Blood Vessels Flashcards
Cardiovascular System
composed of heart, blood vessels, & blood
heart acts as a double pump
right side of heart conveys blood through the pumonary circuit
left side of the heart conveys blood through the systemic circuit
gas exchange occurs at the tissue level, across the walls of capillaries
Blood Vessel Wall Layers
consists of 3 layers called tunics, except capillaries
- tunica externa (adventitia): Loose CT; anchors to surrounding structures & in larger vessels contains vasa vasora
- Tunica media: circular arranged smooth muscle & may have an external elastic lamina; SyNS input controls vessel diameter
- Tunica intima: endothelium + BM & subendothelial layer of loose CT & may have an internal elastic lamina
Arteries vs Veins
thickness of each layer varies between vessels; determined largely by blood pressure (BP)
Arteries have thin elastic membranes in their media (External elastic lamina) and intima (internal elastic lamina)
Arteries remain open when cut, can spring back into shape, & can withstand changes to BP
Arteries do not have valves
Elastic Arteries
Largest arteries in body, closest to heart
Tunica externa contains vasa varorum
thick tunica media dominated by elastin in form of fenestrated sheets between layers of smooth muscle
tunica intima is relatively thick
FN:
conduct blood away from heart to smaller arteries during systole
modulate changes in BP during cardiac cycle
propels blood between heart contractions
Muscular Arteries
Medium sized arteries function to distribute blood to body tissues & organs according to tissue demands
Tunica externa is relatively thick & often separated from tunica media by external elastic lamina
Tunica media contains more smooth muscle & less elastin compared to elastic arteries
Tunica intima is thin & has a prominent internal elastic lamina
Small Arteries & Arterioles
differentiated by # of smooth muscle layers; small arteries have 3-8 layers & arterioles have 1-2 layers of smooth muscle
arterioles have no elastic laminae & 1 tunica externa is inconspicious
terminal end of arteriole is called a metarteriole; smooth muscle fibers act as sphincters & produce periodic blood flow into capillaries
fn: Arterioles regulate flow into capillary beds through changes in vascular resistance
vascular tone controlled by SyNS, local conditions, & hormones
Capillaries
capillaries are the smallest blood vessels; connect arterial flow with venous return
networks of capillaries anastomose within the parenchyma of an organ
consists of endothelium & basement membrane
precapillary sphincters control blood flow into the capillaries
lack tunica media and externa
fn: allow for exchange of gases & metabolites
- continuous
- fenestrated
- sinusoids
Veins
65-70% of blood volume found in venous system
SyNS stimulation of venous smooth muscle causes venoconstriction & move blood out of this blood reservoir into arteriolar/capillary systems
have thinner walls & a larger diameter compared to companion artery
Venules
Postcapillary venules consist of endothelium, BM, & pericytes
primary site of action of vasoactive agents such as histamine & thus site of the extravasation of tissue during an inflammatory response
Veins
Structural changes from small to large veins not as distinct as in arteries
Have thin walls relative to total diameter due to venous blood being under low pressure; tunica externa is thickest
lack internal and external elastic aminae
many veins contain valves
rely on compression of adjacent structures to exert pressure on the contained blood
Skeletal Muscle Pump
blood pressure in veins too low to overcome gravity
venous valves prevent backflow
skeletal muscle contraction helps move blood back to heart
