Capillaries I

Question 1

Structure of cell membrane

Answer 1

Consists of 2 layers of antipathic phospholipids

Form bilayers in solution

Question 2

Function of cell membrane

Answer 2

Provide support and protection
Cell-to-cell regulation
Controls what enters or leaves the cells
Regulates cell function

Question 3

How does solute and fluid exchange occur at capillaries

Answer 3

Connect terminal arterioles to venules
Smallest diameter blood vessels endothelium, 1 cell thick, semi-permeable
Found near every cell in the body - higher density in active tissue

Question 4

Why are lipid soluble solutes transported over short distances

Answer 4

Time takes for 1 randomly moving molecule to move a net distance in 1 direction increases with the distance squared

Question 5

Continuous capillaries

Answer 5

Moderate permeability; tight gaps between enighbouring cells; constant basement membrane
Blood-brain barrier
Muscle, skin, fat, connective tissue

Question 6

Fenestrated capillaries

Answer 6

High water permeability, fenestration structures, modest disruption of membrane
‘High water turnover’ tissues e.g. salivary glands, kidney, anterior eye, choroid plexus

Question 7

Discontinuous capillaries

Answer 7

Very large fenestrated structures, disrupted membrane

When movement of cells is required, RBCs in liver, spleen, bone marrow

Question 8

Intracellular cleft

Answer 8

10-20nm wide
Are in between adjacent cells that are not linked by tight junctions and this allows solutes and fluids to move through between cells - aid permeability

Question 9

Caveolae and vesicles

Answer 9

Large pore system - form of endocytosis and exocytosis

Question 10

Glycocalyx

Answer 10

Covers endothelium, negatively charged material, blocks solute permeation and access to transport mechanisms, highly regulated
Very dynamic can be broken down and remade as required

Question 11

Permeability

Answer 11

Rate of solute transfer by diffusion across unit area of membrane per unit concentration difference

Question 12

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

Answer 12

Reduction in area for diffusion
Increased path length through membrane
Restricted diffusion in pore produces hydrostatic issues

Question 13

What are the controls of diffusion rate

Answer 13

Blood flow
Fall in interstitial concentration
Recruitment of capillaries

Question 14

Why is Blood flow a control

Answer 14

More blood = more solute

Increased blood vol = less time for equilibriation to occur across capillaries

Question 15

Why is a fall in interstitial concentration a control

Answer 15

During metabolism more solute is used up thereby increasing the concentration difference
Metabolism increases blood flow - increase O2 delivery - controlled by arterioles

Question 16

Why is recruitment of capillaries a control

Answer 16

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