Chapter 8 : Heart & Blood Vessels
Blood vessels transport blood
Blood Vessels : Three major types : ARTERIES // VAINS // CAPILLARIES
ARTERIES transport blood AWAY from the heart
Arteries : Large, thick wall of muscles to withstand high pressure heart. Largest one = aorta (diameter 2,5cm)
Transport blood AWAY from the haert
Ability to stretch under pressure allows to store blood & providing it to the capillaries even between heartbeats
because the elasticity maintains blood pressure between beats !
Structure of the walls of large/medium arteries = 3 layers surrounding the LUMEN (hollow interior vessel) :
o Endothelium : thin inner layer - flattened squamous epithelial cells. Fit closely together to minimize friction
o Smooth muscle with interwoven elastic CT : Thickest layer. Tonic contraction stiffens arteries and helps
resist high pressure. Elastic CT ensures arteries can stretch passively to accommodate entering blood.
o Supportive layer of CT with Collagen : Outer. Anchors vessels to surrounding tissues, protect from injury.
Aneurysm : damaged Endothelium => blood between 2 outer layers => splits them apart => “ballooning”
Some causes these layers to bulge inward => narrows lumen => reduces blood flow to organs (some bulg outward)
Some severe chest pain, other painless until rupture or “blowout” (massive internal bleeding & often dead).
Take years to develop, can be detected & surgery.
Inward-bulging ones can be detected by stethoscope (flowing blood => specific sound) and CT (tomography).
ARTERIOLES AND PRECAPILLARY SPHINCTERS regulate blood flow
Arterioles = smallest arteries (diameter < 0.3) => Blood pressure much lower => Allows simpler structure (NO outer
layer and smooth muscle layer less thick). Functions :
Transport & Storage
Regulate amount of blood flowing to each capillary by contracting smooth muscle layer => change diam of lumen.
o VASOCONSTRICTION (of A & Ps) : contraction of smooth muscle => Reduces diam=> reduces bloodflow
o VASODILATION (of A & Ps) = relaxation of smooth muscle => Increases diam and blood flow
Precapillary sphincters = bands of smooth muscle right where an arteriole joins a capillary => “Gates” that control
blood flow into capillaries.
Factors influencing vasoconstriction/vasodilation : Nerves, Hormones, Conditions in local environment of & Ps (cold
=> vasoconstriction) , Emotions (vasodilation partly responsible for bloodflow in penis/clitoris if sexually aroused).
CAPILLARIES : where blood exchanges substances with tissues
Capillaries = the smallest vessels, thin-walled, 0,001 mm => RBCc must sometimes bend to squeeze through !
Capillary beds : extensive networks of Cs. Porous extensive branching for exchange of elements with tissues !
Capillary walls : one layer of SQUAMOUS EPITHELIAL CELLS with pores : large enough for exchange between blood
and interstitial fluid (around living cells ) but small enough to retain RBCs and most plasma proteins inside. Some WBCs
can squeeze in and enter tissue
=> Capillaries are (as only) biological strainers that permit selective exchange of substances with the interstitial fluid.
Blood vessels transport blood
Blood Vessels : Three major types : ARTERIES // VAINS // CAPILLARIES
ARTERIES transport blood AWAY from the heart
Arteries : Large, thick wall of muscles to withstand high pressure heart. Largest one = aorta (diameter 2,5cm)
Transport blood AWAY from the haert
Ability to stretch under pressure allows to store blood & providing it to the capillaries even between heartbeats
because the elasticity maintains blood pressure between beats !
Structure of the walls of large/medium arteries = 3 layers surrounding the LUMEN (hollow interior vessel) :
o Endothelium : thin inner layer - flattened squamous epithelial cells. Fit closely together to minimize friction
o Smooth muscle with interwoven elastic CT : Thickest layer. Tonic contraction stiffens arteries and helps
resist high pressure. Elastic CT ensures arteries can stretch passively to accommodate entering blood.
o Supportive layer of CT with Collagen : Outer. Anchors vessels to surrounding tissues, protect from injury.
Aneurysm : damaged Endothelium => blood between 2 outer layers => splits them apart => “ballooning”
Some causes these layers to bulge inward => narrows lumen => reduces blood flow to organs (some bulg outward)
Some severe chest pain, other painless until rupture or “blowout” (massive internal bleeding & often dead).
Take years to develop, can be detected & surgery.
Inward-bulging ones can be detected by stethoscope (flowing blood => specific sound) and CT (tomography).
ARTERIOLES AND PRECAPILLARY SPHINCTERS regulate blood flow
Arterioles = smallest arteries (diameter < 0.3) => Blood pressure much lower => Allows simpler structure (NO outer
layer and smooth muscle layer less thick). Functions :
Transport & Storage
Regulate amount of blood flowing to each capillary by contracting smooth muscle layer => change diam of lumen.
o VASOCONSTRICTION (of A & Ps) : contraction of smooth muscle => Reduces diam=> reduces bloodflow
o VASODILATION (of A & Ps) = relaxation of smooth muscle => Increases diam and blood flow
Precapillary sphincters = bands of smooth muscle right where an arteriole joins a capillary => “Gates” that control
blood flow into capillaries.
Factors influencing vasoconstriction/vasodilation : Nerves, Hormones, Conditions in local environment of & Ps (cold
=> vasoconstriction) , Emotions (vasodilation partly responsible for bloodflow in penis/clitoris if sexually aroused).
CAPILLARIES : where blood exchanges substances with tissues
Capillaries = the smallest vessels, thin-walled, 0,001 mm => RBCc must sometimes bend to squeeze through !
Capillary beds : extensive networks of Cs. Porous extensive branching for exchange of elements with tissues !
Capillary walls : one layer of SQUAMOUS EPITHELIAL CELLS with pores : large enough for exchange between blood
and interstitial fluid (around living cells ) but small enough to retain RBCs and most plasma proteins inside. Some WBCs
can squeeze in and enter tissue
=> Capillaries are (as only) biological strainers that permit selective exchange of substances with the interstitial fluid.
