Cardiovascular System

Overview of the Cardiovascular System

Primary function: transport O₂, nutrients, and hormones to tissues and remove CO₂ and metabolic wastes.

Major components:

  • Pump = heart, generates pressure

  • Pipes = arteries, veins, capillaries

  • Transport medium = blood

Three circulations:

  • Pulmonary circulation: right side → lungs → left side

  • Systemic circulation: left side → body → right side

  • Coronary circulation: blood supply to the heart itself

Anatomy of the Heart

Location: Mediastinum, between the lungs, behind the sternum.

Size: roughly the size of a fist; ~250–350 g in adults.

Layers of the Heart Wall

  • Endocardium — inner lining; smooth endothelial lining helps minimize friction; lines chambers and valves.

  • Myocardium — contractile cardiac muscle; rich in mitochondria; branched cells connected by intercalated discs and gap junctions; thickest layer, especially in the left ventricle.

  • Epicardium — outer layer of the serous membrane; visceral pericardium.

  • Pericardium — protective sac around the heart filled with pericardial fluid; reduces friction and limits overfilling.

Heart Chambers

Chamber

Receives From

Pumps To

Blood Type

Right atrium

Superior vena cava, inferior vena cava, coronary sinus

Right ventricle

Deoxygenated

Right ventricle

Right atrium

Pulmonary trunk → pulmonary arteries → lungs

Deoxygenated

Left atrium

Pulmonary veins

Left ventricle

Oxygenated

Left ventricle

Left atrium

Aorta → systemic circulation

Oxygenated

Key point: The right heart handles deoxygenated blood to the lungs; the left heart handles oxygenated blood to the body.

Blood Flow Through the Heart

  1. Blood enters the right atrium from:

    • Superior vena cava — upper body

    • Inferior vena cava — lower body

    • Coronary sinus — from the heart’s own circulation

  2. Right atrium contracts, pushing blood through the tricuspid valve into the right ventricle.

  3. Right ventricle contracts, forcing blood through the pulmonary semilunar valve into the pulmonary trunk/pulmonary arteries.

  4. Blood travels to the lungs, where gas exchange occurs: CO₂ out, O₂ in.

  5. Blood returns via pulmonary veins to the left atrium.

  6. Left atrium contracts, sending blood through the mitral/bicuspid valve into the left ventricle.

  7. Left ventricle contracts powerfully, ejecting blood through the aortic semilunar valve into the aorta, then to the entire body.

Coronary Circulation

The heart requires its own blood supply.

  • Right and left coronary arteries branch from the ascending aorta.

  • Cardiac veins return blood to the right atrium via the coronary sinus.

Electrical Conduction System

Pathway:
SA node (pacemaker) → AV node (delay) → Bundle of His → right and left bundle branches → Purkinje fibers

  1. Electrical impulse begins as the SA node (pacemaker)

  2. Impulse is conducted to the muscle cells of the atrium, causing contraction

  3. Cells of atrium pass impulse to the AV node

  4. AV node distributes impulse though the Bundle of His and it right and left branches, which further ramifies in Puurkinje fibers, conveying impulses to the ventricular wall and papillary muscles

Cardiac Conduction System - Normal Function of the Heart ...


Electrocardiogram

  • Electrocardiography – non-invasive test for measuring and recording electrical activity of the heart

    • Diagnose cardiac arrhythmias, heart attacks, other heart conditions

    • Electrodes

ECG Wave

Correct Meaning

P wave

Atrial depolarization (contraction)

QRS complex

Ventricular depolarization; atrial repolarization is hidden

T wave

Ventricular repolarization (relaxation

Cardiac Cycle

Cardiac Cycle: period of time that begins with contraction of the atria and ends with ventricular relaxation.

  • Systole: period of contraction heart undergoes when pumping blood.

  • Diastole: period of relaxation as the chambers fill with blood.

Cardiac Output: Amount of blood pumped through the heart per minute.

  • Heart Rate (HR): heart beats per minute.

    • One heartbeat = contraction (systole) + relaxation (diastole).

  • Stroke Volume: amount of blood ejected by the ventricle with each single heartbeat.

    • Normal range = 60 to 100 mL in adults.

Phases:

  • Atrial systole: completes ventricular filling.

  • Ventricular ejection: semilunar valves open; stroke volume ejected.

  • Passive filling: AV valves open; ~80% of ventricular filling occurs passively.

Heart sounds:

  • S₁ “lub”: AV valves closing.

  • S₂ “dub”: semilunar valves closing.

Key terms and equations:

  • Stroke Volume (SV) = EDV − ESV

  • Cardiac Output (CO or Q) = Heart Rate (HR) × Stroke Volume (SV)

  • MAP ≈ DP + 1/3 × (SP − DP)

9. Structure of Blood Vessels

Vessel Type

Function

Features

Arteries

Carry blood away from heart under high pressure

Control blood flow and blood pressure

Tunica intima, THICKER tunica media and tunica externa

Thicker walls than veins

Capillaries

Exchange gases, nutrients, wastes

Microscopic vessels composed of thin layer of endothelium, supported by connective tissue

Venules/Veins

Return blood from capillaries; reservoir (~65% of blood volume)

Tunica intima, THINNER tunica media and tunica externa; thinner walls than arteries

Has valves

Blood Pressure

  • Systolic pressure (SP): pressure during ventricular contraction.

  • Diastolic pressure (DP): pressure during relaxation.

  • Mean arterial pressure (MAP): average pressure pushing blood through arteries.
    MAP ≈ DP + 1/3 × (SP − DP)

Regulation:

  • Short-term: baroreceptors in aorta and carotid arteries detect pressure changes.

  • Long-term: kidney control via blood volume regulation, especially the renin-angiotensin-aldosterone system.