Component 3.2 - Mammalian Circulation Flashcards
Why is double circulation in a mammal more efficient than single circulation in a fish?
Because oxygenated blood can be pumped around the body at higher pressure
What is the innermost layer of a blood vessel and what is its function?
Endothelium - it is one cell thick and is surrounded by the tunica intima.
It is a smooth lining, reducing friction with a minimum resistance to blood flow
What is the middle layer of the blood vessel and what is it made up of?
The tunica media - contains elastic fibres and smooth muscle
Why is the tunica media thicker in arteries than in veins?
Elastic fibres stretch and recoil, pushing blood through the artery. This maintains blood pressure as the blood is transported further from the heart.
What is the outer layer of the blood vessel called? What is it made of?
Tunica externa - it contains collagen fibres, which resist overstretching
What is the function of arteries?
Carry blood away from the heart. Their thick muscular walls withstand the pressure of the blood derived from the heart.
Arteries -> Arterioles -> Capillaries
How do capillaries help return blood to the heart?
Blood from the capillaries collects into venules, which take blood into veins.
How are veins different to arteries?
1) They have valves
2) They have a larger diameter lumen
3) Thinner walls with less muscle than arteries - blood pressure and flow rate are lower
How does blood return to the heart from veins?
For veins above the heart, blood returns to the heart by gravity and for other veins it moves by the pressure from surrounding muscles.
Describe the structure of capillaries
They have thin walls, which are only one layer of endothelium on a basement membrane.
There are pores between the cells making the walls permeable. So exchange of substances duh as glucose and water can take place between blood and tissues.
How does the diameter of capillaries link with their function?
Capillaries reduces the rate of blood flow due to friction against their wall and this means that there is plenty of time for the exchange of materials.
Why can the heart be thought of as two separate pumps?
One deals with oxygenated blood - pumping blood to the rest of the body.
One deals with deoxygenated blood - pumping blood to the lungs.
What is the heart made of and why is this suitable?
It consists largely of cardiac muscle, a specialised tissue which can relax and contract rhythmically of its own accord.
It is involuntary muscle and unlike voluntary muscles it never tires.
How can heart rate be modified?
By nervous and hormonal stimulation
