this video is covering the key concepts of the cardiovascular system in the video we will look at the circulatory system and structure of blood vessels the heart the cardiac cycle and pressure changes heart rate and exercise and tissue fluid mammals such as humans have a cardiovascular system made up of the heart and blood vessels that carry the blood by mass transport this is a closed system as the blood remains in the blood vessels and is separate to the tissue fluid that bathes the cells it is also a double circulatory system as the blood passes through the heart twice for each complete circuit of the body you can see in this diagram that the pulmonary circulation carries the blood to the lungs to get rid of carbon dioxide and collect more oxygen and the systemic circulation carries the blood to the rest of the body this is different to the single circulatory system of fish where the blood is pumped to the gills and then the oxygenated blood goes all around the body before it returns to the heart to be pumped to the gills again for gaseous exchange the main advantages of the double circulation is that the oxygenated blood can be delivered at high pressure to the body and that the oxygenated and deoxygenated blood do not mix the blood vessels in the body are grouped into three main types capillaries arteries and veins the arteries and veins consist of three layers here we are looking at an artery the outer layer the Tunica externa is made of connective tissue primarily collagen fibers which provide structural support and shape the middle layer the Tunica Media is composed of smooth muscle cells which are responsible for regulating the diameter of the archery and thus controlling blood blood flow and blood pressure elastic fibers and collagen are also present to provide structural support and elasticity the inner layer the Tunica intima is made up of sormus endothelium that forms a smooth friction reducing lining for blood flow arteries carry blood away from the heart under high pressure most arteries carry oxygenated blood except for the pulmonary artery which carries blood from the right ventricle to the left lungs so that carbon dioxide can diffuse out of the blood into the alvioli and oxygen can diffuse from the alvioli into the blood as the heart contracts and pushes blood into the arteries the pressure inside the arteries increases the arteries are prevented from bursting due to the thick layer of muscle and elastic fibers which can stretch as the blood enters and then recoil as the heart relaxes try to remember that the term Cy refers to the contraction of the heart and diast refers to the relaxation of the heart the recoiling of the artery during diast helps push the blood along the stretching and recoiling is what we feel as our pulse the narrow Lumen of the arteries also helps maintain the flow of the blood by reducing the inner volume of the arteries and so maintaining the pressure the stretching and recoiling of the archery walls also helps smooth the differences in pressure of the blood between when the heart contracts cysty and when the heart relaxes diasty the further the blood is away from the heart the steadier and lower the blood pressure arteries Branch into smaller arterials which also contain smooth muscle in their walls this smooth muscle can contract and make the Lumen of the arterials narrower controlling the flow of blood to different parts of the body capillar join arterials to the smaller veins called venules capillaries are the site of exchange of materials such as oxygen carbon dioxide and nutrients between cells in the tissue and the blood in the capillary capillaries are very narrow and their walls are just one cell thick some capillaries fenestrated capillaries have pores between the cells that allow small molecules such as glucose and some hormones through these type of capillaries are typically found in the small intestine kidney and endocrine glands capillaries form highly branched capillary beds and the total cross-sectional area of these beds is greater than that of the arterials leading into them therefore the pressure of the blood drops as it enters them also as the Lumin of the blood vessels gets narrower the resistance to blood flow increases significantly as a result blood flow slows down when it enters capillaries and this allows time for more efficient exchange of gases and nutrients with the surrounding tissues the Lumen of each capillary is just wide enough to allow one red blood cell through at a time the narrow Lumen and thin walls of capillaries minimize the diffusion distance and the highly branched structure of the capillary bed increases the surface area to make exchange of materials as efficient as possible the capillaries connect with venules which are thin W blood vessels that connect up to veins veins carry blood usually deoxygenated blood under low pressure back to the Atria of the heart the pulmonary vein however carries oxygenated blood from the lungs to the left atrium ready for it to be pumped around the body as mentioned earlier veins have three layers to their structure the outer layer for structural support the mid middle elastic and muscle layer and then the smooth endothelial lining however because they are carrying blood under low pressure the walls of veins do not need to be as thick or as elastic as those of archeries to assist with the return of blood at low pressure back to the heart the Lumen of veins is wider than of arteries to reduce friction which would otherwise slow down the movement of the blood they also contain valves these valves open as blood is pushed up the veins by Contracting sceletal muscle on either side of the flexible wall of the veins the valves then shut to prevent the back flow of blood as it is pulled down by gravity as the muscles relax this diagram shows some of the major blood vessels of the body the hepatic artery which leads to the capillaries of the liver and the hepatic vein that leads away from the capillary bed of the liver the renal artery and vein which lead to and from the kidneys the pulmonary arterium vein to and from the lungs and the coted archery leading To The Head and the jugular vein carrying the blood back from the head these archeries are branching from the aorta and the veins leading back to the inferior or Superior vnea this blood vessel here is different to the others this is the hepatic portal vein this has a capillary bed at both ends as it carries blood from the digestive system to the liver for it to be processed now that we have looked at the blood vessels let's look at the heart when tackling a question about the heart remember that you need to think carefully about which side is which you have to remember it is a mirror image so this side is the left side which pumps oxygenated blood all around the body and this side is the right side which pumps deoxygenated blood to the lungs to be reox oxygenated the heart has four chambers two atria and two ventricles the left and right hand sides of the heart are separated by the septum the two atria at the top of the heart have thin walls and collect the blood returning to the heart via veins this is the right atrium collecting the deoxygenated blood returning to the heart from the body via the superior and inferior venne and this is the left atrium collecting the oxygenated blood returning to the heart from the lungs by the pulmonary veins the Atria then contract and push the blood into the ventricles you can see the left ventricle has a much thicker wall than the right as the left has to pump the oxygenated blood at high pressure all around the body the right ventricle only has to pump the blood to the lungs so it requires less Force so there is lower pressure preventing damage to the capillaries in the lungs when the ventricles contract they push the blood out of the heart through arteries the left ventricle pushes blood out of the heart through the aorta to the body the right ventricle pushes the blood out of the heart through the pulmonary artery to the lungs atrioventricular valves are found between the Atria and ventricles tendons attaching the valves to the lower internal walls of the ventricles means these valves will only open one way inward from the atrium into the ventricles this means that as the ventricles contract to push the blood out of the heart the atrio ventricular valves snap shut preventing the backf flow of the blood into the Atria the semi lunar valves in the pulmonary vein and aorta allow blood to be pushed through them from the ventricles but when the ventricles relax they shut preventing the backflow of blood into the ventricles both the atrio ventricular and semi lunar valves ensure blood flows in One Direction only through the heart the shutting of the valves gives the L dub sound of the heart Lu is the Atri ventricular valve shutting and the dub is due to the semi lunar valves cardiac muscle cells contract rhythmically from when they are formed to when they die and they do this without tiring the muscle is myogenic which means it can contract rhythmically without external neural stimul ulation however when necessary the Cardiovascular Center in the Medela of the brain can speed heart rate up or slow it down as we will see soon the continual contractions of the heart require a constant supply of energy so the heart has to have its own blood supply coronary arteries seen on the surface of the heart here Supply the muscle cells with oxygen and nutrients and coronary veins carry the waste away if the blood is prevented from getting to part of the heart then the area of the heart affected will stop Contracting and the cells will eventually die one of the main causes of this restricted blood flow is a condition known as atherosclerosis which can lead to oclusion or blockage of the coronary arteries the process begins with damage to the inner endothelial lining of the arteries possibly due to high blood pressure or inflammation when the endothelium is damaged it becomes more permeable allowing lipids to enter the artery wall these lipid particles accumulate and form plaques as plaques grow they can protrude into the artery Lumen narrowing the space through which blood can flow this reduction in blood flow is known as an occlusion the accumulation of plaque also leads to the hardening and thickening of the arterial walls s reducing their flexibility and elasticity in advanced stages plaques can rupture or become unstable causing blood clots which further obstruct blood flow if a clot completely blocks a coronary artery it can result in a heart attack now let's look at the cardiac cycle and the pressure changes in the heart and blood vessels the cardiac cycle can be split into three phases atrial and ventricular diast or relaxation atrial syy or contraction and ventricular syy in atrial and ventricular diast when the Atria and ventricles are relaxed blood is passively Flowing from the Atria into the ventricles through the atrioventricular valves the left atrium receives oxygenated blood from the lungs through the pulmonary vein and the right atrium receives deoxygenated blood from the body via the inferior and Superior venina the contraction of the heart is then initiated by a group of specialized muscle cells called the sinoatrial node or pacemaker in the wall of the right atrium electrical impulses from the sinoatrial node spread out across the Atria bringing about atrial Cy and the Atria contracts simultaneously forcing the remaining blood through the atrio ventricular valves into the ventricles at this stage the walls of the ventricles are still relaxed so pressure in the ventricles is low the atrioventricular valves are open and blood can easily enter this low pressure also means that the semi lunar valves are shut the electrical impulses from the sinoatrial node then reach the atrioventricular node another group of specialized cells approximately 0.1 second after receiving the impulse from the sin8 atrial node the atrio ventricular node sends out its own electrical impulses these impulses pass down the central septum of the heart through special conducting fibers and reach the apex of the heart they then spread upwards stimulating cyly in both ventricles simultaneously from the bottom upwards as they contract the pressure inside the ventricles increases the atrio ventricular valve shut the semi lunar valves open and the blood is pushed up and out of the aorta on the left side and the pulmonary artery on the right hand side during ventricular syy the Atria start to relax atrial diast so the pressure in the Atria reduces finally the ventricles return to diast then the whole cardiac cycle starts again if we look at this graph showing various pressure changes we can see here that that this is diasty when pressure is low then here the atrium is Contracting then the Atri ventricular valve shut here as the ventricles contract the contraction of the ventricles causes a huge increase in blood pressure as shown here and the semi lunar valves are open allowing blood into the aor and so the aortic blood pressure increases the ventricles then start to relax so the semi lunar valve shut then the aor coils giving a small spike in pressure and here you can see the atrium and ventricle in diasty and the Atri ventricular valves open to allow blood to move from the Atria Into The ventricle when we exercise our heart rate increases this is because there is an increase in demand for energy therefore there needs to be an increase in aerobic cellular respiration if if there is an increase in aerobic respiration then more oxygen is required and more carbon dioxide is released into the blood which needs to be carried up to the lungs to be excreted the blood needs to be pumped to the lungs to remove the carbon dioxide and to collect more oxygen as carbon dioxide levels increase the pH of the blood decreases slightly this change in pH is detected by chemo receptors in the Medela oblongata corid artery and aortic Arch these chemo receptors trigger the medulla oblongata to send out nervous impulses along the acceleratory nerve to the sinoatrial node in the wall of the right atrium this causes a sinoatrial node to increase the rate of electrical signals it sends out thereby increasing the overall heart rate this means more blood is pumped around the body providing oxygen to the cells for a aerobic respiration and removing the waste carbon dioxide also in the cotted artery an aortic Arch as well as in the heart are Barrow receptors these sensory receptors continuously monitor changes in blood pressure and provide feedback to the Medela oblongata to help maintain blood pressure and heart rates within a normal range when blood pressure increases too much such as it can during exercise the Medela obl garta brings about a reduction in heart rate conversely if blood pressure drops too low then the Medela will bring about an increase in heart rate to increase blood pressure by increasing cardiac output which is the volume of blood the heart pumps out of the left ventricle per unit time with the anticipation of exercise the Medela oblongata also stimulates the adrenal glands to release adrenaline also known as epinephrine adrenaline is the phal flight hormone and it also stimulates the sinoatrial node to increase the rate at which it sends out electrical signals thereby increasing heart rate and preparing the body for physical activity as we mentioned earlier capillaries are the primary site of exchange of materials between the blood and the cells but we didn't look at how this exchange occurs this process involves interstitial or tissue fluid tissue fluid is a liquid formed from blood plasma which serves as a means of supplying the tissues with essential solutes such as oxygen and glucose in exchange for waste products such as carbon dioxide at the arterial end of the capillary there is high hydrostatic pressure due to the blood being pumped along the arteries into arterials and then into the capillaries this hydrostatic pressure pushes blood plasma carrying oxygen and nutrients out through the pores of capillary walls forming tissue fluid this fluid moves into the interstitial space the space surrounding the cells of the body tissues and this process is known as pressure filtration as fluid moves out of the capillaries another Force called osmotic pressure comes into play osmotic pressure is due to the presence of plasma proteins especially albumin in the blood these proteins exert osmotic pressure pulling water back into the capillaries to maintain osmotic balance as the blood flows along the capillaries from the arterial end to the Venus end there is a progressive loss of water and so an increase in solute concentration this increases the osmotic pressure at the same time the hydrostatic pressure is decreasing eventually osmotic pressure outweighs hydrostatic pressure and the tissue fluid starts to get drawn back into the capillaries along with the waste collected from the cells about 90% % of the tissue fluid is reabsorbed back into the capillaries by the osmotic pressure created by plasma proteins the remaining fluid along with the waste products and large molecules is collected by lymphatic vessels as lymph lymphatic capillaries are microscopic vessels that have openings in them that allow the absorption of tissue fluid along with large molecules waste products and foreign particles the lymph is pushed along lymphatic vessels by contaction of smooth muscle in the walls and by movement of the body like with veins valves help prevent back flow and ensure the oneway flow of lymph as lymph moves through larger lymphatic vessels it eventually reaches lymph nodes lymph nodes are small bean-shaped structures distributed along the lymphatic system they contain fosic macres which engulf foreign substances pathogens and abnormal cells present in the lymph lymphocytes are also present to help prevent infection the lymphatic system eventually Returns the fluid to the veins near the heart preventing the accumulation of excess fluid in the tissues and maintaining fluid balance you may be asked to compare the components of blood plasma and tissue fluid so let's finish by looking at these water makes up the majority of both plasma and tissue fluid in the plasma there are large proteins incl including albumins but in tissue fluid only smaller proteins that can fit through the capillary walls are present in the plasma there are more nutrients because in the tissue fluid some have been taken up by the cells there is less carbon dioxide in plasma because in the tissue fluid carbon dioxide is diffused out from the cells which have been carrying out aerobic respiration in the plasma there is more oxygen because some of the oxygen in the tissue fluid has been taken up by the cells to be used in aerobic respiration plasma carries red and white blood cells all around the body in the tissue fluid there may be a few white blood cells which have managed to migrate through the walls of the capillaries especially during inflammation but other than that there are no blood cells in the tissue fluid now that we've come to the end of this key concept video on the cardiovascular system here is a summary of the key points you may want to pause the video to read through them as they'll be useful for your exam revision