Circulatory System and Circulation PDF

3. Circulatory system and circulation 3.1. Circulatory system: 3.1.1. Importance:  The circulatory system is of very important systems of the body as it ensures the exchange of substances between all the tissues of the body and the external environment and the transport of various substances...

3. Circulatory system and circulation 3.1. Circulatory system: 3.1.1. Importance:  The circulatory system is of very important systems of the body as it ensures the exchange of substances between all the tissues of the body and the external environment and the transport of various substances from one bodily organ to another. 3.1.2. Functions:  Although each part of the circulatory system has its individual functions, the system as a whole performs the following functions:  1- It provides essential chemical substances to the cells of the body which are needed for their metabolism.  2- It transports chemical waste products to those organs from where they can be excreted from the body.  3- It plays a most significant role in the prevention of and defense against invasion of infectious micro-organisms.  4- It assists in maintenance of normal body temperature and homeostasis of 1  3. Circulatory system and circulation 3.1. Circulatory system: 3.1.3. Components:  It consists of a strong, muscular heart, in which the atria (auricles) primarily receive blood, and the muscular ventricles pump blood out through the blood vessels, arteries carry blood away from the heart, capillaries exchange materials with tissue fluid, and veins return blood to the heart.  Arteries, the strongest of the blood vessels, are able to expand and constrict because their walls have substantial layers of both elastic and muscle fibers.  Arterioles are small arteries whose constriction can be regulated by the nervous system.  Capillaries are the most important part of a closed circulatory system because exchange of nutrient and waste molecules takes place across their thin walls.  Venules and veins collect blood from the capillary beds and take it to the heart.  Valves within the veins point, or open, toward the heart, preventing a back flow of 2 blood.  3. Circulatory system and circulation 3.1. Circulatory system: 3.1.3. Components (cont.): 3  3. Circulatory system and circulation 3.1. Circulatory system: 3.1.3. Components (cont.): 3.1.3.1&2. Heart and blood vessels: 3.1.3.1.1. Nature:  The heart is a great organ of the body whose usual function is to contract periodically (pulsate) in order to pump blood to various parts of the body. 3.1.3.1.2. Function:  It pumps the blood at one end and receives it at the other end by the returning vessels or the veins.  To keep the blood circulating in a uniform direction it is provided with valves which prevent the backward flow of the blood. 4  3. Circulatory system and circulation 3.1. Circulatory system: 3.1.3. Components (cont.): 3.1.3.1&2. Heart and blood vessels: 3.1.3.1.3. Structure:  The 4-chambered heart of mammals consists of two atria (upper chambers) and two ventricles (lower chambers).  The wall of the heart is composed of three layers knows as endocardium, myocardium and epicardium.  The endocardiurn consists of connective tissues lined by an endothelium that is continuous with that of blood vessels.  The myocardium is a muscle layer.  It is thin in the atria but very thick in the ventricles.  The epicardium consists of epithelial cells and 5 connective tissue.  3. Circulatory system and circulation 3.1. Circulatory system: 3.1.3. Components (cont.): 3.1.3.1&2. Heart and blood vessels: 3.1.3.1.3. Structure (cont.):  The myocardium of the atria is somewhat separated from the myocardium of the ventricular chambers by a ring of fibrous tissue.  The two thin walled atria are separated from each other by an interatrial septum while the two thicker- walled ventricles possess a common wall in the interventricular septum.  Atria and ventricles are connected by a fibrous A-V ring.  The ring is penetrated on the right side of the tricuspid 6 valve and on the left of the mitral (or bicuspid) valve.  3. Circulatory system and circulation 3.1. Circulatory system: 3.1.3. Components (cont.): 3.1.3.1&2. Heart and blood vessels: 3.1.3.1.3. Structure (cont.):  One-way flow of the blood through the heart is accomplished by two sets of valves.  One set, the atrioventricular valves, separates the ventricles from the atria.  When the ventricles contract, the atrioventricular valves prevent blood in the ventricles from entering the atria.  The other set of valves, the semilunar valves, separates the aorta and pulmonary trunk from the left and right ventricles, respect.  The atrioventricu1ar valves are composed of leaf like portion called cusps (points).  On the right side of the heart three cusps ‫ أعناق‬are present which form the tricuspid.  The bicuspid valve, or mitral valve is located on the left side of 7 the heart.  3. Circulatory system and circulation 3.1. Circulatory system: 3.1.3. Components (cont.): 3.1.3.1&2. Heart and blood vessels: 3.1.3.1.3. Structure (cont.): 8  3. Circulatory system and circulation 3.1. Circulatory system: 3.1.3. Components (cont.): 3.1.3.1&2. Heart and blood vessels: 3.1.3.1.4. Cardiac cycle: 1. Definition:  The sequence of one systole followed by one diastole is termed a cardiac cycle. 2. Duration:  It lasts eighteenths of a second. 3. Systole and diasystole:  The work of heart consists of rhythmic contraction and relaxations of the auricles and ventricles.  A contraction phase of a chamber of the heart is called systole and, a relaxation phase, diastole.  The contractions and relaxation of the different parts of the heart take place in a definite order.  The auricles contract first followed by ventricular systole.  Ventricular systole is always followed by ventricular diastole and so. 9  3. Circulatory system and circulation 3.1. Circulatory system: 3.1.3. Components (cont.): 3.1.3.1&2. Heart and blood vessels: 3.1.3.1.5. Heart beat: 1. Definition:  The contraction of the heart (systole) and the relaxation of the heart (diastole) constitute heart beat. 2. Stroke volume:  In each time the heart beats, each ventricle pumps out 70ml blood.  This volume is termed stroke volume. 3. Numbers, heart rate and cardiac out-put:  The heart beats about 70 time in minute (in man) and this is termed the heart rate, the stroke volume and heart rate on multiplication given the volume of blood pumped out by each 10 ventricle per minute. This termed the cardiac out-put.  3. Circulatory system and circulation 3.2. Circulation: 3.2.1. Pulmonary circulation: 3.2.2. Systemic circulation: 3.2.3. Portal system: 11  3. Circulatory system and circulation 3.2. Circulation: 3.2.1. Pulmonary circulation:  All blood entering the right atrium of the heart is deoxygenated.  Blood passes from the right atrium into the right ventricle, which then pumps it out through the pulmonary trunk.  The pulmonary trunk branches into the two pulmonary arteries that carry blood to arterioles and capillaries in the lungs.  After passing through lung capillaries located around the alveoli, blood returns to the left atrium of the heart through pulmonary venules and veins. 12  3. Circulatory system and circulation 3.2. Circulation: 3.2.2. Systemic circulation:  Blood returning from the pulmonary circulation is oxygenated.  This oxygenated blood passes from the left atrium into the left ventricle, which then pumps it out through the aorta, the large arterial trunk that supplies the entire systemic circulation.  The aorta sends branches to all parts of the body.  The first of these branches are the coronary arteries for the heart.  Heart cells do not exchange material with the blood being pumped through the chambers, therefore, blood flow through the coronary arteries is critical for normal functioning of the heart.  Blockage of any coronary artery quickly results in a "heat attack" with resultant damaged heart muscle and impaired heart function. 13  3. Circulatory system and circulation. 3.2. Circulation: 3.2.3. Portal system:  A portal system is one that begins and ends in capillaries.  The human body has only one such major system.  The hepatic portal system, in this system, the first set of capillaries occurs at the digestive organs and the second occurs in the liver.  Blood passes from the capillaries of the digestive organs into venules that join the major vein "the hepatic portal vein" that takes the products of digestion to the liver.  Here, the hepatic portal vein breaks into a second set of capillaries, the food products may be or stored in the liver until they are aceded‫ تتفوق‬to maintain the constancy of blood composition.  Blood then passes through the hepatic vein, a vessel that leaves the liver to enter the vena cava. 14  3. Circulatory system and circulation 3.1. Circulatory system: 3.1.1. Importance: 3.1.2. Functions: 3.1.3. Components: 3.1.3.1&2. Heart and blood vessels: 3.1.3.1&2.1. Nature: 3.1.3.1&2.2. Function: 3.1.3.1&2.3. Structure: 3.1.3.1&2.4. Cardiac cycle: 3.1.3.1&2.5. Heart beat: 3.1.3.3. Blood: 3.2. Circulation: 3.2.1. Pulmonary circulation: 3.2.2. Systemic circulation: 15 3.2.3. Portal svstem: