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Physiology Exam 2 > 22 - Coronary Circulation > Flashcards

22 - Coronary Circulation Flashcards

1
Q

What period of the cardiac cycle is the flow of coronary blood into the left ventricle the lowest?

A

At the end of the isovolumetric contration (i.e. left ventricle contraction)

This is during systolic periods

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2
Q

Why is coronary perfusion in the left ventricular mycardium low during systolic periods and high during diastolic periods?

A 
Systolic = contraction
Diastolic = relaxation

This is because flow is proportional to the pressure difference

When flow is low, perfusion is low

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3
Q

How is flow related to resistance?

A

Flow is inversely proportional to the resistance

(vessel radius)^4 = 16x resistance

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4
Q

When the left ventricle contracts, what happens to the pressure in the coronary artery?

A

Coronary artery pressure increase

The pressure increases due to compression and the radius of the vessel becomes approximately zero (it closes)

Note that the valves are NOT open during this time

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5
Q

What happens to the coronary artery during ventricular relaxation (diastolic period)?

A

The aortic valve is closing and the ventricle relaxes, so the coronary vessel is NOT compressed

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6
Q

What happens to the pressure inside the coronary artery?

A

Pressure decreases

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7
Q

What does this mean for the perfusion?

A

Recall that as the flow increases, the perfusion also increases

During the diastolic period of ventricular relaxation, the perfusion of blood is the BEST

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8
Q

What is the definition of perfusion?

A

In physiology, perfusion is the process of a body delivering blood to a capillary bed in its biological tissue.

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9
Q

When would we see minimal flow and perfusion?

A

At the end of the isovolumentric contractions

That means that when the left ventricle is most contracted, there is minimal perfusion

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10
Q

The left ventricle is maximally perfused during the ______________ period when the muscle is _____________

A

Diastolic period

Relaxed

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11
Q

What is cardiac dilation?

A

Cardiac dilation is a condition where the size of the heart cavity becomes enlarged and stretched, thinning out the heart muscle (myocardium). Causes of this enlargement include heart muscle inflammation, prior heart attack, and long-term alcohol abuse.

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12
Q

What does cardiac dilation do to the tension in the walls of the ventricles?

A

This INCREASES the tension in the walls of the ventricles

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13
Q

What does cardiac dilation do to the perfusion of the myocardium (heart muscle)?

A

Since the wall tension corresponds to the pressure gradient, when tension increases, so does the pressure

High pressure means that there will be low flow, and therefore low perfusion

So, cardiac dilation decreases perfusion

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14
Q

What part of the heart do we most commonly see myocardial infarcts (heart attacks)?

A

Left ventricle

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15
Q

What does “transmural” mean in terms of an MI?

A

It goes through the whole ventricular wall

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16
Q

Is a transmural MI common or uncommon?

A

Common - this is what we usually see

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17
Q

Why do we most commonly see left ventricle MIs?

A

Because the left ventricular coronary flow is decreased the most during systole

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18
Q

Why do we commonly see transmurual MIs?

A

Because the inner myocardia vessels are the most compressed during systole, therefore have the least amount of flow

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19
Q

When would we see a subendocardial MI?

A

This is when the the MI is within the inner myocardium

We wee this when both diastolic and systolic perfusion are low

20
Q

When would you have both low perfusion in both the diastolic and systolic periods?

A

If you have…

  • A dilated heart
  • Aortic regurgitation
21
Q

What is the effect of aortic regurgitation on myocardial perfusion?

A

It decreases the perfusion time because there is a drop in aortic pressure

22
Q

What does an increased heart rate do to the length of the diastolic period?

A

It shortens the diastolic period

23
Q

What does this do to perfusion of the heart?

A

Recall that the heart becomes well perfused during diastole (relaxed heart), so if the diastole is shortened, the perfusion is decreased

Increased heart rate = shorter diastole = less perfusion

24
Q

What does norepinephrine do to the length of the diastolic period?

A

Decreases the diastolic time

Increase in norepinephrin = shorter diastolic period = less perfusion

25
Q

What happens when the body temperature reaches 106 F (41 C)?

A

Convulsions can occur and you can go into a coma

26
Q

What happens when the body temperature reaches 107.6 F (42 C)?

A

The blood is damaged

27
Q

What happens when the body temperature reaches 110 F (43.3 C)?

A

This is the highest cellular temperature that is compatible with life, any higher and you will die

28
Q

What is the Q10 effect?

A

It applies to low temperature and states that the rate of cellular processes will decrease by 1/2 to 1/3 for every 10 degrees the body drops in temperature

29
Q

What are some times that this can be beneficial?

A

Cooling during open heart surgery has a protective effect on the brain

30
Q

What is the relationship between cellular damage and death in terms of extreme cold body temperatures?

A

Organ failure or death may actually occur before cellular damage occurs because the cold does NOT damage the cells right away, it just slows down all the processes to the point where you can no longer live

31
Q

What is the average body temperature taken orally?

A

98.6 F or 37 C

32
Q

What is the average body temperature taken rectally?

A

Approx. 1 degree above oral

33
Q

What is the average body temperature taken in the ear?

A

Same as oral

34
Q

What is the average body temperature taken in the axillary?

A

Approx. 1 degree below oral

35
Q

What are three causes of normal variation in body temperature?

A
  • Circadian rhythms or diurnal variability (higher in the afternoon and evening)
  • Ovulation (higher from ovulation to menstruation)
  • Exercise (higher)
36
Q

What is the difference between the core temperature and the shell temperature?

A

The core temperature is the temperature of the heart, brain, thoracic and abdominal organs

The shell temperature is the temperature of the skin and subcutaneous fat

37
Q

What is the average core temperature?

A

100 F (37.8 C)

38
Q

Why does the shell temperature vary?

A

The temperature of the skina and subcutaneous fat varies greatly in order to maintain a constant core temperature

39
Q

What are three avenues of heat exchange between the body and the environment?

A
  • Radiation
  • Conduction
  • Evaporation
40
Q

Describe heat exchange through radiation

A
  • The human body emits electromagnetic waves
  • When the waves hit a surface that is cooler than the body, heat is lost
  • The body absorbs waves that are emitted from objects having a warmer surface than the body
41
Q

Describe heat exchange through conduction

A
  • Conduction occurs by direct contact only
  • Heat transfer moves down a thermal gradient
  • The rate of heat exchange is determined by the temperature difference and the thermal conductivity of the surfaces
42
Q

What happens to the conductivity of the skin with increased vasodilation?

A

The skin becomes MORE conductive when the vessels are vasodilated, meaning there is more blood flow

vasodilation = more blood flow = increased conductivity

43
Q

Describe heat exchange through evaporation

A
  • As water leaves the body, it takes with it a high number of calories
  • This is due to the high specific heat of water (specific heat is the energy required to raise one unit of water one degree in one unit of time)
  • This takes energy from the body in the form of heat
44
Q

Describe heat exchange through convection

A
  • Heat is dissipated by current or movement of air or water down its thermal gradient
  • Example: cooling by the wind
  • Convection occurs more rapidly in water
45
Q

What do cutaneous cold receptors do during a decrease in temperature?

A

They will increase firing when there is a decrease in temperature

46
Q

What do cutaneous warmth receptors do during an increase in temperature?

A

They will increase firing when there is an increase in temperature

Physiology Exam 2 (11 decks)

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