Cardiac Function 2

Question 1

What is CO (or Q)?

Answer 1

• cardiac output

- volume of blood pumped out by each ventricle per minute

Question 2

CO =

Answer 2

SV (stroke volume) x HR

Question 3

Average CO =

Answer 3

~5 L/min at rest

Question 4

Average blood volume in body =

Answer 4

~5.5 L

Question 5

How is CO controlled?

Answer 5

• through regulation of HR and SV

- extrinsic and intrinsic regulation

Question 6

What are extrinsic mechanisms? Give an example.

Answer 6

• from external

- neural and hormonal

Question 7

What are intrinsic mechanisms?Give an example.

Answer 7

• from within

- autoregulation

Question 8

How is HR determined?

Answer 8

by SA node firing frequency

Question 9

SA node intrinsic firing rate = . This means that HR =

Answer 9

• 100/min

- no extrinsic control on heart; HR = 100

Question 10

SA node is under control of ____ and ______.

Answer 10

• ANS

- hormones

Question 11

What system dominates HR changes at rest?

Answer 11

• parasympathetic system

- HR = 75

Question 12

What system dominates HR changes during excitement/exercise?

Answer 12

• sympathetic system

- HR increases

Question 13

Describe how increased sympathetic activity leads to increased heart rate.

Answer 13

• increased sympathetic activity (nerves or epinephrine)
• targets SA node
• opens funny & Ca 2+ channels
• increase rate of AP firing
• increase heart rate

Question 14

In looking at the effects of the autonomic nervous system on SA nodal cell potentials, the slope of the depolarization period to threshold is…

Answer 14

steep

Question 15

In looking at the effects of the autonomic nervous system on SA nodal cell potentials, how does is slowly turn into parasympathetic?

Answer 15

• slope slowly decreases

- membrane potential slowly decreases

Question 16

Describe how increased parasympathetic activity leads to decreased heart rate.

Answer 16

• increased parasympathetic activity
• targets SA node
• K+ channels open; Ca 2+ channels close
• decrease rate of AP firing and hyperpolarize cell
• decrease heart rate

Question 17

How does epinephrine effect HR?

Answer 17

• same effect as sympathetic nervous system
• increases action potential frequency at SA node
• increases velocity of action potential conduction in muscle fibres

Question 18

How do thyroid hormones, glucagon, and insulin have an effect on HR?

Answer 18

contraction

Question 19

Activity of sympathetic neurons projecting to SA node does what to HR?

Answer 19

raises HR

Question 20

Activity of parasympathetic neurons projecting to SA node does what to HR?

Answer 20

lowers HR

Question 21

Levels of circulating epinephrine does what to HR?

Answer 21

raises HR

Question 22

What are the 3 primary factors affecting stroke volume?

Answer 22

• ventricular contractility
• end-diastolic volume
• afterload

Question 23

Describe the influence of ventricular contractility.

Answer 23

• more forceful contraction will expel more blood

- sympathetic control of ventricular contraction

Question 24

Describe the sympathetic control of ventricular contraction.

Answer 24

• sympathetic innervation of muscle cells

- Norepinephrine → β1 adrenergic receptors → cAMP

Question 25

Describe the second-messenger system.

Answer 25

- augment open Ca 2+ channels - increase Ca 2+ release from sarcoplasmic reticulum (SR) - increase myosin ATPase rate - enhance rate of Ca 2+ - ATPase activity on SR

Question 26

With changes in ventricular contractility induced by sympathetic activity, what goes up?

Answer 26

tension

Question 27

Describe how parasympathetic innervation of contractile cells effects stroke volume.

Answer 27

not significant

Question 28

Describe how hormones affect stroke volume.

Answer 28

- epinephrine binds to adrenergic receptors | - thyroid hormones, insulin, and glucagon increase force of contraction

Question 29

What is Starling's law (Frank Starling law)?

Answer 29

- influence of end-diastolic volume on stroke volume | - output (SV) = input (VR)

Question 30

Describe how according to Starling's law, increased EDV leads to increased SV.

Answer 30

- increased EDV (VR) stretches muscle fibres - fibres closer to optimal length - optimal length = greater strength of contraction - result = increased SV

Question 31

Name 2 factors affecting EDV.

Answer 31

- end diastolic pressure = preload | - afterload

Question 32

What makes up end diastolic pressure (preload)?

Answer 32

- filling time - atrial pressure - central venous pressure

Question 33

What is afterload?

Answer 33

pressure in aorta during ejection

Question 34

Increased venous return results in...

Answer 34

- increased EDV | - increased SV

Question 35

Increased sympathetic activity or epinephrine results in...

Answer 35

- increased contractility | - increased SV

Question 36

Decreased arterial pressure (afterload) results in ...

Answer 36

increased SV