Blood vessels Flashcards
Do arteries carry blood to or away from the heart?
Carry away from the heart
What do arteries subdivide into?
Smaller vessels called arterioles
What do arterioles subdivide into?
Microscopic vessels called capillaries
What do capillaries join up to form?
Veins
What returns blood to the heart?
Veins
Compared to the diameter of their lumen, do arteries have thick or thin walls?
A thick wall compared to the diameter of the lumen
Describe the layers and structure of the arteries
Outer layer of fibrous tissue, then a thick layer of elastic tissue and smooth muscle, then a very thin layer of folded endothelial tissue
What happens when the ventricles contract?
Blood enters the arteries at high pressure
When the ventricles contract and blood enters the arteries at high pressure, what gets stretched?
It stretches the folded endothelium and elastic walls
When the ventricles relax, what keeps the blood pressure up?
It’s the elastic recoil of the artery wall (when the wall shrinks back to its original size)
Important organs like the kidneys wouldn’t be able to function if what happened?
The blood pressure dropped too far between heartbeats
Are arterioles narrower than arteries?
Yes
Compared to arteries, what do arterioles have a higher proportion of and lower proportion of?
A higher proportion of smooth muscle fibres and a lower proportion of elastic tissue
What happens when the circular muscle fibres of an arterioles contract?
The diameter of the lumen is reduced, so less blood flows through that vessel
Can arterioles control the amount of blood flowing to a particular organ?
Yes
Capillaries can only be seen with what?
A microscope
What do capillary walls consist of?
A single layer of endothelial cells (cells that line the blood vessels)
What do some capillaries have between the endothelial cells?
Tiny gaps
What do the very thin walls and gaps between cells allow in capillaries?
Allow water and substances like glucose and oxygen to diffuse quickly from the blood into the cells
What diffuses from the cells in the capillaries into the blood?
Waste products such as carbon dioxide and urea
In organs there are 1000s of capillaries contained, so there’s a huge surface area for what?
The exchange of substances
As blood flows quite slowly in capillaries, what does this allow for?
Allows for more time for diffusion to occur
What size lumen and wall does a vein have? (What does the wall contain)
A large lumen and a relatively thin wall (the thin wall contains some elastic tissue and smooth muscle)
Do veins have valves?
Yes
What happens when the leg muscles contract?
They bulge and press on the walls of the veins, pushing the blood up the veins
What happens when the leg muscles relax?
The cleaves close. This action helps the blood return to the heart
