Dominic Stone
The heart is made up of three layers: the pericardium, myocardium, and endocardium. The myocardium, or cardiac muscle, forms the thick middle layer of the heart. The primary function of the cardiac muscle is to pump blood into circulation by generating sufficient force. Cardiac muscle cells, or cardiomyocytes, are the contractile cells of the cardiac muscle. The coronary arteries branch from the aorta and surround the outer surface of the heart, supplying blood to the myocardium. The blood is then drained away by the coronary veins into the right atrium. Veins and arteries have two further tunics that surround the endothelium: the middle tunic is composed of smooth muscle, which is one of the main cell types of human blood vessels.
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What You'll Learn
- The coronary veins drain deoxygenated blood from the heart muscle
- The myocardium is surrounded by the epicardium and the endocardium
- Cardiac muscle cells are also called cardiomyocytes
- The sinoatrial node sends electrical signals to the cardiac muscle cells
- The cardiac muscle is responsible for the contractility of the heart
The coronary veins drain deoxygenated blood from the heart muscle
The heart is a three-layered structure with a thick layer of myocardium or cardiac muscle sandwiched between the inner endocardium and the outer epicardium (also known as the visceral pericardium). The inner endocardium lines the cardiac chambers, covers the cardiac valves, and joins with the endothelium that lines the blood vessels that connect to the heart. The outer epicardium forms part of the pericardial sac that surrounds, protects, and lubricates the heart. The cardiac muscle is responsible for the contraction and relaxation that generates the pressure needed to pump blood through the circulatory system.
The heart is a high-energy organ that requires a constant supply of oxygen and nutrients. The coronary arteries supply oxygenated blood to the heart muscle. The coronary arteries are the first branches of the aortic root. The blood is then drained away by the cardiac veins through the coronary sinus into the right atrium. The coronary veins drain deoxygenated blood from the heart muscle. The great cardiac vein, the middle cardiac vein, the small cardiac vein, the smallest cardiac veins, and the anterior cardiac veins are all involved in removing deoxygenated blood from the heart muscle. The anterior cardiac veins drain the anterior surface of the right ventricle, while the small cardiac vein drains the posterior surfaces of the right atrium and ventricle. The middle cardiac vein collects blood from the areas supplied by the posterior interventricular artery, and the posterior cardiac vein receives blood from the regions supplied by the marginal artery.
The cardiac veins are typically situated parallel to the arteries. The anatomy of the veins of the heart is variable, but generally, it is formed by the heart veins that go into the coronary sinus and the heart veins that go directly to the right atrium. The right and left coronary arteries are involved in supplying oxygenated blood to the heart muscle. The right coronary artery proceeds along the coronary sulcus and distributes blood to the right atrium, portions of both ventricles, and the heart conduction system. The marginal arteries that supply blood to the superficial portions of the right ventricle usually arise from the right coronary artery.
The cardiac veins play a crucial role in the circulation of blood in the heart. The constant activity of the heart demands a well-supplied flow of blood. The heart uses about 5% of the total oxygen consumed by the body despite comprising only 0.5% of the body mass. The heart pumps about 2,000 gallons of blood each day, which is enough to fill an 8-by-10-foot swimming pool.
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The myocardium is surrounded by the epicardium and the endocardium
The myocardium, also known as cardiac muscle, is the thick middle layer of the heart. It is surrounded by the outer epicardium and the inner endocardium. Together, these three layers make up the heart wall.
The myocardium is composed of cardiac muscle fibres, which enable the heart to contract. It is the thickest layer of the heart, with its thickness varying in different parts of the heart. The myocardium of the left ventricle, for instance, is the thickest part as this ventricle is responsible for generating the power needed to pump oxygenated blood from the heart to the rest of the body.
The outer layer of the heart is called the epicardium or visceral pericardium. It is a thin layer of loose connective tissue, including elastic fibres and adipose tissue. The epicardium functions to protect the inner heart layers and assists in the production of pericardial fluid, which fills the pericardial cavity and helps to reduce friction between the pericardial membranes during heart contractions. The coronary blood vessels, which supply the heart wall with blood, are also found in this layer.
The endocardium is the innermost layer of the heart. It is composed of endothelial cells and controls myocardial function. This layer lines the inner heart chambers, covers the heart valves, and is continuous with the endothelium of large blood vessels. The endocardium also provides protection to the valves and heart chambers. An infection of the endocardium can lead to a condition known as endocarditis, which is typically the result of an infection of the heart valves or endocardium by certain bacteria, fungi, or other microbes.
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Cardiac muscle cells are also called cardiomyocytes
Cardiac muscle tissue, also known as myocardium, is one of the three types of muscle tissue in the body, and is found only in the heart. The myocardium forms the thick middle layer of the heart, sandwiched between the inner endocardium and the outer epicardium (or visceral pericardium). The heart consists mostly of cardiac muscle cells or cardiomyocytes.
The primary function of cardiomyocytes is to contract, which generates the pressure needed to pump blood through the circulatory system. Each cardiomyocyte needs to contract in coordination with its neighbouring cells, known as a functional syncytium, to efficiently pump blood from the heart. If this coordination breaks down, the heart may not pump at all, as can occur during abnormal heart rhythms such as ventricular fibrillation. The contraction of individual cardiac muscle cells produces force and shortening in these bands of muscle, with a resultant decrease in the heart chamber size and the consequent ejection of the blood into the pulmonary and systemic vessels.
Cardiomyocytes contain T-tubules, pouches of cell membrane that run from the cell surface to the cell's interior, which help to improve the efficiency of contraction. The majority of these cells contain only one nucleus, unlike skeletal muscle cells which contain many nuclei. Cardiac muscle cells contain many mitochondria which provide the energy needed for the cell in the form of adenosine triphosphate (ATP), making them highly resistant to fatigue. Invaginations of the sarcolemma into the cytoplasm of the cardiomyocyte are called T-tubules, and they contain numerous proteins like L-type calcium channels, sodium-calcium exchangers, calcium ATPases, and beta-adrenergic receptors that allow for the exchange of ions with extracellular fluid surrounding the cell.
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The sinoatrial node sends electrical signals to the cardiac muscle cells
The sinoatrial node (SA node) is a cluster of myocytes with pacemaker activity. It is a small, oval-shaped region of specialised cardiac muscle cells, known as pacemaker cells, located in the upper back wall of the right atrium. The SA node is about 15mm long, 3-4mm wide, and 1mm thick, and is found directly below and to the side of the superior vena cava.
The SA node is the heart's natural pacemaker. It sends electrical signals to the cardiac muscle cells, which initiate action potentials that pass through the cardiac muscle cells and cause them to contract. These action potentials are rapid changes in membrane potential, produced by the movement of charged atoms (ions). The SA node continuously generates electrical impulses, setting a healthy heart's normal rhythm and rate.
The cardiac muscle cells, or cardiomyocytes, are the contractile myocytes of the cardiac muscle. They are surrounded by an extracellular matrix produced by supporting fibroblast cells. Each cardiomyocyte needs to contract in coordination with its neighbouring cells to form a functional syncytium, which efficiently pumps blood from the heart.
The process of contraction and relaxation requires a constant supply of oxygen and nutrients to meet the energy demands of the cardiac muscle. Blood supply is delivered to the myocardium by the coronary arteries, which originate from the aortic root and lie on the outer or epicardial surface of the heart. The coronary veins then drain the blood away into the right atrium.
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The cardiac muscle is responsible for the contractility of the heart
The cardiac muscle, also known as the myocardium, is one of three major categories of muscles found in the human body, the other two being smooth muscle and skeletal muscle. The myocardium forms the thick middle layer of the heart, sandwiched between the inner endocardium and the outer epicardium (or visceral pericardium).
The contractile units of the cardiac muscle are known as sarcomeres, which are made up of thick and thin protein filaments. The thick filaments are made of myosin, while the thin filaments are made of actin, troponin, and tropomyosin. These filaments are arranged in a characteristic cross-striated pattern, similar to that seen in skeletal muscle. The cardiac muscle also demonstrates striations, with an alternating pattern of dark A bands and light I bands attributed to the precise arrangement of the myofilaments and fibrils that are organized in sarcomeres along the length of the cell.
The contraction of the cardiac muscle is regulated by the sinoatrial node of the heart, which serves as the heart's pacemaker. The pacemaker cells are only weakly contractile and are connected to neighbouring contractile cells via gap junctions. They are located in the sinoatrial node, positioned on the wall of the right atrium, near the entrance of the superior vena cava. The sinoatrial node regulates the rhythmic contractions of the cardiac muscle, which are not under voluntary control.
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Frequently asked questions
Cardiac muscle, or myocardium, makes up the thick middle layer of the heart. It is one of three types of muscle in the body, the other two being skeletal and smooth muscle. The myocardium is surrounded by a thin outer layer called the epicardium (or visceral pericardium) and an inner endocardium.
Cardiac muscle does not surround veins. Veins are surrounded by a middle tunic made of smooth muscle and an outermost layer of connective tissue.
The primary function of cardiac muscle is to pump blood into circulation by generating sufficient force. The cardiac muscle must contract with enough force and blood to supply the metabolic demands of the entire body.
The cardiac muscle receives an electrical signal from the sinoatrial node, triggering the cardiac muscle cells in the atria to contract. The signal pauses at the atrioventricular node before spreading to the walls of the ventricles so that blood is pumped through the body.
