Health Science 20 Circulatory System Notes Functions of the Circulatory System The circulatory system functions mainly as the body s transport system. It transports: o Oxygen o Nutrients o Cell waste o Hormones o Other materials Parts of the Circulatory System Circulatory system is made up of: o Heart o Blood Vessels o Blood o Lymphatic System The Heart Heart is made up of cardiac muscle tissue. Is surrounded by a double walled sac called the pericardium. It has 4 chambers: o Two atria (right and left) which are superior to the two ventricles (also right and left). Atria are separated by septums Atria receive blood from the body/lungs Right atrium receives blood from the body and pumps to right ventricle Left atrium receives blood from the lungs and pumps to left ventricle o Two ventricles, which propel blood to the body/lungs Right ventricle pumps blood to the lungs Left ventricle pumps blood to the rest of the body Heart has four valves (that allow blood to flow in only one direction) o Tricuspid valve (between right atrium and ventricle) o Pulmonary valve (blood passes from right ventricle through this valve on way to lungs) o Mitral (bicuspid) valve (between left atrium and ventricle) o Aortic valve (blood passed from left ventricle, through aortic valve to aorta and rest of body)
Heart contractions are regulated by two systems: the autonomic nervous system and the nodal system. Nodal system causes the heart to contract in two ways: o Atria contraction (filling ventricles with blood) o Ventricle contraction (pumping blood to body) Group of cells in the right atrium (SA node or pacemaker) controls the contractions of the atrium (atria contract simultaneously) and sends a signal to the AV node which causes the ventricles to contract when the atria are beginning to relax. Path of Blood through the Heart Blood enters the heart through the superior and inferior vena cava into the right atrium. Blood is pumped into the right ventricle. Blood is pumped into the pulmonary trunk (which splits into the pulmonary arteries) to travel to the lungs for oxygenation (pulmonary circuit) Blood returns to the heart through the pulmonary veins into the left atrium. Blood is pumped into the left ventricle. Blood is pumped into the aorta to be pumped to the body cells (systemic circuit) Note: Veins bring blood back to the heart, while arteries take blood away from the heart. Cycles of the Circulatory System Cardiac (or Coronary) Circuit: path that blood travels within the heart Pulmonary Circuit: path of blood from heart to the lungs and back Systemic circuit: path of blood from the heart to the body and back Note: The heart has a lot of blood in it constantly, but this blood does not nourish the heart. Coronary arteries branch from the base of the aorta and encircle the heart. Coronary veins empty into the right ventricle.
Left side of heart pumps and receives oxygen rich blood. Right side pumps and receives oxygen poor blood.
Blood Pressure This is the force the blood exerts against the walls of our blood vessels. Pressure is created by the pumping of the heart. The cardiac cycle refers to the events that occur in one complete heartbeat. Both the atria and ventricles contract then relax. On average this happens about 75 times per minute. (heart rate = 75 beats/minute) In the systole portion of the heartbeat: o Atria are relaxed (chambers are filling with blood) o Tricuspid and mitral valves are closed o The ventricles contract o Pressure on the arteries is high In the diastole portion of the heartbeat: o Relaxation of the ventricles (filling with blood from atria) o Aortic and pulmonary valves are closed o Contraction of the atria o Pressure on arteries is low Category of blood pressure Category Systolic/Diastolic Normal 120-129 / 80-84 High-Normal 130-139 / 85-89 High blood pressure 140/90 + (measured in doctor s office) High blood pressure 135/85 + (measured at home) Electrocardiography An electrocardiograph (ECG) is a representation of the heart s electrical activity recorded from electrodes on the surface of the body. A typical ECG contains three recognizable waves: o P wave: Small wave, signals the depolarization of the atria immediately before the contraction o QRS Complex: depolarization of the ventricles immediately before the contract o T wave: repolarization of the ventricles This test helps evaluate the heart s function and identify any problems that might exist. The ECG can help determine the rate and regularity of heartbeats, the size and position of the heart s chambers, and whether there is any damage present.
The information is interpreted by a machine and drawn as a graph. The graph consists of multiple waves, which reflect the activity of the heart. The height, length, and frequency of the waves are read in the following way: o The number of waves per minute on the graph is the heart rate. o The distance between the waves on the graph is the heart rhythm. The shapes and waves of the graph show how well the heart s electrical impulses are working, the size of the heart, and how well the individual components are working together. (Can show us heart damage.) Blood Vessels (Vascular System) Blood vessels are the pathways that move blood through the body. Arteries o Carry blood AWAY from the heart (generally oxygenated (red) blood except in the pulmonary circuit). o Have a thick layer of smooth muscle which makes them elastic. o Capable of withstanding high pressures. o Smaller inner diameter than veins. o Arteries divide into smaller arteries, eventually leading into smaller branches called arterioles, which then lead to capillaries. Capillaries o Thin walled consist of a single layer of endothelial cells. o Gas, nutrient, and waste exchange happen at the capillary level of the vascular system. o Connects arteries to veins. o Intertwine among body cells. Veins o Largest diameter of blood vessels. o Capillaries empty into venules, which turn into veins. o Carry blood TOWARD the heart (generally deoxygenated (blue) blood except in pulmonary circuit). o Thin walled. o Have valves that prevent back flow of blood.