Blood Vessels Flashcards
When does blood pressure decrease?
When the blood moves away from the heart.
What is the lumen?
The central space or cavity of a blood vessel.
Where is the endothelium located?
Around the central lumen.
What is the endothelium surrounded by?
Layers of tissue.
Which blood vessel has the thickest endothelium layer and the most elastic fibres?
Arteries as they have to withstand high pressure from the blood.
In which direction do arteries carry blood?
Away from the heart.
What is the structure of an artery?
They have an outer layer of connective tissue containing elastic fibres and a thick middle layer containing smooth muscle with more elastic fibres.
What do the arteries do to accommodate the surge of blood after each contraction of the heart?
The thick elastic walls contract and relax.
What is vasoconstriction?
The contraction of the smooth muscle in the walls of the arterioles.
What is vasodilation?
The relaxing of the smooth muscle in the walls of the arterioles.
How is blood flow increased during exercise?
The vasodilation of the arterioles supplying the muscles.
What happens to the abdominal organs during exercise?
The arterioles supplying these organs vasoconstrict reducing blood flow.
What are venules?
Capillaries that have merged into one another.
How thick are the walls of capillaries?
One cell thick.
What is the function of capillaries?
They allow the exchange of substances with other tissues.
What is the structure of a vein?
They have an outer layer of connective tissue containing elastic fibres but a much thinner muscular wall than arteries with a wide lumen.
Why are valves present in veins?
To prevent the backflow of blood as blood is flowing back to the heart at low pressure and generally against the force of gravity.
What causes pressure filtration?
Higher blood pressure at the arteriole end of the capillary bed.
What does pressure filtration result in?
The plasma, with small soluble molecules, being forced out of the capillaries into the tissues.
What is the difference between tissue fluid and blood plasma?
Tissue fluid does not contain plasma proteins.
What does tissue fluid contain?
Glucose, oxygen, and dissolved substances.
What diffuses out of the cells into the tissue fluid to be excreted?
Carbon dioxide and waste substances.
Where does tissue fluid re-enter the capillaries?
At the venule end of the capillary bed by osmosis.
What happens to excess tissue fluid?
It enters the lymph vessels and passes into the lymphatic system.
What is the structure of lymph vessels?
They have thin walls and valves.
Where does the lymphatic system return the lymph fluid to?
The circulatory system.
