Blood Vessels Flashcards
How is blood transported in a closed blood circulatory system?
In a continuous system of tubes
These tubes are called the blood vessels
How much blood circulates in the blood vessels? (On average)
5 litres
What are the three main types of blood vessels?
Arteries
Capillaries
Veins
What does an artery do?
Transport blood away from the heart
How many layers do the walls of arteries consist of?
Three
What are the three layers in artery walls?
Outer
Middle
Inner
What is the outer layer of artery walls like?
Fibrous connective tissue
What is the middle layer of artery walls like?
Smooth muscle tissue and elastic fibres
What is another name for the inner layer of artery walls?
Endothelium
What is the endothelium made of?
Squamous epithelium
What does the muscle layer in an artery wall do?
Allows the artery to stretch when blood under high pressure is pumped from the heart into the artery
It helps to resist the high pressure and avoid distortion
The elastic fibres also help with this
What is a lumen?
The inner space of a tube-shaped structure
What is the shape of the lumen of an artery like?
More regular and smaller than that of a vein
What do arteries do as they get further away from the heart?
They branch and become smaller and smaller
The outer two layers become thinner
What are arterioles?
These smaller, branched arteries
Do arteries have valves?
Apart from the pulmonary artery and the aorta, no
Why don’t arteries have valves?
Because of the high pressure present in arteries
What are capillaries?
Arterioles that have become microscopically small tubes
Where do capillaries occur?
As a branched network between cells in the tissue
What do the walls of capillaries consist of?
A single thin layer of endothelium
What do capillaries do?
Allow for gaseous exchange between blood and cells to happen
How large is the lumen of a capillary?
So small that red blood corpuscles can only move through in single file
Why is it useful for red blood corpuscles to move through capillaries in single file?
This slows the blood flow so that the exchange of gases into and out of cells can take place more effectively
What do capillaries do as they move away from the arterioles?
They reunite
What are venules?
The blood vessels formed from reunited capillaries
What are veins?
Blood vessels formed from united venules
What do veins do?
Transport blood back to the heart
What do vein walls consist of?
The same three layers as artery walls
How do vein walls differ from artery walls?
The outer two layers are thinner
What is the lumen of a vein like?
Larger and more irregular than that of an artery
What is the pressure under which the blood in veins flows?
Low
Why are the walls of veins thinner than those of arteries?
They do not need to withstand as much pressure
How does blood flow through veins?
The contraction of skeletal muscles close to the veins helps the blood to move in the direction of the heart
Do veins have valves?
Apart from the pulmonary veins, yes
Why do veins need valves?
Blood travels up from the legs to the heart
This goes against gravity
Gravity pulls the blood back down
The valves stop this backflow
What kinds of valves exist in the valves?
Semilunar valves
