2.4-2.8

• arteries carry blood at high pressure away from the heart
• Arteries have a narrower lumen than veins
• Arteries have a thick outer wall and a thick layer of smooth muscle and elastic fibres
• Elastic walls of arteries stretch and recoil to accommodate the surge of blood after each contraction of the heart.
• vasoconstriction is a contraction of smooth muscle in arteries to decrease blood flow
• vasodilation is the relaxation of smooth muscles in arteries to increase blood flow
• veins carry blood at low pressure back to the heart
• Veins' outer layer contains elastic fibers
• Veins' muscular walls are much thinner than that of arteries
• Veins have a wider central lumen than arteries
• Veins contain valves which prevent backflow of blood
• Capillaries are tiny vessels where the exchange of substances with the tissue occurs
• Cappilary walls are only one cell thick, allowing gases, nutrients, and waste to be exchanged with ease between blood and tissues
• Pressure filtration occurs causing the plasma to filter into the surrounding tissues forming tissue fluid.
• Tissue fluid and plasma have a similar composition, with the exception of plasma proteins
• Tissue fluid doesn't contain plasma proteins because they are too large to pass through capillary walls
• Tissue fluid supplies the cells with oxygen and glucose and allows cells to remove metabolic waste products.
• At the venule at the end of the capillary, much of the tissue fluid is reabsorbed and returned to the bloodstream.
• Any excess fluid is absorbed by lymphatic vessels and returns it to the circulatory system
• Units for cardiac output are milliliters per minute
• Units for stroke volume is milliliters per beat
• Units for heart rate is beats per minute
• The cardiac cycle is the pattern of contraction and relaxation of the heart during one complete heartbeat.
• 1 cardiac cycle takes approximately 0.8 seconds
• Contraction of the heart is known as systole
• Relaxation of the heart is known as diastole
• 1. Atrial systole (contraction) - closure of valves in vena cava and pulmonary vein prevents backflow of blood
• 1. Atrial systole (contraction) -pressure difference between atria and ventricles force opens the atrioventricular valve and the ventricles fill.
• 2. Ventricular systole (contraction), atrial diastole (relaxation) - Atrioventricular valves close due to pressure difference (the lubb sound) and this prevents backflow into the atria
• 2. Ventricular systole (contraction), atrial diastole (relaxation) - semilunar valves open due to pressure difference. Blood ejected into the aorta and pulmonary artery
• 3. Atrial and ventricular diastole (relaxation) - Higher pressure in aorta and pulmonary artery than the ventricles, causing the semilunar valves to close (causes the dupp sound). this prevents backflow of blood into ventricles.
• 3. Atrial and ventricular diastole (relaxation) - Higher pressure in vena cava and pulmonary vein so atria fill and blood flows into ventricles.
• The auto-rhythmic cells of the sino-atrial node or pacemaker cells, located in the wall of the right atrium, set the rate at which the heart contracts
• The timing of the cardiac muscle contraction is controlled by impulses from the sino-atrial node spreading through the atria causing atrial systole.
• They then travel to the atrioventricular node located in the centre of the heart.
• Impulses from the atrioventricular node travel down fibres in the central wall of the heart and then up through the walls of the ventricles, causing ventricular systole.
• an ECG (electrocardiogram machine) can detect currents generated by impulses
• the medulla regulates the rate of the sinoatrial node through the antagonistic action of the autonomic nervous system.
• A sympathetic nerve releases noradrenaline which increases the heart rate
• A parasympathetic nerve releases acetylcholine which decreases the heart rate