Cardiovascular.

http://www.medicalartlibrary.com/artery-system/

The superior vena cava and inferior vena cava (not shown) bring deoxygenated blood from the body into the right atrium, from which it enters the right ventricle. Blood leaves the right ventricle via the pulmonary trunk.

The pulmonary trunk delivers deoxygenated blood to the lungs. It splits into the right and left pulmonary arteries which go to the right and left lung.

Oxygenated blood from the lungs re-enters the heart via the pulmonary veins (not shown) on the posterior aspect of the left atrium. From here it enters the left ventricle and is delivered to the body via the aorta.

The right and left coronary arteries arise from the base of the aorta and are embedded in the epicardial fat on the surface of the heart. Branches shown are the right coronary artery, marginal artery (right) and left anterior descending arterty (left).

The left anterior descending artery lies in the anterior interventricular sulcus, which separates the left and right ventricles.

The aortic branches shown are the left common carotid artery to the head and neck, the left subclavian artery, to the left arm and body wall. The brachiocephalic trunk divides into the right carotid and subclavian arteries.

The ligamentum arteriosum is the fibrous remnant of the ductus arteriosus which allows blood to bypass the lungs in the developing fetus. The ductus closes at birth normally within two weeks.

This cross section of the heart shows the right ventricle, tricuspid valve, left ventricle, bicuspid (mitral) valve, left atrium, right atrium, superior vena cava, inferior vena cava, aorta, aortic valve, papillary muscle, chordae tendineae, and trabeculae carneae.

The heart ventricular walls consist of three layers:
the 1.epicardium, the 2.myocardium (cardiac muscle), and the 3.endocardium.

The muscular wall separating the two ventricles is the interventricular septum.

When the heart must work harder to pump blood because of increased systemic vascular resistance, the heart’s left ventricle muscular walls get thicker, such as a biceps muscle will get larger after weight training,

This is called left ventricular hypertrophy. The most common cause is high blood pressure or hypertension.

Vascular Resistance

The body uses blood vessel diameter as one way to help regulate blood pressure. A normal blood vessel has some degree of smooth muscle contraction (or "tone") that determines the diameter of the vessel. Nerves controlling the muscle fibers in the media and certain substances in the blood, can cause the vessel to contract (vasoconstriction) or to expand (vasodilation). When blood pressure is too high, blood vessels expand to allow more blood flow. This decreases systemic vascular resistance and lowers blood pressure. When blood pressure is low, vessels constrict to increase resistance and blood pressure.

Healthy arterial walls stretch easily in response to blood pressure. Arteries damaged by atherosclerosis become rigid, their walls are infiltrated by calcium, fatty and fibrous tissue which makes them less flexible. The lumen becomes narrowed, decreasing blood flow.

The coronary arteries supply oxygen to the heart muscle. When an artery is narrowed by atherosclerotic plaque, the blood flow and therefore, oxygen supply to the heart muscle is decreased, causing myocardial ischemia (angina).

If a blood clot or atheroma blocks the artery completely, oxygen is cut off and the area of the heart muscle supplied by the artery can die. This is called a myocardial infarction or "heart attack".

The structures shown on this illustration are:
the right coronary artery, a blood clot occluding the left anterior descending artery, and a myocardial infarct.

The wall of an artery contains 3 layers: the tunica intima, the tunica media, and the tunica externa. The intima is the thinnest layer, only one cell thick, it surrounds the lumen of the blood vessel through which blood flows. The media is usually the thickest containing layers of smooth muscle cells and elastic fibers. The externa is made up of mostly elastic and collagen fibers.

Atherosclerosis occurs when the intima becomes damaged, possibly by infection or inflammation. Cholesterol and other fatty material collects in the artery wall. Muscle cells and fibrous tissue move in and calcium and cell debris accumulate. This creates a thickening called an atheroma or atherosclerotic plaque.

In the United States atherosclerosis surpasses cancer as the leading cause of death and illness.

When arteries to the heart (coronary arteries) and brain become narrowed by plaque, a blood clot may become lodged, cutting off blood flow and causing a heart attack or stroke.

The main arteries are:

aorta

Head & Neck:

external carotid artery
internal carotid artery
common carotid artery

Arm:

subclavian artery
brachial artery
radial artery
ulnar artery

Leg:

common iliac artery
external iliac artery
femoral artery
popliteal artery
anterior tibial artery
posterior tibial artery.

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The heart is a muscular organ about the size of a fist, located just behind and slightly left of the breastbone. The heart pumps blood through the network of arteries and veins called the cardiovascular system.

The heart has four chambers:

• The right atrium receives blood from the veins and pumps it to the right ventricle.
• The right ventricle receives blood from the right atrium and pumps it to the lungs, where it is loaded with oxygen.
• The left atrium receives oxygenated blood from the lungs and pumps it to the left ventricle.
• The left ventricle (the strongest chamber) pumps oxygen-rich blood to the rest of the body. The left ventricle’s vigorous contractions create our blood pressure.

The coronary arteries run along the surface of the heart and provide oxygen-rich blood to the heart muscle. A web of nerve tissue also runs through the heart, conducting the complex signals that govern contraction and relaxation. Surrounding the heart is a sac called the pericardium.

Heart Conditions

• Coronary artery disease: Over the years, cholesterol plaques can narrow the arteries supplying blood to the heart. The narrowed arteries are at higher risk for  complete blockage from a sudden blood clot (this blockage is called a heart attack).
• Stable angina pectoris: Narrowed coronary arteries cause predictable chest pain or discomfort with exertion. The blockages prevent the heart from receiving the extra oxygen needed for strenuous activity. Symptoms typically get better with rest.
• Unstable angina pectoris: Chest pain or discomfort that is new, worsening, or occurs at rest. This is an emergency situation as it can precede a heart attack, serious abnormal heart rhythm, or cardiac arrest.
• Myocardial infarction (heart attack): A coronary artery is suddenly blocked. Starved of oxygen, part of the heart muscle dies.
• Arrhythmia (dysrhythmia): An abnormal heart rhythm due to changes in the conduction of electrical impulses through the heart. Some arrhythmias are benign, but others are life-threatening.
• Congestive heart failure: The heart is either too weak or too stiff to effectively pump blood through the body. Shortness of breath and leg swelling are common symptoms.
• Cardiomyopathy: A disease of heart muscle in which the heart is abnormally enlarged, thickened, and/or stiffened. As a result, the heart's ability to pump blood is weakened.
• Myocarditis: Inflammation of the heart muscle, most often due to a viral infection.
• Pericarditis: Inflammation of the lining of the heart (pericardium). Viral infections, kidney failure, and autoimmune conditions are common causes.
• Pericardial effusion: Fluid between the lining of the heart (pericardium) and the heart itself. Often, this is due to pericarditis.
• Atrial fibrillation: Abnormal electrical impulses in the atria cause an irregular heartbeat. Atrial fibrillation is one of the most common arrhythmias.
• Pulmonary embolism: Typically a blood clot  travels through the heart to the lungs. 
• Heart valve disease: There are four heart valves, and each can develop problems. If severe, valve disease can cause congestive heart failure.
• Heart murmur: An abnormal sound heard when listening to the heart with a stethoscope. Some heart murmurs are benign; others suggest heart disease.
• Endocarditis: Inflammation of the inner lining or heart valves of the heart. Usually, endocarditis is due to a serious infection of the heart valves.
• Mitral valve prolapse: The mitral valve is forced backward slightly after blood has passed through the valve. 
• Sudden cardiac death: Death caused by a sudden loss of heart function (cardiac arrest).
• Cardiac arrest: Sudden loss of heart function.

• Heart Tests

• Electrocardiogram (ECG or EKG): A tracing of the heart’s electrical activity. Electrocardiograms can help diagnose many heart conditions.
• Echocardiogram: An ultrasound of the heart. An echocardiogram provides direct viewing of any problems with the heart muscle’s pumping ability and heart valves.
• Cardiac stress test: By using a treadmill or medicines, the heart is stimulated to pump to near-maximum capacity. This may identify people with coronary artery disease.
• Cardiac catheterization: A catheter is inserted into the femoral artery in the groin and threaded into the coronary arteries. A doctor can then view X-ray images of the coronary arteries or any blockages and perform stenting or other procedures.
• Holter monitor: If a doctor suspects an arrhythmia, a portable heart monitor can be worn. Called a Holter monitor, it records the heart's rhythm continuously for a 24 hour period.
• Event monitor: If a doctor suspects an infrequent arrhythmia, a portable heart monitor called an event monitor can be worn. When you develop symptoms, you can push a button to record the heart's electrical rhythm.

• Heart Treatments

• Exercise: Regular exercise is important for heart health and most heart conditions. Talk to your doctor before starting an exercise program if you have heart problems.
• Angioplasty: During cardiac catheterization, a doctor inflates a balloon inside a narrowed or blocked coronary artery to widen the artery. A stent is often then placed to keep the artery open.
• Percutaneous coronary intervention (PCI): Angioplasty is sometimes called a PCI or PTCA (percutaneous transluminal coronary angioplasty) by doctors.
• Coronary artery stenting: During cardiac catheterization, a doctor expands a wire metal stent inside a narrowed or blocked coronary artery to open up the area. This lets blood flow better and can abort a heart attack or relieve angina (chest pain).
• Thrombolysis: “Clot-busting” drugs injected into the veins can dissolve a blood clot causing a heart attack. Thrombolysis is generally only done if stenting is not possible.
• Lipid-lowering agents: Statins and other cholesterol (lipid) lowering drugs reduce the risk for heart attack in high-risk people.
• Diuretics: Commonly called water pills, diuretics increase urination and fluid loss. This reduces blood volume, improving symptoms of heart failure.
• Beta-blockers: These medicines reduce strain on the heart and lower heart rate. Beta-blockers are prescribed for many heart conditions, including heart failure and arrhythmias.
• Angiotensin-converting enzyme inhibitors (ACE inhibitors): These blood pressure medicines also help the heart after some heart attacks or in congestive heart failure.
• Aspirin: This powerful medicine helps prevent blood clots (the cause of heart attacks). Most people who have had heart attacks should take aspirin.
• Clopidogrel (Plavix): A clot-preventing medicine that prevents platelets from sticking together to form clots. Clopidogrel is especially important for many people who have had stents placed.
• Antiarrhythmic medications: Numerous medicines help control the heart’s rate and electrical rhythm. These help prevent or control arrhythmias.
• AED (automated external defibrillator): If someone has sudden cardiac arrest, an AED can be used to assess the heart rhythm and send an electrical shock to the heart if necessary.
• ICD (Implantable cardioverter defibrillator): If a doctor suspects you are at risk for a life-threatening arrhythmia, an implantable cardioverter defibrillator may be surgically implanted to monitor your heart rhythm and send an electrical shock to the heart if necessary.
• Pacemaker: To maintain a stable heart rate, a pacemaker can be implanted. A pacemaker sends electrical signals to the heart when necessary to help it beat properly.
• http://www.webmd.com/heart/picture-of-the-heart#3
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• http://www.livescience.com/34655-human-heart.html

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  Credit: Dreamstime

  The human heart is an organ that pumps blood throughout the body via the circulatory system, supplying oxygen and nutrients to the tissues and removing carbon dioxide and other wastes.

  "The tissues of the body need a constant supply of nutrition in order to be active," said Dr. Lawrence Phillips, a cardiologist at NYU Langone Medical Center in New York. "If [the heart] is not able to supply blood to the organs and tissues, they'll die."

  Human heart anatomy

  In humans, the heart is roughly the size of a large fist and weighs between about 10 to 12 ounces (280 to 340 grams) in men and 8 to 10 ounces (230 to 280 grams) in women, according to Henry Gray's "Anatomy of the Human Body." 

   

  The physiology of the heart basically comes down to "structure, electricity and plumbing," Phillips told Live Science.

  

  

  The human heart is about the size of a fist.

  Credit: tlornaShutterstock

  The human heart has four chambers: two upper chambers (the atria) and two lower ones (the ventricles), according to the National Institutes of Health. The right atrium and right ventricle together make up the "right heart," and the left atrium and left ventricle make up the "left heart." A wall of muscle called the septum separates the two sides of the heart.

  A double-walled sac called the pericardium encases the heart, which serves to protect the heart and anchor it inside the chest. Between the outer layer, the parietal pericardium, and the inner layer, the serous pericardium, runs pericardial fluid, which lubricates the heart during contractions and movements of the lungs and diaphragm.

  The heart's outer wall consists of three layers. The outermost wall layer, or epicardium, is the inner wall of the pericardium.  The middle layer, or myocardium, contains the muscle that contracts. The inner layer, or endocardium, is the lining that contacts the blood.

  The tricuspid valve and the mitral valve make up the atrioventricular (AV) valves, which connect the atria and the ventricles. The pulmonary semi-lunar valve separates the right ventricle from the pulmonary artery, and the aortic valve separates the left ventricle from the aorta. The heartstrings, or chordae tendinae, anchor the valves to heart muscles.

  The sinoatrial node produces the electrical pulses that drive heart contractions.

  Human heart function

  The heart circulates blood through two pathways: the pulmonary circuit and the systemic circuit.

  In the pulmonary circuit, deoxygenated blood leaves the right ventricle of the heart via the pulmonary artery and travels to the lungs, then returns as oxygenated blood to the left atrium of the heart via the pulmonary vein.

  In the systemic circuit, oxygenated blood leaves the body via the left ventricle to the aorta, and from there enters the arteries and capillaries where it supplies the body's tissues with oxygen. Deoxygenated blood returns via veins to the venae cavae, re-entering the heart's right atrium.

  Of course, the heart is also a muscle, so it needs a fresh supply of oxygen and nutrients, too, Phillips said.

  

  The cardiovascular system circulates blood from the heart to the lungs and around the body via blood vessels.

  Credit: The BioDigital HumanTM developed by NYU School of Medicine and BioDigital Systems LLC

  "After the blood leaves the heart through the aortic valve, two sets of arteries bring oxygenated blood to feed the heart muscle," he said. The left main coronary artery, on one side of the aorta, branches into the left anterior descending artery and the left circumflex artery. The right coronary artery branches out on the right side of the aorta.

  Blockage of any of these arteries can cause a heart attack, or damage to the muscle of the heart, Phillips said. A heart attack is distinct from cardiac arrest, which is a sudden loss of heart function that usually occurs as a result of electrical disturbances of the heart rhythm. A heart attack can lead to cardiac arrest, but the latter can also be caused by other problems, he said.

  The heart contains electrical "pacemaker" cells, which cause it to contract — producing a heartbeat.

  "Each cell has the ability to be the 'band leader' and [to] have everyone follow," Phillips said. In people with an irregular heartbeat, or atrial fibrillation, every cell tries to be the band leader, he said, which causes them to beat out of sync with one another.

  A healthy heart contraction happens in five stages. In the first stage (early diastole), the heart is relaxed. Then the atrium contracts (atrial systole) to push blood into the ventricle. Next, the ventricles start contracting without changing volume. Then the ventricles continue contracting while empty. Finally, the ventricles stop contracting and relax. Then the cycle repeats. 

  Valves prevent backflow, keeping the blood flowing in one direction through the heart.

  

  

  
  

  Facts about the human heart

  • A human heart is roughly the size of a large fist.
  • The heart weighs between about 10 to 12 ounces (280 to 340 grams) in men and 8 to 10 ounces (230 to 280 grams) in women.
  • The heart beats about 100,000 times per day (about 3 billion beats in a lifetime).
  • An adult heart beats about 60 to 80 times per minute.
  • Newborns' hearts beat faster than adult hearts, about 70 to 190 beats per minute.
  • The heart pumps about 6 quarts (5.7 liters) of blood throughout the body.
  • The heart is located in the center of the chest, usually pointing slightly left.