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The heart is a muscular organ that pumps blood around the body. It is made up of cardiac muscle, also known as the myocardium, which is one of three types of vertebrate muscle tissues, the others being skeletal muscle and smooth muscle. The heart is a vital organ for the body's overall health and function, and it is important to take good care of it through exercise, a healthy diet, and not smoking.
| Characteristics | Values |
|---|---|
| What is the heart | A muscular organ |
| Types of vertebrate muscle tissues | Three – cardiac muscle, skeletal muscle, and smooth muscle |
| Cardiac muscle | Also called heart muscle or myocardium |
| Cardiac muscle composition | Individual cardiac muscle cells or cardiomyocytes joined by intercalated discs |
| Cardiac muscle location | Forms a thick middle layer between the outer layer of the heart wall (the pericardium) and the inner layer (the endocardium) |
| Blood supply to cardiac muscle | Via the coronary circulation |
| Cardiac muscle contraction | Similar to skeletal muscle but with some differences |
| Cardiac muscle control | Under involuntary control |
| Heart chambers | Four – two atria and two ventricles |
| Heart function | To pump blood to the organs and tissues of the body |
| Heart diseases | Coronary artery disease, ischemic conditions, angina, myocardial infarction, heart attack, heart failure, and arrhythmia |
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What You'll Learn
The heart is a muscular organ
The heart has three layers: the outer layer of the heart wall (the pericardium or epicardium), the middle layer (the myocardium), and the inner layer (the endocardium). The myocardium is the thickest layer and is made up of cardiac muscle. The endocardium is not cardiac muscle but is made up of simple squamous epithelial cells. The outer layer of the heart, the pericardium, is a fibrous sac that surrounds, protects, and lubricates the heart.
The heart begins as a single chamber, but four separate chambers are created through the growth of various septa. The top two chambers are called atria and receive blood from other parts of the body. The bottom two chambers are called ventricles and pump blood to other parts of the body. The ventricle walls are thicker, containing more cardiac muscle. The heart also contains valves that help keep blood flowing in the correct direction.
The heart is under involuntary control and is made up of sarcomeres that allow for contractility. The contractile functions of the heart require ATP, which can be obtained through various substrates, including fatty acids, carbohydrates, proteins, and ketones. The coordinated contractions of the cardiac muscle are controlled by special cells called pacemaker cells, which set the rhythm of the heart contractions.
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Cardiac muscle
The heart is a muscular organ that pumps blood throughout the body. It is made up predominantly of a type of muscle tissue called cardiac muscle. Cardiac muscle is also called myocardium. It is one of the three major categories of muscles in the human body, the other two being smooth muscle and skeletal muscle.
The coordinated contractions of cardiac muscle are controlled by special cells called pacemaker cells, which are a type of cardiomyocyte. These cells set the rhythm of the heart contractions and are only weakly contractile. They are located in the sinoatrial node (the primary pacemaker) on the wall of the right atrium. The pacemaker cells generate electrical impulses that tell the cardiac muscle cells to contract and relax, controlling the heart rate and determining how fast the heart pumps blood.
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Coronary circulation
The heart is a muscular organ that pumps blood throughout the body. It is made up of a type of muscle tissue called cardiac muscle, which is one of three types of vertebrate muscle tissues, the others being skeletal muscle and smooth muscle. The heart has three layers—the pericardium, myocardium, and endocardium. The myocardium, or cardiac muscle, forms a thick middle layer between the outer layer of the heart wall (the pericardium) and the inner layer (the endocardium).
The coronary circulation is the circulation of blood in the arteries and veins that supply the heart muscle (myocardium). Coronary circulation delivers oxygenated blood to the heart muscle through the coronary arteries and cardiac veins, which then drain the blood after it has been deoxygenated. The coronary arteries originate from the aortic root and lie on the outer or epicardial surface of the heart. The coronary veins then drain the blood into the right atrium. The coronary circulation is of major importance as interruptions can quickly cause heart attacks (myocardial infarctions) due to oxygen starvation of the heart muscle.
The coronary circulation can be classified as right-dominant, left-dominant, or co-dominant, depending on which artery supplies the posterior descending artery. The right coronary artery supplies blood to the right side of the heart, including the right ventricle, right atrium, and the SA (sinoatrial) and AV (atrioventricular) nodes, which control the heart rhythm. The left coronary artery supplies blood to the left atrium and left ventricle. The left anterior descending artery (LAD) is a branch of the left coronary artery that gives rise to smaller branches that interconnect with the branches of the posterior interventricular artery, forming anastomoses, or areas where vessels unite to allow blood circulation even if there is a partial blockage in another branch.
The most common cause of compromised coronary circulation is coronary artery disease (CAD), which is caused by the buildup and rupture of plaques that decrease the diameter of the coronary lumen, resulting in a mismatch between oxygen demand and delivery. Atherosclerosis, or the buildup of plaque in the inner lining of an artery, is the most common cause of heart disease. This causes the artery to become narrow or blocked, reducing the flow of oxygen and nutrients to the heart muscle and leading to serious health problems, including heart attacks.
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Cardiomyocytes
The heart is a muscular organ that pumps blood throughout the body. It is made up of three layers, with the middle layer, called the myocardium, being largely cardiac muscle. This cardiac muscle is a special type of muscle tissue that is only found in the heart.
Cardiac muscle cells, or cardiomyocytes, are the contractile myocytes of the cardiac muscle. They are the primary cell type in the myocardium that terminally differentiate into muscular cells. Cardiomyocytes are striated, branched, and contain many mitochondria. They are under involuntary control, contracting in a coordinated manner to enable the heart to work as a pump.
The intercalated discs connect individual cardiomyocytes to an electrochemical syncytium, forming long fibers. These discs are responsible for force transmission during muscle contraction and enable the rapid transmission of electrical impulses through the network. The jagged appearance of the intercalated disc is caused by the strong attractive forces between the sarcolemmae of the joining myocytes, which are bound together by desmosomes.
The sarcolemma of cardiac muscle cells contains voltage-gated calcium channels, specialized ion channels that skeletal muscle does not possess. The rise in calcium causes the cell's myofilaments to slide past each other in a process called excitation-contraction coupling. 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.
Specialized modified cardiomyocytes, known as pacemaker cells, set the rhythm of the heart contractions. They are located in the sinoatrial node (the primary pacemaker) on the wall of the right atrium.
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Heart conditions
The heart is a muscular organ, with the vital function of pumping blood to the organs and tissues of the body. The heart is made up of three layers, with the middle layer, called the myocardium, largely composed of cardiac muscle. This is a special type of muscle tissue that is only found in the heart.
There are many heart conditions that can affect the organ's ability to function properly. Here are some of the most common heart conditions:
Cardiomyopathy
This is a disease of the heart muscle that reduces its ability to pump blood effectively. Cardiomyopathy can be caused by a restricted blood supply to the muscle, which can lead to angina and myocardial infarction. It can also be caused by chemotherapy for cancer, or by athletic heart syndrome, where extensive exercise causes the heart to grow in size.
Congenital Heart Disease
Congenital heart disease is a heart condition that is present from birth. It occurs when something goes wrong during the formation of the heart before birth. Congenital heart disease can lead to problems immediately after birth, or there may be no symptoms until adulthood. Septal abnormalities, which are holes in the wall separating the left and right sides of the heart, are among the most common congenital heart problems. Other types of abnormalities include pulmonary stenosis, where a narrow valve reduces blood flow to the lungs.
Coronary Artery Disease
This is a common form of heart disease that occurs when the blood supply to the heart is disrupted due to a build-up of plaque on the walls of the coronary arteries. This can lead to reduced blood flow and put the heart at risk of not getting enough oxygen. Coronary artery disease can cause chest pain (angina) and increase the risk of heart attack, heart failure, and arrhythmia.
Arrhythmia
Arrhythmia is a condition where the heart beats too quickly, too slowly, or in an irregular pattern. It can be caused by coronary artery disease or other heart problems. Atrial fibrillation is a type of arrhythmia where the heart beats fast or irregularly, affecting a significant number of people.
Heart Failure
Heart failure occurs when the heart is not strong enough to pump blood effectively to meet the body's needs. It can be caused by coronary artery disease, thyroid disease, high blood pressure, cardiomyopathy, or other conditions. Heart failure can cause fluid to pool in the lungs, ankles, or legs.
It is important to note that maintaining heart health is crucial for overall well-being. Regular aerobic exercise, a healthy diet, and avoiding smoking can help promote a healthy heart.
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Frequently asked questions
The heart is a muscular organ. It is made up of a type of muscle tissue called cardiac muscle or myocardium. This is one of three types of vertebrate muscle tissues, the others being skeletal muscle and smooth muscle.
The cardiac muscle is responsible for the contractility of the heart and, therefore, the pumping action. The heart pumps blood to the organs and tissues of the body.
Coronary artery disease happens when the blood supply to the tissues of the heart is disrupted. This can lead to heart attack, heart failure, and arrhythmia.
The myocardium is the thick, middle layer of the three-layered heart wall. It is made up of cardiac muscle and is surrounded by the outer layer of the heart wall (the pericardium or the epicardium) and the inner layer (the endocardium).
