Heart Anatomy and Dimensions

Heart Dimensions

• The heart is approximately 12 centimeters long.
• It is about 9 centimeters wide.
• The heart is around 6 centimeters thick.
• Two-thirds of the heart's mass is positioned to the left of the body's midline.
• The heart weighs approximately 250 grams.

Heart Location

• The heart resides within the mediastinum, a region within the thoracic cavity.
• The mediastinum is the space between the lungs, extending from the sternum to the vertebral column.
• The mediastinum does not include the clavicle (collarbone).
• The mediastinum is bordered by the diaphragm, sternum, and vertebral column.

Heart Anatomical Position

• The sternum and 3rd to 6th costal cartilages lie directly anterior to the heart.
• The heart's upper boundary reaches the 3rd costal cartilage at the right sternal edge and the 2nd intercostal space at the left sternal edge.
• The right margin of the heart extends from the 3rd right costal cartilage to the 6th right costal cartilage.
• The body of the sternum and 3rd to 6th costal cartilages cover the heart when viewed anteriorly.
• The right boundary of the heart primarily lies between the 3rd and 6th right costal cartilages.
• The upper limit of the heart at the left sternal edge corresponds to the 2nd intercostal space.
• The upper boundary of the heart is at the level of the 3rd costal cartilage on the right and 2nd intercostal space on the left.

Heart Anatomical Landmarks

• The inferior margin of the heart extends from the sternal end of the right 6th costal cartilage to the apex.
• The apex of the heart is located at the 5th intercostal space along the midclavicular line. This is also where you can palpate the heartbeat.
• The left boundary of the heart extends from the 2nd intercostal space to the apex.
• The heart's apex is situated at the 5th intercostal space at the midclavicular line.
• The inferior margin of the heart begins at the sternal end of the 6th costal cartilage.
• The left margin of the heart extends from the 2nd intercostal space to the apex.

Heart Surface Anatomy

• The anterior (sternocostal) surface faces the sternum and ribs, primarily consisting of the right atrium and right ventricle.
• The inferior (diaphragmatic) surface rests on the diaphragm, primarily containing the right and left ventricles.
• The posterior surface faces the back, mainly composed of the left atrium.
• The left ventricle forms the majority of the left lateral surface, while the right ventricle forms the majority of the right lateral surface.

Heart Borders and Key Features

• The right ventricle forms the inferior border of the heart.
• The left ventricle and a portion of the left atrium constitute the left border of the heart.
• The right atrium makes up the right border of the heart.
• The left ventricle forms the apex of the heart.
• The apex of the heart is located in the 5th intercostal space in the midclavicular line.
• The base of the heart is formed by the atria, primarily the left atrium, located at the uppermost part of the heart.
• The base of the heart faces posteriorly.
• The left ventricle contributes to the apex, resting on the diaphragm.

The Pericardium

• The pericardium is a double-layered membrane that surrounds and protects the heart.
• The pericardium holds the heart in place within the chest cavity.
• The pericardium provides a frictionless environment for the heart, preventing damage or stress during movement.
• The pericardium protects the heart from infections and overexpansion.
• It allows the heart to expand and contract freely during its pumping action.
• The pericardium is a barrier that protects the heart from external damage and overexpansion.
• If the frictionless movement of the heart within the pericardium is impaired, it can lead to damage and inflammation of the heart tissues.

Pericardium Structure and Functions

• The pericardium is a double-layered sac that encloses the heart, providing protection and support.
• It is composed of two main parts: the fibrous pericardium and the serous pericardium.

Fibrous Pericardium

• The fibrous pericardium is the outermost layer of the pericardium, a tough and inelastic connective tissue layer.
• It is fused to the diaphragm inferiorly and the great vessels (aorta and pulmonary trunk) superiorly.
• Anchoring the heart to the mediastinum and preventing overstretching are its primary roles.

Serous Pericardium

• The serous pericardium is a thin, double-layered membrane that lies deep to the fibrous pericardium.
• It's composed of two layers: the parietal layer and the visceral layer.

Parietal Layer

• The parietal layer is the outer layer of the serous pericardium.
• It is fused to the fibrous part of the pericardium.

Visceral Layer

• The visceral layer, also known as the epicardium, is the inner layer of the serous pericardium.
• It adheres directly to the surface of the heart.

Pericardial Cavity

• The space between the parietal and visceral layers of the serous pericardium is called the pericardial cavity.
• This cavity is filled with a thin layer of pericardial fluid.
• Pericardial fluid reduces friction during heartbeats, allowing the heart to move smoothly within the pericardial sac.

Pericardial Fluid

• Pericardial fluid is found between the visceral and parietal layers of the serous pericardium, which surrounds the heart.
• Acts as a lubricant, reducing friction during heart movements to allow the heart to beat efficiently.
• Typically, 15-50 mL of fluid is present in the pericardial sac.

Pericarditis

• Inflammation of the pericardium.
• Can cause chest pain, which may radiate to the left arm or shoulder.
• A pericardial friction rub, a distinctive scratchy sound, is often present and can be heard with a stethoscope in approximately 40% of patients.
• Typically, an ST segment elevation is observed on an electrocardiogram (ECG).
• The cause of the pericardial friction rub is the inflamed layers of the pericardium rubbing against each other.

Heart Wall Layers

• Epicardium: Outermost layer of the heart wall, also known as the visceral layer of the serous pericardium. It's composed of epithelial tissue and connective tissue, and contains adipose (fat) tissue and blood vessels supporting the myocardium.
• Myocardium: Middle, thickest layer of the heart wall, primarily responsible for contractions. Composed of cardiac striated muscle tissue. Its powerful, rhythmic contractions are enabled by the striated muscle fibers within the myocardium.
• Endocardium: Innermost layer of the heart wall, composed of a thin, smooth layer of endothelium overlying connective tissue. Provides a smooth lining for the heart chambers and valves, aiding in blood flow.

The Heart: Chambers and Surface Features

• The heart has four chambers: two atria (superior) and two ventricles (inferior).
• Atria are the receiving chambers for blood returning to the heart.
• The two atria are separated by the interatrial septum.
• The atria are further enhanced by small extensions called auricles that increase the capacity of each atrium.
• The ventricles are the pumping chambers of the heart.
• The ventricles are separated by the interventricular septum.
• The right ventricle pumps deoxygenated blood to the lungs while the left ventricle pumps oxygenated blood to the rest of the body.
• The coronary sulcus marks the division between the atria and ventricles on the surface of the heart.
• The sulci (grooves) are also important for identifying the boundaries between the left and right ventricles,
  • The anterior interventricular sulcus is in the front of the heart, and the posterior interventricular sulcus is on the back of the heart.
• The coronary arteries run along these sulci.

Right Atrium Structure & Function

• Anterior wall: Contains pectinate muscles giving it a rough appearance.
• Interatrial septum: Separates the right and left atria.
• Fossa ovalis: A depression in the interatrial septum, remnants of the foramen ovale in fetal circulation.
• Blood flow: Receives deoxygenated blood from the body through the superior vena cava (upper body), inferior vena cava (lower body), & coronary sinus (heart's myocardium).
• Tricuspid valve: Controls one-way blood flow from the right atrium to the right ventricle, has three cusps.
• Main function: Receives deoxygenated blood from the body and pumps it to the right ventricle to be sent to the lungs for oxygenation.

Right Atrium Additional Structures

• Auricles: Pouch-like extensions that increase the right atrium's capacity.
• Pectinate muscles: Increase the atrial wall's surface area and assist in contraction.
• Superior vena cava: Enters the right atrium from the superior (top) direction.
• Inferior vena cava: Carries deoxygenated blood from the lower body.
• Coronary sinus: Opens into the right atrium near the inferior vena cava.

Right Ventricle Structure and Function

• The right ventricle is responsible for pumping deoxygenated blood to the lungs for oxygenation.
• The right ventricle's inner surface is characterized by raised bundles of cardiac muscle fibers called trabeculae carneae, which strengthen the ventricular wall and aid in efficient contraction.
• Tricuspid Valve: Prevents backflow of blood from the right ventricle into the right atrium during ventricular contraction.
  • The leaflets of the tricuspid valve are connected to the papillary muscles by thin, tendon-like cords called chordae tendineae.
  • The papillary muscles contract to maintain tension on the chordae tendineae, ensuring the valve remains closed during ventricular contraction.
• Pulmonary Valve: Located at the exit of the right ventricle, it prevents backflow of blood from the pulmonary trunk into the right ventricle.
• Interventricular Septum: A thick wall of cardiac muscle that separates the right ventricle from the left ventricle, preventing the mixing of oxygenated and deoxygenated blood.

Right Ventricle Blood Flow

• Blood enters the right ventricle from the right atrium through the tricuspid valve.
• The right ventricle contracts, forcing blood through the pulmonary valve and into the pulmonary trunk.
• The pulmonary trunk branches into the right and left pulmonary arteries, carrying deoxygenated blood to the lungs.

The Left Atrium: Receiving Oxygenated Blood

• The left atrium receives oxygenated blood from the lungs via four pulmonary veins.
• It is located on the left side of the heart and forms most of the heart's posterior surface.
• The left atrium is typically larger than the right atrium.
• Blood passes from the left atrium to the left ventricle through the mitral valve.
• The mitral valve (bicuspid valve) has two cusps and prevents backflow of blood into the left atrium during ventricular contraction.
• The left atrium's main function is to receive oxygen-rich blood and pass it to the left ventricle, playing a crucial role in systemic circulation.
• The left ventricle then pumps the oxygenated blood to the rest of the body.
• Blood enters the left atrium during atrial contraction (systole), ensuring efficient blood movement towards the left ventricle.
• Dysfunction of the left atrium can lead to ineffective flow of oxygen-rich blood into the left ventricle, disrupting the circulatory system.

Importance of Left Atrial Function

• The left atrium acts as a temporary storage chamber for oxygenated blood before it is pumped out to the body.
• A properly functioning left atrium maximizes the efficiency of the heart's pumping action, allowing for adequate blood circulation.

Left Ventricle Structures and Function

• Trabeculae carneae are muscular ridges that strengthen the ventricular wall, aiding in contraction.
• The chordae tendineae are fibrous cords that attach to the cusps of the mitral valve preventing prolapse (backward flow) during contraction.
• Papillary muscles are muscular projections that anchor the chordae tendineae, ensuring proper valve closure during ventricular contraction.
• The aortic valve is responsible for allowing blood to exit the left ventricle into the aorta, the main artery supplying blood to the body.
• Coronary arteries branch from the aorta, supplying oxygenated blood to the heart muscle itself which is essential for its function.
• The left ventricle possesses a thicker muscular wall compared to the right ventricle, enabling high pressure necessary for pumping blood throughout the entire body.
• The descending aorta, extending from the aortic arch, carries oxygenated blood to the lower body.
• The mitral valve, positioned between the left atrium and left ventricle, plays a crucial role in preventing blood backflow into the left atrium.
• The left ventricle pumps oxygenated blood into the aorta, initiating systemic circulation, the delivery of oxygenated blood to the body.

Myocardial Thickness and Heart Chamber Function

• The atria have thin myocardial walls (2-3 mm) because they only need to pump blood into the ventricles, which requires minimal pressure.
• The left ventricle has the thickest myocardium (10-15 mm) since it pumps oxygenated blood throughout the entire body, requiring significantly higher pressure to overcome systemic arterial resistance.
• The right ventricle has a thinner myocardium (4-5 mm) than the left ventricle because it only pumps deoxygenated blood to the lungs, a shorter distance compared to the systemic circulation.
• The thicker the myocardial wall, the higher the pressure required to pump blood over a longer distance.
• The thickness of the myocardium directly reflects the functional demands of each heart chamber, demonstrating a correlation between wall thickness and pumping pressure.

Fibrous Skeleton of the Heart

• Composed of dense connective tissue
• Provides structural support for the heart valves
• Serves as an attachment point for myocardial muscle bundles
• Acts as an electrical insulator between the atria and ventricles
• This insulation ensures the atria contract before the ventricles

Structure of the Fibrous Skeleton

• Consists of four fibrous rings surrounding the heart's valves
• These rings fuse together, forming triangular areas called fibrous trigones
• The fibrous trigones reinforce the heart's framework
• The fibrous skeleton is continuous with the connective tissue of the heart's chambers, ensuring structural integrity

Function of the Fibrous Skeleton

• Valve Function: Prevents valves from collapsing, ensuring proper blood flow
• Structural Foundation: Provides a stable frame for the heart chambers and valves, preventing excessive stretching and distortion
• Electrical Insulation: Prevents the direct transmission of electrical signals between the atria and ventricles, allowing for coordinated contraction

Atrioventricular Valves

• The Tricuspid valve is located on the right side of the heart between the right atrium and right ventricle.
• The Mitral (Bicuspid) valve is located on the left side of the heart between the left atrium and left ventricle.
• Atrioventricular (AV) valves open during atrial contraction allowing blood to flow from atria into ventricles.
• Chordae tendineae are fibrous cords that anchor AV valve cusps to papillary muscles within the ventricles.
• Chordae tendineae stay slack during ventricular relaxation, allowing AV valve cusps to open.
• Chordae tendineae tighten during ventricular contraction to prevent AV valve cusps from inverting into atria.
• The Tricuspid valve has three cusps.
• The Mitral (Bicuspid) valve has two cusps.
• AV valves close during ventricular contraction, preventing backflow of blood into atria.
• AV valve mechanism allows one-way blood flow from atria to ventricles.

Semilunar Valves

• Semilunar valves are located in the heart and prevent backflow of blood from arteries back into the ventricles. This helps ensure unidirectional blood flow.
• There are two semilunar valves in the heart: the pulmonary valve and the aortic valve.
• The pulmonary valve sits between the right ventricle and the pulmonary trunk.
• The aortic valve sits between the left ventricle and the aorta.
• Semilunar valves possess three cusps, resembling half-moon shapes.
• During ventricular contraction, the pressure in the ventricles exceeds the pressure in the arteries, causing the semilunar valves to open, allowing blood to flow into the arteries.
• When the ventricles relax and pressure in the ventricles drops, the pressure in the arteries becomes greater, causing blood to flow back towards the heart. This backflow of blood fills the cusps of the semilunar valves, which then close.
• The closure of semilunar valves generates the "dub" sound of the heart, which is a characteristic part of the heart's sounds.
• Unlike the atrioventricular valves, the semilunar valves do not have chordae tendineae or papillary muscles. This is because the semilunar valves are located at the exit of the ventricles, while atrioventricular valves are located between the atria and the ventricles.
• The semilunar valves are crucial components of the heart that regulate blood flow, ensuring efficient pumping and distribution of blood throughout the body.

Great Vessels of the Heart

• Superior vena cava and inferior vena cava return deoxygenated blood to the right atrium. The superior vena cava collects blood from the upper body, and the inferior vena cava collects blood from the lower body.
• Pulmonary arteries carry deoxygenated blood from the right ventricle to the lungs. They are the only arteries in the body that carry deoxygenated blood.
• Pulmonary veins carry oxygenated blood from the lungs to the left atrium. They are the only veins in the body that carry oxygenated blood.
• Aorta is the largest artery in the body. It carries oxygenated blood from the left ventricle to the rest of the body. The aorta branches into smaller arteries that supply blood to each region of the body, including the ascending aorta, aortic arch, and descending aorta.

Key Points

• Deoxygenated blood is blood that has released oxygen into the body's tissues.
• Oxygenated blood is blood that carries oxygen from the lungs to the body's cells.
• The right atrium is the upper chamber of the right side of the heart.
• The right ventricle is the lower chamber of the right side of the heart.
• The left atrium is the upper chamber of the left side of the heart.
• The left ventricle is the lower chamber of the left side of the heart.
• The systemic circulation is the circulation of blood throughout the body.

Great Vessels of the Heart

• Pulmonary Veins: Carry oxygenated blood from the lungs to the left atrium of the heart.
• Inferior Vena Cava: Carries deoxygenated blood from the lower part of the body to the right atrium of the heart.
• Aorta: The largest artery in the body, carries oxygenated blood from the left ventricle to the systemic circulation.
• Pulmonary Artery: Unlike most arteries, it carries deoxygenated blood from the right ventricle to the lungs.
• Superior Vena Cava: Empties deoxygenated blood from the head and upper body into the right atrium.
• Four pulmonary veins enter the left atrium.
• Aortic Arch: Branches off the ascending aorta and distributes oxygenated blood to the head and upper body.
• Pulmonary Artery: Carries deoxygenated blood from the right ventricle to the lungs.
• Aorta: Carries oxygenated blood away from the left ventricle of the heart.
• Aorta Structure: Consists of three main parts: an ascending aorta, an aortic arch, and a descending aorta.

Coronary Arteries

• The left coronary artery originates from the left coronary ostia and travels near the left auricle before branching.
• The Left Anterior Descending (LAD) artery supplies both ventricles and the interventricular septum.
• The LAD artery has branches like the diagonal and septal branches, and is crucial for supplying the left ventricle, which pumps oxygenated blood to the body.
• The circumflex artery supplies the left ventricle and left atrium.
• The circumflex artery has obtuse marginal branches.
• The right coronary artery supplies the right atrium, right ventricle, SA node, and AV node.
• Blockage in the LAD artery is commonly associated with severe cardiac events.
• The circumflex artery is crucial for maintaining the functionality of the left side of the heart.
• The diagonal and septal branches of the LAD artery ensure blood flow to both ventricles and the interventricular septum.
• The circumflex artery typically has two obtuse marginal branches.

Right Coronary Artery (RCA) and its Branches

• The RCA is a major coronary artery that originates from the right coronary ostia in the aorta.
• The RCA supplies blood to the right atrium and portions of both ventricles.
• The RCA's branches:
  • Right Ventricular Branch supplies blood to the anterior surface of the right ventricle.
  • Posterior Descending Artery (PDA) supplies blood to the posterior ventricles and the inferior surface of the heart.
• The PDA is a crucial branch because it provides blood flow to both the posterior and inferior surfaces of the heart.
• The PDA is typically the terminal branch of the RCA.
• The RCA is essential for the right side of the heart's function, which pumps deoxygenated blood to the lungs for oxygenation.

Coronary Sinus Location and Function

• The coronary sinus is located on the posterior surface of the heart.
• It is the largest vein in the coronary circulation system.
• The coronary sinus's primary function is to drain deoxygenated blood from the heart muscle and empty it into the right atrium.

Principal Coronary Veins

• The middle cardiac vein drains blood from the left and right ventricles.
• The small cardiac vein primarily drains blood from the right atrium and right ventricle.
• The anterior cardiac veins drain blood directly into the right atrium.

Other Veins Associated with the Coronary Sinus

• Great cardiac vein: It drains blood from the left ventricle and left atrium and empties into the coronary sinus.
• Posterior vein of the left ventricle: It drains blood from the posterior surface of the left ventricle and empties into the coronary sinus.

Importance of Coronary Veins for Cardiac Function

• The coronary veins play a crucial role in maintaining efficient cardiac function and overall circulatory health by returning deoxygenated blood from the heart muscle back to the right atrium.
• This completes the cycle of blood flow through the heart, ensuring the heart muscle receives oxygenated blood.

Structure of the Coronary Sinus

• The coronary sinus has a large capacity, enabling it to collect blood from multiple veins.

Explore the key measurements and location of the heart within the thoracic cavity. This quiz covers the dimensions such as length, width, and mass, along with the heart's position in the mediastinum. Test your knowledge of cardiovascular anatomy!