Cardiac Physiology

Question 1

How does heart muscle contract?

Answer 1

Stimulated by nerves and is self-excitable
The entire muscle contracts as a unit
Long (250 ms) absolute refractory period

Question 2

What is the general structure of cardiac muscle tissue?

Answer 2

Intercalated discs connect the cells together to allow contraction as a unit

Question 3

How is cardiac muscle arranged?

Answer 3

Spiral arrangement around the heart chambers, contraction reduces the diameter– apex of ventricles gets pulled up

Question 4

What do the SA and AV nodes provide for the heart?

Answer 4

Rhythmic and automatic beating, initiate action potentials in heart muscles, they have unstable resting potentials called pacemaker potentias

Question 5

What do pacemaker potentials do?

Answer 5

Depolarize slowly

Question 6

What does the SA node do?

Answer 6

Contraction of the atria and stimulates the AV node (in right wall of right atrium)

Question 7

What does the AV node do?

Answer 7

Contraction of the ventricles (in left wall of right atrium)

Question 8

How many impulses does the SA node generate per minute?

Answer 8

70-80 times

Question 9

What does the AV node do in the sequence of excitation

Answer 9

delays the impulse 0.1 seconds to allow atria to contract

Question 10

How long do the atria and ventricles contract for?

Answer 10

Atria (0.1)

Ventricles (0.3)

Question 11

Where are the nodes of the heart?

Answer 11

Both in the right atrium

Question 12

Where do bundle branches carry the impulse?

Answer 12

To the apex

Question 13

Where do the Purkinje fibers carry the impulse to?

Answer 13

To the apex then the ventricular walls

Question 14

What happens when the SA node fails?

Answer 14

AV node takes over at 50 BPM

Question 15

What happens if the AV node is damaged?

Answer 15

Ventricle impulse is blocked, atria keep pumping normally but ventricles contract at 30 bpm via the Purkinjie fibers

Question 16

What does an ectopic focus of the SA node mean?

Answer 16

AV node takes over and makes the RHR 50 BPM, adequate to deliver blood

Question 17

What does an ectopic focus of the AV node mean?

Answer 17

Purkinje fibers have to take over as the pacemaker, only produce RHR 30 BPM, not enough to deliver blood–requires artificial pacemaker

Question 18

What are the steps of the EKG?

Answer 18

P wave
QRS complex
T wave
Atrial repolarization

Question 19

What is the P wave?

Answer 19

Atrial depolarization

Question 20

What is the QRS complex?

Answer 20

Ventricular depolarization

Question 21

What is the T wave?

Answer 21

Ventricular repolarization

Question 22

What is atrial repolarizaiton?

Answer 22

Atrial repolarization (masked by QRS complex)

Question 23

What stimulates the heart?

Answer 23

The cardioacceleratory center of the medulla via the sympathetic system

Question 24

What inhibits the heart?

Answer 24

The cardioinhibitory center of the medulla via the parasympathetic system

Question 25

What is the "lub-dup" sound of the heart?

Answer 25

First sound is AV valves closing, Second sound is the closing of the semilunar valves

Question 26

What is ventricular diastole?

Answer 26

Ventricular filling, first passive (80%) then atrial contraction fills the ventricles

Question 27

What is ventricular systole?

Answer 27

AV valves close, semilunar vales open and ventricles eject blood through them

Question 28

What closes the semilunar valves?

Answer 28

Backflow of blood in aorta and pulmonary trunk

Question 29

What is fibrillation?

Answer 29

Chambers contracting out of sequence

Question 30

What type of fibrillation is more serious?

Answer 30

Ventricular fibrillation

Question 31

How does the SA node signal start the whole contraction of the heart?

Answer 31

SA node stimulates both atria to contract, that signal jumps to the AV node which causes depolarization of the ventricles

Question 32

Why do diastole and systole overlap?

Answer 32

For quick and efficient heart beats

Question 33

What is Cardiac Output?

Answer 33

Amount of blood pumped by each ventricle in one minute, product of HR and stroke volume

Question 34

What is stroke volume?

Answer 34

Amount of blood pumped out by a ventricle with each beat

Question 35

What is the cardiac reserve?

Answer 35

The difference between resting and maximal CO

Question 36

What is EDV?

Answer 36

Amount of blood collected in a ventricle during diastole

Question 37

What is ESV?

Answer 37

Amount of blood remaining in a ventricle after contraction

Question 38

What is the ejection fraction?

Answer 38

SV/EDV, the fraction ejected

Question 39

How is SV calculated?

Answer 39

EDV - ESV

Question 40

What factors affect stroke volume?

Answer 40

Preload Contractility Afterload

Question 41

What is preload?

Answer 41

Amount ventricles are stretched by contained blood

Question 42

What is afterload?

Answer 42

Back pressure exerted by blood in the large arteries leaving the heart

Question 43

What is the Frank-Starling Law of the Heart?

Answer 43

Preload of cardiac muscle before they contract is the critical factor controlling stroke volume

Question 44

How much preload is normal?

Answer 44

130 ml of blood

Question 45

What factors increase contractility?

Answer 45

Hormones Calcium and some drugs Increased stimuli

Question 46

What factors decrease contractility?

Answer 46

Acidosis Increased potassium Calcium channel blockers

Question 47

What is a murmur?

Answer 47

Abnormal heart sound, from turbulent blood flow, most commonly a heart valve malfunction

Question 48

What is a stenotic valve?

Answer 48

Stiffened, does no open completely, and allows backflow

Question 49

What is an incompetent valve?

Answer 49

Scarred or damaged, doesn't close completely, allows backflow

Question 50

What causes valve conditions?

Answer 50

Rheumatic fever

Question 51

How is the sympathetic system activated?

Answer 51

stress, anxiety, excitement, exercise

Question 52

How is the parasympathetic system activated?

Answer 52

acetylcholine, dominates the autonomic stimulation of the heart and slows down heart rate

Question 53

How does the vagus nerve affect the heart?

Answer 53

Release ACh Binds to cholinergic receptors Decreases membrane permeability Slows heart rate and force

Question 54

How do the sympathetic nerves affect the heart?

Answer 54

Release norepinephrine Bind to adrenergic receptors Increases membrane permeability Increases heart rate and force

Question 55

What do beta blockers do?

Answer 55

lower BP

Question 56

What does venous return do?

Answer 56

Increased venous return increases pre-systolic stretching of cardiac muscle

Question 57

What does thyroxine do?

Answer 57

Increases speed and force of heart contractions increases transcription of genes, increases contractile proteins in cardiac muscle

Question 58

What do the carotid and aortic sinuses do?

Answer 58

Measure BP

Question 59

What do the carotid and aortic bodies do?

Answer 59

Monitor pH, pCO2, and pO2