Heart Anatomy and Circulatory System

• The heart is a muscular organ responsible for pumping blood throughout the body
• The circulatory system transports oxygen, nutrients, hormones, and cellular waste

Heart Anatomy

• The heart consists of four chambers: the right atrium, the right ventricle, the left atrium, and the left ventricle
• The atria are the receiving chambers, while the ventricles are the pumping chambers
• The heart also has valves that ensure unidirectional blood flow: the tricuspid valve, the pulmonary valve, the mitral valve, and the aortic valve
• The heart wall consists of three layers: the epicardium, the myocardium, and the endocardium
• The epicardium is the outer layer, the myocardium is the muscular middle layer, and the endocardium is the inner lining
• The myocardium is the thickest layer and is responsible for the heart's contractile function
• The heart is located in the mediastinum, the space between the lungs, and is enclosed by a double-layered sac called the pericardium
• The pericardium consists of the fibrous pericardium and the serous pericardium
• The serous pericardium is further divided into the parietal layer and the visceral layer, with the pericardial cavity in between containing pericardial fluid for lubrication

Blood Flow Through the Heart

• Deoxygenated blood enters the right atrium through the superior vena cava and the inferior vena cava
• Blood flows from the right atrium into the right ventricle through the tricuspid valve
• The right ventricle pumps the deoxygenated blood into the pulmonary artery through the pulmonary valve
• The pulmonary artery carries the deoxygenated blood to the lungs, where it picks up oxygen and releases carbon dioxide
• Oxygenated blood returns to the left atrium through the pulmonary veins
• Blood flows from the left atrium into the left ventricle through the mitral valve
• The left ventricle pumps the oxygenated blood into the aorta through the aortic valve
• The aorta distributes the oxygenated blood to the rest of the body

Cardiac Circulation

• Cardiac circulation refers to the blood supply to the heart muscle itself
• The heart receives its blood supply from the right and left coronary arteries, which originate from the aorta
• The coronary arteries branch into smaller vessels that supply oxygen and nutrients to the myocardium
• Deoxygenated blood from the myocardium drains into the coronary veins, which empty into the coronary sinus, and then into the right atrium

Heart Valves

• The heart valves ensure unidirectional blood flow through the heart
• The atrioventricular valves, which are the tricuspid and mitral valves, prevent backflow of blood from the ventricles into the atria during ventricular contraction
• The semilunar valves, which are the pulmonary and aortic valves, prevent backflow of blood from the arteries into the ventricles during ventricular relaxation
• The valves open and close in response to pressure changes in the heart chambers

Cardiac Muscle Tissue

• Cardiac muscle tissue is responsible for the heart's contractile function
• Cardiac muscle cells are connected by intercalated discs, which contain gap junctions that allow for rapid electrical communication between cells
• This allows the heart to contract as a coordinated unit, ensuring efficient pumping of blood
• Cardiac muscle cells have a long refractory period, which prevents tetanus and ensures that the heart relaxes between beats

Conduction System of the Heart

• The heart has a specialized conduction system that generates and conducts electrical impulses, coordinating the contraction of the heart chambers
• The sinoatrial (SA) node, located in the right atrium, is the heart's natural pacemaker and initiates the electrical impulse
• The impulse spreads through the atria, causing them to contract
• The impulse reaches the atrioventricular (AV) node, located between the atria and ventricles, which delays the impulse slightly
• The impulse travels down the bundle of His, located in the interventricular septum
• The bundle of His divides into the right and left bundle branches, which carry the impulse to the apex of the heart
• The impulse spreads through the Purkinje fibers, which cause the ventricles to contract

Cardiac Cycle

• The cardiac cycle refers to the sequence of events that occur during one complete heartbeat
• It consists of two main phases: systole, or contraction, and diastole, or relaxation
• During atrial systole, the atria contract, pushing blood into the ventricles
• During ventricular systole, the ventricles contract, pumping blood into the pulmonary artery and aorta
• During diastole, the heart chambers relax and fill with blood in preparation for the next contraction

Heart Sounds

• The heart sounds are produced by the closing of the heart valves
• The first heart sound (S1) is produced by the closing of the atrioventricular valves (tricuspid and mitral valves) at the beginning of ventricular systole
• The second heart sound (S2) is produced by the closing of the semilunar valves (pulmonary and aortic valves) at the beginning of ventricular diastole
• Abnormal heart sounds, such as murmurs, can indicate valve dysfunction or other cardiac abnormalities

The heart, a muscular organ with four chambers, pumps blood throughout the body. The circulatory system transports oxygen, nutrients, hormones, and cellular waste. The heart wall consists of the epicardium, myocardium, and endocardium.