The human heart is both a pump and an electrical generator. It not only propels blood through the body but also generates the signals that coordinate each beat. To understand cardiovascular physiology, it is essential to know the pathway of blood flow through the heart and the electrical conduction system that regulates heartbeat.
Flow of Blood Through the Heart
The heart has four chambers and a series of valves that ensure blood flows in one direction. Blood flow can be divided into two circuits:
Right Side of the Heart → Receives deoxygenated blood and pumps it to the lungs.Right Side: Deoxygenated Blood Pathway
This side of the heart handles oxygen-poor blood returning from the body.
Pathway:
1. Superior and Inferior Vena Cava – bring deoxygenated blood from the body.Key Point: The only artery that carries deoxygenated blood is the pulmonary artery.
Left Side: Oxygenated Blood Pathway
This side of the heart handles oxygen-rich blood from the lungs.
Pathway:
7. Pulmonary Veins – bring oxygenated blood to the heart (the only veins carrying oxygen-rich blood).
8. Left Atrium – receives blood from the pulmonary veins.
9. Bicuspid (Mitral) Valve – separates left atrium from ventricle.
10. Left Ventricle – the strongest chamber; pumps blood to the entire body.
11. Aortic Valve – prevents backflow into the ventricle.
12. Aorta – distributes oxygenated blood to all body tissues.
Key Point: The left ventricle has the thickest walls because it pumps blood under high pressure to the entire systemic circulation.
Vascular System Facts
To avoid confusion between arteries and veins:
Arteries → Carry blood away from the heart. Almost always oxygenated (except pulmonary artery).This simple distinction helps students during exams and professionals in clinical practice.
Electrical Conduction of the Heart
The heartbeat is coordinated by an intrinsic conduction system made up of specialized cardiac muscle cells. These cells generate and transmit electrical impulses, ensuring that the atria contract before the ventricles for efficient pumping.
Pathway of Electrical Conduction
Mnemonic: “Send A Big Bounding Pulse”
1. SA Node (Sinoatrial Node) – Natural pacemaker of the heart located in the right atrium.
- Initiates impulses at 60–100 beats/min.
- Sets the normal sinus rhythm.
2. AV Node (Atrioventricular Node) – Located between atria and ventricles.
- Delays conduction slightly so ventricles can fill before contraction.
Linking Blood Flow and Electrical Conduction
The mechanical pumping of blood depends directly on the electrical signals generated by the conduction system. If electrical conduction fails (e.g., arrhythmias, heart block), blood flow is compromised, leading to poor oxygen delivery and organ failure.
Clinical Importance
Disorders of Blood Flow
- Valve diseases (stenosis or regurgitation) disrupt smooth blood flow.
- Heart failure reduces effective pumping, leading to congestion.
- Shock states alter perfusion despite normal heart anatomy.
Disorders of Conduction
- Arrhythmias (atrial fibrillation, ventricular tachycardia).
- Heart block (failure of conduction between atria and ventricles).
- Pacemaker requirement in severe conduction abnormalities.
Comparison Table: Right vs Left Heart
| Feature | Right Side (Deoxygenated) | Left Side (Oxygenated) |
|---|---|---|
| Blood Source | Body (systemic veins) | Lungs (pulmonary veins) |
| Blood Destination | Lungs (pulmonary artery) | Body (aorta) |
| Oxygen Content | Low (oxygen-poor) | High (oxygen-rich) |
| Chamber Pressure | Low | High |
| Valve | Tricuspid & Pulmonic | Mitral & Aortic |
Frequently Asked Questions (FAQ)
Q1. What is the only artery that carries deoxygenated blood?
The pulmonary artery.
Q2. What is the only vein that carries oxygenated blood?
The pulmonary vein.
Q3. Which chamber of the heart pumps blood to the whole body?
The left ventricle.
Q4. Why does the AV node delay conduction?
To allow the ventricles time to fill before contracting.
Q5. What is the natural pacemaker of the heart?
The sinoatrial (SA) node.
Q6. Which valve prevents backflow from the left ventricle to the atrium?
The bicuspid (mitral) valve.
