ANP 1115 - The Heart (Pt. 2)

Question 1

What are the two types of Cell Junctions for Intercalated Discs?

Answer 1

1. Gap Junction: Electric coupling for functional syncytium (heart works as a singular, whole unit)
2. Desmosomes: strong cell-cell adhesion during contraction

Question 2

What is Heart Contraction Stimulated by?

Answer 2

Action Potential - a signal
Muscle Twitch - Response

Question 3

What is the Stimulation of Cardiac Muscle?

Answer 3

Autorhythmicity of ~1% of cardiac muscle cells
- pacemaker cells (specialized cardiac heart cells for spontaneous depolarization)

Question 4

Where does the influx of Ca2 come from?

Answer 4

Influx of Ca2 from ECF (slow channels, a jump-start with 10-20% of Ca2 needed to support contraction)
- Further triggers Ca2 release from SR

Question 5

Why is the Absolute Refractory Period important for Cardiac Muscle?

Answer 5

no possibility of having tetanic contraction
- contracts once ventricles are filled with enough blood

Question 6

What type of respiration does the heart rely on?

Answer 6

Heart relies almost exclusively on aerobic respiration (O2)

Question 7

What does the Absolute Refractory Period almost equal to?

Answer 7

Almost equals to the duration of a muscle twitch
- this allow the heart to fill again

Question 8

What determines heart rate?

Answer 8

Sinus rhythm

Question 9

What are Pacemaker Potentials?

Answer 9

Autorhythmic cells have unstable resting membrane potentials due to:
- “funny” sodium channels that open at negative membrane potentials
- potassium channels that are closing, but slowly drifting toward threshold

Question 10

What do Pacemaker Potentials lead to?

Answer 10

Pacemaker potentials lead to action potentials in autorhythmic cells
- action potentials are due to voltage-gated calcium channels

Question 11

Where does the AP generated by the SA Node pass to?

Answer 11

1. SA node
2. AV node
3. AV bundle (after a short delay)
4. Right & left bundle branches
5. Subendocardial conducting networks (purkinje fibres)

Question 12

What is the Rate of SA node depolarization regulated by?

Answer 12

regulated by the autonomic nervous system:

1. parasympathetic: decreases depolarization rate (threshold reached slower)
2. sympathetic: increases depolarization & depolarization rates of SA node

Question 13

What effects does Tonic Parasympathetic output have?

Answer 13

Under resting conditions, tonic parasympathetic output has a dampening effect on heart rate

Question 14

What is Bradycardia?

Answer 14

Slower than normal HR (<60)

Question 15

What is Tachycardia?

Answer 15

Faster than normal HR (>100)

Question 16

What is Sinus Rhythm?

Answer 16

Heartbeat dictated by SA (60-100 bpm)

Question 17

How does an Electrocardiogram work?

Answer 17

Records electrical changes during heart activity and relies on the conductive activity of body fluids

Question 18

What is the P-Wave?

Answer 18

Atrial depolarization (atria contract)

Question 19

What is the QRS complex?

Answer 19

Ventricular depolarization (ventricle contracts)

Question 20

What is the T-Wave?

Answer 20

Ventricular Repolarization (ventricle relax)

Question 21

Where is Atrial Repolarization?

Answer 21

QRS complex

Question 22

What is Systole?

Answer 22

Contraction of heart
- pumping OUT

Question 23

What is Diastole?

Answer 23

Relaxation of heart
- filling

Question 24

What is the Cardiac Cycle?

Answer 24

1. Atrial Systole + diastole
2. Ventricular Systole + diastole

Question 25

What is the Period of Ventricular Filling?

Answer 25

Mid-to-late diastole - pressure low but P atria > P ventricles - AV valves OPEN - SL valves CLOSED

Question 26

What is the End Diastolic Volume?

Answer 26

After 70% ventricular filling, AV valves begin to close - P wave & atrial systole - Atrial pressure increases & final 30% of blood enters ventricles (EDV)

Question 27

What is Ventricular Systole?

Answer 27

Comprises of QRS complex & T waves - ventricles begin to contract - increased pressure closes AV valves - period of isovolumetric contraction - increased pressure opens SL valves (ventricular ejection phase)

Question 28

What is Isovolumetric Relaxation?

Answer 28

Early Diastole - ventricles relax - pressure decreases rapidly - backflow of aortic / pulmonary blood closes SL valves (diacritic notch)

Question 29

How is ventricular Systole determined?

Answer 29

Ventricular systole = 3/8 of cardiac cycle

Question 30

What is Quiescent Period?

Answer 30

Period in which atria and ventricle in diastole - TOTAL heart relaxation

Question 31

What are the two features Driving Cardiac Cycle?

Answer 31

1. blood flow through heart controlled entirely by pressure changes 2. blood flows from higher to lower pressure through any available opening

Question 32

What are the two Heart Sounds?

Answer 32

1. First heart sound: closure of AV valves; beginning of systole - pressure in left ventricle high enough to close mitral valve 2. Second heart sound: closure of semilunar valves; end of systole - pressure drops low enough so aortic valve close

Question 33

What are the Heart Sounds caused by?

Answer 33

Heart sounds due to vibrations of heart / chest due to valve closure

Question 34

What are Heart Murmurs?

Answer 34

Abnormal heart valves

Question 35

What are Heart Murmurs caused by?

Answer 35

1. Due to valvular stenosis 2. Due to Valvular Insufficiency

Question 36

What is Valvular Stenosis?

Answer 36

High velocity jet of blood through narrow opening - higher pitch of sounds - valves do not open 100% - heart has to work harder

Question 37

What is Valvular Insufficiency?

Answer 37

Leakage of blood back causes sounds when there should be silence - sound of blood leaking back when valve is not closed 100%

Question 38

What is Abnormal Blood Flow?

Answer 38

Pulmonary valve stenosis - Narrowed pulmonary valve opening causes the blood to be turbulent and noisy - heard as a heart murmur on auscultation

Question 39

What is Cardiac Output?

Answer 39

Volume of blood pumped from each ventricle per minute - focus on the left ventricle

Question 40

What is the Average Cardiac Output for resting, healthy male?

Answer 40

5 L/min

Question 41

How is Stroke Volume Calculated?

Answer 41

SV = EDV - ESV EDV = end diastolic volume ESV = end systolic volume

Question 42

What is Stroke Volume?

Answer 42

Volume of blood pushed out with each beat

Question 43

How is Cardiac Output Calculated?

Answer 43

CO = HR * SV CO = Cardiac Output HR = Heart Rate SV = Stroke Volume

Question 44

What is the Influence of Exercise on HR & SV?

Answer 44

CO increases 4-5 times in a fit person CO increases 7 times in a well-trained marathon runner

Question 45

What is Heart Rate determined by?

Answer 45

Determined by rate of spontaneous depolarization of SA node: 1. autonomic fibres inner acting SA node 2. Circulating hormones (eg. epinephrine) 3. Plasma electrolyte concentrations (Ca, Na, K, H) 4. Body Temperature (useful in surgery)

Question 46

What are the Effects of Norepinephrine and Acetylcholine on HR?

Answer 46

NE (symp): increases rate of spontaneous depolarization - heart rate increases ACh (parasymp np): decreases rate of spontaneous depolarization - hyperpolarizes pacemaker cells - heart rate decreases

Question 47

What is the Dominant NS at resting conditions?

Answer 47

Parasympathetic NS is dominant - Vagal Tone: vagus nerve dominant to SA node (slow heart rate; overrides when increase activity of symp or exercise)

Question 48

What is Extreme Tachycardia?

Answer 48

Leads to reduced CO - Blood volume low - injury: fast circulation of blood; hardly any time for ventricles to fill - Reduced Cardiac Output - Smaller Stroke Volume