Anatomy and Location of the Heart

• The heart pumps 10,000,000 liters (2.6 million gallons) of blood through 60,000 miles of vessels per year based on 75 contractions per minute.

Location of the Heart

• The heart resides in the thoracic cavity within the mediastinum, between the lungs.
• A tough membrane, the pericardium (pericardial sac), separates the heart from other mediastinal structures.
• The heart sits in its own space called the pericardial cavity.
• The dorsal surface is near the vertebrae, while the anterior surface is deep to the sternum and costal cartilages.
• The great veins (superior and inferior venae cavae) and great arteries (aorta and pulmonary trunk) attach to the superior surface, called the base.
• The base sits at the level of the third costal cartilage.
• The apex, or inferior tip, is just left of the sternum between the fourth and fifth ribs, near their articulation with the costal cartilages.
• The right side is deflected anteriorly, while the left side is deflected posteriorly.
• The apex slightly deviates to the left, creating the cardiac notch on the medial surface of the left lung's inferior lobe.

CPR (Cardiopulmonary Resuscitation)

• The heart's position in the torso between the vertebrae and sternum allows for CPR if a patient's heart stops.
• Applying pressure on the sternum between T4 and T9 manually compresses blood within the heart, pushing it into the pulmonary and systemic circuits.
• Compressions should be at least 5cm deep and at a rate of 100 per minute.
• CPR is performed until the patient regains spontaneous contraction or is declared dead by healthcare professionals.
• Improper CPR can result in broken ribs, a broken sternum, or liver damage.

Shape and Size of the Heart

• The heart resembles a pinecone and is roughly the size of a fist: 12 cm long, 8 cm wide, and 6 cm thick.
• A female heart weighs approximately 250–300 grams, while a male heart weighs approximately 300-350 grams.
• In athletes, especially those specializing in aerobic sports, the heart can be larger.
• Exercise can cause cardiac muscle cells to increase in size through hypertrophy, adding protein myofilaments.
• Enlarged hearts can also result from pathologies like hypertrophic cardiomyopathy and can cause sudden death in otherwise healthy young people.

Chambers and Circulation

• The heart contains four chambers: two atria (right and left) and two ventricles (right and left).
• The atria receive blood and contract to push blood into the ventricles.
• The ventricles serve as the primary pumping chambers, propelling blood to the lungs or the rest of the body.
• The pulmonary circuit transports blood to and from the lungs for gas exchange.
• The systemic circuit transports oxygenated blood to the rest of the body and returns deoxygenated blood and carbon dioxide to the heart .
• The right ventricle pumps deoxygenated blood into the pulmonary trunk, which leads to left and right pulmonary arteries toward the lungs.
• These vessels branch into pulmonary capillaries, where carbon dioxide exits the blood, and oxygen enters.
• Oxygenated blood returns via pulmonary veins to the left atrium, which pumps it into the left ventricle.
• The left ventricle pumps oxygenated blood into the aorta for systemic circulation.
• Blood flows from the aorta into systemic capillaries for oxygen and nutrient delivery to tissues.
• Deoxygenated blood flows from capillaries to venules, then to larger veins.
• The superior vena cava and inferior vena cava return blood to the right atrium, which pumps the blood into the right ventricle to restart the cycle.

Membranes

• The pericardium (pericardial sac) directly surrounds the heart and defines the pericardial cavity.
• The pericardium consists of two sublayers:
  • A sturdy outer fibrous pericardium
  • An inner serous pericardium.
• The fibrous pericardium, made of tough, dense connective tissue, protects the heart and maintains its position in the thorax.
• The serous pericardium has two layers:
  • The parietal pericardium
  • The inner visceral pericardium (epicardium).
• A pericardial cavity filled with lubricating serous fluid lies between the epicardium and pericardium.
• The epicardium consists of a mesothelium, which is a simple squamous epithelium, reinforced with loose connective tissue.
• The mesothelium secretes serous fluid to reduce friction during heart contractions.

Heart: Cardiac Tamponade

• Cardiac tamponade (pericardial tamponade) results from excess fluid buildup within the pericardial space.
• Fluid, usually blood, accumulates within the pericardial cavity with each heart contraction.
• The excess fluid puts pressure on the heart, preventing full relaxation and reducing blood volume in the chambers.
• Over time, less blood is ejected, and can be caused by hypothyroidism.
• Rapid accumulations of 100 mL of fluid can trigger cardiac tamponade.
• Other causes include myocardial rupture, pericarditis, cancer, or cardiac surgery.
• Treatment involves the insertion of drainage tubes into the pericardial cavity to remove excess fluid.

Surface Features of the Heart

• Inside the pericardium, the four chambers are visible.
• Leaf-like extensions of the atria near the superior surface are called auricles.
• Auricles have thin walls and fill with blood, emptying into the atria; also known as atrial appendages.
• Fat-filled grooves called sulci (singular: sulcus) are along the superior surfaces of the heart, containing major coronary blood vessels.
• The deep coronary sulcus is located between the atria and ventricles.
• The anterior interventricular sulcus runs on the anterior surface between the left and right ventricles.
• The posterior interventricular sulcusis visable on the posterior surface of the heart.

Layers of the Heart

• The wall of the heart is composed of three layers: the epicardium, the myocardium, and the endocardium.
• The epicardium is the outermost layer and is also the visceral pericardium, its innermost layer.
• The myocardium is the middle, thickest layer, made of cardiac muscle cells on a collagenous fiber framework with blood vessels and nerve fibers.
• Myocardial contraction pumps blood through the heart and into major arteries.
• Muscle cells swirl and spiral around the chambers in a figure 8 pattern, which contributes to blood pumping ability.
• The left ventricle's muscle is thicker than the right to overcome the high resistance of the systemic circuit.
• The endocardium is the innermost layer composed of a simple squamous epithelium called endothelium.
• The endothelium lines the chambers and covers the heart valves, and is continuous with the endothelial lining of blood vessels.
• The endothelium may regulate contraction of the muscle by secreting endothelins while maintaining a homeostatic balance

Septa

• Septa are walls or partitions dividing the heart chambers.
• The interatrial septum is located between the two atria.
• It features the fossa ovalis: a depression that is a remnant of the foramen ovale.
• The foramen ovale allowed fetal blood to pass directly from the right atrium to the left, bypassing the pulmonary circuit, and is closed after birth by the septum primum.
• The interventricular septum is located between the two ventricles and is intact after fetal development.
• It is thicker than the interatrial septum because the ventricles generate greater pressure during contraction.
• The atrioventricular septum lies between the atria and ventricles.
• Openings in the atrioventricular septum is where blood is moved through atria and ventricles.
• Valves between the atria and ventricles are called atrioventricular valves.
• Valves at the pulmonary trunk and aorta openings are known as semilunar valves.
• The atrioventricular septum structurally is connected by the cardiac skeleton, comprised of dense connective tissue that includes the four rings.
• The openings to the pulmonary trunk and aorta serve as a point of attachment for the heart valves.
• The skeleton is a boundary in the heart electrical conduction system.

Heart: Heart Defects

• A common interatrial septum pathology is patent foramen ovale, where the septum primum does not close at birth.
• Patent foramen ovale can remain undetected or benign but may require surgical repair.
• Patent foramen ovale is detected by auscultation to observe a heart murmur that can be confirmed from an echocardiogram.
• Coarctation of the aorta is a congenital narrowing of the aorta located at the ligamentum arteriosum insertion point, restricting blood flow.
• Patent ductus arteriosus is a congenital condition where the ductus arteriosus fails to close, causing blood to flow from the aorta into the pulmonary trunk.
• Septal defects are openings in the interatrial, interventricular or atrioventricular septum.
• Tetralogy of Fallot is a congenital condition with an opening in the interventricular septum caused by pulmonary trunk blockage, resulting in decreased oxygen saturation.
• Cyanosis (blue coloration of the skin) is caused by a severe septal defect when individuals have insufficient oxygenated blood.
• Septal defects are detected through auscultation and confirmed with medical imaging.

Right Atrium

• Serves as the receiving chamber for blood returning from systemic circulation.
• The superior vena cava drains blood from regions superior to the diaphragm.
• The inferior vena cava drains blood from the lower limbs and abdominopelvic region.
• The coronary sinus drains the heart myocardium.
• The anterior surface has prominent ridges of the pectinate muscles
• The atria receive venous blood continuously and demonstrate a contractile phase.
• The opening between the atrium and ventricle is guarded by the tricuspid valve.

Right Ventricle

• Receives blood from the tricuspid valve, comprised of several chordae tendineae.
• Connects each of the flaps to a papillary muscle that extends from the inferior ventricular surface.
• Has three papillary muscles: anterior, posterior, and septal muscles, corresponding to three sections of the valves.
• When the ventricle contracts, pressure rises, and to prevent backflow papillary muscles contract generating tension by securing the chordae tendineae.
• The walls are lined with trabeculae carneae, muscular ridges covered by endocardium.
• The moderator band reinforces the walls and plays a crucial role in cardiac conduction.
• Contracts and ejects blood into the pulmonary trunk for blood to then branch into the left and right pulmonary arteries.
• The pulmonary semilunar valve prevents back flow from the pulmonary trunk.

Left Atrium

• Blood returns, post gas exchange in the pulmonary capillaries, high in oxygen and via pulmonary veins.
• Has an auricle that includes pectinate ridges.
• Blood flows from the pulmonary veins back into the atrium, through an opening into the left ventricle.
• Contracts at the end of the ventricular relaxation.

Left Ventricle

• The muscular layer is much thicker compared to the right.
• Shares a similarity with the right ventricle, containing trabeculae carneae.
• There is no moderator band, however a mitral valve is connected to papillary muscles via chordae tendineae.
• Two papillary muscles on the left versus three on the right.
• It ejects blood into the aorta through the aortic semilunar valve.

Heart Valve Structure and Function

• Valves ensure unidirectional blood flow.
• Between the right atrium and right ventricle is the right atrioventricular valve (tricuspid valve), made from flaps of endocardium and connective tissue.
• The flaps are connected by chordae tendineae to the papillary muscles, which control the opening and closing of the valves.
• The pulmonary semilunar (pulmonary valve) valve emerges from the right ventricle at the base of the pulmonary trunk, comprised of small flaps of endothelium with connective tissue.
• The opening between the left atrium and left ventricle contains the mitral (bicuspid) valve or the left atrioventricular valve with two cusps.
• Attached by chordae tendineae to two papillary muscles that project from the wall of the ventricle.
• The aortic semilunar (aortic valve) valve prevents back-flow from the aorta, composed of three flaps.

Heart Valves

• Heart valves are incompetent resulting in valvular heart disease.
• These conditions may be congenital, a disease process or can come from trauma.
• Valvular disorders can result from inflammation of the heart, known as carditis.
• Mitral regurgitation is the most common valve disorder, detected in approximately 2 percent of the population.
• The resulting type of insufficiency is named for the corresponding valve.
• If one of the cusps of the valve is forced backward by the force of the blood the condition is a prolapsed valve.
• Stenosis is a condition in which the heart valves stiffen after its flexibility is lost and causes the heart the work harder to pump blood.
• Auscultation, or listening to one's heart via heart sounds, is a diagnostic tool in order to trigger abnormal heart sounds.

Coronary Arteries

• The coronary arteries supply blood to the myocardium.
• The aorta's first portion, arising from the left ventricle, gives rise to coronary arteries.
• The left posterior aortic sinus and anterior aortic sinus give rise to the left and right coronary arteries, respectively.
• Coronary vessel branches that remain on the surface of the artery and follow the sulci is known as epicardial coronary arteries.
• The left coronary artery supplies the left atrium and ventricle, and the interventricular septum and follows the circumflex artery.
• The larger anterior interventricular artery (left anterior descending artery, or LAD) is the second major branch with smaller branches that interconnect.
• The Anastomoses is the interconnection area, even if there is partial blockage in another branch.
• The right coronary artery gives rise to one or more marginal afteries, inferior to the atrium and runs along the posterior surface. The posterior interventricular artery, also known as the posterior descending artery, supplies a branhc to the inter ventricular sulcus, apex a

Heart: Myocardial Infarction

• Myocardial infarction (MI) the outcome of low blood flow (ischemia) and oxygen (hypoxia) in the heart.
• An MI often occurs when a coronary artery is blocked through the buildup of plaque.
• Can be diagnosed by confirming with the patient's ECG/EKG or the creatine kinase MB levels being high
• Can administered with suppemental oxygen and other thrombolytic agents and medicine.
• Risk factors for MI include high cardiovascular disease, age and smoking.

Coronary Veins

• Coronary veins generally parallel the large surface arteries.
• The great cardiac vein is initially seen on the surface following the interventricular sulcus and drains the areas along that artery.
• The posterior cardiac vein parallels the circumflex.
• The middle cardiac vein drains areas supplied by the posterior interventricular artery and is paralell to it
• The small cardiac vein drains blood from the right atrium and ventricle’s posterior.
• The coronary sinus empties directly into the right atrium.
• The anterior cardiac veins parallels the small cardiac arteries

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• Oxygenated blood refers to having blood containing higher levels of oxygen
• Deoxygenated blood is blood with lower levels of oxygen
• The pulmonary circuit carries deoxygenated blood from the right side of the heart, and brings oxygenated blood back to the left side.
• The systemic circulation transports oxygenated and deoxygenated blood throughout the body.