Capillaries I: Solute exchange -

Question 1

Define the Capillary membrane?

Answer 1

Barrier between the fluid and the circulation and the interstitial fluid. The capillary membrane is made up of endothelial cells.

Question 2

Define the cell membrane?

Answer 2

A phospholipid bilayer. The barrier between the intracellular fluid and the extracellular fluid.

Question 3

Describe cell metabolism? (3pts)

Answer 3

1. Metabolism creates a need to transport solutes and fluids
2. Metabolism utilises oxygen and nutrients. It produces end products of metabolism such as carbon dioxide and waste products
3. Cell metabolism is continually generating concentration gradients that facilitate the movement.

Question 4

What happens as the cell is actively respiring?

Answer 4

As the cell is actively respiring carbon dioxide concentrations will increase within the cell which will create a concentration gradient. As the concentration builds up carbon dioxide will diffuse too areas of lower concentration. As the cell actively respired it will use up oxygen so the concentration of oxygen will decrease within the cell.

Question 5

Describe the cell membane?

Answer 5

1. The cell membrane is a barrier to solute transport
2. The cell membrane is a phospholipid bilayer. It is made up of a hydrophobic non polar fatty acid tail which orientate towards each other and hydrophilic polar phosphate head which faces outwards towards the electrolyte containing solutions
3. The cell membrane provides support and protection
4. The cell membrane provides cell to cell recognition e.g the immune system
5. The cell membrane controls what enters or leaves the cell e.g ion movement in nerves
6. The cell membrane regulates cell function e.g insulin-mediated glucose uptake

Question 6

Describe passive transport?

Answer 6

1. Movement of molecules down a concentration gradient

2. Does not require energy

Question 7

Describe active transport?

Answer 7

1. Movement of molecules against a concentration gradient

2. Requires energy ( uses ATP)

Question 8

Name passive transport processes?

Answer 8

1. Diffusion
2. Osmosis
3. Convection
4. Electrochemical flux

Question 9

Describe solute and fluid exchange that occurs at capillaries? (5pts)

Answer 9

1. The capillaries connect the terminal arterioles to venules
2. The capillaries are the smallest diameter blood vessels consisting of a single layer of endothelial cells. They are one cell thick and create a semi permeable capillary membrane
3. Capillaries are found near every cell in the body but at a higher density in highly active tissues
4. Solute exchange across the capillaries relies on passive diffusion
5. Fluid exchange occurs along pressure gradients. The regulation of plasma and interstitial fluid is important in regulating blood volume.

Question 10

Describe the properties of passive diffusion?

Answer 10

1. Does not require energy
2. Molecule move randomly
3. Molecules move from an area of high concentration to an area of low concentration till equilibrium is reached
4. It is great for transport of lipid-soluble solutes over very short distances e.g 02 and C02.
5. Passive diffusion occurs only across short distances.

Question 11

What do aqueous pores in the membrane do?

Answer 11

Permit water to flow across the membrane

Question 12

What is Fick’s law?

Answer 12

Js= - D A △C/ X

Question 13

Describe continuous capillaries? (4pts)

Answer 13

1. These capillaries have moderate permeability. They have tight gaps between neighbouring endothelial cells
2. Capillaries have a constant basement membrane
3. Capillaries have a blood-brain barrier
   4, Found in muscles, skin, fat and connective tissue

Question 14

Describe fenestrated capillaries?

Answer 14

1. Capillaries have high water permeability
2. Capillaries have fenestration structures
3. Capillaries have bigger gaps between neighbouring endothelial cells which allows modest disruption of the membrane
4. Found in high water turnover tissues such as salivary glands

Question 15

Describe discontinuous capillaries? (3pts)

Answer 15

1. Very large fenestration structures
2. Disrupted membrane
3. Found when the movement of cells is required- red blood cells in the liver, spleen and bone marrow

Question 16

Name 3 structural features of capillaries? (3pts)

Answer 16

1. Intracellular cleft- 10-20nm wide
2. Caveolae and vesicle- large pore system
3. Glycocalyx
4. Covers the endothelium
5. Negatively charged material
6. Blocks solute permeation and access to transport mechanisms
7. Highly regulated
8. The glycocalys is very dynamic, it can be broken down and remade as required,

Question 17

Descrive permeability?

Answer 17

Permeability is how freely a solute crosses a membrane

Question 18

What does inflammation do?

Answer 18

Inflammation causes large gaps to open in the membrane

Question 19

Describe how blood flow controls diffusion rate? (2pts)

Answer 19

1. More blood flow brings more solutes. Increased blood volume means there is less time for equilibration to occur across capillaries
2. Flow limited diffusion is where there is slow flow in a long capillary.

Question 20

How does fall in intersisital concentration affect diffusion rate?

Answer 20

During metabolism more solute is used up thereby increasing the concentration difference. Also metabolism increases blood flow- increased oxygen delivery is controlled b y arterioles

Question 21

Describe recruitment of capillaries?

Answer 21

Dilation of arterioles leads to increased number of capillaries perfused which increases total surface area for diffusion. This shortens the diffusion distance between the capillary and the cell