Lecture 16 - The Heart and Circulation - Peripheral Flashcards
what is the relationship between O2 delivery and O2 utilization?
- approx 5:1 ratio (delivery:utilization)
what are the 5 components of the cardiovascular system?
- arteries
- arterioles
- capillaries
- venules
- veins
what is the role of the arteries?
- carry blood away from the heart
what is the role of the arterioles?
- control blood flow, feed capillaries
what is the role of the capillaries?
- provide site for nutrient and waste exchange
- where oxygenated blood becomes deoxygenated
what is the role of the venules?
- collect blood from capillaries
what is the role of the veins?
- carry blood from venules back to the heart
what is the structure of the arterioles and arteries?
- high-pressure tubing
- connects left ventricle to tissue
- contain smooth muscle that constricts/relaxes to regulate peripheral blood flow
- innervated by sympathetic nervous system (efferents)
- no gas exchange takes place between arterial blood and surrounding tissues
what is the structure of the capillaries?
- blood vessel network
- thin, allow 1 red blood cell to squeeze through single file
- thin walls allow for diffusion (rapid transfer)
- velocity progressively decreases as blood moves into capillaries
- blood stays for a long time to allow for full diffusion of oxygen
how is arterial blood measured?
- using ultrasound
- look for lumen (where the blood is flowing through)
what are the two factors of hemodynamics?
- pressure (force that drives flow)
- resistance (force that opposes flow)
what is pressure in blood flow?
- provided by heart contraction
- blood flow from region of high pressure o low pressure
- without gradient there is no flow
- physical force
what is resistance in blood flow?
- provided by physical properties of vessels
- causes pressure differential from arterial to the venous circulation
- modification of vessel radius is the most important determinant of resistance
- controlled by size of vessels (constriction vs dilation )
how do you calculate blood flow from a hemodynamic perspective?
Q = MAP / TPR (aka Ohm’s law)
- where MAP = mean arterial pressure
- where TPR = total peripheral resistance
how do you calculate MAP?
- arterial pressure - venous pressure
- where arterial pressure = 2/3DBP + 1/3 SBP
- diastolic + systolic (contraction phase lasts 1/3 of the time so x 1/3)
what are the 3 different blood pressures?
- systolic pressure
- diastolic pressure
- mean arterial pressure
what is systolic pressure?
- contraction period
- highest pressure in artery (during systole)
- top number of blood pressure measurement (~110-120)
- needs to be high to send blood from the heart
what is diastolic pressure?
- lowest pressure in the artery (during diastole)
- bottom number (~70-80)
- during the period of the heart filling
what is normal blood pressure?
- 120/80
what is MAP?
- mean arterial pressure
- average pressure on the arterial walls throughout entire cardiac cycle
- not just the average of the 2 (calculated with 2/3 and 1/3)
how do you calculate venous pressure?
- CVP
- venous pressure is very low
- stands for central venous pressure
what is CVP?
- blood pressure taken in the vena cava
- reflects amount of blood returning to the heart
- ability of right heart to pump blood into pulmonary circulation
- normal ranges from 0-8 mmHg (very low)
- uses PICC lines
what is the blood flow response to exercise?
- SBP changes/increases the most and diastolic doesn’t change much
- average of both increases so significantly because of systolic change
why does MAP increase?
- to allow us to get blood to where it needs to go
how is TPR calculated?
- viscosity of blood x length of vessel / vessel radius
- n x L / r^4
- dictates where the flow goes
what are the 3 factors that determine resistance to cardiac output?
- poiseuille’s law
1. viscosity (blood thickness)
2. length of conducting tube
3. radius of blood vessel (vasoconstriction)
which of the 3 factors can we change?
- radius
- can constrict/dilate to change TPR
- divert blood to regions that need it the most (muscle being used over intestine, etc.)
where is blood found mostly during rest?
- splanchic and kidneys
where is blood found mostly during exercise?
- muscles
where does blood flow not change?
- cardiac system
- brain
- we always need blood here so we don’t pass out
- and skin to a certain extent for temperature regulation
what is the effect of smooth muscles on arterioles?
- smooth muscles’ cross-bridges develop tension and initiate contraction
- increased Ca = contraction
- decreased Ca = relaxation
- dilation is triggered when blood flows against the inner layer of the lumen
what factors change vasomotor tone?
- vasoconstriction = narrowing of blood vessel
- vasodilation = widening of blood vessel
what is vasoconstriction?
- caused by smooth muscle contraction
- lumen becomes smaller
- to decrease blood flow to an area that doesn’t need it
what is vasodilation?
- caused by smooth muscle relaxation
- lumen becomes larger
- for blood to flow to an area that is being worked and requires more blood
