Chapter 17: The Cardiovascular System – The Heart (Anatomy & Physiology Study Notes)

Chapter 17: The Cardiovascular System – The Heart

17.1 Location and Basic Structure of the Heart

The heart is a muscular organ that functions as a pump to deliver blood throughout the body. It is a central component of the cardiovascular system, which also includes blood vessels and blood.

• Cardiovascular System: Composed of the heart, blood vessels (arteries, veins, capillaries), and blood. Its primary function is to transport nutrients, gases, hormones, and waste products throughout the body.

• Heart: A muscular organ that acts as two pumps, propelling blood through two separate circuits: the pulmonary and systemic circuits.

Location and Basic Anatomy

• The heart is located in the chest, slightly to the left, within the mediastinum (a subdivision of the thoracic cavity that also contains the trachea, esophagus, and major blood vessels).

• It sits in a subcavity of the mediastinum called the pericardial cavity.

• The heart is cone-shaped, with the apex pointing toward the left hip and the base facing the posterior rib cage.

• It is about the size of a fist (250–350 grams).

• Consists of four chambers: superior right and left atria, and inferior right and left ventricles.

• The atrioventricular sulcus marks the boundary between atria and ventricles; the interventricular sulcus separates the right and left ventricles.

Major Blood Vessels

• Veins bring blood to the heart: the superior and inferior venae cavae deliver blood to the right atrium; pulmonary veins deliver blood to the left atrium.

• Arteries carry blood away from the heart: the right ventricle pumps blood into the pulmonary trunk; the left ventricle pumps blood into the aorta.

• These main veins and arteries are called the great vessels.

17.1 Functions of the Heart

The heart maintains blood circulation through two main circuits: pulmonary and systemic.

• Pulmonary Circuit: The right side of the heart pumps deoxygenated blood to the lungs via the pulmonary arteries. Gas exchange occurs in the lungs, and oxygenated blood returns to the left side of the heart via pulmonary veins. This is a low-pressure circuit.

• Systemic Circuit: The left side of the heart pumps oxygenated blood to the body via the aorta. Gas exchange occurs in systemic capillaries, and deoxygenated blood returns to the right side of the heart via the vena cava. This is a high-pressure circuit.

Other Functions

• Helps maintain blood pressure by regulating the rate and force of contractions.

• Acts as an endocrine organ: the atria produce atrial natriuretic peptide (ANP), a hormone that lowers blood pressure by decreasing sodium and water retention in the kidneys.

17.2 The Pericardium, Heart Wall, and Heart Skeleton

The heart is surrounded by protective layers and connective tissue structures that support its function.

• Pericardium: A double-walled sac surrounding the heart, consisting of:

  • Fibrous Pericardium: Tough, outer layer made of collagen bundles; anchors the heart and limits its expansion.

  • Serous Pericardium: Thin, inner layer that produces serous fluid. The outer part is the parietal pericardium, which folds to become the visceral pericardium (epicardium) adhering to the heart.

• Pericardial Cavity: Space between parietal and visceral layers, filled with pericardial fluid to reduce friction during heart movement.

• Heart Wall:

  • Epicardium: Outer layer (visceral pericardium).

  • Myocardium: Thick, middle layer composed of cardiac muscle cells (myocytes) arranged in a spiral pattern; responsible for contraction.

  • Fibrous Skeleton: Dense irregular connective tissue providing structural support, electrical insulation, and anchorage for cardiac muscle fibers and valves.

  • Endocardium: Inner layer of endothelial cells and connective tissue; forms a barrier regulating electrolyte and chemical concentrations in the myocardium.

Clinical Connections

• Thoracotomy: Surgical opening of the thoracic cavity for access to thoracic organs; involves incisions through the sternum or ribs.

• Cardiac Tamponade: Accumulation of excess fluid in the pericardial cavity, compressing the heart and reducing its ability to fill and pump blood. Treatment involves fluid removal.

• Myocarditis (COVID-19 Connection): Inflammation of the myocardium, often due to viral infection (e.g., SARS-CoV-2), leading to decreased cardiac function.

17.2 The Great Vessels, Chambers, and Valves of the Heart

The Great Vessels

• Superior Vena Cava (SVC): Drains deoxygenated blood from the upper body to the right atrium.

• Inferior Vena Cava (IVC): Drains deoxygenated blood from the lower body to the right atrium.

• Pulmonary Trunk: Receives deoxygenated blood from the right ventricle and splits into right and left pulmonary arteries to the lungs.

• Pulmonary Veins: Four veins (two from each lung) return oxygenated blood to the left atrium.

• Aorta: Largest artery, carries oxygenated blood from the left ventricle to the systemic circuit; begins as the ascending aorta and curves as the aortic arch.

Chambers of the Heart

• Atria: Right atrium (large, thin-walled, anterior) and left atrium (smaller, thicker-walled, posterior). Both have auricles for expansion. The right atrium has pectinate muscles on its anterior wall.

• Interatrial Septum: Separates the atria; contains the fossa ovalis, a remnant of the fetal foramen ovale.

• Ventricles: Right ventricle (wider, thinner walls) pumps to the lungs; left ventricle (thicker walls) pumps to the body. Both have trabeculae carneae (muscular ridges) and papillary muscles attached to chordae tendineae (tendinous cords).

• Interventricular Septum: Separates the ventricles and contracts with them.

Valves of the Heart

• Atrioventricular (AV) Valves: Prevent backflow from ventricles to atria.

  • Tricuspid Valve: Between right atrium and right ventricle (three cusps).

  • Bicuspid (Mitral) Valve: Between left atrium and left ventricle (two cusps).

  • Supported by chordae tendineae and papillary muscles.

• Semilunar (SL) Valves: Prevent backflow from arteries to ventricles.

  • Pulmonary Valve: Between right ventricle and pulmonary trunk.

  • Aortic Valve: Between left ventricle and aorta.

  • No chordae tendineae or papillary muscles.

Valvular Heart Diseases

• Insufficient Valve: Fails to close fully, causing backflow (regurgitation).

• Stenotic Valve: Stiffened by calcium deposits, impeding blood flow.

• Both can cause heart murmurs (audible "swooshing" sounds).

Valve	Location	Number of Cusps	Function
Tricuspid (AV)	Right atrium–right ventricle	3	Prevents backflow to right atrium
Bicuspid/Mitral (AV)	Left atrium–left ventricle	2	Prevents backflow to left atrium
Pulmonary (SL)	Right ventricle–pulmonary trunk	3	Prevents backflow to right ventricle
Aortic (SL)	Left ventricle–aorta	3	Prevents backflow to left ventricle

*Additional info: The above table summarizes the main heart valves, their locations, number of cusps, and primary function.*