Heart
From Wikipedia, a free encyclopedia written in simple English for easy reading.
The heart is an organ in the body. It is a large muscle in the chest. It pumps blood through tubes called blood vessels.
People sometimes talk about the heart as the place responsible for feelings. This is why love is shown as a heart. But feelings are really sensed in the brain. The heart only helps us feel by giving blood to the brain.
Cardiac means about the heart.
Myocardium means the heart muscle. (Myo is from the Latin word for muscle. -cardium is from the Greek word for heart 'kardia'.)
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[edit] Structure
The human heart has four chambers or closed spaces. Some animals have only two or three chambers.
In humans, the four chambers are two atria and two ventricles. There is a right atrium and ventricle. These get blood that comes to the heart. They pump this blood to the lungs. In the lungs blood picks up oxygen and drops carbon dioxide. Blood from the lungs goes to the left atrium and ventricle. The left atrium and ventricle send the blood out to the body.
Blood is carried in blood vessels. These are arteries and veins. Blood going to the heart is carried in veins. Blood going away from the heart is carried in arteries. The main artery going out of the right ventricle is the pulmonary artery. (Pulmonary means about lungs.) The main artery going out of the left ventricle is the aorta.
The veins going into the right atrium are the superior vena cava and inferior vena cava. These bring blood from the body to the right heart. The veins going into the left atrium are the pulmonary veins. These bring blood from the lungs to the left heart.
When the blood goes from the atria to the ventricles it goes through heart valves. When blood goes out of the ventricles it goes through valves. The valves make sure that blood only goes one way in or out.
The four valves of the heart are:
- Atria to ventricle valves
- Tricuspid valve – blood goes from right atrium to right ventricle
- Mitral valve – blood goes from left atrium to left ventricle
- Ventricles to arteries
- Pulmonic valve – blood goes out of the right ventricle to the lungs (through the pulmonic artery)
- Aortic valve – blood goes out of the left ventricle to the body (through the aorta)
The heart has three layers. The outer covering is the pericardium. This is a tough sack that surrounds the heart. The middle layer is the myocardium. This is the heart muscle. The inner layer is the endocardium. This is the thin smooth lining of the chambers of the heart.
[edit] Cardiac cycle
A heart beat is when the heart muscle contracts. This means the heart pushes in and this makes the chambers smaller. This pushes blood out of the heart and into the blood vessels. After the heart contracts and pushes in, the muscle relaxes or stops pushing in. The chambers get bigger and blood coming back to the heart fills them.
When the heart muscle contracts (pushes in) it is called systole. When the heart muscle relaxes (stops pushing in), this is called diastole. Both atria do systole together. Both ventricles do systole together. But the atria do systole before the ventricles. Even though the atrial systole comes before ventricular systole, all four chambers do diastole at the same time. This is called cardiac diastole
It goes: atrial systole -> ventricular systole -> cardiac diastole. When this happens one time, it is called a cardiac cycle.
[edit] Electricity travels though the heart
Systole (when the heart pushes in) happens because the muscle cells of the heart get smaller. When they get smaller we also say they contract. Electricity going through the heart makes the cells contract. The electricity starts in the sino-atrial node (acronym SAN.) The SAN is a group of cells in the right atria. These cells start an electrical impulse. This electrical impulse goes through both atria and makes them contract. This is atrial systole. Then the electrical impulse goes through the atrio-ventricular node (acronym AVN.) The AVN makes the impulse go slower. Going slower through the AVN makes the impulse get to the ventricles later. This is why ventricular systole happens after atrial systole.
After going through the AVN the electrical impulse goes through the conduction system of the ventricle. Conduction means heat or electricity going through something. This is the way that the electrical impulse is sent to the ventricles. The first part of the conduction system is the bundle of His. His is the name of the doctor who discovered it. Bundle means things like string or wire grouped together in parallel. The bundle goes through the ventricle muscle but is separate from it. Then the bundle of His divides into left and right bundle branches. The left bundle branch goes to the left ventricle. The right bundle branch goes to the right ventricle. At the end of the bundle branches, the electrical impulse goes into the ventricular muscle. This makes the ventricle contract and makes ventricular systole.
It goes: SAN -> atria (systole) -> AVN -> bundle of His -> bundle branches – ventricles (systole)
[edit] ECG
ECG is an acronym for ElectroCardioGram. It is also written EKG for ElectroKardioGram in German. The ECG shows what the electricity in the heart is doing. An EKG is done by putting electrodes on a person's skin. The electrodes see the electricity going through the heart. This is written on paper by a machine. This writing on the paper is the ECG.
Doctors learn about the person's heart by looking at the ECG. The ECG shows some diseases of the heart like heart attacks or problems with the rhythm of the heart (how the electricity goes through the heart's conduction system.)
The ECG shows atrial systole. This is called a P-wave. Then ventricular systole happens. This is called the QRS or QRS-complex. It is called a complex because there are three different waves in it. The Q-wave, R-wave, and S-wave. Then the ECG shows ventricular diastole. This is called the T-wave. Atrial diastole happens then too. But it is not seen separate from ventricular diastole.
The PR-Interval is the space between atrial systole (P) and ventricular systole (QRS). The QT-Interval is from when the QRS starts to when the T ends. The ST-segment is the space between the QRS and T.
