Cardiovascular System 9, Mechanisms of venous return

what we want to do now is consider the mechanisms a venous return now it's obvious that when the heart is pumping it's going to generate a blood pressure 120 millimeters over 80 perhaps 120 millimeters when the ventricle is contracting and that's going to send the blood to your fingers your toes your head and everywhere but of course you don't have little hearts in your feet to pump the blood bag so how is the blood getting back from the periphery to the center of the body to get back to the atrium to be recirculated around again and the several components to answer this question but first of all let's think about the veins so here we have a vein in the leg perhaps and we know that there are valves in this vein and these valves are pointing out of the way like this and this is of course vital because the blood can go from below here the blood could go from below there up to there and from below that up to there it can go up the way but then if the blood tries to go back the way these valves will shut so they can open that way and they will shut that way and that ensures a one-way flow of blood from the periphery down here to the center of the body so that's good now what people don't always appreciate is that there are actually two systems of veins in the legs and indeed two systems of veins in the arms this one I've drawn here is near the surface of the skin there and these are the ones that you can see through the surface of the skin because they Trude and of course these are very useful in the arms for taking blood samples so they're the superficial veins but there are other veins that go in the way like this so that vein will carry on but there's a vein that goes in the like this and again this has got valves and we noticed the valve is that way round meaning the blood can go from the superficial vein through this vein here but where does it go well this blood goes into the deep veins into the deep venous system so here we have deep veins and the thing about deep veins is they are inside the muscles so here surrounding this D vein we have the skeletal muscles so this vein is inside a skeletal muscle and as you probably know the skeletal muscles are surrounded by a tough muscle bashier tough fibrous tissue on the outside of the muscle group so we have the superficial veins the deep veins and these veins perforate the muscle fascia we go through the muscle fascia to get inside the muscle so they're often called perforator veins short perforator veins and they're taking blood from the superficial to the deep venous system and that goes on off of and in the case of the legs that's going up towards the inferior vena cava and there are also valves in these deeper veins as well and again these valves are pointing up the way so the blood can go up but can't go back we don't want the regurgitation now these superficial veins the blood is at relatively low pressure but there are movements of the muscle against the skin generating some pressures in these veins and that will cause the wall of the vein to be pressed on like that and when you press on the wall of the vein that's going to increase the pressure inside the vein so external pressure will increase intravenous pressure if that happens the blood will try and go back down but it can't because that valve will shut preventing the regurgitation of the blood but that one will open as indeed will that one in the perforated vein sometimes actually called Communicator veins as well so what this means is the direction of travel is from the superficial veins through to the deep veins and if blood tries to go from the deep veins back to the superficial veins it can't is prevented from doing so by the presence of the valves the perforating communicator vanes and then when this muscle contracts for example if you're walking if this is going through the calf muscles and the calf muscle contracts that's going to squeeze on this vein let me show you now it's going to squeeze it's going to squeeze like that really hard it's going to slam that valve some that vein pretty well shut because the muscle contraction is vigorous using a lot of energy so all of a sudden when the muscle contracts that will greatly increase the pressure inside that compartment of the deeper vein and when the pressure increases in the deep vein that will immediately close the valve below I will shut preventing regurgitation of the blood back to the periphery but that valve will be opened and as a result of that because it's a high-pressure muscle contraction squeezing the wall of the vein the blood will absolutely scoot back up towards the inferior vena cava and this is such an effective mechanism is called the calf muscle pump and it's vital to know about in any form of health care because if patients lie around with immobile leg muscles then the circulation of blood through the deep veins is going to become sluggish if the circulation of the blood through the deep veins is sluggish then that increases the risk of thrombus formation and that of course is deep venous thrombosis it's a vino thromboembolism the clot from the deep vein will pass straight back up into the inferior vena cava from the inferior inferior vena cave of the bird will pass straight into the right atrium through the tricuspid valve through the pulmonary valve into the pulmonary arterial system what happens next depends on how big the clot is if it's a big clot it can block off a very early stage in the pulmonary artery if it's a smaller clot it will lodge further into the pulmonary arterial system either way is called a pulmonary embolism and it will infarct part of the lung tissue and of course it's a life-threatening condition because it's going to stop the flow of the blood going through the lungs if the blood can't flow through the lungs it won't get back to the left side of the heart the Bloods not getting back to the left atrium how can the left ventricle pump it out well it can't and we will get a sudden cessation of the circulatory system in the condition of obstructive shock so very important that we tell our patients to keep their ankles moving so all the time keep reminding them ruggle your ankles when you're in bed don't cross your legs keep your legs moving and of course mobilize patients as early as possible because we do lose thousands of patients a year through deep venous thrombosis so the blood absolutely scoots back up it's called the calf muscle pump absolutely brilliant mechanism as long as of course you're able to move the muscle now even if you can't move the muscle if you can just twitch it a little bit that's good because that will increase the pressure and even the tone of the muscle will cause some degree of pressure but better to move the muscle this is why sometimes soldiers on parade when they have to stand still for long periods of time without moving their legs can faint because the blood will pool in the superficial veins if the Bloods pooling in the superficial veins it's not getting back to the right side of the heart to be oxygenated if the blood is not getting back to the right side of the heart is not getting back to the left atrium to be pumped out in the left ventricle so we're going to get failure of the systemic circulation so very important to keep these muscles moving all of them are sore so the leg muscles and indeed waggling the toes moving feet will have some effect because there's muscles in the feet and there's muscles in the thighs so we need to try and keep all of the leg muscles moving and if patients can't do this for themselves then we can do it for them we can do passive exercises by moving their feet by wiggling their ankles for them which you might want to do in unconscious patients unconscious patients for example to keep the circulation going now sometimes it's fair to say that these valves fail that would be a pathological situation but if these valves fail can you see that when that muscle contracts blood could be ejected from the high-pressure deep veins to the superficial veins where the pressure is supposed to be low so you could get regurgitation of high-pressure blood into the superficial veins that's okay to begin with because that valve will stop it going any further but if that valve is subject to high pressure for a long period of time that valve will fail and then that valve will fail and the veins will become blown out and torturous and of course this is the condition of varicose veins varicosity so we need to keep moving around to try and prevent varicose veins although there is of significant some genetic component in varicose veins as well now also very often where there's deep veins the arteries the deep arteries light adjacent to the vein so imagining our vein there and you have an artery there the art was of course a pulsatile because the pulse goes through them so they'll be expanding and contracting so that will somewhat impose onto the veins so we're going to get some alterations in the blood pressure in the veins because of the pulsation of adjacent arteries that will provide some venous return but by far away the main mechanism is the contraction of the skeletal muscles and there's a couple of more mechanisms I'm going to tell you about so stay tuned for the next clip

Channel: Dr. John Campbell

Views: 78,871

Keywords: venous return, how veins work, veins, DVT, deep venous thrombosis, campbell, campbellteaching, NCLEX, nurse education, medical education, blod flow, circulation, CVS, cardiovascular system

Id: KaCm_73M3Es

Length: 12min 27sec (747 seconds)

Published: Fri Jan 08 2016