Topic 11: Cardiovascular System - Cardiac Output - Control - SV

Question 1

What is stroke volume controlled by?

Answer 1

• intrinsic control and extrinsic controls

Question 2

How is SV controlled intrinsically? (2)

Answer 2

• heart has built-in ability to vary stroke volume
• adjust to demands

Question 3

What occurs in intrinsic control of stroke volume? (6)

Answer 3

• increase venous return which increases EDV
• increases heart muscle stretch
• increases force of contraction
• at rest, cardiac fibers are at less than optimal length and therefore stretch to approach optimal length
• more cross bridges attach so morce force
• this increases SV within physiological limits

Question 4

What is the purpose of intrinsic control of SV?

Answer 4

more blood in to more blood out

Question 5

What is the relationship between EDV and SV called?

Answer 5

• Frank-Starling’s Law of the Heart

Question 6

What is Frank-Starlings Law of the Heart?

Answer 6

• force of ejection is directly proportional to length of ventricular contractile fibers (within physio limits)

Question 7

How do we get increased venous return in intrinsic control of SV? (2)

Answer 7

1) exercise - venous return speeded up
2) lower HR - has longer to fill so less of an effect than exercise

Question 8

What factors contribute to extrinsic control of HR? (3)

Answer 8

• ANS and SNS
• hormones
• other factors

Question 9

How does the ANS and SNS affect extrinsic control of SV? (2)

Answer 9

• increase force of contraction for a given EDV
• increases HR

Question 10

How does ANS-SNS extrinsically control force of contraction for SV? (4)

Answer 10

1) increase force of contraction (for a given EDV)
- this increases SV bc SNS stimulated, increasing opening of calcium channels
- increase calcium in cytosol
- therefore more cross bridges form to increase force

Question 11

How does SNS increase HR in extrinsic control of SV? (3)

Answer 11

• increases HR so less time to fill
• therefore have decreased EDV at higher HR
• however increased force decreased ESV to compensate for decrease in EDV

Question 12

By both increase force and HR by ANS-SNS extrinsically, what does that do to SV?

Answer 12

• allows at least maintenance of SV even at high HR (usually an increase)

Question 13

What effect extrinsically does PSNS have on SV?

Answer 13

no significant effect

Question 14

Overall, what does SNS and PSNS do extrinsically to CO?

Answer 14

SNS increases CO
PSNS decreases CO

Question 15

How do hormones play a role extrinsically to SV? (2)

Answer 15

• Epi and NE has same mechanism as SNS to increase force
• thyroid hormone increases force and number of epi receptor number

Question 16

In regards to other factors controlling SV, what factors increase force of contraction? (2)

Answer 16

• increase in external calcium (more calcium moves in on AP)
• digitalis (drug) that increases calcium inside

Question 17

In regards to other factors controlling SV, what factors decrease force of contraction? (3)

Answer 17

• acidosis
• increase external K+
• calcium channel blockers (drugs) like verapamil