Cardiovascular Physiology 22

Question 1

What is the Stroke Volume?

Answer 1

The volume of blood the ventricle ejects during each contraction of during systole

Question 2

What three factors affect the stroke volume?

Answer 2

• End-diastolic volume (EDV)
• Contractility of the ventricles
• Afterload

Question 3

What is the End-Diastolic Volume (EDV) or Preload?

Answer 3

The volume of blood in the ventricles at the end of ventricular diastole or after the ventricles have completed filling

Question 4

What is an Intrinsic mechanism?

Answer 4

A mechanism that originates or occurs inside the heart

Question 5

What is the Intrinsic mechanism that that heart has to alter stroke volume?

Answer 5

The ventricles contract more forcefully when they have been stretched prior to contraction

Question 6

How is the increased stretch of ventricles to increase stroke volume accomplished?

Answer 6

By filling the ventricle more fully with blood

Question 7

What is the relationship between the EDV and the stroke volume defined by?

Answer 7

The Frank-Starling Mechanism

Question 8

How does the heart fill the ventricles more fully with blood to increase stroke volume?

Answer 8

By increasing the venous return (the amount of blood returning to the heart from the veins)

Question 9

How does the increase of venous return affect cardiac output?

Answer 9

It increases EDV which increases stroke volume which increases cardiac output

Question 10

What is the Preload?

Answer 10

The tension or load on ventricular myocardium before it begins to contract

Question 11

How can Sympathetic stimulation affect venous return?

Answer 11

Sympathetic stimulation of the venous smooth muscle will act to increase the return of blood to the heart through vein constriction

Question 12

What is the extrinsic mechanism to increase stroke volume?

Answer 12

The sympathetic nervous system increases constriction to the veins which increases EDV which increases stroke volume

Question 13

Where does an Extrinsic mechanism originate?

Answer 13

Outside the heart

Question 14

Why doesn’t the Parasympathetic nervous system increase venous volume?

Answer 14

Because most blood vessels in the body only have sympathetic innervation to their smooth muscle

Question 15

What kind of mechanism is the Frank-Starling Mechanism?

Answer 15

An intrinsic mechanism

Question 16

What does the Frank-Starling mechanism function independent of?

Answer 16

Neural or hormonal stimulation

Question 17

What does the Frank-Starling mechanism say about EDV and SV?

Answer 17

As you increase EDV you increase SV

Question 18

What is the main determinant of cardiac muscle fiber (sarcomere length)?

Answer 18

The degree of diastolic filling: preload

Question 19

How does the EDV affect sarcomeres?

Answer 19

As the ventricles become more filled with blood, the sarcomeres stretch out which puts more load on the sarcomeres

Question 20

How does the increased load on sarcomeres affect stroke volume?

Answer 20

It stretches out the sarcomeres causing them to contract more forcefully increasing stroke volume

Question 21

How does the Frank-Starling mechanism match the output of the ventricles?

Answer 21

If the EDV in one ventricle increases, this increases the SV volume leaving which increases the the venous return in the other ventricle

Question 22

How does the Frank-Starling mechanism work in terms of sarcomeres?

Answer 22

A greater EDV causes sarcomeres to stretch out due to the increased volume of blood allowing for greater myosin cross bridges to occur uncrowding the sarcomere allowing for maximal force when it contracts