentration

- NaCl splits to Na and Cl in solution so 1 mole —> 2 moles

Question 12

Define osmosis and state how osmotic potential can be measured

Answer 12

• Diffusion of Water from a hypotonic to hypertonic solution across a semi-permeable membrane
• Osmotic potential is measurable by height difference in a U-Tube

Question 13

What is an Aquaporin Channel and where are they most prevalent?

Answer 13

• Integral membrane protein that allows rapid diffusion of water across a membrane
• Found in tissues involved in water movement (Kidney)

Question 14

What prevents movement of H+ through an Aquaporin Channel?

Answer 14

Positive charge in the residues lining the channel

Question 15

Describe 3 characteristics of an Aquaporin Channel

Answer 15

• 10 varieties within the human body
• Made of 6 transmembrane proteins in an alpha-helix
• Water molecule move single file
• Dependent on solute gradient