Ch 13/14 Cardiovascular Physiology (Day 2)

Question 1

Anatomy of the Heart

Answer 1

–>see slide image

Question 2

Atrioventricular Valves

Answer 2

Between atria and ventricles (ensures one-way blood flow)

• Tricuspid valve on the right side
• Bicuspid valve, or mitral valve, on the left side

Question 3

Semilunar Valves

Answer 3

Between ventricles and arteries (ensures one-way blood flow)

• Pulmonary valve
• Aortic valve

Question 4

Ventricular Contraction

Answer 4

AV valves (tricuspid, bicuspid/mitral) closed
Semilunar valves (pulmonary/aortic) open

Question 5

Ventricular Relaxation

Answer 5

AV (tricuspid, bicuspid/mitral) valves open
Semilunar valves (pulmonary, aortic) closed

Question 6

Heart

Answer 6

pump generating driving pressure for blood flow through the circulation

• Heart generates pressure when it contracts (systole) –> pumping blood into arteries
• Arteries maintain pressure by acting as an elastic pressure reservoir between cardiac contractions (i.e. during diastole)

Question 7

Cardiac Cycle

Answer 7

Pumping is periodic, i.e. cardiac activity characterized by cycles of active pumping (systole) followed by resting (diastole).

Question 8

systole

Answer 8

contraction/pumping out

Question 9

diastole

Answer 9

relaxation/filling

Question 10

Pressure changes during cardiac cycle

Answer 10

1) Ventricles begin contraction, pressure rises, and AV valves close (lub); isovolumetric CONTRACTION
2) Pressure builds, semilunar valves open, and blood is ejected into arteries. (pressure of ventricles is much higher)

3) Pressure in ventricles falls; semilunar valves close (dub); isovolumetric relaxation.
- -> Dicrotic notch – slight inflection in aortic pressure during isovolumetric RELAXATION

4) Pressure in ventricles falls below that of atria, and AV valve opens. Ventricles fill (passive).
5) Atria contract, sending last of blood to ventricles (active)

Question 11

What are the pressure differences between L and R side of heart?

Answer 11

left side is 5-6x higher

Question 12

isovolumetric

Answer 12

volume is NOT changing

Question 13

heart sounds

Answer 13

lub: closing of AV valves at start of isovolumetric contraction
dub: closing of semilunar valves during isovolumetric relaxation

Question 14

EDV/ESV

Answer 14

1) EDV (end diastolic volume) - ESV (end systolic volume) = SV (stroke volume)
2) Ventricle does not eject all its volume—can be altered

Question 15

preload

Answer 15

pressure has reached a point where the mitral valve closes

Question 16

afterload

Answer 16

pressure the heart is working against

Question 17

stroke volume

Answer 17

overall work that is being done by the heart

-increases as EDV and ESV get further apart

Question 18

Cardiac Muscle: Contractile cells

Answer 18

Striated fibers organized into sarcomeres

Question 19

Cardiac Muscle: Autorhythmic (pacemaker cells)

Answer 19

• Signal for contraction (generate electric signal)
• Smaller and fewer contractile fibers
• No organized sarcomeres

Question 20

Cardiac Muscle

Answer 20

1. contractile cells
2. auto rhythmic (pacemaker) cells

Myocardial muscle cells are branched, have a single nucleus, and are attached to each other by specialized junctions known as intercalated disks (gap junctions).

Question 21

Electrical conduction in myocardial cells

Answer 21

Auto rhythmic (pacemaker) cells spontaneously fire action potentials. Depolarizations of the autorhythmic cells spread rapidly to adjacent contractile cells through gap junctions.

• approx 70bpm
• difference in action potential patterns determine function

Question 22

Electrical Activity of the Heart

Answer 22

• Automaticity
  1. Sinoatrial node (SA node) - “pacemaker”; located in right atrium
  2. AV node & Purkinje fibers - secondary pacemakers; slower rate than the “sinus rhythm”

Question 23

Conduction System of the Heart

Answer 23

1. Action potentials spread via intercalated discs.
2. SA node –> AV node (atrial contraction)
   - ->pause at AV node so that ventricles contract and THEN ventricles contract (so they don’t happen at same time)
3. AV node (base of right atrium) and Bundle of His conduct stimulation to ventricles.
4. In interventricular septum, bundle of His –> right and left bundle branches.
5. Branch bundles –> Purkinje fibers –> ventricular contraction.

Question 24

Sinoatrial (SA) Valve

Answer 24

• Sets the pace of the heartbeat at 70 bpm

- AV node (50 bpm) and Purkinje fibers (25–40 bpm) can act as pacemakers under some conditions

Question 25

Atrioventricular (AV) Valve

Answer 25

- Routes the direction of electrical signals so heart contracts from apex to base (i.e. from bottom --> top) - AV node delay due to slower conduction through nodal cells

Question 26

Excitation-Contraction Coupling of the heart

Answer 26

1. action potential enters from adjacent cell 2. voltage-gated Ca channels open --> Ca enters cell 3. Ca induces Ca release through ryanodine receptor-channels 4. local release causes Ca spark 5. summed Ca sparks create a Ca signal 6. Ca ions bind to troponin to initiate contraction - ->muscle pre-stretch may help this binding 7. relaxation occurs when Ca unbinds from troponin 8. Ca is pumped back into SR for storage 9. Ca is exchanged w/Na by NCX anti porter 10. Na gradient is maintained by Na/K ATPase -->diff from skeletal muscle: some Ca coming in from cytoplasmic space

Question 27

Action Potential: Cardiac Contractile Cell

Answer 27

Phases: 0. Na channels open 1. Na channels close 2. Ca channels open/fast K channels close 3. Ca channels close/slow K channels open - ->repolarization 4. resting potential

Question 28

Why does tetany NOT occur in cardiac muscle?

Answer 28

Skeletal muscle fiber: refractory period is SHORT compared with duration of contraction VERSUS Cardiac muscle fiber: refractory period lasts almost as LONG as the entire muscle twitch.

Question 29

Action Potential: Pacemaker (Autorhythmic) Cells

Answer 29

-->generate their own action potentials (70 times/min = bpm) - Slow, spontaneous depolarization; aka “diastolic depolarization” – between heartbeats, inward I(Na+) triggered by HYPERPOLARIZATION --> determines HR - At −40mV, voltage-gated Ca2+ channels open, triggering action potential and contraction. - Repolarization occurs with the opening of voltage-gated K+ channels.

Question 30

Electrocardiogram (ECG)

Answer 30

- ->picks up movement of ions in body tissues in response to this activity. - Does NOT record action potentials, but results from WAVES OF DEPOLARIZATION - Does NOT record contraction or relaxation, but the ELECTRICAL EVENTS leading to contraction and relaxation

Question 31

Waves of an ECG

Answer 31

P wave: atrial depolarization -->P-Q interval: atrial systole QRS wave: ventricular depolarization -->S-T segment: plateau phase, ventricular systole T wave: ventricular repolarization

Question 32

ECG Waves and Heart Sounds

Answer 32

“Lub” occurs after the QRS wave as the AV valves close “Dub” occurs at the beginning of the T wave as the SL valves close