Victor Forge
The human heart is a powerhouse organ that pumps blood throughout the body. It is made up of muscle and tissue, with four muscular sections or chambers that briefly hold blood before moving it. The heart wall is a three-layered structure, with a thick layer of myocardium (cardiac muscle) sandwiched between the inner endocardium and the outer epicardium or visceral pericardium. The myocardium is the heart's middle and thickest layer, responsible for the contractile function of the cardiac pump. It is composed of cardiomyocytes, the contractile myocytes of the cardiac muscle. These cells are stimulated to contract by pacemaker cells, which set the rhythm of the heart contractions.
| Characteristics | Values |
|---|---|
| Name | Cardiac muscle, myocardium |
| Location | Middle layer of the heart walls |
| Composition | Cardiomyocytes, collagen fibres, intercalated discs, extracellular matrix |
| Function | Contraction and relaxation to pump blood through the cardiovascular system |
| Control | Involuntary, controlled by pacemaker cells and the autonomic nervous system |
| Development | Originates from the mesoderm layer during the 3rd week of embryonic development |
| Diseases | Cardiomyopathies, ischemic heart disease, ventricular fibrillation |
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What You'll Learn
- Cardiac muscle tissue, also called myocardium, forms the heart wall's middle layer
- The heart wall has three layers, with the myocardium sandwiched between the inner endocardium and outer epicardium
- Cardiomyocytes are the contractile cells of the myocardium that allow the heart to pump blood
- The cardiac muscle is striated and composed of individual cardiac muscle cells joined by intercalated discs
- The heart muscle is one of the earliest functioning embryonic organs, contracting and beating throughout a person's lifetime
Cardiac muscle tissue, also called myocardium, forms the heart wall's middle layer
The heart is a muscular organ that pumps blood throughout the body. It is the main organ of the cardiovascular system. The heart is made up of muscle and tissue, with cardiac muscle tissue, also known as myocardium, forming the heart walls' middle layer.
Cardiac muscle is one of three major categories of muscles found in the human body, the other two being smooth muscle and skeletal muscle. Cardiac muscle is made up of sarcomeres, which allow for contractility. However, unlike skeletal muscle, cardiac muscle is under involuntary control. It is composed of individual cardiac muscle cells, known as cardiomyocytes, joined by intercalated discs. Cardiomyocytes are rectangular, branching cells that typically contain only one centrally-located nucleus. The nucleus is the "control center" of a cell, containing all of its genetic material.
Cardiac muscle tissue is only found in the heart, where it performs coordinated contractions that allow the heart to pump blood through the circulatory system. These contractions require a constant supply of oxygen and nutrients to meet the energy demands of the cardiac muscle. Blood supply is delivered to the myocardium by coronary arteries, which are the first branches of the aortic root.
Cardiac muscle cells are the contracting cells that allow the heart to pump blood. Each cardiomyocyte needs to contract in coordination with its neighboring cells, known as a functional syncytium. If this coordination breaks down, the heart may not pump at all, as can occur during abnormal heart rhythms such as ventricular fibrillation.
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The heart wall has three layers, with the myocardium sandwiched between the inner endocardium and outer epicardium
The heart is a muscular organ that pumps blood throughout the body. It is a vital organ of the cardiovascular system. The heart wall has three layers, with the myocardium sandwiched between the inner endocardium and outer epicardium.
The myocardium is the cardiac muscle or heart muscle that forms the middle and thickest layer of the heart wall. It is composed of cardiac muscle cells or cardiomyocytes, which are stimulated to contract and relax, pumping blood through the cardiovascular system. The myocardium is supplied with blood by the coronary arteries, which are the first branches of the aortic root.
The endocardium is the innermost layer of the heart wall. It lines the cardiac chambers, covers the cardiac valves, and joins with the endothelium that lines the blood vessels connected to the heart. The endocardium is also known as the subendocardium in the context of the cardiac drainage system, which comprises lymphatic capillaries and pre-collector vessels within each layer of the heart wall.
The outer layer of the heart wall is the epicardium, also known as the visceral pericardium or the subepicardium. It forms part of the pericardial sac that surrounds, protects, and lubricates the heart. The pericardial sac produces fluid to prevent the heart from rubbing against other organs.
The heart wall is thus composed of three layers, with the myocardium at its centre, surrounded by the inner endocardium and outer epicardium. These layers work together to facilitate the vital function of pumping blood throughout the body.
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Cardiomyocytes are the contractile cells of the myocardium that allow the heart to pump blood
The heart is a muscular organ that pumps blood throughout the body. It is the main organ of the cardiovascular system, a network of blood vessels that delivers oxygen and nutrients to cells and removes carbon dioxide and waste products. The heart beats thousands of times a day, and this is made possible by the cardiac muscle, also known as the myocardium.
The myocardium is the thick middle layer of the heart, sandwiched between the inner endocardium and the outer epicardium. The heart wall is a three-layered structure, with the myocardium making up the bulk of the heart. The myocardium is composed of cardiac muscle cells, also known as cardiomyocytes, which are the contractile cells of the myocardium. Cardiomyocytes are striated, branched, and contain many mitochondria. They are tubular structures composed of chains of myofibrils, which are rod-like units within the cell.
The myofibrils consist of repeating sections of sarcomeres, which are the fundamental contractile units of muscle cells. Sarcomeres are composed of long proteins that organize into thick and thin filaments, called myofilaments. The thick myofilaments contain the protein myosin, while the thin myofilaments contain the protein actin. When the muscle contracts, the myofilaments slide past each other, producing the formation of "cross-bridges," which causes contraction of the heart and generates force.
The primary function of cardiomyocytes is to contract, and this contraction generates the pressure needed to pump blood through the circulatory system. Each cardiomyocyte must contract in coordination with its neighbouring cells, working together 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 cardiomyocytes is regulated by calcium concentrations within the cell, with higher calcium concentrations leading to increased contraction.
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The cardiac muscle is striated and composed of individual cardiac muscle cells joined by intercalated discs
The heart is a hard-working muscle that beats thousands of times a day to keep us alive. It is the main organ of the cardiovascular system, a network of blood vessels that pumps blood throughout the body. The heart is made up of three layers: the pericardium, myocardium, and endocardium. The myocardium, or cardiac muscle, is the muscular middle layer of the heart.
Cardiac muscle is one of three major categories of muscles in the human body, along with smooth muscle and skeletal muscle. It is composed of cardiac muscle cells, also known as cardiomyocytes or myocytes, which are striated, branched, and contain many mitochondria. Each cardiomyocyte contains a single, centrally located nucleus surrounded by a cell membrane called the sarcolemma. The sarcolemma contains voltage-gated calcium channels, which are specialized ion channels that skeletal muscles do not possess.
Cardiac muscle cells are connected to one another at their ends by intercalated discs, which are part of the cardiac muscle sarcolemma. These intercalated discs contain gap junctions and desmosomes. The gap junctions allow the cardiomyocytes to be connected with surrounding muscle fibers and the specialized fibers of the heart's conduction system. This enables the cardiomyocytes to contract together synchronously in a wave-like pattern, allowing the heart to work as a pump and blood to be pumped into the vessels of the circulatory system.
The contractions of the heart (heartbeats) are controlled by specialized cardiac muscle cells called pacemaker cells, which directly control heart rate. These cells respond to signals from the autonomic nervous system to speed up or slow down the heart rate and can also respond to various hormones that modulate heart rate to control blood pressure.
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The heart muscle is one of the earliest functioning embryonic organs, contracting and beating throughout a person's lifetime
The heart is a fist-sized organ that pumps blood throughout the body. It is the circulatory system's main organ and is composed of muscle and tissue. The heart is one of the first functional organs in the embryo, starting to beat around 22–23 days after conception, even before it has fully formed.
The heart is composed of four muscular sections (chambers) that briefly hold blood before moving it. Electrical impulses make the heart beat, moving blood through these chambers. The heart's main function is to move blood throughout the body, bringing oxygen and nutrients to cells and removing carbon dioxide and waste.
The heart is composed of cardiac muscle, also known as the myocardium, which makes up the muscular middle layer of the heart. The myocardium forms the muscular bulk of the embryonic heart. Cardiac muscle is one of three major categories of muscles in the human body, along with smooth muscle and skeletal muscle. Cardiac muscle is made up of sarcomeres that allow for contractility, and it beats involuntarily without any conscious input.
Cardiac muscle cells, or cardiomyocytes, are slowly replaced throughout a person's lifetime, although this process slows as we age. Researchers have been able to create cardiomyocytes in the lab using embryonic stem cells and induced pluripotent stem cells (iPSCs), with the hope that these could be used to repair injured heart muscle. However, there are currently no proven stem cell treatments for heart disease.
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Frequently asked questions
Cardiac muscle, also called myocardium, forms the heart walls.
Myocardium is the middle and thickest layer of the heart wall. It is made up of cardiomyocytes, which are rectangular, branching cells.
Cardiomyocytes are contractile cells that make up the myocardium. They are responsible for the heart's pumping action.
The heart wall is made up of three layers: the inner endocardium, the middle myocardium, and the outer epicardium or pericardium.
The myocardium is responsible for the contractile function of the heart, allowing it to pump blood through the cardiovascular system.
