Capillaries I - Solute exchange

Question 1

What does metabolism create?

Answer 1

→ A need to transport solute and fluids

Question 2

What do cell membranes consist of?

Answer 2

→ Phosphate head (Polar)

→ Fatty acid tail (non-polar)

Question 3

What do cell membranes form?

Answer 3

→ Bilayers in solution

Question 4

What are the functions of cell membranes?

Answer 4

→ Provide support and protection
→ Cell-to-cell recognition
→Controls what enters and leaves the cell
→ Regulates cell function

Question 5

What are properties of Passive transport?

Answer 5

→ Movement of molecules down a gradient
→ Concentration/pressure/osmotic/electrical
→ Does not require energy
→ Simple (O2/CO2) or facilitated (ions/glucose)

Question 6

What are properties of Active transport?

Answer 6

→Movement of molecules against a gradient

→ Requires energy (uses ATP)

Question 7

What gradient does diffusion use and give an example

Answer 7

→ concentration gradient

→ O2 uptake from the lungs into the blood

Question 8

What gradient does convection use and give an example

Answer 8

→Pressure gradient

→ blood flow from heart to blood vessels

Question 9

What gradient does osmosis use and give an example

Answer 9

→ Osmotic pressure gradient

→ Water uptake by cells

Question 10

What gradient does electrochemical flux use and give an example

Answer 10

→ Electrical and concentration gradient

→ Ion flow during an action potential in a nerve

Question 11

Where does solute and fluid exchange occur?

Answer 11

→ At capillaries

Question 12

What do capillaries connect?

Answer 12

→ Connect terminal arterioles to venules

→ Extension of inner lining of an arteriole

Question 13

How thick are capillaries?

Answer 13

→ 1 cell thick

Question 14

Where are capillaries found?

Answer 14

→ found near every cell in the body

→higher density in highly active tissues (muscles, liver, heart, kidneys, brain)

Question 15

What is the function of capillaries?

Answer 15

→ Solute exchange
→ Fluid exchange
→ Regulation of plasma and interstitial fluid

Question 16

What controls the rate of solute transport?

Answer 16

→Properties of passive diffusion
→Properties of solutes and membranes
→ Properties of capillaries

Question 17

What are properties of passive diffusion?

Answer 17

→Does not require any energy
→ molecules move randomly
→ Move from areas of high to low concentrations
→ transport of lipid soluble solutes over short distances

Question 18

What are properties of the solute that affect transport?

Answer 18

→ Concentration gradient
→ size of solute
→ Lipid solubility of solute

Question 19

What are properties of the membrane that affect transport?

Answer 19

→ Membrane thickness/ composition
→ Aqueous pores in the membrane
→ Carrier mediated transport
→ Active transport mechanisms

Question 20

What is Fick’s law?

Answer 20

→solute movement (mass per unit time) can be determined by four factors:

→the diffusion coefficient of the solute (the ease of movement through the solvent)
→the area
→the concentration gradient (C1 - C2)
→ the distance (between C1 and C2)

Question 21

What value does Fick’s law have down a concentration gradient?

Answer 21

→ a negative value

Question 22

What are the three types of capillaries?

Answer 22

→ Continuous capillaries
→ Fenestrated capillaries
→ Discontinuous capillaries

Question 23

What are properties of continuous capillaries?

Answer 23

→Moderate permeability
→Tight gaps between neighboring cells
→ constant basement membrane

Question 24

What are properties of fenestrated capillaries?

Answer 24

→ High water permeability
→ Fenestration structures
→ modest disruption of the membrane

Question 25

Where are fenestrated capillaries found?

Answer 25

→ in high water turnover tissues | → salivary glands, kidneys, synovial joints, anterior eye, choroid plexus, gut mucosa

Question 26

Where are continuous capillaries found?

Answer 26

→ blood-brain barrier | → Muscle, skin, fat, connective tissue

Question 27

What are properties of discontinuous capillaries?

Answer 27

→ Very large fenestration structures | → disrupted membrane

Question 28

Where are discontinuous capillaries found?

Answer 28

→ When the movement of cells is needed | → RBCs in liver, spleen + bone marrow

Question 29

How wide is the intercellular cleft?

Answer 29

→ 10-20nm wide

Question 30

What are the caveolae + vesicles?

Answer 30

→ large pore systems

Question 31

What is the glycocalyx?

Answer 31

→ Covers the endothelium → -vely charged → Blocks solute permeation and access to transport mechanism → highly regulated → dynamic and can be broken down and remade as required

Question 32

What is permeability?

Answer 32

→ Permeability is the rate of solute transfer by diffusion across a unit area of membrane per unit concentration difference (ie. how freely a solute crosses a membrane).

Question 33

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

Answer 33

→ a reduction in the area for diffusion (A) →an increased path length through the membrane (x) → restricted diffusion in the pore produces hydrostatic issues (D)

Question 34

What is filtration?

Answer 34

→going through gaps, pores and fenestrations | → as fluid moves through the dissolved glucose goes with it

Question 35

What is the glucose concentration in plasma?

Answer 35

→ 1g/liter

Question 36

What is the total volume of plasma filtrate flowing into tissues per day?

Answer 36

→ 8 liters

Question 37

What is the maximum filtration of glucose per day?

Answer 37

→ 8g/day

Question 38

What does filtration transport account for?

Answer 38

→ 2% of glucose transport

Question 39

How does 98% of glucose get transported?

Answer 39

→ into the interstitial space via passive diffusion | → via GLUT transporter

Question 40

How does blood flow control diffusion rate?

Answer 40

→More blood brings more solutes | → Increased blood volume means less time for equilibration to occur across capillaries

Question 41

What is flow limited diffusion?

Answer 41

→ slow flow in a long capillary | → O2/CO2 equilibrate over the proximal section and there is little diffusion across the rest of the vessel

Question 42

When can flow limited diffusion occur and what can this lead to ?

Answer 42

→ In sepsis when blood pressure and flow are low | → can lead to ischaemia

Question 43

How can a fall in interstitial concentration affect diffusion rate?

Answer 43

→More solute is used up → increases the concentration difference →metabolism increases blood flow →Increased O2 delivery controlled by arterioles

Question 44

How can recruitment of capillaries affect diffusion rate?

Answer 44

→ Dilation of arterioles leads to more perfused capillaries → Increases total SA for Fick's Law → Shortens diffusion distance between capillary and cell

Question 45

During strenuous exercise how much does O2 transport to the muscle increase by?

Answer 45

40x