Page 1 :
A+ BIOLOGY-IX, , STD-9-BIOLOGY-FIRST BELL-CLASS-16, Chapter – 3, , Simple Nutrients into cells, Working of the heart,  The heart beats continuously with a rhythm., Pacemaker,  The rhythmic contraction and expansion of the heart help to pump blood with the help of a special, type of muscle present at anterior part of the right atrium. This part is called pace maker (SA, node),  The sinoatrial node (SA node) controls the initiation of the contraction and relaxation of the heart,, and the regulation of heartbeat.,  It is situated on the wall of the right atrium.,  It functions like an electric cell. So it is called pacemaker., Function of pacemaker,  Initiates the contraction and relaxation of the heart.,  Regulates the rate of heartbeat., Working of the heart, , A+ BLOG-www.apluseducare.blogspot.com or Whatsapp 9746544422, , Page 1

Page 2 :
A+ BIOLOGY-IX, Working of the heart,  The carbon dioxide rich blood is carried to the right atrium through venacava.,  The oxygenated blood from the lungs is carried to the left atrium through pulmonary vein.,  The right atrium contracts and the tricuspid valve opens. Carbon dioxide rich blood in the right, atrium enters the right ventricle through the tricuspid valve.,  The oxygenated blood from the left atrium enters the left ventricle through the bicuspid valve that, opens,  Carbon dioxide rich blood in the right ventricle is carried to the lungs through the pulmonary artery, as a result of the ventricular contraction. It helps to receive oxygen and eliminate carbon dioxide, from the lungs.,  The oxygenated blood from the left ventricle is carried to all the parts through aorta and its branches, as a result of ventricular contraction. It helps to supply oxygen to all the body parts and receive, carbon dioxide from the cells.,  Again the carbon dioxide rich blood or the deoxygenated blood from body parts is carried to the right, atrium and the oxygenated blood from the lungs is carried to the left atrium and the process is, repeated.,  The carbon dioxide-rich blood from different parts of the body reaches the right atrium. The, oxygen-rich blood from the lungs reaches the left atrium through the pulmonary veins., Subsequently the atria contract. Where does the blood go when the atria contract?,  When the atria contract, blood from the right atrium goes to the right ventricles and from the left, atrium to the left ventricle.,  Further, the ventricles contract. Does the blood flow back to the atria when the ventricles, contract? Why?,  Blood will not flow back to the atria.,  Reason: The tricuspid valve and bicuspid valve prevent the blood from flowing back.,  When the ventricles contract, which blood vessels does blood flow to?,  From the right ventricle, blood flows into the pulmonary artery. From the left ventricle, blood flows, into the aorta. You know that blood supplies oxygen to all cells, and receives carbon dioxide from, them. Reception of oxygen and expulsion of carbon dioxide take place in the lungs.,  If so, What causes an increase in the level of carbon dioxide in the blood present in the venae, cavae?,  The blood in the venae cavae is the blood collected from all the different tissues in the body. It, contains the carbon dioxide formed in the tissues due to metabolic activities. (This blood is to be sent, to the lungs for oxygenation.),  What causes an increase in the level of oxygen in the blood present in pulmonary veins?,  Blood receives oxygen at the lungs. It is this oxygenated blood that flows through the pulmonary, veins to the heart., A+ BLOG-www.apluseducare.blogspot.com or Whatsapp 9746544422, , Page 2