Cardiovascular System - Detailed Summary
1. Functions of the Cardiovascular System
• The cardiovascular system is a closed system consisting of the heart and blood vessels.
• Main functions:
• Transport oxygen, nutrients, hormones, and waste.
• Maintain blood pressure and circulation.
• Aid in immune function (through WBCs in blood).
2. Anatomy of the Heart
• Location: Thoracic cavity, between the lungs, within the mediastinum.
• Size: About the size of a fist.
• Orientation:
• Apex: Points toward the left hip (bottom).
• Base: Directed toward the right shoulder (top, where large blood vessels attach).
Heart Layers (Inside to Outside)
1. Endocardium – Inner lining of the heart, smooth to prevent clotting.
2. Myocardium – Thick muscular layer responsible for contraction.
3. Epicardium (Visceral Pericardium) – Outer covering of the heart.
• Pericardium: A double-walled sac surrounding the heart.
• Parietal Pericardium: Outer layer.
• Visceral Pericardium: Inner layer (epicardium).
• Pericardial Fluid: Lubricates and reduces friction during heartbeats.
3. Chambers of the Heart
The heart has four chambers:
• Atria (Right & Left): Upper receiving chambers.
• Ventricles (Right & Left): Lower pumping chambers.
• Right Side of the Heart: Pumps deoxygenated blood to the lungs (Pulmonary Circulation).
• Left Side of the Heart: Pumps oxygenated blood to the body (Systemic Circulation).
4. Heart Valves
Valves prevent backflow of blood:
1. Atrioventricular (AV) Valves – Between atria and ventricles:
• Right AV Valve: Tricuspid Valve
• Left AV Valve: Bicuspid (Mitral) Valve
2. Semilunar Valves – Between ventricles and arteries:
• Pulmonary Semilunar Valve: Right ventricle → Pulmonary artery
• Aortic Semilunar Valve: Left ventricle → Aorta
• Chordae Tendineae (“Heart Strings”) anchor AV valves to prevent them from inverting.
5. Blood Flow Through the Heart
1. Deoxygenated Blood Pathway (Blue):
• Superior/Inferior Vena Cava → Right Atrium → Tricuspid Valve → Right Ventricle → Pulmonary Semilunar Valve → Pulmonary Artery → Lungs
2. Oxygenated Blood Pathway (Red):
• Lungs → Pulmonary Veins → Left Atrium → Bicuspid Valve → Left Ventricle → Aortic Semilunar Valve → Aorta → Body
6. Electrical Conduction System (Intrinsic Conduction System)
The heart has automaticity (can contract on its own).
• Sinoatrial (SA) Node (“Pacemaker”) – Sets the heart’s rhythm (~75 bpm).
• Atrioventricular (AV) Node – Delays impulse so atria can contract first.
• AV Bundle (Bundle of His) – Carries signal to ventricles.
• Purkinje Fibers – Cause ventricles to contract.
Disruptions in this system can cause arrhythmias (irregular heartbeats).
7. Cardiac Cycle (Heartbeat)
Each cycle consists of:
1. Atrial Systole – Atria contract, pushing blood into ventricles.
2. Ventricular Systole – Ventricles contract, pumping blood to the lungs/body.
3. Diastole – Heart relaxes and fills with blood.
• Heart Sounds:
• “Lub” – Closing of AV valves during ventricular contraction.
• “Dub” – Closing of semilunar valves during ventricular relaxation.
8. Cardiac Output (CO)
• Definition: The amount of blood pumped by each ventricle per minute.
• Formula:
• CO = Heart Rate (HR) × Stroke Volume (SV)
• Average CO = 5.25 L/min
Factors affecting CO:
• Sympathetic nervous system → Increases HR (exercise, stress)
• Parasympathetic nervous system → Decreases HR (rest, sleep)
• Hormones (epinephrine, thyroxine) → Increase HR
9. Blood Vessels & Circulation
• Arteries: Carry oxygenated blood away from the heart (except pulmonary artery).
• Veins: Carry deoxygenated blood to the heart (except pulmonary vein).
• Capillaries: Tiny vessels for gas/nutrient exchange.
Blood Vessel Structure
1. Tunica Intima – Inner layer, smooth to reduce friction.
2. Tunica Media – Middle layer, made of smooth muscle (controls blood pressure).
3. Tunica Externa – Outer layer for support.
10. Major Circulatory Routes
• Pulmonary Circulation: Right ventricle → Lungs → Left atrium.
• Systemic Circulation: Left ventricle → Body → Right atrium.
Special Circulations:
• Hepatic Portal Circulation: Blood from digestive organs goes through the liver before reaching the heart.
• Fetal Circulation: Blood bypasses the lungs using special shunts (foramen ovale, ductus arteriosus).
11. Blood Pressure & Disorders
• Blood Pressure (BP): The force of blood against vessel walls.
• Normal BP: ~ 120/80 mmHg
• Hypertension (High BP): >140/90 mmHg – Can damage arteries.
• Hypotension (Low BP): <90/60 mmHg – Can cause dizziness or shock.
Factors affecting BP:
• Cardiac Output (CO)
• Blood Volume
• Vessel Resistance (narrower arteries = higher BP)
12. Common Cardiovascular Disorders
• Hypertension (High Blood Pressure): Can lead to stroke, heart attack.
• Atherosclerosis: Hardening of arteries due to plaque buildup.
• Myocardial Infarction (Heart Attack): Blockage in coronary artery cuts off oxygen.
• Arrhythmia: Irregular heartbeats due to conduction system issues no
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