8.2. BLOOD VESSELS

Question 1

what are elastic fibres?

Answer 1

• composed of elastin
• can stretch and recoil
• provide vessel walls with flexibility

Question 2

what is smooth muscle?

Answer 2

• contracts or relaxes
• changes size of the lumen (channel within the blood vessel)

Question 3

what is collagen?

Answer 3

• provides structural support to maintain shape and volume of the vessel

Question 4

what is the function of arteries?

Answer 4

• carry blood away from the heart to the tissues of the body
• carry oxygenated blood except pulmonary artery
• blood in under higher pressure than the blood in the veins

Question 5

what is the function of the pulmonary artery?

Answer 5

• carries deoxygenated blood from the heart to the lungs
• during pregnancy, also carries blood to the umbilical artery, which carries deoxygenated blood from the feotus to the placenta

Question 6

what is the structure of the arteries?

Answer 6

• walls contain elastic fibres, smooth muscle and collagen

Question 7

how does the structure relate to function of the arteries?

Answer 7

• elastic fibres = withstand force of blood pumped out of the heart and stretch (within limits maintained by collagen) to take larger blood volume. in between contractions of the heart, elastic fibres recoil and return to original length
• lining of artery (endothelium) = smooth so blood flows easily over it

Question 8

what do elastic fibres also help to maintain?

Answer 8

• continuous flow by evening out the surges of blood pumped from the heart
• you can still feel a pulse

Question 9

what are arterioles?

Answer 9

• link the arteries and the capillaries

Question 10

how is the structure related to the function in arterioles?

Answer 10

• more smooth muscle and less elastin in walls than arteries, as they have little pulse surge, but can constrict or dilate to control flow of blood into individual organs
• when smooth muscle contracts it constricts the vessels and prevents blood flowing into a capillary bed (vasocontriction)
• when smooth muscle relaxes, blood flows through the capillary bed (vasodilation)

Question 11

what are capillaries?

Answer 11

• microscopic blood vessels that link the arterioles with the venules
• form an extensive network through all tissues of the body
• lumen of the capillary is so small that red blood cells have to travel through in single file
• substances are exchanged through the capillary walls between the tissue cells and the blood

Question 12

where do most substances pass out of the capillaries to the fluid surrounding the cells?

Answer 12

• the gaps between the endothelial cells that make up the capillary wall (relatively large gaps)
• the exception is the capillaries in the central nervous system, which have very tight junctions between the cells

Question 13

what is blood like in the cappilaries?

Answer 13

• most organs, blood entering capillaries from arterioles is oxygenated
• when it leaves into the venules, it is deoxygenated and has more carbon dioxide
• lungs and placenta are exceptions, deoxygenated into capillaries and oxygenated blood out

Question 14

how are capillaries adapted for their role?

Answer 14

• provide a very large surface area for diffusion of substances into and out of the blood
• total cross-sectional area of capillaries is always greater than arteriole supplying them so the rate of blood flow falls which gives more time for the exchange of materials by diffusion between the blood and the cells
• walls are a single endothelial cell thick, giving a thin layer for diffusion

Question 15

what is the function of veins?

Answer 15

• carry blood away from the cells of the body towards the heart and, with two exceptions, they carry deoxygenated blood
• pulmonary vein carries oxygenated blood from the lungs to heart and umbilical vein carries oxygenated blood from the placenta to the foetus

Question 16

where does deoxygenated (usually) blood flow after the capillaries?

Answer 16

• into venules then veins
• then to two main vessels carrying deoxygenated blood to the heart (inferior vena cava from the lower parts of the body and superior vena cava from the head and upper body)

Question 17

what makes veins different?

Answer 17

• they do not have a pulse as the surges from the heart pumping are lost as blood passes through the narrow capillaries
• have a large reservoir of blood

Question 18

what is the blood pressure like in the veins?

Answer 18

• very low compared to arteries

Question 19

how do veins prevent the backflow of blood?

Answer 19

• have valves present

Question 20

what is the structure of veins?

Answer 20

• walls have lost of collagen and relatively little elastic fibre
• vessels have a wide lumen and a smooth, thin lining (endothelium) so the blood flows easily

Question 21

what is the structure of venules?

Answer 21

• very thin walls with a little smooth muscle
• several venules join to form a vein

Question 22

what are the three main adaptions allowing veins to carry blood to the heart under low pressure and against gravity?

Answer 22

• majority of veins have one way valves at intervals
• many of the bigger veins run between the big, active muscles in the body e.g. arms and legs
• breathing movements of the chest act as a pump

Question 23

how is having valves good for the veins?

Answer 23

• valves are flaps/ infoldings of inner lining of the vein
• when blood flows in the direction of the heart, the valves open so the blood can pass through
• if the blood starts to flow backwards, the valves close to prevent this from happening

Question 24

why does having veins between active muscles in the body help?

Answer 24

• when the muscles contract, they squeeze the veins, forcing the blood towards the heart
• the valves prevent backflow when the muscles contract

Question 25

how do the breathing movements of the chest act like a pump for the veins?

Answer 25

• pressure changes and the squeezing actions move blood in the veins of the chest and abdomen towards the heart