capillaries and tissue fluid

Question 1

what is the function of the arteries?

Answer 1

carries blood away from the heart at a high pressure.

Question 2

explain how the structure of arteries relates to their function.

Answer 2

thick elastic tissue - can stretch as ventricles contract and recoil as ventricles relax, to maintain high pressure.
thick muscle tissue/wall - withstand high blood pressure.
narrow lumen - maintains high pressure.

Question 3

what is the function of the arterioles?

Answer 3

directs blood to different capillaries/tissues.

Question 4

explain how the structure of arterioles relates to their function.

Answer 4

thicker muscle layer than arteries:
- (contracts) narrows lumen (vasoconstriction) reduces blood flow to capillaries.
- (relaxes) widens lumen (vasodilation) increases blood flow to capillaries.
thinner elastic layer:
- pressure surges are lower (as they are further from the heart/ventricles)

Question 5

what is the function of the capillaries?

Answer 5

allow efficient gas exchange of substances between blood and tissue fluid.

Question 6

explain how the structure of capillaries relates to their function.

Answer 6

one cell thick - reduces diffusion distance.
capillary bed - increases surface area for diffusion.
narrow lumen - reduces blood flow rate so more time for diffusion.
pores in walls between cells - allows larger substances through.
one RBC moves through at a time - more surface in contact with membrane.

Question 7

what is the function of the veins?

Answer 7

to carry blood back to the heart at a lower pressure.

Question 8

explain how the structure of veins relates to its function.

Answer 8

wider lumen than arteries - maximises volume of blood carried.
very little elastic and muscle tissue - as blood pressure is lower.
contain valves - prevent back flow of blood (maintains unidirectional flow)

Question 9

describe the lymphatic system.

Answer 9

lymph capillaries are found in spaces between cells and drain excess fluid, take it into lymphatic system and redistribute around the body.

Question 10

explain the formation of tissue fluid (at arteriole end of capillary)

Answer 10

• there is a higher blood pressure in the capillary than in tissue fluid.
• this forces o2, glucose and water out of the capillary and move into the space surrounding the cells.
• larger proteins (and RBCs) remain in the capillary, lowering the water potential.

Question 11

explain the return of tissue fluid to the circulatory system (at venule end of capillary)

Answer 11

• pressure reduces as fluid leaves the capillary.
• co2, urea and water moves back into the blood (capillary) - water enters capillary via osmosis down a concentration gradient.
• excess water and remaining tissue fluid is absorbed by lymph capillaries and returned to the circulatory system through veins.

Question 12

suggest and explain causes of excess tissue fluid accumulation.

Answer 12

• low concentration of protein in blood plasma - means that water potential in the capillary is not as low so less water is absorbed at venule end by osmosis (more tissue fluid formed at arteriole end) so lymph system may not be able to drain excess fast enough.
• high blood pressure - increases outward pressure from arteriole end and reduces inward pressure at venule end (then repeat same points)