Properties of Vasculature Flashcards
list the job of each vascular segment
- large arteries: distribute blood under high pressure and promote continuous flow
- small arteries/arterioles: smooth arterial pulsations and regulate flow into capillaries (stopcocks of vasculature)
- capillaries: exchange substances (gases, nutrients, waste) between blood and systemic tissues
- venules: collect blood from capillaries
- veins: deliver blood back to heart and serve as a major reservoir for blood
explain the characteristics of each branch of the vascular tree that allow it to do its job
aorta and larger arteries: very elastic; distend to absorb energy/volume during systole (compliant) and recoil to maintain propulsion during diastole (elastic); windkessel effect
small arteries/arterioles: moving down the arterial tree, the vessel lumen becomes smaller and compliance/elasticity decreases, with arterioles muscular walls allowing them to relax or constrict to regulate blood flow
capillaries: thin-walled with pores and a small lumen for exchange
venules: thin, small, close to capillaries to collect blood and send to veins
veins: have thin, muscular walls that contract/relax to vary their capacity and are highly distensible/compliant to act as a reservoir for 60-70% of total blood volume
provide examples of tissues in which each of the three capillary types are found
- continuous capillaries: most common type; in skin, muscle, CNS, and lungs
- fenestrated: in renal glomeruli, intestinal mucosa, and exocrine glands
- sinusoidal: in liver, bone marrow, and spleen
graph normal pressure profiles in the heart and segments of the pulmonary and systemic circulations
left ventricle: 130
aorta and arteries: decrease from 130-80
arterioles: 80-40
capillaries: 40-15
venules and veins: 15-5
vena cava and right atrium: 5-3
right ventricle: 40-20
pulmonary artery and arteries of lungs: 15ish
arterioles of lungs: 15ish
capillaries: 10ish
small veins of lungs: 5ish
pulmonary veins and left atrium: 5ish
explain the relationship between pressure, volume, and flow in the circulatory system
- aortic/arterial pressure is pulsatile; systolic/diastolic is 120/80 due to the high volume and pressure once it leaves the left ventricle
- pressure continues to drop across the systemic capillary bed with a mean pressure of 17-25 as arterioles smooth down the flow
- pressure is nearly zero once blood reaches the right atrium from systemic circulation
- pressures in pulmonary circulation are much lower than corresponding systemic segments because pulmonary blood has such a short distance to travel compared to systemic
list factors contributing to vascular resistance according to Pouiselle’s law
resistance depends on the dimensions of the tube (length/radius) and characteristics of the fluid (viscosity)
the most powerful determinant is vessel radius!!! the 4th power law states that resistance varies inversely with the 4th power of the vessel radius, so if driving pressure is kept constant, doubling the vessel radius with drop resistance/increase flow by 16-fold; this means that vessels that can change radius most dramatically have the greatest effect on resistance and flow and these are the arterioles
hematocrit is the most important determinant of blood viscosity; greater blood viscosity increases resistance to flow
explain the effects of increasing hematocrit of blood flow
increased hematocrit increases viscosity and decreases blood flow
what are the 3 main principles of circulatory function and which is most important?
the circulatory system strives to maintain 3 things
1. tissue blood flow that meets each tissue’s needs
2. cardiac output that moves into circulation all the blood returned to the heart (Frank-Starling)
3. constant, normal mean arterial blood pressure (this one is the most important, the circulatory system will maintain this above all else!!!)
describe normal blood flow
laminar; blood moves alone the length of the vessel, forming concentric layers that do not mix; inner layers move faster than the outermost (slowed by friction by vessel wall)
when may turbulent blood flow develop? (3)
- irregularity of vessel wall
- high blood viscosity
- low blood viscosity
what determines total vascular resistance?
the arrangement of blood vessels within a system
describe the relationship between arrangement of blood vessels to total vascular resistance for a series arrangement of vessels and for a parallel arrangement of vessels
series arrangement: total vascular resistance is equal to the sum of resistance in each vessel type when vessels arranged one after another
parallel arrangement: total resistance is less than the resistance of any one parallel vessel when, within each vessel type, blood vessels branch to form parallel circuits that supply different tissues
what does adding a parallel vessel/circuit do to total vascular resistance and how does this relate to amputees?
adding a parallel vessel/circuit decreases total resistance by providing an additional pathway for flow, so amputation of a limp increases systemic vascular resistance by removing one of those parallel circuits
which vessel type contributes the greatest resistance and why is it not capillaries?
arterioles contribute the greatest resistance (2/3 of SVR); even though capillaries are the smallest vessels, there are many more capillaries (billions) than arterioles (millions) so the total resistance across many capillary beds arranged in parallel is less than the total resistance across fewer arterioles arranged in parallel (more alternate paths with capillaries)
