Blood Vessels and Circulation
venous reserve
the amount of blood that can be shifted from veins in the liver, skin, and lungs to general circulation
anastomosis
a joining of blood vessels
function of arteries
carry blood away from the heart
sinusoid capillaries
resemble fenestrated capillaries that are flattened and irregularly shaped. they commonly have gaps between endothelial cells. they permit the free exchange of water and solutes as large as plasma proteins.
where would you expect valves to be most critical?
venules and medium veins
describe how the venous system volume can change
1. venoconstriction 2. venous reserve
where are precapillary sphincters?
guards the entrance to each capillary
arteriosclerosis
a thickening and toughening of arterial walls. account for about half of all deaths in the united states. tends to develop in people whose plasma has elevated levels of lipids.
capillary bed
an interconnected network of capillaries
explain why veins are referred to as blood reservoirs and capacitance vessels
capacitance vessels- expands easily (about 8 times as much as its corresponding artery
how does the capillary's structure support its function?
capillary walls are thin and diffusion distances are short because they weave throughout active tissues and for networks around muscle fibers. blood flows through capillaries relatively slowly so there is time for diffusion or active transport of materials.
mechanisms that regulate blood flow through arterioles and capillary beds
cardiac output, peripheral resistance, blood pressure
why are arterioles called resistance vessels?
changes in an arteriole's diameter affect the amount of force required to push blood through a constricted vessel than through a dilated one. the force opposing blood flow is called resistance.
characteristics of arterioles
considerably smaller than muscular arteries. have a poorly defined tunica externa. contain smooth muscle cells. the diameter changes in response to local conditions or sympathetic stimulation.
fenestrated capillaries
contain pores that penetrate the endothelial lining. allow rapid exchange of water and solutes between blood and interstitial fluid. located in choroid plexus of the brain, in endocrine organs, absorptive areas of the intestinal tract. permeability depends on region.
which is the most common type of capillary?
continuous capillaries
how do precapillary sphincters affect blood flow through the capillary bed?
contraction of smooth muscle cells narrows the entrance, reducing or stopping blood flow. when the sphincter relaxes, blood flows into the capillary.
venoconstriction
decreases the amount of blood within the venous sstem, increasing the volume in the arterial system. can keep blood volume with arteries at a near-normal level despite a significant blood loss.
compare and contrast arteries and veins.
differences: - walls of arteries are thicker than those of veins. the tunica media of an artery contains more smooth muscle and elastic fibers. -the lumen appears smaller than the corresponding vein. arteries keep their circular shape when sectioned while veins tend to collapse and look flattened. -arteries are more resilient. when stretch they keep their shape and lengthen, while veins cannot tolerate as much distortion without tearing. -veins typically contain valves -arteries have rippled endothelium due to vessel constriction while the endothelium of veins is smooth -arteries have internal elastic membranes and veins do not similarities:
importance of the elastic and contractile nature of arteries
elasticity permits the vessel diameter to change passively in response to changes in blood pressure. contractility enables them to actively change in diameter.
differentiate between elastic and muscular arteries.
function: elastic arteries carry large volumes of blood away from the heart. muscular arteries distribute blood to the body's skeletal muscles and internal organs. -elastic arteries contain a high density of elastic fibers and few smooth muscle cells. -muscular arteries have a thick tunica media which contains more smooth muscle cells than elastic arteries. location: elastic- pulmonary trunk and aorta muscular- external carotid arteries of neck, brachial arteries, femoral arteries
how are anastomosis useful in the event of a bloog vessel occlusion? where are these especially important?
if one artery is blocked, capillary circulation will continue. especially important in esophegael, rectal, and paraumbilical regions
vasomotor tone
produced by constant action of sympathetic vasoconstrictor nerves
describe the distribution of blood throughout the body
venules and medium-sized veins- 25% large venous networks- 21% large veins- 18% systemic capillaries- 7% heart- 7% muscular arteries- 5% elastic arteries- 4% pulmonary veins- 4% pulmonary arteries- 3% pulmonary capillaries- 2% arterioles- 2%
course of circulation of blood through blood vessels on the way back to the heart
venules collect blood from capillary beds, then moves to medium sized veins to large veins.
describe the walls and pressure within veins
walls are thinner than those of corresponding arteries and have lower pressure. their diameters are also generally large than arteries.
aneurysm
when local arterial pressure exceeds the capacity of the elastic components of the tunics. this results in a bulge in the weakened wall of the artery. this can result in a catastrophic blowout.
5 types of blood vessels
1. arteries 2. arterioles 3. capillaries 4. venules 5. veins
three types of capillaries
1. continuous 2. fenestrated 3. sinusoid
differentiate between the 3 different layers of the blood vessel wall
1. tunica intima- inner layer, contains endothelial lining and connective tissue 2. tunica media- middle layer. contains concentric sheets of smooth muscle tissue. binded to the tunica intima and tunica externa by collagen fibers. is thicker than the turnica externa in arteries. 3. tunica externa-outer layer. connective tissue sheath. thicker in veins than the tunica media
relationship of the 5 types of blood vessels to each other.
arteries transport oxygenated blood away from the heart (except the pulmonary artery), arterioles transport blood from arteries to cappillaries, capillaries supply the tissues of the body with blood and removes waste from surrounding cells. venules drains blood for capillaries into the veins, and veins transport deoxygenated blood towards the heart (except the pulmonary vein)
perfusion
blood flow through tissues which carries O2 and nutrients to the tissues and CO2 and wastes away.
vasa vasorum
means "vessel of vessels" they are small arteries and veins in the walls of large vessels that supply the smooth muscle cells and fibroblasts of the tunica media and tunica externa. they are needed because the walls of arteries and veins are too thick to allow diffusion between the bloodstream and surrounding tissues.
function of capillaries
site of diffusion between blood and interstitial fluid / tissues
how does the sympathetic nervous system affect contractility in arteries?
stimulation arterial smooth muscles contract, constricting the artery. (vasoconstriction). when the muscles relax, vasodilation occurs.
varicose veins
superficial distended veins caused by the weakening and stretching of valves (causing blood pooling in veins)
how does an artery respond in hemostasis?
the artery contracts which helps to reduce bleeding
continuous capillaries
the endothelium is a complete lining. located in all tissues except epithelia and cartilage. permit passage of water, small solutes, and lipid-soluble materials to diffuse into the interstitial fluid. they prevent the loss of blood cells and plasma proteins.
why are valves necessary in veins but not arteries?
the pressure in venules and veins is so low that it cannot overcome the force of gravity. the valves are needed so that the blood will flow in one direction only. the arterial system is high-pressure.
identify the branch of the autonomic system that innervates blood vessels. what layer of blood vessel wall do these innervate?
the sympathetic division- targets smooth muscle
