The cardiovascular system

The Cardiovascular System

• The heart is a transport system with two pumps
• The right side receives oxygen-poor blood from tissues and pumps it to the lungs to remove CO2 and pick up O2 (pulmonary circuit)
• The left side receives oxygenated blood from the lungs and pumps it to body tissues through the systemic circuit

Heart Anatomy

• The heart has four chambers: two atria and two ventricles
• The atria are thin-walled, receiving chambers
• The ventricles are thick-walled, pumping chambers, with the left ventricle being thicker due to greater pressure
• Valves (tricuspid, mitral/bicuspid, pulmonary, aortic) prevent backflow of blood

Heart Location

• The heart sits in the mediastinum, the central area of the chest.
• More precisely, it's located between the lungs, behind the sternum, and above the diaphragm.

Heart Layers

• Pericardium: Sac-like structure that encloses the heart.
• Myocardium: Thick muscle layer that forms the heart walls.
• Endocardium: Inner layer lining the heart chambers

Receiving Chambers - Atria

• Small, thin-walled chambers
• Left atrium: Receives oxygenated blood from the lungs (4 pulmonary veins)
• Right atrium: Receives deoxygenated blood from the body (Superior vena cava, Inferior vena cava, coronary sinus)

Discharging Chambers - Ventricles

• Thicker walls than atria, the actual pumps of the heart
• Right ventricle: Pumps deoxygenated blood to the lungs
• Left ventricle: Pumps oxygenated blood to the body

Valves

• Prevent backflow of blood
• Atrioventricular (AV) valves: Tricuspid (right side), Mitral/Bicuspid (left side)
• Semilunar valves: Pulmonary (right side), Aortic (left side)

Blood Flow Through Heart

• Blood flows into the right atrium (Superior and Inferior vena cava, Coronary sinus)
• Through tricuspid valve to right ventricle
• To pulmonary semi-lunar valve to pulmonary trunk (pulmonary circulation)
• To lungs to pick up oxygen
• Oxygenated blood returns to the left atrium (pulmonary veins)
• Through mitral/bicuspid valve to left ventricle
• Through aortic semi-lunar valve into the aorta (systemic circulation)
• To the body tissues

Coronary Arteries

• Functional blood supply to the heart muscle itself, delivered when the heart is relaxed
• Left main coronary artery, circumflex, and left anterior descending coronary arteries are crucial supply routes
• Both the left and the right coronary arteries arise from the base of the aorta

Cardiac Muscle

• Cardiac cells tightly encircle heart chambers
• Striated muscle, 1% specialized for electrical excitation (conduction system)

Cardiac vs. Skeletal Muscles

• Cardiac muscle relies almost exclusively on aerobic respiration
• Skeletal muscle can use both aerobic and anaerobic respiration
• Cardiac muscle has more mitochondria, is more adaptable to other fuels

The Conduction System

• Specialized cells that initiate and conduct electrical impulses, rapidly spreading via gap junctions throughout the heart to ensure coordinated contractions.
• Sinoatrial node (SA node): The pacemaker of the heart, initiating impulses.
• Atrioventricular node (AV node): Delays the impulse to allow the atria to empty before ventricles contract
• Bundle of His, bundles branches, and Purkinje fibers conduct the impulse throughout the ventricles

Intrinsic Conduction System

• Non-contractile cells initiate and distribute impulses
• Pacemaker cells generate the heartbeat with an unstable resting potential (continuous depolarization)

The Heartbeat

• Action potentials spread from cell to cell through the heart
• The SA node is the pacemaker: initial depolarization begins, setting the contraction rate
• Atrioventricular node (AV node): delays the impulse, allowing the atria to fully empty to improve blood pumping efficiency

The ECG

• Tool to measure electrical events:
• P wave: Atrial depolarization
• QRS complex: Ventricular depolarization
• T wave: Ventricular repolarization

Sinus Rhythm and Electrocardiography (ECG)

• Sinus rhythm: Normal heart rhythm, initiated by the SA node
• Arrhythmias: Irregular heart rhythms; some examples include fibrillations or ectopic beats
• Defibrillation or pacemakers: Medical devices used to restore regular heart contractions if needed

Anatomical Differences Between Ventricles

• Left ventricle walls are 3 times thicker than the right to generate the greater pressure needed to pump blood throughout the body
• The right ventricle pumps blood to the lungs, requiring less pressure

Phases of Cardiac Cycle

• Series of events during one heartbeat. Four stages: atrial systole, atrial diastole, ventricular systole, ventricular diastole.
• Pressure changes in chambers, driving blood flow

Extrinsic Innervation

• Autonomic Nervous System modifies heart rate and force
• Sympathetic stimulation increases rate/force
• Parasympathetic stimulation slows heart rate through the vagus nerve.

Cardiac Output

• Volume of blood pumped by each ventricle per minute
• Determined by Heart Rate x Stroke Volume.

Stroke Volume

• Volume of blood expelled during each contraction.
• Affected by end-diastolic volume/preload, Starling's Law, and afterload.

Physiotherapy

• Physical activity can help lower blood pressure, strengthen the heart, control weight, increase circulation, and enhance cellular oxygen usage.