Week 6

Question 1

What is the most common measure of aerobic metabolism?

Answer 1

Oxygen consumption rate (VO2)

Question 2

How does VO2 increase relative to exercise

Answer 2

increases proportionally to exercise until the body’s maximal capacity for aerobic metabolism is reached

Question 3

What other factors besides exercise may cause an increase in VO2?

Answer 3

• When metabolic demands increase
• when endotherms increase body heat generation during cold exposure

Question 4

How are VO2 and CO related

Answer 4

• Strong correlation between the two
• increases based on workload run parallel
• Increases in VO2 are supported by increases in CO

Question 5

Def: Venus return

Answer 5

The sum of all local tissue blood flows

Question 6

How does venous return related to CO

Answer 6

Venous return is the key determinant of CO for small changes in metabolic rate
- Intrinsic control mechanisms help the heart pump the blood it receives

Question 7

How does the body control CO when large amounts of tissue increase metabolism

Answer 7

• When this occurs, vasodilation happens - TPR decreases
• without nervous control arterial pressure would fall and increases in CO would be insufficient to meet O2 demands
• baroreflex maintains arterial pressure so that reductions in TPR only lead to increases in CO

Question 8

What 2 factors effect cardiac output during exercise

Answer 8

1. The pumping ability of the heart (cardiac output curves)
2. Peripheral factors affecting flow to heart (Venus return curves)

Question 9

Factors effecting Cardiac Output

Answer 9

• Q increases in response to increases in right atrial pressure due to intrinsic mechanisms (frank-starling)
• Sympathetic stimulation increases Q at a given P by increasing contractility and the action potential frequency of pacemakers in S-A node
  -Parasympathetic stimulation decreases HR by reducing firing frequency

Question 10

Cardiac Output curves

Answer 10

As atrial pressure increase CO initially increases rapidly and then plateaus
- PNS innervation decreases height of plateau
- SNS innervation increases height of plateau

Question 11

Factors affecting venous return

Answer 11

• Pressures in peripheral vein
• Pressures in right right atrium
• Resistance to venous return

Question 12

How does sympathetic stimulation affect venous return

Answer 12

Causes veins to contract increasing pressure in peripheral veins thus increasing venous return

Question 13

Venous Return Curves

Answer 13

As atrial pressure increases venous return decreases until pressure in the atria is equal to pressure in the venous system

Question 14

How does sympathetic innervation affect venous return curves

Answer 14

Causes a greater venous return at a given atrial pressure

Question 15

How does muscle activity affect venous return

Answer 15

• Reduces resistance to flow through muscle veins (decreased resistance to venous return and increases venous return)

Question 16

How does muscle activity affect venous return curves

Answer 16

• With increased muscle activity the magnitude of the slope increases
• With decreased muscle activity the magnitude of the slope decreases
• All maintain same zero point because pressure in peripheral veins remains constant

Question 17

Control of Cardiac output

Answer 17

• Cardiac output must equal venous return
• Atrial conditions occur at the intersection of the venous return curve and cardiac output curve
• Exercise leads to sympathetic stimulation, shifting the cardiac output curve up and shifting the venous return to the right