The Heart and Pericardial Sac

The Heart

• The heart, about the size of a fist, weighs approximately 300 grams.
• It beats 60-80 times per minute.
• The heart pumps five to six liters of blood per minute throughout the body.

Pericardial Sac

• The pericardial sac is a double-walled structure enclosing the heart and the roots of the great vessels, such as the aorta and pulmonary trunk.
• The pericardium consists of a fibrous layer and a serous layer.
• The visceral pericardium adheres to the outer surface of the heart.

Layers of the Pericardial Sac

• The fibrous layer of the parietal pericardium is composed of dense irregular collagenous connective tissue.
• The serous layer of the parietal pericardium produces serous fluid.
• A cross-section shows the fibrous layer, the serous layer, and the visceral pericardium, which is attached to the heart.

Function of Fibrous Pericardium

• The dense irregular connective tissue of the fibrous pericardium prevents the heart from overfilling and secures it within the mediastinum.

Serous Pericardium

• Parietal layer lines the inside of the fibrous layer.
• Visceral layer adheres to the heart.
• The parietal and visceral layers are continuous.

Pericardial Space

• The pericardial space is located between the parietal and visceral pericardial layers and is filled with pericardial fluid, which serves to lubricate the heart.

Heart Wall Layers

• Endocardium lines the inside of the heart chambers, closely interacting with the blood.
• Myocardium is the muscular layer responsible for pumping blood.
• Visceral Pericardium is the serous membrane on the outside of the heart.
• Epicardium is the visceral pericardium, often used synonymously, along with adipose tissue.
• The pericardial space is filled with pericardial fluid.
• Parietal Pericardium includes the serous and fibrous layers.

Superior Vena Cava (SVC)

• The SVC delivers deoxygenated blood from tissues above the diaphragm to the right atrium.

Inferior Vena Cava (IVC)

• The IVC delivers deoxygenated blood from tissues below the diaphragm into the right atrium.

Coronary Sinus

• The coronary sinus delivers deoxygenated blood from the myocardium via coronary circulation into the right atrium.
• Its opening is in the right atrium.

Right Atrium

• The right atrium receives deoxygenated blood from the SVC, IVC, and coronary sinus.
• The fossa ovalis, a remnant of the foramen ovale that shunted blood in the fetus, is on the interatrial septum.
• It forms the right border of the heart.

Tricuspid Valve

• The tricuspid valve, or right atrioventricular valve, is situated on the floor of the right atrium.
• It opens for blood to flow from the right atrium into the right ventricle.
• The valve closes during systole to prevent backflow into the right atrium.

Right Ventricle

• The right ventricle pumps deoxygenated blood into the pulmonary trunk, leading to the pulmonary arteries and the lungs.
• The right ventricle constitutes the anterior border of the heart.

Atrioventricular (AV) Valves

• The AV valves include the tricuspid valve on the right side and the bicuspid/mitral valve on the left side.
• Papillary muscles, extensions of the myocardium, connect to the AV valves via chordae tendineae (heart strings).

Function of AV Valves

• These valves enable blood to flow from the atrium into the ventricle during diastole.
• They prevent backflow from the ventricle into the atrium during systole by closing tightly.
• The closing of the AV valves produces the first heart sound (S1 or "lub" in "lub-dub").

Chordae Tendineae

• These prevent AV valve leaflets from inverting into the atrium during ventricular contraction.
• Damage or absence can lead to regurgitation.

Pulmonary Valve

• The pulmonary valve sits at the opening of the right ventricle into the pulmonary trunk and is the most anterior heart valve.
• It opens to allow blood to flow from the right ventricle into the pulmonary trunk and arteries.
• The valve closes during diastole, preventing backflow into the right ventricle.

Semilunar Valves

• The semilunar valves are the pulmonary and aortic valves.
• They enable blood to flow out of the ventricles during systole.
• During diastole, they prevent blood from flowing back into the ventricles.
• The closing of these valves produces the second heart sound (S2 or "dub" in "lub-dub").

Pulmonary Arteries

• Pulmonary arteries transport deoxygenated blood from the right ventricle to the lungs.
• These are the only arteries in an adult carrying deoxygenated blood.
• Blood is sent to the lungs for CO2 removal and oxygen pickup.

Gas Exchange in the Lungs

• Oxygen enters alveolar sacs via inhalation
• Pulmonary arteries carry CO2-rich blood through pulmonary capillaries
• CO2 moves from blood into alveolar space
• Oxygen moves from alveolar space into blood

Pulmonary Veins

• Pulmonary veins transport oxygenated blood from the lungs to the left atrium.
• These are the only veins in an adult that carry oxygenated blood.

Left Atrium

• The left atrium receives oxygenated blood from the lungs through the pulmonary veins.
• It forms the most posterior border of the heart, touching the esophagus.

Bicuspid (Mitral) Valve

• This valve features two cusps.
• It's also known as the mitral valve, resembling a mitre or religious hat.
• Additionally called the left AV valve.
• Opens to facilitate blood flow from the left atrium to the left ventricle.
• The mitral valve closes during systole to prevent backflow into the left atrium, producing the S1 heart sound.

Left Ventricle

• The left ventricle receives oxygenated blood from the left atrium and pumps it into the aorta through the aortic valve.
• It has a thicker myocardium than the right ventricle because of higher pressures.
• This ventricle forms the left border and apex of the heart.

Aortic Valve

• It opens for blood to flow from the left ventricle into the aorta.
• Located posterior to the pulmonary valve.
• The left and right coronary arteries originate from the left and right cusps.
• This valve closes during diastole to prevent backflow into the left ventricle, creating the S2 heart sound.

Aorta

• The aorta, the thickest elastic muscular artery, distributes blood to all systemic arteries and arterioles.
• The tunica media consists of about 50% elastic tissue and 50% smooth muscle.

Coronary Circulation

• The heart pumps blood to itself, and the heart delivers blood back to itself.

Coronary Circulation

• The left ventricle pumps oxygenated blood into ascending aorta and that gives rise to the left and right coronary arteries, supplying the myocardium
• The heart muscle tissue sends deoxygenated blood back to the heart via cardiac veins, into the right atrium
• Blood goes from the heart --> through coronary arteries --> to the heart -- through cardiac veins --> back to the heart.

Right Coronary Artery (RCA)

• The RCA supplies the right side of the heart.
• It courses in the coronary sulcus (groove).
• The word "coronary" means "like a crown."
• Gives rise to the sinoatrial (SA) nodal artery, which supplies the SA node (the heart's pacemaker).
• The Posterior Descending Artery (PDA) supplies the posterior interventricular septum.
• It is also called the posterior interventricular artery.

Left Coronary Artery (LCA)

• The LCA supplies the left side of the heart.
• It is relatively short.
• It branches into the left anterior descending artery (LAD) and the left circumflex artery (LCX).

Left Anterior Descending Artery (LAD)

• Originates from the LCA.
• It is located on the anterior part of the heart.
• This artery descends on the front of the heart.
• Supplies the anterior interventricular septum and the apex.
• Also called the anterior interventricular artery.

Left Circumflex Artery (LCX)

• Originates from the LCA.
• It supplies the left lateral wall of the heart.
• This artery courses in the coronary sulcus.

Coronary Sinus

• The coronary sinus drains all tissues of the myocardium.
• It receives blood from the great, middle, and small cardiac veins.

Great Cardiac Vein

• The great cardiac vein drains the same cardiac territory as the LAD.

Middle and Small Cardiac Veins

• The middle and small cardiac veins drain the same territory as the RCA.

Coronary Sinus

• Drains all of the heart.
• Collects venous blood from the great, middle, and small cardiac veins.
• Dumps deoxygenated blood into the right atrium.

Coronary vs Cardiac

• Arteries that supply the heart are called coronary arteries.
• Veins that drain the heart are called cardiac veins.
• The largest vein is called the coronary sinus because it courses in the coronary groove.

Heart Anatomy in a Nutshell

• Deoxygenated blood flows from the right atrium through the tricuspid valve into the right ventricle.
• The right ventricle pumps deoxygenated blood through the pulmonary valve into the pulmonary arteries to the lungs for gas exchange.
• Oxygen-rich blood then exits the pulmonary capillaries in the pulmonary veins and flows into the left atrium.

Pulmonary Circulation

• Blood goes from the right ventricle --> pulmonary capillaries --> left atrium.

Systemic Circulation

• Blood flows to the systemic tissues.
• Oxygenated blood flows through the mitral valve into the left ventricle.
• The left ventricle pumps oxygenated blood through the aortic valve into the aorta and systemic arteries, delivering oxygen to tissues.
• Deoxygenated blood from systemic capillaries flows back to the right atrium to start the process again.
• Blood flows from the heart --> to systemic tissues --> back to the heart.