exchange and the lymphatic system

Question 1

how are capillaries specialised for diffusion?

Answer 1

lots of them
thin-walled
small diameter

Question 2

why do capillaries have thin walls?

Answer 2

presents a small diffusion barrier

Question 3

why do capillaries have a small diameter?

Answer 3

for a big surface area to volume ratio

Question 4

what is the greatest distance a cell can be from a capillary?

Answer 4

100micrometres

Question 5

what are the 3 types of capillary?

Answer 5

continuous
fenestrated
discontinuous

Question 6

what are continuous capillaries?

Answer 6

capillaries with no clefts or channels, they may also have clefts only

Question 7

where would you find capillaries with no clefts or channels (continuous)? why?

Answer 7

the brain, they help with the blood brain barrier

Question 8

where would you find capillaries with only clefts ?

Answer 8

muscle

Question 9

what are fenestrated cappillaries?

Answer 9

capillaries with clefts and channels

Question 10

where are fenestrated capillaries found?

Answer 10

intestine

Question 11

what are discontinuous capillaries?

Answer 11

capillaries with clefts and massive channels

Question 12

where would you find discontinuous capillaries? why?

Answer 12

liver, to allow the transfer of large molecules like proteins

Question 13

describe the process of clotting?

Answer 13

1. damage to the endothelium wall exposes the collagen in the basement membrane.
2. platelets adhere to this to form a platelet plug
3. fibrinogen is converted to fibrin by thrombin.
4. fibrin binds to the platelet plug forming a fibrin clot

Question 14

what are the mechanisms the endothelium of blood vessels uses to stop clotting?

Answer 14

stops blood contacting collagen
produces prostacyclin and NO
produces tissue factor pathway inhibitor
expresses thrombomodulin
expresses heparin
secretes tissue plasminogen activator (t-PA)

Question 15

what do prostacyclin and NO do?

Answer 15

inhibit platelet aggregation

Question 16

what does tissue factor pathway inhibitor do?

Answer 16

stops thrombin production

Question 17

what does thrombomodulin do?

Answer 17

binds thrombin and inactivates

Question 18

what does heparin do?

Answer 18

inactivates thrombin

Question 19

what does tissue plasminogen activator do?

Answer 19

turn plasminogen in to plasmin and digests clot

Question 20

how is diffusion self-regulating?

Answer 20

the more of a substance that is used the more is able to diffuse across to meet the demand, also works the other way around when demand is low

Question 21

how is diffusion non-saturable?

Answer 21

there is no peak rate of movement of substances

Question 22

moving through capillaries, why does diffusion of water out of the capillary decrease?

Answer 22

the hydrostatic pressure decreases

Question 23

why does the movement of water into the capillaries increase moving further through the capillaries?

Answer 23

with water moving out of the cells because of hydrostatic pressure the oncotic pressure increases and more water moves in

Question 24

on average how much water in lost due to hydrostativ force and how much is regained by oncotic pressure?

Answer 24

20L lost. 17 L regained per day

so 3 L remains and must be drained by the lymphatic system

Question 25

what are some causes of oedema?

Answer 25

lymphatic destruction
raised CVP
hypoproteinemia
increased capillary permeability

Question 26

what can cause lymphatic destruction?

Answer 26

filariasis (parasitic worm infects lymphatics), surgery

Question 27

what can cause a raised CVP?

Answer 27

vetricular failure

Question 28

what can cause hypoproteinemia?

Answer 28

nephrosis, liver failure, nutrition

Question 29

what can cause increased capillary permeability?

Answer 29

inflammation eg. rheumatism