Lecture 16 - The Heart and Circulation - Peripheral

Question 1

what is the relationship between O2 delivery and O2 utilization?

Answer 1

• approx 5:1 ratio (delivery:utilization)

Question 2

what are the 5 components of the cardiovascular system?

Answer 2

• arteries
• arterioles
• capillaries
• venules
• veins

Question 3

what is the role of the arteries?

Answer 3

• carry blood away from the heart

Question 4

what is the role of the arterioles?

Answer 4

• control blood flow, feed capillaries

Question 5

what is the role of the capillaries?

Answer 5

• provide site for nutrient and waste exchange
• where oxygenated blood becomes deoxygenated

Question 6

what is the role of the venules?

Answer 6

• collect blood from capillaries

Question 7

what is the role of the veins?

Answer 7

• carry blood from venules back to the heart

Question 8

what is the structure of the arterioles and arteries?

Answer 8

• 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

Question 9

what is the structure of the capillaries?

Answer 9

• 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

Question 10

how is arterial blood measured?

Answer 10

• using ultrasound
• look for lumen (where the blood is flowing through)

Question 11

what are the two factors of hemodynamics?

Answer 11

• pressure (force that drives flow)
• resistance (force that opposes flow)

Question 12

what is pressure in blood flow?

Answer 12

• provided by heart contraction
• blood flow from region of high pressure o low pressure
• without gradient there is no flow
• physical force

Question 13

what is resistance in blood flow?

Answer 13

• 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 )

Question 14

how do you calculate blood flow from a hemodynamic perspective?

Answer 14

Q = MAP / TPR (aka Ohm’s law)
- where MAP = mean arterial pressure
- where TPR = total peripheral resistance

Question 15

how do you calculate MAP?

Answer 15

• 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)

Question 16

what are the 3 different blood pressures?

Answer 16

• systolic pressure
• diastolic pressure
• mean arterial pressure

Question 17

what is systolic pressure?

Answer 17

• 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

Question 18

what is diastolic pressure?

Answer 18

• lowest pressure in the artery (during diastole)
• bottom number (~70-80)
• during the period of the heart filling

Question 19

what is normal blood pressure?

Answer 19

• 120/80

Question 20

what is MAP?

Answer 20

• 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)

Question 21

how do you calculate venous pressure?

Answer 21

• CVP
• venous pressure is very low
• stands for central venous pressure

Question 22

what is CVP?

Answer 22

• 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

Question 23

what is the blood flow response to exercise?

Answer 23

• SBP changes/increases the most and diastolic doesn’t change much
• average of both increases so significantly because of systolic change

Question 24

why does MAP increase?

Answer 24

• to allow us to get blood to where it needs to go

Question 25

how is TPR calculated?

Answer 25

• viscosity of blood x length of vessel / vessel radius
• n x L / r^4
• dictates where the flow goes

Question 26

what are the 3 factors that determine resistance to cardiac output?

Answer 26

• poiseuille’s law
  1. viscosity (blood thickness)
  2. length of conducting tube
  3. radius of blood vessel (vasoconstriction)

Question 27

which of the 3 factors can we change?

Answer 27

• radius
• can constrict/dilate to change TPR
• divert blood to regions that need it the most (muscle being used over intestine, etc.)

Question 28

where is blood found mostly during rest?

Answer 28

• splanchic and kidneys

Question 29

where is blood found mostly during exercise?

Answer 29

• muscles

Question 30

where does blood flow not change?

Answer 30

• cardiac system
• brain
• we always need blood here so we don’t pass out
• and skin to a certain extent for temperature regulation

Question 31

what is the effect of smooth muscles on arterioles?

Answer 31

• 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

Question 32

what factors change vasomotor tone?

Answer 32

• vasoconstriction = narrowing of blood vessel
• vasodilation = widening of blood vessel

Question 33

what is vasoconstriction?

Answer 33

• caused by smooth muscle contraction
• lumen becomes smaller
• to decrease blood flow to an area that doesn’t need it

Question 34

what is vasodilation?

Answer 34

• caused by smooth muscle relaxation
• lumen becomes larger
• for blood to flow to an area that is being worked and requires more blood