Transport in Animals - Blood Vessels Flashcards
how does blood flow through the body
- leaves the heart in arteries
- largest arteries divide into smaller ones, these divide into arterioles
- these divide into capillaries
- these join up to form venules
- these merge to form veins
- veins carry blood back to the heart
what is the function of arteries
carry high pressure blood away from the heart
give adaptations of arteries
- thick wall
- narrow lumen
- folded endothelium
- inner wall is elastic
why are artery walls thick
to withstand high pressure
why is the lumen relatively narrow in arteries
to maintain high pressure
why is the inner wall of arteries folded and elastic
to allow the lumen to expand when blood flow increases
what is the inner layer of arteries and what are its adaptations
- folded endothelium made up of simple squamous cells which make it very smooth but can expand with blood flow
- a layer of elastic tissue allows the wall to stretch and recoil
what is the middle layer of arteries and what are its adaptations
thick layer of smooth muscle and elastic fibres. This can constrict and dilate the vessel
what is the outer layer of arteries and what are its adaptations
collagen and some elastic tissue to allow the wall the stretch and recoil to maintain blood pressure
what are special adaptations of arterioles
- more smooth muscle and fewer elastin fibres in their walls
- smooth muscle allows vasoconstriction and vasodilation
what is the function of capillaries
allow the exchange of materials between blood and tissue fluid (and exchange surfaces)
what do capillaries often form and why
networks, increasing surface area in contact with tissues
what are the adaptations of capillaries
- wall made of flattened endothelial cells, one cell thick
- lumen just big enough for a red blood cell to squeeze through, shortens diffusion path to tissues and reduces rate of flow
- walls are leaky, allowing plasma and dissolved substances to leave the blood
what is the function of veins and venules
carry low pressure blood to the heart
what are the adaptations of veins
- thinner walls than arteries (as don’t need to withstand pressure)
- relatively large lumen
- little smooth muscle
- valves
why do veins have a relatively large lumen
reduces resistance to flow
what is the inner layer of veins
endothelium made of simple squamous cells and a layer of elastic tissue (not folded)
what is the middle layer of veins
thin layer of smooth muscle and elastic fibres
what is the outer layer of veins
mostly collagen fibres
why are veins squeezed by surrounding muscles
to return the blood at low pressure
what are valves and what is their function
- flaps or infolding of the endothelium
- prevent backflow
why does blood pressure oscillate in the arteries
as the heart pumps, when it contracts it generates pressure and when it relaxes it decreases pressure
why does blood pressure drop in the arterioles and the capillaries
- increased distance from the heart
- increase in cross-sectional area due to branching
- capillaries are leaky, loss of plasma reduces volume of blood
