Lecture 2 - Cardiovascular YES

What is the main function of the cardiovascular system?

To transport oxygen, nutrients, hormones, and waste throughout the body.

What are the three main components of the cardiovascular system?

Heart, blood vessels, and blood.

Is the cardiovascular system open or closed?

It is a closed-loop system—blood leaving the heart returns to it.

💧 Pressure, Flow, and Resistance

What direction does blood flow in terms of pressure?

From areas of high pressure to low pressure.

What drives blood flow in the cardiovascular system?

A pressure gradient (ΔP).

What happens if there is no pressure gradient?

No blood flow occurs.

What opposes blood flow through vessels?

Resistance (R).

What are the three main factors affecting resistance?

Vessel radius, blood viscosity, and vessel length.

Which factor has the greatest influence on resistance?

Vessel radius (smaller radius = higher resistance).

What is the relationship between flow, pressure, and resistance?

Flow ∝ ΔP / R.

What two factors determine mean arterial pressure (MAP)?

Cardiac output × Peripheral resistance.

If cardiac output or resistance increases, what happens to MAP?

MAP increases.

If cardiac output or resistance decreases, what happens to MAP?

MAP decreases.

⚙️ Systemic Pressure and Energy Loss

Where is blood pressure highest in the circulation?

In the aorta and arteries.

Where is blood pressure lowest?

In the veins and venae cavae.

Why does pressure decrease as blood moves through the system?

Energy is lost due to friction and branching of vessels.

💓 Heart Anatomy and Valves

Where is the heart located?

In the thoracic cavity, slightly to the left.

What type of tissue makes up most of the heart wall?

Myocardium (cardiac muscle).

What is the function of the pericardium?

Protects and anchors the heart.

What is the purpose of heart valves?

To ensure one-way flow of blood.

What are the four main valves of the heart?

Tricuspid, pulmonary, bicuspid (mitral), and aortic valves.

When do AV valves close?

During ventricular contraction to prevent backflow into the atria.

When do semilunar valves close?

During ventricular relaxation to prevent blood from flowing backward.

What prevents the heart valves from overstretching?

The fibrous skeleton of the heart.

💪 Cardiac vs. Skeletal Muscle

How do cardiac muscle cells differ from skeletal muscle cells?

They are smaller, have one nucleus, and connect via intercalated discs.

What are intercalated discs?

Special junctions that electrically and mechanically connect cardiac cells.

What are desmosomes?

Structures that transfer force between cells.

What are gap junctions?

Channels that allow ions to flow between cardiac cells for electrical conduction.

How much of the cardiac cell volume is mitochondria?

About one-third.

Why are T-tubules larger and branched in cardiac muscle?

To allow faster and more coordinated depolarization.

⚡ Excitation–Contraction Coupling in Cardiac Muscle

What initiates contraction in cardiac muscle?

An action potential from an adjacent cell.

What happens when voltage-gated Ca²⁺ channels open?

Calcium enters from the extracellular fluid.

What does Ca²⁺ entry trigger?

Additional Ca²⁺ release from the sarcoplasmic reticulum via ryanodine receptors (RyR).

What are Ca²⁺ sparks?

Localized releases of calcium that combine to form a full Ca²⁺ signal.

What does calcium bind to for contraction to occur?

Troponin, which allows actin-myosin crossbridge formation.

How does relaxation occur?

Ca²⁺ unbinds from troponin and is pumped back into the SR or exchanged with Na⁺ via NCX.

What maintains Na⁺ and K⁺ gradients in cardiac cells?

The Na⁺/K⁺-ATPase pump.

💥 Cardiac Muscle Contraction Characteristics

What is meant by “graded contractions” in the heart?

The strength of contraction varies with the amount of Ca²⁺ available.

What effect does sarcomere length have on force of contraction?

A longer sarcomere (within limits) produces a stronger contraction.

Why can’t cardiac muscle be tetanized like skeletal muscle?

It has a long refractory period that lasts almost as long as the muscle twitch.

⚡ Action Potential in Contractile Cells

What causes the depolarization phase (phase 0)?

Na⁺ channels open and Na⁺ rushes in.

What happens in phase 1 of the cardiac action potential?

Na⁺ channels close.

What happens in phase 2 (plateau phase)?

Ca²⁺ channels open and fast K⁺ channels close, maintaining depolarization.

What happens in phase 3?

Ca²⁺ channels close and slow K⁺ channels open, causing repolarization.

What is the resting membrane potential in phase 4?

Around –90 mV.

Why does cardiac muscle have a plateau phase?

To ensure full contraction and prevent premature re-excitation.

🧠 Cardiac Autorhythmic (Pacemaker) Cells

How do pacemaker cells differ from contractile cells?

They spontaneously depolarize without external stimulus.

What ion channels cause pacemaker potentials?

If channels that allow both Na⁺ and K⁺ flow.

What causes the pacemaker potential to reach threshold?

Gradual depolarization due to Na⁺ influx exceeding K⁺ efflux.

What ion causes depolarization in pacemaker cells?

Ca²⁺ influx (not Na⁺).

What ion causes repolarization in pacemaker cells?

K⁺ efflux.

Do pacemaker cells ever have a resting potential?

No, their membrane potential constantly drifts toward threshold.

🫀 Electrical Conduction System of the Heart

What is the SA node and its role?

It is the sinoatrial node, the primary pacemaker (~70 bpm).

How does the signal reach the AV node?

Via internodal pathways in the atria.

Why is there a delay at the AV node?

To allow atria to contract before the ventricles.

Where does the signal go after the AV node?

Down the bundle of His → right/left bundle branches → Purkinje fibers.

What direction does depolarization spread in the ventricles?

From the apex upward.

What are the backup pacemakers if the SA node fails?

AV node (~50 bpm) and Purkinje fibers (~25–40 bpm).

📈 Electrocardiogram (ECG) Waves

What does the P wave represent?

Atrial depolarization.

What does the QRS complex represent?

Ventricular depolarization (and hidden atrial repolarization).

What does the T wave represent?

Ventricular repolarization.

What electrical event corresponds to atrial contraction?

P wave.

What electrical event corresponds to ventricular contraction?

QRS complex.

🔄 The Cardiac Cycle

What are the three main phases of the cardiac cycle?

Atrial systole, ventricular systole, and diastole.

What happens during atrial systole?

Atria contract, pushing the last bit of blood into ventricles.

What happens during ventricular systole?

Ventricles contract, AV valves close, and blood is ejected.

What happens during diastole?

All chambers relax, semilunar valves close, and ventricles fill.

What causes the “lub” heart sound?

Closing of the AV valves.

What causes the “dub” heart sound?

Closing of the semilunar valves.

💧 Stroke Volume and Cardiac Output

What is stroke volume (SV)?

The amount of blood pumped by one ventricle per beat.

How is stroke volume calculated?

EDV – ESV = Stroke Volume.

What is cardiac output (CO)?

The volume of blood pumped per minute.

How is cardiac output calculated?

CO = HR × SV.

What is the average cardiac output at rest?

About 5 L/min.

What does the Frank–Starling law state?

The heart pumps all the blood that returns to it (↑ EDV → ↑ SV).

💪 Factors Affecting Stroke Volume

What three factors influence stroke volume?

Preload, contractility, and afterload.

What is preload?

The degree of ventricular stretch before contraction (related to venous return).

What increases venous return?

Skeletal muscle pump, respiratory pump, and sympathetic stimulation.

What is contractility?

The intrinsic ability of the heart to contract independent of preload.

What is afterload?

The resistance the ventricle must overcome to eject blood.

⚡ Inotropic Effects

What is an inotropic effect?

A change in the strength of contraction without changing muscle length.

What causes a positive inotropic effect?

Norepinephrine or epinephrine increasing Ca²⁺ entry into cardiac cells.

What causes a negative inotropic effect?

Low oxygen or drugs that block Ca²⁺ entry.

🩺 Summary Review

What determines blood flow?

Pressure gradient and vascular resistance.

What determines MAP?

Cardiac output × Peripheral resistance.