Solute exchange

Question 1

What does the membrane consist of?

Answer 1

Consists of two layers of amphipathic phospholipids
Phosphate head is polar (hydrophilic)
Fatty acid tail is non-polar (hydrophobic)
Form bilayers in solution

Question 2

What does the cell membrane provide?

Answer 2

Provide support and protection

Question 3

What is passive transport?

Answer 3

Movement of molecules DOWN a gradient

Question 4

Does passive transport require energy?

Answer 4

No

Question 5

What is active transport?

Answer 5

Movement of molecules AGAINST a gradient

Question 6

Does active transport require energy?

Answer 6

Yes

Question 7

Passive transport processes(Diffusion)

Answer 7

Concentration gradient

E.g. O2 uptake from lungs into blood

Question 8

Passive transport processes(Convection)

Answer 8

Pressure gradient

E.g. Blood flow from heart to blood vessels

Question 9

Passive transport processes(Osmosis)

Answer 9

Osmotic pressure gradient

E.g. Water uptake by cells

Question 10

Passive transport processes(Electrochemical flux)

Answer 10

Electrical and concentration gradient

E.g. ion flow during an action potential in a nerve

Question 11

What do capillaries connect?

Answer 11

Connect terminal arterioles to venules

Question 12

How big are capillaries?

Answer 12

Smallest diameter blood vessels endothelium

1 cell thick, semi-permeable

Question 13

Where are capillaries found?

Answer 13

Found near every cell in the body

Question 14

Where is there a higher density of capillaries?

Answer 14

However there is a higher density in highly active tissues (muscles, liver, heart, kidney, brain etc.)

Question 15

How does blood flow in capillaries?

Answer 15

Fluid exchange (flow down pressure gradients)

Question 16

Why is diffusion great for transport across short distances

Answer 16

Time taken (t) for one randomly moving molecule to move a net distance (x) in one specific direction increases with the distance squared

Question 17

What properties of the solute affect transport?

Answer 17

Concentration gradient

Size of the solute

Lipid solubility of solute (lipophilic, lipophobic nature)

Question 18

What Properties of the membrane affect transport?

Answer 18

Membrane thickness/composition

Aqueous pores in the membrane

Carrier-mediated transport

Active transport mechanisms

Question 19

Comment on permeability of continuous capillaries

Answer 19

Moderate permeability; tight gaps between neighbouring cells; constant basement membrane

Question 20

Examples of where continuous capillaries can be found

Answer 20

Blood-brain barrier

Muscle, skin, fat, connective tissue

Question 21

Comment on permeability of fenestrated capillairies

Answer 21

High water permeability, fenestration structures, modest disruption of membrane

Question 22

Where are fenestrated capillaries found?

Answer 22

“High water turnover” tissues – e.g. salivary glands, kidney, synovial joints, anterior eye, choroid plexus (cerebrospinal fluid), gut mucosa

Question 23

What are discontinuous capillaries?

Answer 23

Very large fenestration structures, disrupted membrane

Question 24

What are three other structural features of capillary walls that influence solute transfer?

Answer 24

Intracellular cleft
Caveolae and vesicles
Glycocalyx

Question 25

How wide is the intracellular cleft?

Answer 25

10-20nm

Question 26

What type of system are caveolae and vesicles?

Answer 26

Large pore system

Question 27

What does glycocalyx cover?

Answer 27

Covers endothelium, negatively charged material

Question 28

What does glycocalyx block?

Answer 28

Blocks solute permeation and access to transport mechanism

Question 29

How is glycocalyx regulated?

Answer 29

Highly regulated

Question 30

Comment on glycocalyx?

Answer 30

It is very dynamic and can be broken down and remade as required

Question 31

What is permeability?

Answer 31

Permeability is the rate of solute transfer by diffusion across unit are of membrane per unit concentration difference

Question 32

How does a porous membrane interfere with diffusion of lipid insoluble solute?

Answer 32

A porous membrane interferes with the diffusion of lipid insoluble solute in multiple ways
Reduction in area for diffusion (A)
Increased path length through membrane (x)
Restricted diffusion in pore produces hydrostatic issues (D)
All factors affecting diffusion go into one term – Permeability (P)

Question 33

What is filtration?

Answer 33

Filtration is going through pores, gaps and fenestrations

Question 34

What is glucose concentration in plasma?

Answer 34

Glucose concentration in plasma is 1g/litres

Question 35

What does more blood bring?

Answer 35

More blood brings more solutes

Question 36

What does increased blood volume mean?

Answer 36

Increased blood volume means less time for equilibration to occur across capillaries

Question 37

What is flow limited diffusion?

Answer 37

Where there is slow flow in a long capillary

Question 38

When can flow limited diffusion occur?

Answer 38

Sometime this can occur in sepsis where the blood pressure and flow are low
This can lead to ischaemia

Question 39

What may cause a fall in interstitial concentration?

Answer 39

During metabolism, more solute is used up thereby increased the concentration difference

Question 40

What does metabolism increase?

Answer 40

Also, metabolism increases blood flow – there is increased O2 delivery, which is controlled by the arterioles

Question 41

What does a dilation of arterioles lead to?

Answer 41

Dilation of arterioles leads to increased number of capillaries that are perfused which increases total surface area (A) for diffusion (Fick’s Law)

Question 42

What does perfusion of capillaries lead to?

Answer 42

shortens diffusion distance between capillary and the cell

Question 43

What happens during strenuous exercise?

Answer 43

O2 transport from blood to the muscle increases over 40 times
We increase cardiac output (blood flow), use more O2 (fall in tissue concentration) and open up more capillaries (recruitment)