Cardiovascular Physiology: Heart Structure, Blood Flow, and ECG Analysis

What is the myocardium?

The heart muscle.

Where is the heart located?

In the mediastinum of the thoracic cavity.

What are the four chambers of the heart?

Right atrium, left atrium, right ventricle, left ventricle.

What is the function of hemoglobin?

To carry oxygen (O2) and carbon dioxide (CO2) in the blood.

What are the atrioventricular valves?

Valves located between the atria and ventricles; right valve is tricuspid, left valve is bicuspid (mitral).

What prevents the AV valves from prolapsing?

Papillary muscles contract and pull on the chordae tendinae.

What sound does the closure of the AV valves create?

The 'Lub' sound of the heartbeat.

What happens during diastole?

The heart is at rest, and the atria fill with blood.

What is the first heart sound (S1)?

The 'Lub' sound caused by the closure of the AV valves.

What occurs during ventricular ejection?

Blood is pushed through the pulmonary trunk and aorta as the ventricles contract.

What causes the 'Dup' sound in the heartbeat?

The closure of the semi-lunar valves.

What is isovolumetric ventricular relaxation?

A phase where both semilunar and AV valves are closed, and the volume of blood in the ventricles remains constant.

What is myocardial infarction?

A heart attack caused by plaque buildup in the arteries, leading to decreased blood flow to the myocardium.

What is atherosclerosis?

The buildup of plaque in the arteries, often associated with elevated cholesterol levels.

What are the two types of lipoproteins related to cholesterol?

HDL (High-Density Lipoprotein) and LDL (Low-Density Lipoprotein).

What are the pacemaker cells in the heart?

Cells that set the rate of the heartbeat, primarily located in the sinoatrial (SA) node.

What initiates the action potential in cardiac muscle cells?

The pacemaker cells in the sinoatrial node.

What is the role of calcium ions (Ca2+) in cardiac muscle contraction?

Ca2+ induces contraction by triggering the release of more Ca2+ from the sarcoplasmic reticulum.

What is the function of the chordae tendinae?

To anchor the AV valves and prevent backflow of blood into the atria.

What happens during atrial systole?

The atria contract to complete the filling of the ventricles.

How does blood flow through the heart?

Blood flows from areas of higher pressure to areas of lower pressure.

What is the significance of the cardiac cycle?

It describes the sequence of events in one heartbeat, including contraction and relaxation phases.

What is the role of the sympathetic nervous system in cardiac circulation?

It causes vasoconstriction and increases heart rate through norepinephrine and epinephrine.

What is the function of the Purkinje fibers?

To conduct the depolarization wave to the apex of the heart, initiating ventricular contraction.

What occurs during isovolumic ventricular contraction?

The ventricles contract with all valves closed, increasing pressure without changing blood volume.

What is the role of Na+/Ca2+ antiport in cardiac muscle relaxation?

It helps remove Ca2+ from the cell to facilitate relaxation after contraction.

What initiates action potentials in the heart?

Autorhythmic cells

How do action potentials spread between myocardial cells?

Through gap junctions

What happens when voltage-gated Ca²⁺ channels open?

Ca²⁺ enters the cell, triggering ryanodine receptor channels to release more Ca²⁺ from the sarcoplasmic reticulum.

What is the resting membrane potential of myocardial autorhythmic cells?

-60 mV

What is the significance of the If-channel in autorhythmic cells?

It allows Na⁺ and K⁺ to flow, causing gradual depolarization to threshold.

What occurs during Phase 0 of the action potential in contractile myocardial cells?

Depolarization occurs, and the membrane potential reaches +20 mV.

What characterizes Phase 2 of the action potential?

A plateau phase due to decreased K⁺ permeability and increased Ca²⁺ permeability.

What causes rapid repolarization in myocardial contractile cells?

Closure of Ca²⁺ channels and increased K⁺ permeability.

What neurotransmitter slows heart rate?

Acetylcholine

How do catecholamines affect heart rate?

They increase ion flow through If and Ca²⁺ channels, speeding up pacemaker depolarization.

What is the primary pacemaker of the heart?

Sinoatrial (SA) Node

What does an electrocardiogram (ECG) measure?

The electrical activity of the heart.

What does the P wave represent in an ECG?

Atrial depolarization.

What does the QRS complex represent in an ECG?

Ventricular depolarization.

What does the T wave represent in an ECG?

Ventricular repolarization.

What does the PR segment indicate in an ECG?

Conduction through the AV node and AV bundle.

What is the effect of increased Na⁺ and Ca²⁺ permeability on heart rate?

It speeds up depolarization and increases heart rate.

What is the relationship between flow rate and cross-sectional area?

If flow rate increases, velocity increases; if cross-sectional area increases, velocity decreases.

What is the primary driving force for blood flow?

The pressure gradient (ΔP).

What is the significance of intercalated discs in cardiac muscle cells?

They provide electrical links and strength between cells.

What is the primary source of energy for cardiac muscle cells?

Mitochondria extract about 80% of O₂.

What does a prolonged QRS complex indicate?

Injury to the AV bundle, increasing the duration of ventricular impulse spread.

What are the two heart sounds (HS) and when do they occur?

1st HS during early ventricular contraction (AV valves close); 2nd HS during early ventricular relaxation (semilunar valves close).

What causes heart murmurs?

Turbulent blood flow.

What is Poiseuille's law related to?

The relationship between resistance, tube length, radius, and blood viscosity.

What is the length-tension relationship in cardiac muscle?

Force is proportional to sarcomere length and the number of activated crossbridges.

What is the role of calcium in cardiac muscle contraction?

Extracellular Ca²⁺ initiates contraction and influences the strength of contraction.