Structure of the CVS


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Structure of the CVS

  1. 1. Structure & Function of the CVS <ul><li>The components of the CVS are the HEART and BLOOD VESSELS . </li></ul><ul><li>The cardiovascular system is described as a closed, double circulatory system </li></ul><ul><li>The cardiac cycle refers to the pattern of contraction and relaxation of the heart during one complete heartbeat </li></ul>STROKE VOLUME = volume of blood pushed out of the heart during one beat/cycle
  2. 2. Blood Vessels <ul><li>Both arteries and veins consist of the following: </li></ul><ul><li>a central lumen through which blood flows; </li></ul><ul><li>tunica intima - this layer lines the lumen and is made up of endothelium (single layer of smooth cells). It minimises friction between the blood and the wall of the vessel; </li></ul><ul><li>tunica media - this middle layer contains smooth muscle, collagen and elastic fibres; </li></ul><ul><li>tunica externa - this outer layer contains collagen fibres and some elastic fibres </li></ul><ul><li>The walls of capillaries consist only of a single layer of endothelium and have a tiny diameter, approximately 7 μm, which is about the same diameter as a red blood cell. The walls of the capillaries are permeable as a result of tiny gaps which exist between the cells of the endothelium. By the time the blood reaches the capillaries from the arteries the pressure and flow rate have decreased greatly. This is beneficial because a low pressure reduces fluid loss through the permeable capillary walls while a low flow rate allows sufficient time for the exchange of materials between the blood and the body cells </li></ul>
  3. 3. The Cardiac Cycle <ul><li>The atria (upper chambers) contract a fraction of a second before the ventricles contract. During atrial systole , the two atria contract simultaneously, the atrio-ventricular valves (bicuspid and tricuspid valves) are open and blood is forced through into the ventricles. At this point the ventricles are relaxed (in diastole) and the semilunar valves are closed . </li></ul><ul><li>Atrial systole is followed about 0.1 seconds later by ventricular systole . The atrio-ventricular valves are closed and blood is forced out through the semilunar valves into the arteries. </li></ul><ul><li>During atrial and ventricular diastole, blood from the pulmonary veins and the venae cavae fill up the atria. Then the cycle repeats </li></ul>Cardiac Cycle shockwave
  4. 4. Blood Pressure (B.P.) <ul><li>Blood pressure describes the pressure in the aorta (the main artery out of the heart). It can be measured in the large artery in the arm by using an instrument called a sphygmomanometer and a stethoscope </li></ul><ul><li>B.P. measurement is given as a ratio in the form systolic pressure/diastolic pressure </li></ul><ul><li>A typical normal blood pressure reading would be </li></ul><ul><li>‘ 120 / 80 mmHg’ </li></ul><ul><ul><li>systolic blood pressure: pressure in the arteries during systole (when the heart contracts) </li></ul></ul>diastolic blood pressure: pressure in the arteries during diastole (when the heart relaxes)
  5. 5. <ul><li>Systolic B.P. changes during exercise and can increase to 200 mm Hg, but the diastolic blood pressure usually remains constant </li></ul><ul><li>B.P. can be higher in older people and lower in younger people. </li></ul><ul><li>The blood pressure INCREASES when the heart is overworking, placing a strain on the circulatory system </li></ul><ul><li>It is important to maintain the blood pressure within the normal limits as high and low blood pressure can be detrimental to health </li></ul><ul><li>E.g. low blood pressure can cause kidney problems and high blood pressure can result in a heart attack </li></ul>
  6. 6. Heart rate <ul><li>Pulse rate can give very important information about the health of a person. Any deviation from normal heart rate can indicate a medical condition e.g. fast pulse may signal the presence of an infection or dehydration </li></ul><ul><li>The pulse measurement has other uses as well. During exercise or immediately after exercise, the pulse rate can give information about the fitness level and the health of a person </li></ul><ul><ul><ul><li>Normal Values for resting heart rate: </li></ul></ul></ul><ul><ul><ul><ul><li>newborn infants; 100 to 160 beats per minute </li></ul></ul></ul></ul><ul><ul><ul><ul><li>children 1 to 10 years; 70 to 120 beats per minute </li></ul></ul></ul></ul><ul><ul><ul><ul><li>children over 10 and adults; 60 to 100 beats per minute </li></ul></ul></ul></ul><ul><ul><ul><ul><li>well-trained athletes; 40 to 60 beats per minute </li></ul></ul></ul></ul><ul><li>Generally the fitter a person is the lower their resting pulse rate is; very fit athletes may have resting pulse rates as low as 30 - 40 beats per minute. However, resting pulse rates also decrease with age. </li></ul>
  7. 7. Cardiac Output <ul><li>Cardiac output is the volume of blood pumped out of the heart every minute. It is usually measured in litres/minute </li></ul><ul><li>The stroke volume is the volume of blood pumped out of the heart with each heartbeat </li></ul><ul><li>An individual's cardiac output can therefore be worked out by multiplying the HEART RATE by the STROKE VOLUME . This relationship can be written as: </li></ul><ul><li>CARDIAC OUTPUT = HEART RATE X STROKE VOLUME </li></ul><ul><li>(CO) (HR) (SV) </li></ul>Qu. When resting, an individual's pulse rate is 64 beats/minute and their stroke volume is 75 ml. What is their cardiac output? 4.8 l/min (Remember you have to convert the 75 ml to 0.075 l.)