Ch 17.3 cardiac physiology study guide

Cardiac muscle contains two types of cell junctions, know the purpose of each.

→ Desmosomes: Prevents cells separating during contraction
→ Gap Junctions: Allows for easy ion transport

By what method does cardiac muscle produce its ATP?

→ Aerobic respiration

Can cardiac muscle exhibit tetanus?

no, due to long refractory period

autorhythmicity

→ Cardiac muscle sets its own rhythm (rate of contraction)

What role do pacemaker cells play in the heart?

→ Spontaneously generate action potentials (pacemaker potentials)
Triggers action potentials in contractile cells

pacemaker potential:What 3 ion channels are involved?

→ HCN channels, voltage-gated calcium channels, voltage-gated potassium channels

pacemaker potential:What type of ion channel is responsible for the slow initial depolarization?

HCN channels

pacemaker potential:What causes that channel to open?

→ Hyperpolarization

pacemaker potenital:What is threshold for the conducting cells?

→ –40 mV

pacemaker potential:What ion channel opens for full depolarization? What ion enters/exits?

→ Voltage-gated Ca²⁺ channels open; Ca²⁺ enters

pacemaker potential:What allows these cells to repolarize?

→ Voltage-gated K⁺ channels open

pacemaker potential:What is the minimum potential phase?

→ K⁺ continues to exit, and membrane hyperpolarizes

pacemaker potential:What ion movement allows for the minimum potential phase?

→ K⁺ exits

What is the main pacemaker in the conducting system?

→ Sinoatrial (SA) node

What is the intrinsic rate of depolarization in the SA node?

→ 60–70 bpm on its own

Where is the AV node located?

→ Near tricuspid valve

What is the intrinsic rate of depolarization for the AV node?

→ 40–50 bpm on its own (usually overwritten by SA node)

What is the purpose of the AV node delay?

→ Brief delay in signal (allows atria to contract before ventricles)

Trace the pathway of the conducting system through the heart.

1. SA node (upper right atrium)
2. AV node (near tricuspid valve)
3. AV bundle (inferior interatrial septum and upper interventricular septum)
4. Left and right bundle branches (in interventricular septum)
5. Purkinje fibers (in outer walls of ventricles)

Ap in contractile cells:What ion channel and ion movement causes the depolarization?

→ Voltage-gated Na⁺ channels open; Na⁺ enters

Ap in contractile cells:What ion channel and ion movement causes the initial repolarization?

→ Voltage-gated Na⁺ channels inactivate; selected K⁺ channels open and some K⁺ exits

Ap in contractile cells:What two ions are entering/exiting during the plateau phase?

Ca²⁺ enters, K⁺ exits

Ap in contractile cells:What allows for the final repolarization?

→ Voltage-gated Ca²⁺ channels close; most voltage-gated K⁺ channels open and K⁺ exits

What is the purpose of an EKG?

→ Records the changes in electrical activity in the contractile cells

Know what each of the EKG waves represents.

→ P wave: Atrial depolarization
→ QRS complex: Ventricles depolarizing
→ T wave: Ventricle repolarization

Know what the EKG intervals correspond to

→ R–R interval: Entire duration of cardiac action potential
→ P–R interval: Time it takes for depolarization from SA node to spread through atria to the ventricles
→ Q–T interval: Entire duration of ventricular AP

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What causes the two heart sounds?

1st sound: Closing of AV valves (loudest)
→ 2nd sound: Closing of semilunar valves (more quiet)

What (in general) causes heart failure?

→ Enlargement of the myocardium; heart does not pump efficiently

What symptoms result from left sided heart failure?

→ Blood backs up into lungs
Increased pressure in pulmonary veins causing pulmonary edema (fluid in the lungs)

What symptoms result from right sided heart failure?

→ Edema in extremities, enlarging liver and spleen

cardiac cycle:In which phase do the AV valves open? When do they close?

→ Open during passive ventricular filling (diastole); close during isovolumetric contraction

cardiac cycle:In which phase do the semilunar valves open? When do they close?

→ Open during ventricular ejection; close during isovolumetric relaxation

cardiac cycle:When do we do most of our ventricular filling?

→ Passive ventricular filling

cardiac cycle:What allows the two semilunar valves to open?

→ Pressure in ventricles increases

cardiac cycle:. In which phases does blood volume not change in the ventricles? Why doesn’t it change?

→ Isovolumetric contraction and isovolumetric relaxation — all four valves are closed

How does the sympathetic nervous system increase heart rate?

→ N.Epi released
Causes reduced repolarization of conducting cells
Increases HR
Cardioacceleratory centers

How does the parasympathetic nervous system decrease heart rate?

→ ACh released
Causes hyperpolarization of conducting cells
Decreases HR
Cardioinhibitory centers

when increasing Stroke volume:Does preload increase or decrease?

→ Increase

when increasing Stroke volume:Will afterload increase or decrease?

→ Decrease

when increasing Stroke volume:How will contractility change?

→ Increase

when decrease stroke volume:Does preload increase or decrease

→ Decrease

when decrease stroke volume:Will afterload increase or decrease?

→ Increase

when decrease stroke volume:How will contractility change?

→ Decrease

Understand the relationship between EDV and stroke volume, for example if EDV decreases, how does stroke volume change?

→ Decrease EDV = decrease stroke volume

Also understand the relationship between ESV and stroke volume.

→ Increase ESV = decrease stroke volume
Decrease ESV = increase stroke volume

afterload

→ Pressure ventricles must overcome to open SL valves and eject blood

arrythmia

→ Any variation in the rhythm and sequence in the excitation of the heart

Atrial Fibrillation

→ Atrial — atria beat out of sequence with ventricles
Can lead to formation of blood clots (increase risk of stroke)

Bradycardia

→ Slow HR (<60 bpm)

Cardiac Output

→ Volume of blood pumped per minute
CO = HR × SV

Contractility

→ Force of contraction of the heart

Diastole

→ Relaxation of the heart

Ectopic Pacemaker

→ Other pacemaker cells attempt to pace the heart
Results in irregular rhythms

Ejection Fraction

→ EF = (SV / EDV) × 100

End Diastolic Volume

→ Volume of blood in your ventricles once done with filling
Average is around 120–130 mL

End Systolic Volume

→ Volume of blood after ejection
Average is 50–60 mL

Heart Block

→ Blockages in conducting system

Heart Murmur

→ Abnormal sound heard when listening to heart sounds
Often a defective valve

Preload

→ Amount of stretch in cardiac muscle
Determined by EDV

Sinus Rhythms

→ Electrical rhythms set by the SA node

Stroke Volume

→ Volume of blood pumped per heartbeat
SV = EDV – ESV

Systole

→ Contraction of the heart

Tachycardia

→ High HR (>100 bpm)

Venous Return

→ Volume of blood returning to right atrium from systemic circuit

Ventricular Fibrillation

→ Immediately life-threatening
Electrical activity malfunctions