Heart Anatomy: Chambers, Vessels, and Pericardial Sac

Heart Anatomy Overview

• Focus on heart anatomy.
• Layers and functions of the pericardial sac covered.
• Explanation of chambers, valves, and great vessels.
• Identification of primary coronary arteries and cardiac veins.

Heart Overview

• The human heart is about the size of a fist and weighs approximately 300 grams
• It beats 60 to 80 times per minute during a person's lifetime, pumping five to six liters of blood

Pericardial Sac

• The pericardial sac is a double-walled sac that encloses the heart and the roots of the great vessels like the aorta and pulmonary trunk.
• It consists of a fibrous layer and a serous layer, which includes the visceral pericardium adhering to the outside of the heart

Fibrous Layer

• The fibrous layer of the parietal pericardium is made of dense irregular collagenous connective tissue.
• It prevents the heart from overfilling and it fixes the heart in the mediastinum.

Serous Pericardium

• The serous pericardium has two layers the Parietal layer which lines the inside of the fibrous layer and the Visceral layer, which adheres to the heart.
• The parietal and visceral layers are continuous with each other.

Pericardial Space

• The pericardial space is between the parietal and visceral pericardial layers.
• It has pericardial fluid, which lubricates the heart.

Heart Wall Layers

• Endocardium: innermost layer, associated with blood in the heart chambers
• Myocardium: the heart muscle responsible for pumping blood
• Visceral pericardium: outermost serous membrane layer
• Epicardium: formed by the visceral pericardium plus adipose tissue; often used synonymously with visceral pericardium.

Heart Chambers and Vessels

• Superior Vena Cava (SVC): delivers deoxygenated blood from tissues above the diaphragm to the right atrium
• Inferior Vena Cava (IVC): delivers deoxygenated blood from tissues below the diaphragm to the right atrium
• Coronary Sinus: delivers deoxygenated blood from the myocardium via coronary circulation into the right atrium.

Right Atrium

• Receives deoxygenated blood from the SVC, IVC, and coronary sinus.
• Fossa ovalis: a remnant of the foramen ovale in a fetus, which shunted blood from the right atrium to the left atrium to bypass the lungs.
• It forms the right border of the heart.

Tricuspid Valve

• Located on the floor of the right atrium, also known as the right AV valve
• Opens to allow blood flow from the right atrium into the right ventricle.
• Closes during systole to prevent backflow of blood into the right atrium

Right Ventricle

• Pumps deoxygenated blood into the pulmonary trunk, leading to the pulmonary arteries towards the lungs
• Forms the anterior border of the heart.

Atrioventricular (AV) Valves

• AV valves (tricuspid and bicuspid) enable blood to flow from the atrium into the ventricle during diastole
• During systole, they prevent blood from flowing back into the atrium from the ventricle.
• Papillary muscles: extensions of the myocardium
• Chordae Tendineae: connect papillary muscles to the tricuspid and bicuspid valves via heart strings
• Chordae tendineae prevent the valve leaflets from prolapsing into the atrium
• Closing of the AV valves makes the "lub" (S1) sound
• Without chordae tendineae, regurgitation can occur, causing blood to move from the ventricle to the atrium.

Pulmonary Valve

• The most anterior heart valve.
• Opens to allow blood flow from the right ventricle into the pulmonary trunk and arteries.
• Closes during diastole to prevent backflow of blood into the right ventricle.

Semilunar Valves

• Semilunar valves (pulmonary and aortic) enable blood to flow out of the ventricles during systole
• Prevent blood from regurgitating back into the ventricles during diastole
• Closing the semilunar valves makes the "dub" (S2) sound

Pulmonary Arteries

• Transport deoxygenated blood from the right ventricle to the lungs
• The only arteries in an adult that transport deoxygenated blood.

Gas Exchange in the Lungs

• Oxygen is inhaled into alveolar sacs.
• Pulmonary arteries bring CO2-rich blood through pulmonary capillaries.
• Gas exchange occurs in pulmonary capillaries, where CO2 diffuses into the alveolar space and oxygen diffuses into the pulmonary capillaries.
• Blood exiting the pulmonary capillaries in the pulmonary veins is rich in oxygen.

Pulmonary Veins

• Transport oxygenated blood from the lungs to the left atrium
• The only veins in an adult that transport oxygenated blood.

Left Atrium

• Receives oxygenated blood from the lungs.
• Forms the most posterior border of the heart, touching the esophagus in the thoracic cavity.

Bicuspid (Mitral) Valve

• The bicuspid valve has two cusps.
• Also called the mitral valve because it resembles a mitre (religious hat).
• Also called the left AV valve.
• Opens to allow blood flow from the left atrium to the left ventricle.
• Closes during systole to prevent backflow of blood into the left atrium, making the S1 heart sound.

Left Ventricle

• Receives oxygenated blood from the left atrium and pumps it into the aorta through the aortic valve
• Has a much thicker myocardium than the right ventricle (80-120 mmHg vs 10-20 mmHg pressures to open aortic vs pulmonary valve)
• Forms the left border and apex of the heart.

Aortic Valve

• Opens to allow blood flow from the left ventricle into the aorta
• Located behind or posterior to the pulmonary valve
• The left cusp gives rise to the left coronary artery, and the right cusp gives rise to the right coronary artery
• Closes during diastole and prevents backflow of blood into the left ventricle, making the S2 sound.

Aorta

• The thickest elastic muscular artery that distributes blood to all systemic arteries and arterioles.
• Consists of ~50% elastic tissue and ~50% smooth muscle in the tunica media.

Coronary Circulation

• The heart pumping blood into the heart: the left ventricle pumps oxygenated blood into the ascending aorta, which then gives rise immediately to left and right coronary arteries which then supply the heart.
• The heart muscle tissue gives us deoxygenated blood back to the heart via cardiac veins into the right atrium.

Right Coronary Artery (RCA)

• Supplies the right side of the heart and courses in the coronary sulcus around the right side of the heart like a crown
• Gives rise to the sinoatrial node’el artery (SA nodal artery), which supplies SA node (the pacemaker of the heart)
• Posterior Descending Artery (PDA): supplies the posterior interventricular septum

Left Coronary Artery (LCA)

• Supplies the left side of the heart.
• Small and courses briefly in the coronary sulcus
• The LCA gives off two major branches: Left Anterior Descending Artery (LAD) and Left Circumflex Artery (LCX).

Left Anterior Descending Artery (LAD)

• The LAD descends on the front of the heart like an anterior division.
• Supplies the anterior interventricular septum.
• Also supplies apex of the heart.

Left Circumflex Artery (LCX)

• The LCX supplies the left lateral wall of the heart.

Coronary Sinus

• Drains the tissues of the myocardium.
• The great cardiac vein drains the same cardiac territory as the LAD
• Middle and small cardiac veins drain the same territory as the right coronary artery
• The coronary sinus collects venous blood from the great, middle, and small cardiac veins and dumps it into the right atrium.

Heart Anatomy - In a Nutshell

• Deoxygenated blood flows from the right atrium through the tricuspid valve to the right ventricle
• Blood is then pumped through the pulmonary valve into the pulmonary arteries to the lungs to receive oxygen and expel co2
• Oxygen-rich blood then exits the pulmonary capillaries into the pulmonary veins to the left atrium (pulmonary circulation: heart → lungs → heart)
• Oxygenated blood flows through the mitral valve into the left ventricle, then pumped through the aortic valve into the aorta and systemic arteries
• Oxygenated blood goes to tissues, then deoxygenated blood goes back to the heart (systemic circulation: heart → systemic tissues → heart) and into the right atrium.