Anatomy of heart

Cardiovascular System I: Heart

Introduction to Heart Anatomy

The heart is a muscular organ essential for pumping blood throughout the body. Its structure, location, and associated vessels are foundational topics in anatomy and physiology, providing the basis for understanding cardiovascular function and disease.

Location and Orientation of the Human Heart

Mediastinum and Position

• Mediastinum: The heart is located in the mediastinum, a central compartment of the thoracic cavity between the lungs.

• Boundaries: Extends from just slightly above the sternum to the diaphragm, and from the vertebral column to the sternum.

• Size: Roughly the size of an adult's clenched fist.

• Orientation: The heart is oriented obliquely, with the base directed toward the right shoulder and the apex pointing toward the left hip.

• Surface Landmarks: The apex is located at the fifth intercostal space, just medial to the midclavicular line (the point of maximal impulse, PMI).

Example: During a physical examination, the PMI is palpated to assess heart function.

Thoracic Cavity and Ribs

• True Ribs: The first seven pairs of ribs, directly attached to the sternum via costal cartilage.

• False Ribs: Ribs 8-10, attached indirectly to the sternum.

• Floating Ribs: Ribs 11-12, not attached to the sternum.

• Relation to Heart: The heart lies deep to the sternum and ribs, protected by the rib cage.

Gross Anatomy of the Heart

External Features

• Base: The broad, superior portion of the heart where major vessels enter and exit.

• Apex: The pointed, inferior tip of the heart.

• Surfaces: The heart has anterior, inferior (diaphragmatic), and left surfaces.

• Grooves (Sulci): Coronary sulcus (encircles the heart, marking the boundary between atria and ventricles), anterior and posterior interventricular sulci (mark the position of the interventricular septum).

Chambers of the Heart

• Atria: The two superior chambers (right and left atrium) that receive blood returning to the heart.

• Ventricles: The two inferior chambers (right and left ventricle) that pump blood out of the heart.

• Septum: The interatrial septum separates the atria; the interventricular septum separates the ventricles.

Associated Great Vessels

• Superior and Inferior Vena Cava: Return deoxygenated blood from the body to the right atrium.

• Pulmonary Trunk and Arteries: Carry deoxygenated blood from the right ventricle to the lungs.

• Pulmonary Veins: Return oxygenated blood from the lungs to the left atrium.

• Aorta: Distributes oxygenated blood from the left ventricle to the systemic circulation.

Layers of the Heart Wall and Pericardium

Pericardium

• Fibrous Pericardium: The tough, outermost layer that protects and anchors the heart.

• Serous Pericardium: A double-layered membrane consisting of the parietal layer (lines the fibrous pericardium) and the visceral layer (epicardium, adheres to the heart surface).

• Pericardial Cavity: The space between the parietal and visceral layers, filled with serous fluid to reduce friction during heartbeats.

Heart Wall Layers

• Epicardium: The outermost layer, also known as the visceral pericardium.

• Myocardium: The thick, muscular middle layer responsible for contraction and pumping action.

• Endocardium: The innermost layer, lining the heart chambers and covering the valves.

Cardiac Skeleton (Annulus Fibrosus Cordis)

Structure and Function

• Definition: A dense network of connective tissue (collagen and elastic fibers) forming rings around the heart valves.

• Functions:

  • Provides structural support for the heart valves.

  • Prevents overstretching of the valves.

  • Acts as an electrical insulator between the atria and ventricles.

Valves of the Heart

Types and Locations

• Atrioventricular (AV) Valves:

  • Tricuspid Valve: Between right atrium and right ventricle.

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

• Semilunar Valves:

  • Pulmonary Valve: Between right ventricle and pulmonary trunk.

  • Aortic Valve: Between left ventricle and aorta.

Function: Valves ensure unidirectional blood flow through the heart, preventing backflow.

Valve Operation During Cardiac Cycle

• AV valves open during ventricular relaxation (diastole) and close during ventricular contraction (systole).

• Semilunar valves open during ventricular contraction and close during relaxation.

Coronary Circulation

Coronary Arteries

• Right Coronary Artery (RCA): Supplies right atrium, right ventricle, and parts of the conduction system.

• Left Coronary Artery (LCA): Divides into the anterior interventricular artery (left anterior descending, LAD) and circumflex artery, supplying the left atrium, left ventricle, and interventricular septum.

Coronary Veins

• Great Cardiac Vein: Drains blood from the anterior heart into the coronary sinus.

• Middle Cardiac Vein: Drains the posterior heart.

• Small Cardiac Vein: Drains the right atrium and ventricle.

• Coronary Sinus: Main vein collecting deoxygenated blood from the myocardium and returning it to the right atrium.

Clinical Correlation: Myocardial Infarction (Heart Attack)

Pathophysiology

• Myocardial Infarction (MI): Occurs when blood flow through a coronary artery is blocked, leading to ischemia and death of heart muscle tissue.

• Common Causes: Atherosclerosis (plaque buildup), thrombosis (blood clot).

• Symptoms: Chest pain, shortness of breath, referred pain to the left arm or jaw.

• Diagnosis: Electrocardiogram (ECG) changes, elevated cardiac enzymes.

Example: An ST-segment elevation on ECG is a classic sign of acute MI.

Summary Table: Heart Chambers, Valves, and Associated Vessels

Chamber	Valve	Vessel (In/Out)	Blood Flow Direction
Right Atrium	Tricuspid (to ventricle)	Superior/Inferior Vena Cava (in)	To Right Ventricle
Right Ventricle	Pulmonary Semilunar	Pulmonary Trunk (out)	To Lungs
Left Atrium	Bicuspid (Mitral)	Pulmonary Veins (in)	To Left Ventricle
Left Ventricle	Aortic Semilunar	Aorta (out)	To Body

Additional info: The notes above expand on the provided images and fragmented text, supplying standard anatomical definitions, clinical context, and a summary table for clarity and completeness.