Unit 1: Arteries, Veins & Capillaries
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Flow chart for blood circulation
Heart—> arteries —> capillaries—> veins —> heart
Fill in the blank: Blood pressure _________ as blood moves away from the heart
Decreases
What carries blood away from the heart
Arteries
What carries blood back to the heart
Veins
What do arteries contain
• Outer layer of connective tissue with elastic fibers • thick smooth muscle with elastic fibers • inner endothelial lining • narrow lumen
Why do the elastic walls of arteries stretch & recoil
To accommodate the surge of blood after each heartbeat
What do the elastic fibers do in an artery
Stretch & recoil
What is it called when The smooth muscle in arteries contract
Vascoconstrict
What is it called when the smooth muscle in arteries dilates
Vasodilation
Why does the smooth muscle in arteries vasoconstrict and vasodilate
To control blood flow - it dilates where we need blood the most and restricts other areas
What do veins contain
• outer layer of connective tissues with elastic fibers • inner endothelial lining • thin smooth muscle • wide lumen • valves
Why do veins have valves
To prevent the back flow of blood
What does the wide lumen do in veins
Reduces resistance
Why do veins have thinner walls
Due to blood being carried back to heart at low pressure
How thick are capillaries
1 cell thick
Do capillaries have thick or thin walls
They have thin walls
What can capillaries allow
Exchange of substances with tissues through their thin walls
What happens during pressure filtration
• blood is at high pressure arriving from the arteriolar to the capillaries • This differenace causes much of the plasma to be forced through thin walls into the fluid surrounding the cells. This fluid is now called tissue fluid.
What is the difference between blood plasma and tissue fluid
Tissue fluid does not contain any plasma proteins beacuse they don’t fit
What happens after pressure filtration
Diffusion of soluble food , oxygen and useful ions into nearby cells such as carbon dioxide & urea diffuse out into tissue fluid. Much of the tissue fluid then returns to capillaries by osmosis.
What happens to the tissue fluid that does not get absorbed back into the blood
It gets absorbed into thin walled lymphatic vessels which are found in connective tissue.
What is the tissue fluid called that gets absorbed by the lymphatic vessels
Lymph
How does the lymphatic system work
No pump like heart - Flow of lymph is by vessels being periodically compressed when muscles contract.
Lymphatic system flow chart
Blood arrives at capillary at - High pressure Plasma ⬇️ —————Pressure filtration I ⬇️ I Diffusion Tissue I ⬇️ Fluid I—————-Osmosis ⬇️ Absorbed into lympathic system Lymph