Logan Steele
The human heart is a vital organ that pumps blood throughout the body. The heart is made up of muscle tissue, with the outer layer called the pericardium, the muscular middle layer called the myocardium, and the thin inner layer called the endocardium. The myocardium contracts and relaxes to pump blood out of the heart, while the endocardium forms the inner walls and heart valves. The heart's electrical system, powered by the sinoatrial (SA) node, enables the heart to contract and pump blood effectively. Cardiac muscle cells contain branched fibres that contract together, allowing the heart to work as a pump. The heart's ability to pump blood can be impacted by conditions such as coronary artery disease, congestive heart failure, and arrhythmia.
| Characteristics | Values |
|---|---|
| Location | Under the rib cage, to the left of the breastbone (sternum) and between the lungs |
| Composition | Three layers of muscle tissue: Pericardium, Myocardium, and Endocardium |
| Function | Pumps oxygen and nutrient-rich blood throughout the body |
| Blood supply | Coronary arteries, a branch of the aorta |
| Contraction | Contraction and relaxation of the heart muscle pump blood, this requires a constant supply of energy |
| Mitochondria | Has 10 times more mitochondria than normal muscle cells, enabling better oxygen utilisation |
| Electrical activity | Electrical impulses travel through the heart, causing it to contract |
| Pacemaker cells | Sinoatrial (SA) and Atrioventricular (AV) nodes fire spontaneously, sending electrical activity throughout the heart |
| Cardiac fibroblasts | Act as scaffolding for the tissue, responsible for tissue scarring |
| Fuel | Flexible in terms of fuel, can burn glucose, free fatty acids, and lactate |
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What You'll Learn
The heart's muscular walls
The heart is a vital organ that pumps oxygen-rich blood throughout the body. The heart is encased in a protective sac called the pericardium, which produces fluid to lubricate the heart and prevent it from rubbing against other organs. The pericardium is composed of three layers of muscle tissue.
The outermost layer of the heart wall is called the epicardium, which is a part of the pericardium. Beneath the epicardium lies the myocardium, a thick, muscular middle layer that contracts and relaxes to pump blood out of the heart. The myocardium is composed of cardiac muscle cells, which contain branched fibres connected by intercalated discs. These fibres allow the cardiomyocytes to contract together synchronously, enabling the heart to function as a pump. The myocardium is highly flexible in terms of fuel and can utilise energy more efficiently than other muscles in the body. This is due to its high concentration of mitochondria, which allows it to extract and utilise oxygen more effectively.
The innermost layer of the heart is the endocardium, which forms the inner walls and heart valves. The muscle fibres in the endocardium are arranged differently from those in the epicardium, turning almost 90 degrees. This unique arrangement allows the heart to contract with a twisting motion, similar to wringing out a cloth. The endocardium is also responsible for the formation of the endocardial cushions, which separate the left and right atria and ventricles.
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Heart failure
The heart is a muscular pump, a little larger than a fist, located under the rib cage, to the left of the breastbone and between the lungs. It is composed of heart muscles or the myocardium, between an inner layer called the endocardium and an outer layer called the epicardium. The heart's primary function is to pump oxygen and nutrient-rich blood throughout the body to sustain life. This is achieved through the contraction of the heart muscles, which is fuelled by a constant and continuous supply of energy.
The condition can be caused by coronary artery disease, which occurs when the coronary arteries narrow to the point that blood flow to the heart muscle is limited. This can lead to reduced oxygen supply to the heart muscle, causing chest pain and, in severe cases, cell death.
The treatment for heart failure varies depending on the stage and symptoms. While there is no cure, the condition can be managed through medications and healthy lifestyle changes, such as diet and exercise. With treatment and lifestyle modifications, it is possible to achieve remission and lead a full and enjoyable life.
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Electrical impulses
The heart is a vital organ that pumps blood throughout the body. It is composed of cardiac muscle cells, which contract and relax to pump blood. The heart has an electrical conduction system that sends electrical impulses throughout the heart, triggering the heartbeat.
The electrical impulses that drive the heartbeat originate in a small bundle of specialized cells called the SA node (sinoatrial node), located in the right atrium. This node functions as the heart's natural pacemaker, spontaneously generating electrical activity without requiring external stimulation.
The SA node initiates the cardiac action potential, which consists of five phases: resting, upstroke, early repolarization, plateau, and final repolarization. During the resting phase, the Na/K ATPase pump maintains the negative intracellular potential by exchanging three sodium ions for two potassium ions. In the upstroke phase, sodium channels open, resulting in a rapid influx of sodium ions and depolarization of the cell.
As the electrical impulses propagate through the heart, they cause the atrial walls to contract. This contraction forces blood into the ventricles, which then contract, pumping blood out of the heart. The cardiac muscle cells are interconnected by intercalated discs, allowing them to contract synchronously and ensuring the efficient pumping of blood.
The heart's ability to contract and pump blood can be impacted by various factors, including coronary artery disease, when plaque buildup or blood clots narrow the coronary arteries, reducing blood flow and oxygen supply to the heart muscle. This can lead to conditions such as congestive heart failure, where the heart becomes too weak to effectively pump blood throughout the body.
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Coronary artery disease
The heart is a muscular organ located under the rib cage, to the left of the breastbone and between the lungs. It is responsible for pumping oxygen and nutrient-rich blood throughout the body, supplying essential oxygen and nutrients to body tissues and removing waste products.
The primary symptom of CAD is angina, characterized by chest pain and discomfort. This pain occurs due to the narrowed arteries blocking blood flow to the heart muscle and the rest of the body. In some cases, CAD may present as a heart attack or cardiac arrest, where the heart suddenly stops pumping blood. Other symptoms include shortness of breath, nausea, fatigue, and heart palpitations.
The treatment and management of CAD involve a combination of lifestyle changes, medications, and surgical procedures. Lifestyle modifications include adopting a healthier diet with reduced sodium and fat, increasing physical activity, achieving a healthy weight, and quitting smoking. Medications are often prescribed to address risk factors such as high cholesterol, high blood pressure, and irregular heartbeat. Surgical procedures may be necessary to restore blood flow to the heart and can include procedures such as angioplasty, stenting, or coronary artery bypass grafting.
It is important to note that CAD is a serious condition that requires medical attention. Individuals concerned about their heart health or experiencing symptoms indicative of CAD should consult with a healthcare professional for personalized advice, diagnosis, and treatment options.
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Cardiac fibroblasts
The identity and origin of disease-activated fibroblasts within the heart have been a subject of ongoing debate. Tissue-resident fibroblasts of embryonic origin are found throughout the adult mouse heart, and recent studies indicate that they differentiate into and constitute the majority of disease-activated fibroblasts and myofibroblasts after cardiac injury.
Better understanding the signalling pathways in cardiac fibroblasts may provide insight into potential therapeutic targets for treating heart failure. For example, cytokines such as interleukin-6 (IL-6) are critical in myocardial function and cardioprotection. Continuous activation of the gp130 receptor has been linked to myocardial hypertrophy, and constant IL-6Rα stimulation can reduce infarct size and protect against apoptosis.
Gap junctions are essential in maintaining a normal heartbeat, and direct interactions between myocytes and cardiac fibroblasts occur via gap junctional connexins (Cx40, Cx43, and Cx45) to facilitate electrical conduction in the heart.
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Frequently asked questions
The heart is made up of three layers of muscle tissue: the pericardium, myocardium, and endocardium. The myocardium is the thick, muscular middle layer that contracts and relaxes to pump blood out of the heart to the rest of the body.
The heart pumps blood through a system of blood vessels called the circulatory system. The atria and ventricles work together, contracting and relaxing to make the heart beat and pump blood. The heart beats about 100,000 times a day, pumping around 2,000 gallons of blood each day.
When the heart can't pump blood properly, it is known as heart failure. This can cause blood to back up and fluid to accumulate in the lungs or body tissues. It can also affect the kidneys' ability to dispose of waste. Conditions such as coronary artery disease, arrhythmia, and high blood pressure can impact the heart's ability to pump blood effectively.
