4. Membrane Transport Mechanisms

Question 1

What is the distribution of water in the body?

Answer 1

60% of body water
1/3 of water is ECF, 2/3 is ICF
75% of ECF is interstitial, 25% is plasma

Question 2

What are the main ions in ECF?

Answer 2

Cation - Na+

Anion - Cl-

Question 3

What can pass through membranes?

Answer 3

Hydrophobic molecules (gases, vey small uncharged polar molecules) can pass easily

Question 4

Can water and urea pass through membranes?

Answer 4

Yes as they are small uncharged polar molecules however not as easily as gases

Question 5

What cannot pass through the membrane?

Answer 5

Large charged polar molecules, ions and charged polar molecules

Question 6

How do some molecules such as water, urea and ions pass through capillary walls?

Answer 6

Pass through fenestrations

Question 7

What is passive movement?

Answer 7

No energy, down concentration gradient

Question 8

What is active transport?

Answer 8

Movement against concentration gradient, requires ATP

Question 9

What is vesicular transport?

Answer 9

Molecules move in vesicles
Active process
Includes pinocytosis and phagocytosis

Question 10

What is flux?

Answer 10

Describes how fast a solute moves

Number of moles crossing unit area of membrane per unit time (moles/cm^2/s)

Question 11

Rate of flow of uncharged solute due to diffusion is directly proportional to…

Answer 11

Rate of change of concentration with distance in direction of flow

Question 12

What happen when concentration gradient of substance is 0?

Answer 12

System must be in equilibrium and net flux will be 0

Question 13

How dies the thickness of the membrane affect flux?

Answer 13

Thicker membrane, flux is slower

Question 14

What is diffusion proportional to/inversely proportional to?

Answer 14

Proportional to surface area of barrier

Inversely proportional to its thickness

Question 15

Describe the diffusion of 2 solutes

Answer 15

Each substance diffuses down its own concentration gradient, independent of concentration gradients of other substances

Question 16

What is facilitated diffusion?

Answer 16

Move from high to low through protein channel

Passive

Question 17

What are gated channels and how do they work?

Answer 17

Proteins that only open in presence of stimulus
Stimulus usually different to transported molecule
Ion gated or voltage gated

Question 18

What is active transport?

Answer 18

Pump against concentration
Uses protein pump
Requires ATP

Question 19

How are large molecules transported?

Answer 19

Exocytosis
Endocytosis
Requires ATP, vesicles and vacuoles

Question 20

What are osmoles?

Answer 20

Measure of solutions ability to create osmotic pressure, thus affect movement of water

Question 21

What are osmoles proportional to?

Answer 21

Number of osmotic particles formed in solution

1 mole of nonionisable substance = 1 osmole

Question 22

What is osmolality?

Answer 22

When concentration of water is expressed in osmoles/kg of water
Osmolar concentration of solution is osmolality
You measure osmolality not osmolarity

Question 23

What is osmosis?

Answer 23

Diffusion of water from high hypotonic solution to hypertonic solution across a semi-permeable membrane
Diffuses until osmotic force of both sides is equal

Question 24

What are aquaporins?

Answer 24

Integral membrane proteins

Channel for transfer of water

Question 25

What is the structure of aquaporins?

Answer 25

At centre of channel are positively charged residues that prevent movement of charged ions (H+) and therefore don’t disrupt H+ ion gradients in ATP production