This summary Human Biology includes books, slides and lecture notes. Titles are clearly marked in color, and expressed figures are all included. The text is written in English. Good luck, it worked for me ;-)!
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.
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