Physiology and Health: The Structure and Function of Arteries, Capillaries and Veins
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Where does blood circulate?
From the heart through the arteries to the capillaries then to the veins and back to the heart
There is a decrease in blood pressure when?
Blood moves away from the heart
What are blood vessels?
Tubes with walls composed of different tissues depending on the function of the vessel
What is the central space or cavity of blood vessels called?
The lumen
What is the lumen lined with?
A layer of cells called the endothelium
The endothelium lining the central lumen of blood vessels is surrounded by what?
Layers of tissues that differ between arteries, capillaries and veins
Arteries carry blood where?
Away from the heart
Blood is pumped through arteries at what pressure?
A high pressure
Arteries have an outer layer of connective tissue containing what?
Elastic fibres and a thick middle layer containing smooth muscle with more elastic fibres
The thick elastic walls of the arteries do what to accommodate the surge of blood after each contraction of the heart?
Stretch and recoil
The smooth muscle in the walls of arteries can contract and relax causing what to control blood flow?
Vasoconstriction and vasodilation
The ability of the arteries to vasoconstrict or vasodilate allows what?
The changing demands of the body’s tissues to be met
During exercise the arteries supplying the muscles vasodilate, which does what?
Increases the blood flow
During exercise the arteries supplying the abdominal organs vasoconstrict, which does what?
Reduces the blood flow to them
Capillary walls are only one cell thick, which allows what?
Quick and efficient exchange of substances with tissues through their thin walls
Veins carry blood where?
Towards the heart
Veins have an outer layer of connective tissue containing what?
Elastic fibres but a much thinner muscular wall than arteries
What is different about the lumen of a vein and the lumen of an artery?
The lumen of a vein is relatively wider
Valves are present in veins to prevent what?
Backflow of blood
Why are valves needed?
As the blood is flowing back to the heart at low pressure and generally against the force of gravity
Pressure filtration causes what?
Plasma to pass through capillary walls into the tissue fluid surrounding the cells
Tissue fluid and blood plasma are similar in composition, with the exception of what?
Plasma proteins, which are too large to be filtered through the capillary walls
What does tissue fluid contain and what does it do?
Glucose, oxygen and dissolved substances, which supply the tissues with all their requirements
Useful molecules such as glucose and oxygen diffuse into cells and carbon dioxide and other metabolic waste substances do what?
Diffuse out of the cells and into the tissue fluid to be excreted