Cardiovascular System and Cardiac Action Potential

Question 1

what is cardiovascular electrophysiology?

Answer 1

the study of electrical activity of the heart

Question 2

what is cardiovascular mechanics?

Answer 2

the understanding how the contractile properties of the heart affect its function
(the forces that mediate the work)

Question 3

what is cardiovascular hemodynamics?

Answer 3

the study of blood flow and the factors that control it?

Question 4

what are the components of the cardiovascular system?

Answer 4

• the heart (left side and right side)
• arteries
• veins
• lungs
• capillaries

Question 5

why can we consider the heart to be a dual pump system?

Answer 5

• left side = systemic pump that carries oxygenated blood via arteries throughout the body
• right side = pulmonary pump that carries the deoxygenated blood to the lungs

Question 6

what is the significance of the capillaries?

Answer 6

they are the site of exchange in the body from blood to tissues back into the blood

Question 7

what is the order of blood flow throughout the body?

Answer 7

right atrium –> tricuspid valve –> right ventricle –> pulmonary valve –> pulmonary arteries –> lungs –> pulmonary veins –> left atrium –> mitral valve –> left ventricle –> aortic valve –> aorta –> systemic circulation –> superior/inferior vena cava –> right atrium

Question 8

describe how the contraction of the left heart work?

Answer 8

the mitral valve is controlled by the contraction of the papillary muscles contracting to pull the chordae tendinae which pull the mitral valve open
- coordination of contraction is important for opening and closing

Question 9

why are valves important?

Answer 9

prevent backflow

Question 10

what is the distribution of cardiac output to the body systems?

Answer 10

• 100% of blood travels through the hear and to the lungs
• after being released by left side:
• 15% to brain
• 5% to coronary
• 25% to renal
• 25% to GI
• 25% to skeletal muscle
• 5% to skin

Question 11

how much is the normal cardiac output and venous return?

Answer 11

5L/min
- that is how much blood we have in the body

Question 12

why do the kidneys get so much blood?

Answer 12

kidneys are important for chemical balance of the blood and help control blood pressure

Question 13

how much cardiac output is there during activity?

Answer 13

can be as much as 18L/min cycling through the heart –> increased blood flow

Question 14

where is majority of the blood located and why?

Answer 14

• in the veins
• because they are larger
• when you need higher output, the veins are squeezed to release blood into the heart at a faster rate for circulation

Question 15

what can the heart function be characterized into?

Answer 15

• electrical and mechanical events
• electrical events generate by the heart trigger AP which triggers the mechanical contraction of the heart to compliment each other

Question 16

what are the electrical events that occur in the heart?

Answer 16

• cardiac action potential
• cardiac refractory period
• conduction of the action potential
• modulation of electrical activity by the autonomic nervous system (HR)
• ECG

Question 17

where are the pacemaker cells located?

Answer 17

SA node

Question 18

what properties determine the normal electrical activity of the heart?

Answer 18

• automaticity
• excitability (responsiveness)
• conductivity

Question 19

what is automaticity and what cells are related to it?

Answer 19

• the ability of the heart to spontaneously fire action potentials on its own (without stimulus from NS)
• pacemaker cells (=modified cardiac cells)

Question 20

what is excitability and what is related to it?

Answer 20

• the ability of cardiac cells to respond to electrical activity (under normal conditions) of pacemaker cells
• refractory period

Question 21

what is conductivity and what is related to it?

Answer 21

• the ability of the heart to conduct action potentials from its site of origin to all cardiac cells
• cardiac muscle anatomy (functional syncytium)

Question 22

why is the refractory period so important for excitability?

Answer 22

• ensure the heart fully contracts and fully relaxes before another contraction occurs
• this prevents tetanic contraction form occurring which would keep the heart in a constant state of contraction

Question 23

why is cardiac muscle anatomy so important for conductivity?

Answer 23

the cell anatomy is connected and coupled together so the stimulation is passed very easily between cells to contract in unison instead of delayed and unsynchronized

Question 24

what are the ion concentrations and gradients extracellularly and intracelullarly?

Answer 24

Question 25

comparison of cardiac muscle cells and their action potentials

Answer 25

Question 26

Phases of contractile cell action potential

Answer 26

Question 27

Phases of pacemaker cell action potential

Answer 27

Question 28

what are "funny" channels?

Answer 28

- non-specific, non-selective cation channels - tend to be open all the time - drive automaticity and enable immediate regeneration of AP

Question 29

how does the sympathetic nervous system control contraction during exercise?

Answer 29

increases calcium entry and increase potassium leaving which therefore increases speed of contraction during exercise

Question 30

what is the functional refractory period? what are the phases? what is the purpose?

Answer 30

- the refractory period after the action potential first fires - 2 main parts: effective refractory and supranormal refractory - allows time for recovery for ion channels to be activated when the next stimulus is applied - prevents tetanic contraction of the cardiac muscle

Question 31

parts of the effective refractory period? what is significant about them?

Answer 31

- absolute = when another AP cannot be triggered no matter what - relative = AP can be triggered but low likelihood

Question 32

the supranormal refractory period is important because...

Answer 32

= "vulnerable phase" = when another AP can be triggered and is vulnerable to one prior to reaching resting voltage

Question 33

why are intercalated disks important for function?

Answer 33

- they allow cardiac myocytes to operate at a functional syncytium - because they have gap junctions and desmosomes to keep cells intact and connect/couple the cells to stimulate neighboring cells

Question 34

what is the importance of gap junctions?

Answer 34

- they are located between cardiac muscle cells - allow current to flow from the depolarized cell to a neighboring cell that has not been electrically stimulated yet - basically allows it to contract all the cells fast and at the same time - allows spread of AP

Question 35

what are the components that make up the pacemakers of the heart?

Answer 35

- SA node - AV node - purkinje fibers - nodes = bundle of pacemaker cells - all cells can generate spontaneous action potentials but with different frequencies

Question 36

what is the normal pacemaker of the heart?

Answer 36

SA node

Question 37

pacemaker tissues and their rate of action potentials production?

Answer 37

SA node = 70-80 AP/min AV node = 40-60 AP/min Purkinje Fibers = 20-40 AP/min

Question 38

what is overdrive suppression?

Answer 38

it results in the SA node serving as the normal pacemaker

Question 39

what role does the autonomic nervous system have? para? sympa?

Answer 39

serves to modulate the rate of firing of cardiac action potentials - para activation reduces the AP firing rate - sympa activation increases the AP firing rate ~ antagonistic control

Question 40

antagonistic control of of the heart by NS

Answer 40