The sequence starts when blood is returning to the heart at low pressure via the atria (from the pulmonary vein and vena cava, relaxation of the atria is called atrial diastole). Oxygenated blood enters the left atrium and deoxygenated blood enters the right atrium. The tricuspid and bicuspid valves are closed. As the blood fills in the atria, the pressure overcomes the pressure of the ventricles and thus opens the valves.
Then the two atria contract simultaneously, this is called atrial systole, forcing the blood into the ventricles.
The ventricles contract, called ventricular systole, this causes the pressure in the ventricles to increase and the atrioventricular valves are then closed to prevent backflow. At the same time, the pressure opens the semilunar valves of the aorta and the pulmonary artery, and these allow the blood to flow into the blood vessels. The closing of the atrioventricular valves produces the first heart sound (lub).
Soon after, the ventricle relaxes (ventricular diastole), closing the semilunar valves. This prevents the backflow of blood from the pulmonary artery and aorta. The closing of the semilunar valves produces the second heart sound (dub).
6.2.4- Outline the control of the heart in terms of myogenic muscle contraction, the role of pacemaker, nerves, medulla of the brain and the epinephrine (adrenaline).
The heart consists of cardiac muscles on its wall. The contraction of the cardiac muscle is myogenic, which means that it can contract on its own without being stimulated by a nerve. In other words it does not depend on the brain to give it confirmation for a heartbeat.
The pacemaker is the region which is responsible for sending the signal for each contraction. It is found in the wall of the right atrium. Nerves and hormones can transmit messages to the pacemaker.
- 1 nerve carries signal from the brain to the pacemaker to tell it to speed up the heartbeat
- Another one carries signal from the brain to the pacemaker to tell it to reduce the heartbeat
- Adrenalin, carried to the pacemaker by bloodstream, tells the pacemaker to speed up the beating of the heart.
6.2.5- Explain the relationship between the structure and function of arteries, capillaries and veins.
Arteries carry blood that's pumped out by the thick walls of the ventricles. They have thick walls because this is when the blood has the highest pressure and to maintain the pressure, the lumen is narrowed. These walls are made of connective tissue, elastic and muscle fibres and a layer of endothelial cells. The elastic tissue allows the arteries to expand and recoil and also to withstand ruptures during contraction and relaxation. This helps the flow of the blood in the circulation.
Veins have thinner walls, wider lumen and valves to prevent backflow of blood. They carry blood from the body back to the heart. They have thinner layers of connective, elastic and smooth muscle fibres.
Capillaries only have one layer of endothelium as their walls. This allows substances to pass in and out of capillaries for exchange of materials. They have a very narrow diameter, but there are many capillaries allowing a large exchange of materials.
6.2.6- State that blood is composed of plasma, erythrocytes, leucocytes (phagocytes and lymphocytes) and platelets.
Blood is composed of plasma, erythrocytes (red blood cells), leucocytes (phagocytes and lymphocytes) and platelets.
6.2.7- State that the following are transported by the blood: nutrients, oxygen, carbon dioxide, hormones, antibodies, urea and heat.
Nutrients, oxygen, carbon dioxide, hormones, antibodies, urea and heat are transported by blood throughout the body.