Blood vessels
Three kinds of vessel
- Blood travels in three kinds of tube.
- Each is built for its job.
- The space inside any vessel is its lumen.
Arteries, veins, capillaries
| Vessel | Wall | Valves? | Job |
|---|---|---|---|
| arteries | thick, muscular, elastic | no | carry blood away from the heart, high pressure |
| veins | thin, wide lumen | yes | carry blood back to the heart, low pressure |
| capillaries | one cell thick | no | exchange gases, glucose and wastes with cells |
- (Supplement) Arteries' thick elastic walls cope with high pressure; veins need valves because their low-pressure blood could flow backwards; capillaries are thin and narrow for fast exchange.
Practice
Arteries:
Arteries carry blood away from the heart at high pressure, with thick muscular elastic walls.
Practice
Why do veins have valves?
Low-pressure blood in veins could flow back, so valves keep it moving one way.
Practice
Capillaries are well suited to exchange because they:
A one-cell-thick wall gives a short diffusion distance; many capillaries give a large surface area.
Main blood vessels (Supplement)
| Connects | Artery (out) | Vein (in) |
|---|---|---|
| heart ↔ body | aorta | vena cava |
| heart ↔ lungs | pulmonary artery | pulmonary vein |
| ↔ kidney | renal artery | renal vein |
- The liver has a hepatic artery, hepatic vein, and a hepatic portal vein bringing blood from the gut.
Practice
Match each organ to the artery that supplies it.
Aorta → body, pulmonary artery → lungs, renal artery → kidney.
You've got it
Key idea
- arteries carry blood away (thick walls, high pressure); veins carry it back (valves, low pressure)
- capillaries are one cell thick — for exchange of gases, glucose and wastes
- name pairs: aorta/vena cava, pulmonary artery/vein, renal artery/vein