Exam #2: Coronary Circulation & Temperature Regulation

Question 1

Where do the large coronary arteries lie? Where do they branch?

Answer 1

Coronary arteries lie on the epicardial surface of the heart & extend into the myocardium. Extensions of the coronary vessels in the myocardium are referred to as “mycocardial vessels” & deeper extensions are called “subendocardial vessels”

*Note that subendocardial vessels are the most sensitive to compressive forces exerted by ventricular dynamics.

Question 2

What is the inlet pressure for the coronary circulation i.e. what is the pressure gradient that allows for flow through the coronary vessels?

Answer 2

Coronary vessels branch off the aortic pressure (i.e. aorta= inlet pressure) & empty into the right atrium (i.e. outlet pressure).

Thus, Flow= aortic pressure- RAP/ resistance

Question 3

When is the LV maximally perfused? Why?

Answer 3

Diastole

Q=dP/R – because aortic (inlet) pressure is high during diastole & RAP (outlet) pressure is low during diastole
- High dP= High Flow

Question 4

When is the minimally perfused?

Answer 4

Systole, at the end of isovolumic contraction

Question 5

Which side of the heart is better perfused throughout the cardiac cycle?

Answer 5

Right because of smaller compressive forces

Question 6

Draw the wall tension influences on the coronary circulation.

Answer 6

N/A

Question 7

When is tension the greatest that will compress the coronary vessels? What is the effect on the coronary vessels?

Answer 7

• The end of isovolumic contraction

- Low perfusion

Question 8

How will a dilated cardiomyopathy i.e. a big heart, affect the wall tension?

Answer 8

• It will increase wall tension–>compressive forces on the coronary vessels & poor perfusion

Remember, large hearts are never well perfused

Question 9

Describe the cascade the follows from an increase in cardiac metabolism, from e.g. an increase in HR.

Answer 9

1) Increased metabolism
2) Hypoxia
3) ATP turnover
4) Adenosine accumulation
5) Vasodilation

Question 10

What is adenosine a byproduct of?

Answer 10

ATP turnover

Question 11

What does adenosine cause?

Answer 11

Vasodilation

Question 12

How does the SNS regulate coronary flow? What is the difference between the direct effect & the indirect effect?

Answer 12

Sympathetic stimulation of the heart has two effects, a direct effect an an indirect effect.

Direct effect= NE mediated vasoconstriction by binding to alpha-1 receptors

Indirect effect= NE mediated increases in myocardial metabolism, which leads to the accumulation of metabolites that ultimately cause vasodilation (adenosine)

Question 13

What is the temperature set-point?

Answer 13

Individual normal range for body core temperature

Average= 98.6 F

Question 14

How does the core temperature compare to the skin temperature (core vs. shell)?

Answer 14

Basal core temperature is constant (within 1 degree F of 100F), except in the case of fever

• can change with activity & stress
• can change with circadian rhythm

Skin/shell temperature varies widely with changes in surrounding temperature

Question 15

How is heat produced?

Answer 15

Metabolism

Question 16

How is heat lost? How is heat loss prevented?

Answer 16

• Heat conduction through the body
• Heat conduction through skin

Fat prevents heat loss.

Question 17

What is radiation?

Answer 17

Infrared heat rays (EM)

*Relies on a heat gradient.

Question 18

What is conduction?

Answer 18

Direct contact between two objects, which will transfer down the thermal gradient

Question 19

What is conductivity?

Answer 19

The rate of heat conduction

Air= low/ slow
Water= high/ fast

Question 20

How does the thermal conductivity of the skin vary?

Answer 20

Heat= vasodilation & increased conductivity

Cold= vasoconstriction & decreased conductivity

Question 21

What is convection?

Answer 21

Loss of heat by current

Question 22

What mechanism can the human body use to cool the body? What regulates sweating?

Answer 22

• Sweating i.e. evaporation (note that this doesn’t work if you’re dripping sweat–humidity)
• ACh is released from SNS to regulate sweating

Note that this it the ONLY mechanism that can result in cooling in an environment warmer than body temperature.

Question 23

How does non-thermoregulatory “nervous” sweating occur? What is “special” about thermoregulatory sweating?

Answer 23

• Alpha-1 activation on sweat glands= nervous sweating

- Thermoregulatory sweating involves ACh release & M2 receptors in the SNS

Question 24

What is the role of the CNS in thermoregulation? Draw the feedback loops for reduced body temperature & increase temperature.

Answer 24

N/A

Question 25

Where are heat & cold sensitive neurons?

Answer 25

Anterior hypothalamic-preoptic area

Question 26

What happens when heat-sensing neurons are activated?

Answer 26

Sweating

Cutaneous vasodilation

Question 27

What happens when cold-sensing neurons are activated?

Answer 27

Shivering
Inhibition of sweating
Vasoconstriction

Question 28

Are there more heat or cold receptors in the skin?

Answer 28

Cold

Question 29

Where are the deep temperature sensory receptors?

Answer 29

Core:

• Spinal cord
• Abdominal cavity
• Great veins

Question 30

What is the function of the hypothalamus in thermoregulation?

Answer 30

Specifically, the posterior hypothalamus is an integration site for the sensory input

Question 31

Outline the “I’m too hot” response.

Answer 31

• Vasodilation of cutaneous vessels
• Sweating
• Decreased heat production (decreased shivering & thermogenic reactions)

Question 32

Outline the “I’m too cold” response.

Answer 32

• Cutaneous vasoconstriction
• Piloerection
• Increase thermogenesis

Question 33

Describe how shivering is initiated.

Answer 33

The dorsomedial portion of the posterior hypothalamus is the primary motor center for shivering

1) Activation of the dorsomedial posterior hypothalamus when body temperature falls, transmits signal to spinal cord for muscles to “get ready”
2) Further fall in temperature–>enough signal for actual shivering

Question 34

How is heat production stimulated chemically?

Answer 34

1) Stimulation of the cellular metabolism by the SNS
2) Uncoupled oxidative phosporylation–>heat energy release vs. ATP production

*Note that this is especially efficient in brown fat (infants)

Question 35

Outline the release of thyroxine secretion. When does thyroxine secretion occur?

Answer 35

Thyroxine secretion the the long term adaptation to cold.

1) TRH–> anterior pituitary
2) TSH from anterior pituitary–>thyroid
3) Release of T3 & T4 from thyroid, increasing cellular metabolism

Question 36

How is the temperature set-point changed?

Answer 36

Prolonged changes in temperature will shift the set point in the direction of the temperature change.

Question 37

What are the responses to cold? What are complications of responses to cold?

Answer 37

Vasoconstriction
- Decreased blood to extremities 
- Increases possibility of frostbite 
- Digestive disturbances 
- Angina 
Increased metabolic heat produciton

Question 38

What are the responses to heat? What are the complications of responses to heat?

Answer 38

Perspiration
- Dehydration

Cardiac problems

• Heat increases permeability of cardiac cells
• Increased HR

Decreased BP b/c of cutaneous vasodilation

Excessive heat damages cells