Biology Notes

The heart's electrical system The atria and ventricles work together, alternately contracting and relaxing to pump blood through your heart. The electrical system of your heart is the power source that makes this possible. Your heartbeat is triggered by electrical impulses that travel down a special pathway through your heart: SA node (sinoatrial node)  – known as the heart’s natural pacemaker. The impulse starts in a small bundle of specialized cells located in the right atrium, called the SA node. The electrical activity spreads through the walls of the atria and causes them to contract. This forces blood into the ventricles. The SA node sets the rate and rhythm of your heartbeat. Normal heart rhythm is often called normal sinus rhythm because the SA (sinus) node fires regularly. AV node (atrioventricular node).  The AV node is a cluster of cells in the center of the heart between the atria and ventricles, and acts like a gate that slows the electrical signal before...

Normal Heart Beat 1.  The SA node sets the rate and rhythm of your heartbeat. 2.  The SA node fires an impulse. The impulse spreads through the walls of the right and left atria, causing them to contract. This forces blood into the ventricles. 3.  The impulse travels to the AV node. Here, the impulse slows for a moment before going on to the ventricles. 4.  The impulse travels through a pathway of fibers called the HIS-Purkinje network. This network sends the impulse into the ventricles and causes them to contract. This forces blood out of the heart to the lungs and body. 5.  The SA node fires another impulse. The cycle begins again.

What is the Cardiovascular System? The cardiovascular system refers to the heart, blood vessels and the blood. Blood contains oxygen and other nutrients which your body needs to survive. The body takes these essential nutrients from the blood. At the same time, the body dumps waste products like carbon dioxide, back into the blood, so they can be removed. The main function of the cardiovascular system is therefore to maintain blood flow to all parts of the body, to allow it to survive. Veins deliver used blood from the body back to the heart. Blood in the veins is low in oxygen (as it has been taken out by the body) and high in carbon dioxide (as the body has unloaded it back into the blood). All the veins drain into the superior and inferior vena cava which then drain into the right atrium. The right atrium pumps blood into the right ventricle. Then the right ventricle pumps blood to the pulmonary trunk, through the pulmonary arteries and into the lungs. In the lungs the blood pic...

Blood vessels Blood vessels have a range of different sizes and structures, depending on their role in the body. Arteries Oxygenated blood is pumped from the heart along arteries, which are muscular. Arteries divide like tree branches until they are slender. The largest artery is the aorta, which connects to the heart and picks up oxygenated blood from the left ventricle. The only artery that picks up deoxygenated blood is the pulmonary artery, which runs between the heart and lungs. Capillaries The arteries eventually divide down into the smallest blood vessel, the capillary. Capillaries are so small that blood cells can only move through them one at a time. Oxygen and food nutrients pass from these capillaries to the cells. Capillaries are also connected to veins, so wastes from the cells can be transferred to the blood. Veins Veins have one-way valves instead of muscles, to stop blood from running back the wrong way. Generally, veins carry deoxygenated blood from ...

Structure and Function of the Heart Function and Location of the Heart The heart’s job is to pump blood around the body. The heart is located in between the two lungs. It lies left of the middle of the chest. Structure of heart The heart is a muscle about the size of a fist, and is roughly cone-shaped. It is about 12cm long, 9cm across the broadest point and about 6cm thick. The  pericardium  is a fibrous covering which wraps around the whole heart. It holds the heart in place but allows it to move as it beats. The wall of the heart itself is made up of a special type of muscle called  cardiac muscle . Chambers of the Heart There are four chambers of heart. Atria: The upper two chambers are thin walled. They are called atria.  A wall called the  interatrial septum  is between the atria. Ventricles: The lower two chambers are thick walled . they are called ventricles. the ventricle distribute the blood. wall called the  intervent...