1REGULATION OF CARDIAC ACTIVITY________________________________________________NAME: MUZNAROLL NO: 1925238027SESSION: 2019-2021PROGRAM: MS (MORNING)SUBMITTED TO: Dr. SAIMA SHARIF_________________________________________________DEPARTMENT OF ZOOLOGYLAHORE COLLEGE FOR WOMEN UNIVERSITY,LAHORE2019
21.1.IntroductionThe heart is a muscular organ in most animals, which pumps blood through the bloodvessels of the circulatory system. The pumped blood carries oxygen and nutrients tothe body,while carrying metabolic waste suchas carbondioxide tothe lungs. In humans, the heart is approximately the size of a closed fist and is locatedbetween the lungs, in the middle compartment of the chest. In humans, other mammals, and birds, the heart is divided into four chambers: upperleft and right atria and lower left and right ventricles.Commonly the right atrium andventricle are referred together as the right heart and their left counterparts as the leftheart.Fish, in contrast, have two chambers, an atrium and a ventricle, while reptileshave three chambers.In a healthy heart blood flows one way through the heart dueto heart valves, which prevent backflow.The heart is enclosed in a protective sac,the pericardium, which also contains a small amount of fluid. The wall of the heart ismade up of three layers: epicardium, myocardium, and endocardium. The heart pumps blood with a rhythm determined by a group of pacemaking cells inthe sinoatrial node. These generate a current that causes contraction of the heart,traveling through the atrioventricular node and along the conduction system of theheart. The heart receives blood low in oxygen from the systemic circulation, whichenters the right atrium from the superior and inferior venae cavae and passes to theright ventricle. From here it is pumped into the pulmonary circulation, throughthe lungs where it receives oxygen and gives off carbon dioxide. Oxygenated bloodthen returns to the left atrium, passes through the left ventricle and is pumped outthrough the aorta to the systemic circulation−where the oxygen is usedand metabolized to carbon dioxide. The heart beats at a resting rate close to 72 beatsper minute. Exercise temporarily increases the rate, but lowers resting heart rate in thelong term, and is good for heart health. Cardiovascular diseases (CVD) are the most common cause of death globally as of2008, accounting for 30% of deaths. Of these more than three quarters are a resultof coronaryarterydisease and stroke. Riskfactorsinclude: smoking,being overweight, little exercise, high cholesterol, high blood pressure, and poorlycontrolled diabetes, among others. Cardiovascular diseases frequently do not havesymptoms or may cause chest pain or shortness of breath. Diagnosis of heart disease
3is often done by the taking of a medical history, listening to the heart-sounds witha stethoscope, ECG, and ultrasound. Specialists who focus on diseases of the heart arecalled cardiologists, although many specialties of medicine may be involved intreatment.