Apex CV Anatomy

Question 1

What are the 5 phases of the ventricular action potential?

Answer 1

Phase 0: depolarization, upstroke, Na+ in

Phase 1: initial repolarization: K+ out, Cl- in

Phase 2: plateau: Ca+2 in

Phase 3: final repolarization: K+ out

Phase 4: resting phase: Na+ out

Question 2

What is the conduction pathway of the heart?

Answer 2

• SA nod
• intermodal tracts
• AV node
• Bundle of HIS
• Left and right bundle branches
• purkinje fibers

Question 3

What determines the heart rate?

Answer 3

• the intrinsic firing rate of the dominant pacemaker (usually the SA node)
• autonomic tone

Question 4

What cardiac cells are capable of automaticity?

Answer 4

-all cardiac cells

• however each cell type has its own rate of spontaneous depolarization
• the cells with the fastest rate of depolarization determine how often the heart depolarizers

Question 5

How does the autonomic nervous system modulate heart rate?

Answer 5

• at rest, PNS tone exceeds SNS tone
• PNS tone: vagus nerve: right vagus innervates SA node and left vagus innervates AV node
• SNS tone: cardiac accelerator fibers (T1-T4)

Question 6

What 3 variables can we manipulate to alter the heart rate?

Answer 6

• rate of spontaneous phase 4 depolarization
• threshold potential
• resting membrane potential

Question 7

What 3 conditions can increase heart rate?

Answer 7

• the rate of spontaneous phase 4 depolarization increases
• rate of phase 4 remains constant, but threshold potential becomes more negative (shorter distance between RMP and TP)
• rate of phase 4 remains constant, but resting membrane potential becomes less negative (shorter distance between RMP and TP)

Question 8

How does SNS stimulation via norepinephrine increase heart rate?

Answer 8

Increases Na+ and Ca+ conductance. This will increase the rate of spontaneous phase 4 depolarization

Question 9

How does PNS stimulation via acetylcholine slow heart rate?

Answer 9

-increases K+ conductance and hyperpolarizing the SA node. This decreases the resting membrane potential and reduces the rate of spontaneous phase 4 depolarization

Question 10

What is DO2?

Answer 10

• oxygen delivery
• How much O2 is carried in the blood and how fast it is being delivered to the tissues

= 1000mL/min

Question 11

What is CaO2?

Answer 11

• oxygen consumption
• how much O2 is carried in the arterial blood

= 20mL/dL

Question 12

What is EO2?

Answer 12

• oxygen extraction ratio
• how much O2 is extracted by the tissues

For whole body = 25% (individual tissue beds will vary)

Question 13

What is VO2?

Answer 13

• oxygen consumption
• how much oxygen is consumed by the tissues

= 250mL/min (this value is at rest)

Question 14

What is CvO2?

Answer 14

• venous oxygen content
• how much O2 is carried in the venous blood

= 15mL/dL