The outer layer of the heart wall is the epicardium. The epicardium refers to both the outer layer of the heart and the inner layer of the serous visceral pericardium, which is attached to the outer wall of the heart. The epicardium is a thin layer of elastic connective tissue and fat that serves as an additional layer of protection from trauma or friction for the heart under the pericardium.
This layer contains the coronary blood vessels, which oxygenate the tissues of the heart with a blood supply from the coronary arteries. The middle layer of the heart wall is the myocardium—the muscle tissue of the heart and the thickest layer of the heart wall.
It is composed of cardiac muscle cells, or cardiomyocytes. Cardiomyocytes are specialized muscle cells that contract like other muscle cells, but differ in shape. Compared to skeletal muscle cells, cardiac muscle cells are shorter and have fewer nuclei.
Cardiac muscle tissue is also striated forming protein bands and contains tubules and gap junctions, unlike skeletal muscle tissue. Due to their continuous rhythmic contraction, cardiomyocytes require a dedicated blood supply to deliver oxygen and nutrients and remove waste products such as carbon dioxide from the cardiac muscle tissue. This blood supply is provided by the coronary arteries. First, impulses are generated by the sinoatrial node SA , which is found in the wall of the superior vena cava.
It is a small mass of specialised cardiac muscle fibres and associated connective tissue, and is supplied by nerve fibres from the autonomic nervous system. Excitation of the SA node sets of a wave of depolarisation around the atria via gap junctions between the muscle fibres. Next the atrioventricular node AV starts impulse generation around the ventricles. The AV node lies in the interatrial septum. Impulses are sent from the AV node into the AV bundle, or bundle of his, which branches to form Purkinje fibres.
The AV node is also supplied by nerve fibres from the autonomic nervous system that speed up and slow down the heart rate. Purkinje fibres lie in the deepest layer of the endocardium and supply the papillary muscles. Hence the apex of the heart contracts first, followed by the papillary muscles, and then the wave of depolarisation spreads up the walls of the ventricles from the base upwards, as shown in the diagram. The Heart The heart is a muscular pump that propels blood at high pressure round the body through the blood vessels.
Treatment depends on the severity of the condition and may include medications , surgery, and lifestyle changes. Blood pressure is the pressure that blood exerts on the walls of the arteries. When blood pressure is too high , it can become dangerous and put you at risk for heart disease or stroke.
Medications and lifestyle changes can manage it. Arrhythmias happen when your heart beats too fast, too slow, or irregularly. Many things can cause an arrhythmia, such as:. Some people with arrhythmia have no symptoms. If symptoms are present, they may include things like a fluttering feeling in your chest, shortness of breath, or chest pain. Conditions that either overtax or cause damage to the heart can lead to heart failure.
Some examples include:. Common symptoms of heart failure can include feeling fatigued, being short of breath, and swelling in the lower parts of your body. Treatment can depend on the type and severity of heart failure. It can include medications, lifestyle changes, and possibly surgery.
A heart attack happens when blood flow to the heart is blocked. Coronary artery disease often causes heart attacks. Some common warning signs include things like:. A heart attack is an emergency that requires immediate medical attention. In the hospital, medications can be used to treat a heart attack.
In some cases, surgery may be needed as well. It has the vital function of working to pump blood to the organs and tissues of your body. Read this article in Spanish. Hypertensive heart disease refers to heart conditions caused by high blood pressure. Possible symptoms of acute hypertension include sweating and…. Heart attack and heart failure share many of the same risk factors and underlying health conditions.
Learn about the many differences between heart…. Your circulatory or cardiovascular system serves a vital function by delivering oxygen and nutrients to all the organs and tissues of your body.
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