Flashcards in Unit 2: Physiology and Health - The Structure and Function of Arteries, Capillaries and Veins/ The Structure and Function of the Heart Deck (24)
Where is the pathway of blood circulation in the heart?
Blood leaves the heart in the arteries, then flows through the capillaries before returning to the heart in the veins.
In what condition is blood when it leaves the heart?
When blood leaves the heart it is under high pressure (having been pumped out of the heart).
What happens to blood pressure when it flows away from the heart through the circulatory system?
As the blood flows away from the heart and through the circulatory system, there is a decrease in blood pressure.
Where do arteries carry blood to?
Away from the heart.
What is the structure of an artery like?
The endothelium - lining the central lumen of blood vessels is surrounded by layers of tissue. Arteries have an outer layer called connective tissue containing elastic fibres and a middle layer containing smooth muscle with more elastic fibres.
What do the elastic fibres in arteries mean for the artery, and what are they needed for?
The elastic fibres mean that arteries have elastic walls which can stretch and recoil to maintain the surge of blood after each contraction of the heart.
What can smooth muscle in arteries do and what does this cause?
The smooth muscle can contract causing vasoconstriction or relax causing vasodilation to control blood flow.
How do the central lumen of arteries compare to that of veins and why is this?
Arteries have a narrower lumen than veins due to the thicker layer of muscle in arteries.
What do arteries divide into?
Smaller arteries called arterioles.
What do capillaries allow to happen?
Capillaries allow exchange of substances with diffusion through their very thin walls.
What do veins do?
Veins carry blood back to the heart.
What is the structure of a vein like?
Veins have an outer layer of connective tissue containing elastic fibres but a much thinner muscular wall than arteries. Their central lumen is therefore wide than in arteries. Veins contain valves which prevent the backflow of blood.
What are smaller vessels that come together to form veins?
Why do arteries not need valves but veins do?
The blood flow is under so much pressure leaving the heart that it can only flow in one direction. Whereas in veins the blood is under very low pressure, so to prevent the backflow of blood, valves are needed.
What is the difference in blood arriving at the arteriole end of a capillary bed compared to the blood in the capillaries?
Blood arriving at the arteriole end of a capillary bed it at a higher pressure than blood in the capillaries.
As the blood is at a higher pressure at the arteriole end of the capillary bed, what happens to the blood?
The blood is forced into the narrow capillaries, and undergoes pressure filtration.
What happens when blood undergoes pressure filtration?
Much of the plasma (liquid part of the blood) is squeezed out through the thin walls - this liquid is called issue fluid.
What is the only difference between plasma and tissue fluid?
The only difference between plasma and tissue fluid is that plasma contains plasma proteins, whereas tissue fluid does not.
Why does plasma contain plasma proteins but tissue fluid does not?
The protein is too large to be filtered through the capillary walls.
What role does tissue fluid have?
Tissue fluid supplies respiring cells with glucose and oxygen and other substances. Carbon dioxide and other metabolic waste diffuse out of the cells and into tissue fluid to be excreted.
What happens to most of the tissue fluid?
It returns to the blood.
What happens to tissue fluid which does not return to the blood?
The fluid that does not return to the blood (excess tissue fluid) is absorbed by small lymphatic vessels and the fluid is now referred to as lymph.
What do lymphatic vessels do with lymph?
They return the lymph to the circulatory system.