Exchange and Lymphatic System

Question 1

What is the space called between two cells?

Answer 1

Cleft - varies in size depending on how close cells are together

Question 2

Describe the pore size in fenestrated capillaries

Answer 2

Large (fenestrations or pores)

Allows direct travel through the cell

Question 3

Where do you find continuous capillaries?

Answer 3

In the brain where there is no clefts or channels in the capillaries

Question 4

Give an example of what the blood brain barrier might halt the diffusion of?

Answer 4

Potassium

Question 5

Where might you find fenestrated capillaries?

Answer 5

In the intestine - contains clefts and channels

Question 6

Where might you find discontinuous capillaries?

Answer 6

Liver - Lots of proteins are made and need to enter the plasma - leav via sinusoids. Contains clefts and massive channels

Question 7

What part of a blood vessel is very involved in the formation of blood clots?

Answer 7

Endothelium

Question 8

What are the two stages clot formation?

Answer 8

Formation of a platelet plug

Formatin of a fibrin clot

Question 9

When will platelets start releasing clotting factor?

Answer 9

When the integrity of the endothelium is compromised and the platelets have access to the collagen of the basement membrane.

Question 10

What is the function of thrombin?

Answer 10

Question 11

How does the epithelium prevent clot formation?

Answer 11

Stops blood contacting collagen

Produces prostacyclin and NO

Produces tissue factor pathway inhibitor (TFPI)

Expresses thrombomodulin

Expresses heparin

Secretes tissue plasminogen activator

Question 12

What is the effect of stopping blood contacting collagen?

Answer 12

No platelet aggregation

Question 13

What is the effect of prostacyclin and NO?

Answer 13

Both inhibit platelet aggregation

Question 14

What is the effect of tissue factor pathway inhibitor?

Answer 14

Stops thrombin production

Question 15

What is the effect of thrombomodulin?

Answer 15

Binds thrombin and inactivates it

Question 16

What is the effect of heparin?

Answer 16

Also inactivates thrombin

Question 17

What is the effect of tissue plasminogen activator?

Answer 17

Turns plasminogen into plasmin which digests clot

Question 18

Why is diffusion described as self-regulating?

Answer 18

More O2 needed means more O2 enters the cell by means of diffusion

Question 19

Why is diffusion of O2 described as unsaturable?

Answer 19

Since there is no use of protein pumps (there is no chance of all pumps being used at once)

Question 20

Why type of substances can cross membranes?

Answer 20

Non-polar substances

Question 21

What type of substances travel through clefts and channels?

Answer 21

(potassium ions and glucose)

Question 22

What type of molecules are carrier mediated transport?

Answer 22

Glucose transporter

Question 23

What are the pressures responsible for the green and black arrows?

Answer 23

Green - hydrostatic pressure

Black - oncotic pressure

Question 24

Why does water get drawn back into the capillary?

Answer 24

Concentration of proteins increases from left to right (creates osmotic pressure) draws water back in

Question 25

What is the average volumes of water which are lost and regained each day?

Answer 25

Lost - 20L

Regained - 17L

Question 26

What causes Kwashiorkor?

Answer 26

Hypoproteinaemia no production of osmotic pressure and little water renters the capillary.

Question 27

What is oedema defined as?

Answer 27

Accumulation of excess fluid

Question 28

What are the causes of oedema?

Answer 28

Lymphatic obstruction (eg to filariasis surgery)

Raised central venous pressure - due to ventricular failure - increase in hydrostatic pressure

Hypoproteinaemia - water leaves the the capillaries y hydrostatic pressure, re-enters via oncotic pressure - absent in this case. Causes - nephrosis, liver failure and nutrition

Increased capillary permeability - inflammation eg. rheumatism

Question 29

Why does heart failure result in oedema?

Answer 29

Backward failure of the right ventricle leads to congestion of systemic capillaries, This generates excess fluid accumulation in the body. The increased pressure forces additional fluid out of the blood into the tissue, this results in oedema in the tissue. In right sided heart failure this commonly starts in the ankles where venous pressure is high due to the effects of gravity. It may also occur in the abdominal cavity where the fluid build-up is called ascites.