Blood Vessels & the Heart Flashcards
What is the function of elastic fibres in blood vessels?
They are composed of elastin and can stretch / recoil - provides vessel walls with flexibility.
What is the function of smooth muscle in blood vessels?
It contracts / relaxes to change the size of the lumen.
What is the function of collagen in blood vessels?
Collagen provides structural support to maintain the shape and volume of the vessel.
How do the relative proportions of elastic fibres, smooth muscle and collagen change with arterial size?
- elastic fibres - proportion decreases as size decreases
- smooth muscle - proportion increases as size decreases
- collagen - proportion decreases as size decreases. However, proportion in an arteriole is greater than in a medium-sized artery.
What is the role of arteries?
Arteries carry oxygenated blood away from the heart to the tissues of the body.
What are the three layers of artery walls?
- Tunica externa
- Tunica media
- Tunica intima
What is the artery’s tunica intima made up of?
A layer of endothelial cells, a layer of connective tissue and a layer of elastic fibres.
The endothelium is very smooth to reduce friction, allowing for free blood flow.
What is the artery’s tunica media made up of?
Smooth muscle cells and a thick layer of elastic tissue.
The layer of smooth muscle strengthens the arteries so they can withstand high pressure - they can contract to narrow the lumen.
Elastic tissue helps maintain blood pressure in the arteries - recoiling helps even out the surge of blood pumped from the heart.
What is the artery’s tunica externa made up of?
Mostly made of collagen -provides structural support and prevents damage from over stretching.
Why do arteries have a narrow lumen?
To help maintain a high blood pressure.
What are arterioles?
Smaller vessels that link the arteries and capillaries.
How are arterioles structurally different to arteries?
The contain more smooth muscle and less elastin in their walls - meaning they can constrict and dilate to control the flow of blood.
Arteriole contraction is known as vasoconstriction, and relaxing is known as vasodilation.
What are capillaries?
Microscopic blood vessels that link the arterioles with the venules. They are roughly the same diameter as red blood cells.
Capillary networks are exchange surfaces where most substances pass out of the blood into the surrounding tissue.
How are capillaries adapted to be an efficient exchange surface?
- small diameter - forces blood to travel slowly, providing more time for diffusion
- large number of capillaries - provides a larger surface area for diffusion to act upon
- walls made of a single layer of endothelial cells - reduces diffusion distance. Pores in the capillary walls allow for the formation of tissue fluid (blood plasma leaking out)
What is the function of veins?
Veins carry deoxygenated blood from the cells of the body towards the heart.
They also act as a reservoir for blood.
Why do veins contain valves?
The blood pressure in veins is very low compared to in arteries, therefore the majority of veins use valves to prevent the backflow of blood.
How are venular walls different in structure to arterial walls?
The tunica media is much thinner - there is no need for a thick muscular layer as veins do not need to withstand high pressure.
How do the relative proportions of elastin, smooth muscle and collagen change with vein size?
The proportion of all three structural components decreases with size - only collagen is present in the structure of venules.
Why do veins have a wider lumen that arteries?
- ensures blood returns to the heart at an adequate speed
- reduces friction between blood and endothelial cells
- rate of blood flow is slower, larger lumen means volume is blood delivered per unit of time is equal
What is the structure of venules?
Venules connect the capillaries to the veins - they have no elastic fibres and smooth muscle as pressure is incredibly low.
What is the function of the coronary arteries?
The coronary arteries are located on the surface of the heart and provide it with a blood supply.
Which veins bring deoxygenated blood to the heart?
- Inferior vena cava (from the lower body)
- Superior vena cava (from the head and upper body)
What is the pathway followed by blood through the heart?
vena cava –> right atrium –> right ventricle –> pulmonary artery –> lungs –> pulmonary vein –> left atrium –> left ventricle –> aorta
What is the name of the valves that separate the atria from the ventricles?
Atrioventricular valves (tricuspid and bicuspid)
