The Cardiovascular System

Overview

The cardiovascular system is essential for transporting blood, nutrients, gases, and wastes throughout the body. It consists of the heart and a network of blood vessels, forming two main circuits: the pulmonary and systemic circuits.

• Heart: A muscular pump that maintains blood flow through the vessels.

• Blood Vessels: Tubular structures (arteries, veins, capillaries) that deliver blood to and from tissues.

Pulmonary and Systemic Circuits

Major Divisions

The cardiovascular system is divided into two main circuits, each serving a distinct function:

• Pulmonary Circuit: Carries deoxygenated blood from the right side of the heart to the lungs for gas exchange, then returns oxygenated blood to the left side of the heart.

• Systemic Circuit: Delivers oxygenated blood from the left side of the heart to all body tissues and returns deoxygenated blood to the right side of the heart.

Pulmonary Circuit (Right side)

• Supplied by the right side of the heart.

• Arteries carry blood away from the heart; veins return blood to the heart.

Systemic Circuit (Left side)

• Supplied by the left side of the heart.

• Pumps blood into the aorta, the largest artery.

• After delivering oxygen and nutrients, blood returns via the superior and inferior vena cava.

Heart Anatomy

Position, Size, and Shape

The heart is located in the thoracic cavity, specifically in the mediastinum, and is tilted slightly to the left.

The average adult heart weighs about 300g and is around the size of your fist.

• Base: Broad superior portion with points of attachment for the vessels.

• Apex: Inferior, blunt point; apical impulse can be palpated between the fifth and sixth ribs, just below the left nipple.

  • Where you want to put your stethoscope!

The Pericardium

The heart is enclosed in a double-walled sac called the pericardium:

• Parietal pericardium: Outer layer.

  • Tough, fibrous layer.

• Visceral pericardium (epicardium): Inner layer, directly covering the heart.

The cavity between these (pericardial sac) prevents build up of friction as the heart is continuously pumping.

Pericarditis

• Inflammation of the pericardium, often due to viral infection. It causes the membrane to become roughened making each heartbeat painful.

• Can cause a painful friction rub with each heartbeat. The body fights the infection over time to reduce symptoms.

The Heart Wall

The heart wall consists of three layers:

• Epicardium: Outer layer (visceral pericardium).

  • Covers the surface of the heart. It is thin and translucent like tissue paper.

• Myocardium: Thick, muscular middle layer responsible for contraction.

  • Makes up most of the mass in the heart.

• Endocardium: Smooth inner lining of the heart chambers and valves.

Heart Chambers

Internal Features

There are four heart chambers: two superior atria and two inferior ventricles.

• Interatrial septum: Separates the atria; contains the fossa ovalis (remnant of fetal foramen ovale). These are visible on the heart.

• Interventricular septum: Separates the ventricles.

Atria (ABOVE ventricles)

• Atria: thin-walled, superior chambers.

• Auricles: Appendages that increase atrial volume. They receive blood returning to the heart from large veins

  • right atrium receives blood from three systemic veins

Ventricles

Ventricles are thick-walled, inferior chambers that recieve blood from the atria to bring to arteries.

• Right ventricle forms most of the anterior surface; left ventricle dominates the posterior-inferior surface.

• Internal features: trabeculae carneae (regular ridges), papillary muscles (project into ventricle cavity and anchor to open/close valves), chordae tendineae.

• Right ventricle pumps blood into the pulmonary trunk and left ventricle pumps blood into the aorta.

Heart Valves

General Structure

• Four valves, each consisting of 2-3 flaps (cusps) of thin tissue.

• Allow blood flow only going one way.

  • Problems with valves cause blood to mix = very bad!

Atrioventricular (AV) Valves

• Located between atria and ventricles.

• Right AV valve: Tricuspid valve.

• Left AV valve: Mitral (bicuspid) valve.

• Each cusp is anchored to papillary muscles by chordae tendineae.

• When ventricles contract, papillary muscles tense the cords to prevent valve prolapse.

Semilunar Valves

• Located between ventricles and two of the great vessels.

  • Pulmonary semilunar valve: Between right ventricle and pulmonary trunk.

  • Aortic semilunar valve: Between left ventricle and aorta.

• Each has three cusps.

• When the ventricles contract, the semilunar valves open and press the cusps against the wall as blood pressure rises.

Blood Flow Through the Heart

Pathway

Blood flows in a one-way circuit through the heart, ensuring separation of oxygenated and deoxygenated blood. Blood in the left and right chambers does not mix, maintaining efficient oxygen delivery to tissues.

1. Superior/inferior vena cava

2. Right Atrium and tricuspid valve

3. Right ventricle and pulmonary semilunar valve

4. Pulmonary trunk

5. To the lungs

6. Back to the heart

7. Four pulmonary Veins

8. Left Atrium

9. Mitral Valve

10. Left Ventricle

11. Aortic Semilunar Valve

12. Aorta

Coronary Circulation

Arterial Supply

The heart has its own blood supply, known as coronary circulation.

• Although the heart is less than 0.5% of body weight, it receives about 5% of circulating blood to sustain its workload.

  1. Left coronary artery: Supplies the left atrium and branches.

  2. Right coronary artery: Supplies the right atrium and branches.

Venous Drainage

Venous Drainage: the route blood leaves an organ.

• After passing through capillaries, blood drains into veins. Coronary veins then drain into the coronary sinus which empty directly into the right atrium.

Clinical Considerations

Homeostatic Imbalance

• Angina pectoris: Chest pain due to reduced blood flow to the heart muscle (myocardium).

  • Issue in the tissues, weakened by oxygen deficiency.

• Myocardial infarction (MI): Commonly known as a heart attack; occurs when blood flow is blocked, causing tissue death.

  • Prolonged coronary blockage, killing the cells in the myocardial. Cells are replaced with non-contractile scar tissue causing the heart to not pump properly.

Atherosclerosis

• Arteriosclerosis: General stiffening of arteries with age.

• Atherosclerosis: Begins with vessel damage, leading to accumulation of cholesterol, fat, and connective tissue, forming plaques that block blood flow.

  • Can be treated with bypass surgery, angioplasty, or stents.

  • Involves damaged vessels. Macrophages invade the damage tissue and accumulate cholesterol and fat. Platelets adhere to the plaques and secrete growth factors that stimulate smooth muscle and connective tissue growth. These plaques, however, become a mass of lipids and block blood flow.

Summary Table: Key Structures of the Heart