HEART – Detailed Anatomy (Based on Gray’s Anatomy for Students)

Overview

The heart is a muscular, hollow organ located in the mediastinum, between the lungs. Its primary role is to pump blood through the circulatory system, delivering oxygen and nutrients to the body and removing waste products like carbon dioxide.

Position and Orientation

• Located in the middle mediastinum, slightly tilted to the left

• Enclosed within the pericardium (a double-layered sac)

• The apex points downward, forward, and to the left

• The base faces posteriorly toward the vertebral column

External Anatomy

Surfaces of the Heart:

• Anterior (sternocostal) surface – faces the sternum and ribs

• Diaphragmatic surface – rests on the diaphragm

• Left pulmonary surface – faces the left lung

• Right pulmonary surface – faces the right lung

Borders of the Heart:

• Right border – formed by the right atrium

• Inferior border – mostly the right ventricle

• Left border – mainly the left ventricle

• Superior border – formed by both atria and the great vessels

Chambers of the Heart

The heart has four chambers:

1. Right Atrium – receives deoxygenated blood from the superior vena cava, inferior vena cava, and coronary sinus

2. Right Ventricle – pumps blood into the pulmonary trunk → lungs

3. Left Atrium – receives oxygenated blood from the pulmonary veins

4. Left Ventricle – pumps blood into the aorta → systemic circulation

Valves:

• Atrioventricular valves (AV):

• Tricuspid valve (right AV valve)

• Mitral (bicuspid) valve (left AV valve)

• Semilunar valves:

• Pulmonary valve (right ventricle → pulmonary trunk)

• Aortic valve (left ventricle → aorta)

These valves ensure unidirectional blood flow and prevent backflow.

Internal Features

• Right atrium: includes pectinate muscles, fossa ovalis

• Right ventricle: includes trabeculae carneae, papillary muscles, chordae tendineae

• Left atrium: smooth interior, receives four pulmonary veins

• Left ventricle: thick muscular wall, high-pressure chamber

Conducting System

The heart beats rhythmically thanks to its intrinsic conduction system, including:

1. Sinoatrial (SA) node – pacemaker; initiates heartbeat

2. Atrioventricular (AV) node

3. Bundle of His (AV bundle)

4. Right and Left Bundle Branches

5. Purkinje fibers

Blood Supply to the Heart (Coronary Circulation)

• Right Coronary Artery (RCA):

• Supplies right atrium, right ventricle, SA and AV nodes

• Left Coronary Artery (LCA):

• Branches into:

• Anterior interventricular artery (LAD)

• Circumflex artery

• Supplies left atrium, left ventricle, and interventricular septum

Venous drainage: via coronary sinus into the right atrium

Nerve Supply

• Sympathetic fibers (increase heart rate and force)

• Parasympathetic fibers via the vagus nerve (decrease heart rate)

• Cardiac plexus integrates both systems and visceral afferent fibers

Function

• The heart functions as a double pump:

• Right side: sends deoxygenated blood to the lungs

• Left side: sends oxygenated blood to the body

• Works in a coordinated cycle of systole (contraction) and diastole (relaxation)

Clinical Note:

• The left ventricle has the thickest wall because it must generate high pressure to pump blood throughout the body.

• Myocardial infarction (heart attack) occurs when blood flow in coronary arteries is blocked.

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