Skip to main content
Loading Explore guides…
Cardiovascular System · Acedra
Home
Explore
Medicine
Cardiovascular System
Sign in to save
Chat
If YouTube asks you to sign in, open the video on YouTube.
Watch on YouTube
Reload player
Transcript
34 segments
Copy
Hide video
0:05
the circulatory system is also called the cardiovascular system where cardio refers to the Heart and Vascular refers to the blood vessels so these are two key Parts the heart which pumps blood and the blood vessels which carry blood to the body and return it back to the heart again ultimately this is how nutrients like O2 or oxygen get pushed out to the organs and tissues that need it and how waste like CO2 or carbon dioxide which is the main byproduct of cellular respiration gets
0:35
removed the heart itself is about the size of a person's fist which makes sense a bigger person has a bigger Fist and therefore a bigger heart and it's shaped like a cone and sits slightly shifted over to the left side in the media stum which is in the middle of the chest cavity or thorax it sits on top of the diaphragm which is the main muscle that helps with breathing behind the sternum or breast bone in front of the vertebral column squished in between two lungs and is protected by the
1:07
ribs now if you look a little more closely you can see that the heart sits inside a sack of fluid that has two walls called the Cirrus pericardium the outer layer is called the parietal layer and it gets stuck tightly to another layer called the fibrous pericardium which is made of tough dense connective tissue which holds the heart in place and prevents it from overfilling with blood the inner layer is called the visceral layer and it gets stuck tightly to the heart
1:34
itself forming the epicardium or the outer layer of the heart the cells of the Cirrus pericardium both the parietal and visceral layer secrete a protein Rich fluid that fills the space between those layers and serves as a lubricant for the heart allowing it to move around a bit with each heartbeat without feeling too much friction so moving from the outside of the heart to the inside of the heart after the the epicardium there's The myocardium which is the muscular middle
2:04
layer this forms the bulk of the heart tissue because those cardiac muscle cells contract and pump blood in addition to cardiac muscle cells there are crisscrossing connective tissue fibers which are made of collagen that together form the fibrous cardiac skeleton which helps support the muscle tissue The myocardium also has dedicated blood vessels called coronary vessels which lay on the outside of the heart and then penetrate into the The myocardium to bring blood to that layer
2:32
because it needs a lot of energy to pump blood finally there's the innermost layer of the heart called the endocardium which is made of a relatively thin layer of endothelium which is the same layer of cells that line the blood vessels this endocardium blinds the heart chambers as well as the heart valves all right so looking at the right side of the heart deoxygenated blood enters either through the top through a blood vessel called the superior vnea or the bottom through another blood
3:01
vessel called the inferior vnea in the right atrium where Atrium means entryway both venas are veins which bring blood towards the heart there's also a tiny third opening into the right atrium called the coronary sinus which collects blood from coronary vessels returning from The myocardium now all that blood then goes through the first of two atrio ventricular valves that separate the Atria from the ventricles this one's called the tricuspid valve and it allows blood into the right
3:34
ventricle the tricuspid valve has three little flaps or cusps and each cusp looks kind of like a parachute because it has tiny little strings called cordi tendin coming off of it that tether the cusp to a small muscle called the papillary muscle when the heart contracts that papillary muscle keeps the cordite and I taught and both of these help to prevent regurgitation of blood back into the atrium allowing it to only flow out the next valve that being said that contraction
4:05
pumps the blood out the pulmonary valve which just like the tricuspid valve has three cusps and also prevents blood from going backward but unlike the tricuspid valve the pulmonary valve doesn't have any of those cordite tendi once it's past the pulmonary valve the blood goes into the pulmonary arteries which carry blood away from the heart to the left and right lung just remember that arteries start with an A and also carry blood away from the heart so that blood goes from the
4:34
pulmonary artery into a pulmonary arterial which is a little bit smaller and finally into a capillary which is the smallest in the lungs the capillary lines up alongside a small sack of air called an Elvis and when you have a lot of them they're called elvi up until now that blood has been loaded up with carbon dioxide which makes the blood look dark red rather than blue which is how it's usually usually drawn and this is how we'll still draw it to stay consistent now at this point in the
5:04
journey the carbon dioxide moves from the capillary to the Alvis and oxygen moves from the Alvis to the capillary giving the blood that nice bright red color now in the blood each red blood cell has millions of hemoglobin proteins and each of those hemoglobins can bind to four oxygen molecules so each red blood cell can carry millions of oxygen molecules when it's fully loaded the oxygen-rich blood moves into a venu and then eventually into a pulmonary vein that dumps the blood into the left
5:37
atrium this trip from the right ventricle of the heart through the pulmonary artery to the lungs and back to the left atrium of the heart is called the pulmonary circulation after entering the left atrium the blood goes through the second atrio ventricular valve called the mitro valve into the left ventricle the mitro valve only has two cusps or leaflets one in front called the anterior leaflet that's a little smaller and one behind it called the posterior
6:04
leaflet both of these have cordite tendi coming off of them that tether the valve to the papillary muscles in the left ventricle similar to the right side of the heart when it contracts this prevents blood from going backwards finally blood in the left ventricle gets pumped out through the aortic valve which normally has three cusps out to the aorta the largest artery in the body just like in the lungs the aorta branches into arterials which are smaller arteries and finally
6:33
into capillaries which are the smallest and at that point they're at the organs and tissues in the organs the red blood cells line up alongside tissue cells and drop off oxygen as well as pick up carbon dioxide basically the reverse of what happens with the Alvis in the lung loaded up with carbon dioxide the blood turns that dark red color again shown as blue and starts the return Journey to the Heart by going into small venules and and then larger veins now the lower half of the body
7:02
drains into the inferior vena and the upper half drains into the superior vena both of which dump blood back into the right atrium so this trip from the left ventricle of the heart to the body and back to the right atrium of the heart is called the systemic circulation relative to the pulmonary circulation the systemic circulation has a lot more blood vessels which means there's about a five times greater resistance to blood flow which essentially means that it's a lot harder
7:30
to pump blood through even though it's the same amount of blood being pumped as the pulmonary side because of this difference the left ventricle needs to be stronger until so the muscular layer of the left ventricular wall or its myocardium is three times thicker than the right ventricle myocardium okay so let's talk a little bit about pumping each heartbeat sounds something like ldub ldub ldb that first heart sound love is called s one and the noise comes from
8:01
the tricuspid and mitro valves snapping shut when the left and right ventricles contract which happens at about the same time right after the S1 sound the aortic and pulmonic valve open up allowing blood to get pushed out to the body and this period of time is called syy the second heart sound dub is called S2 and the noise comes from the aortic and pulmonic valves snapping shut to prevent blood from flowing backwards after it leaves the vent ventricles effectively ending
8:32
syy right after the S2 sound the tricuspid and mitro valves open back up allowing blood to fill up the ventricles again and this period of time is called diast and that's it each heartbeat can be broken into systo and diast so systolic blood pressure is the pressure in the arteries when the ventricles are squeezing out blood under high pressure in diastolic blood pressure is when the ventricles are filling up with more blood so it's going to be slightly lower pressure all right so if we simplify
9:03
this guy a little bit then the amount of blood that's pumped out by either ventricles over a period of time is called the cardiac output and the rate at which veins return blood back to the Atria is called Venus return which is pretty easy to remember right since the circulatory system is a closed loop cardiac output and Venus return are equal okay so let's use some numbers to make this a little more concrete let's say that about 70 mlit is ejected per squeeze with a heart rate of 70 beats
9:33
per minute or 70 squeezes per minute then 70 * 70 is 4,900 ml per minute which in lers is 4.9 L per minute meaning that this heart's pumping about 4.9 L per minute now in an average adult there's about 5 lers of blood total in the body which just to be clear is different from the cardiac output we just found which was amount pumped per minute now taking this total volume 10% of that or about .5 L is in the pulmonary arteries capillaries and veins which make up the
10:08
pulmonic circulation and 5% about 0.25 L is in one of the four chambers of the heart itself another 15% or 75 lers is in the systemic arteries traveling away from the heart 5% or .25 L is in the systemic capillaries and the remaining 65% or 3.25 L is in the systemic veins returning to the heart now in terms of where all that systemic arterial blood goes about 15% goes to the brain 5% nourishes the heart itself 25% goes to the kidneys another 25% goes to the gastrointestinal organs
10:49
yet another 25% goes to the skeletal muscles and the last 5% goes to the skin these numbers can obviously change for example during exercise but this does give you a general sense of things all right so that was the systemic arterial blood but you'll notice that there's a lot more blood in the systemic veins with that being said arteries are generally lower volume while also being under much higher pressure and in contrast veins are usually high volume low pressure
11:20
vessels and this explains why arteries and veins have different structures for example veins often have valves to help fight gravity and keep blood flow blowing in One Direction back to the heart whereas arteries don't need these valves because they're under higher pressure if we take a closer look at blood vessels they have three layers also called tunics or coverings that surround the vessel Lumin which is the hollow part of the vessel that holds the blood the innermost tunic is called the
11:48
Tunica intima which includes the endothelial cells which creates a slick surface that minimizes friction for blood moving through it next there's the tuna media or middle tunic which is mostly made of smooth muscle cells and sheets of elastin protein both the cells of the Tunica intima and tuna media generally get the nutrients they need from the blood and alumin finally there's the tuna externa or outside tunic which is made up of loosely woven fibers of collagen protein
12:20
that protect and reinforce the blood vessel and anchor it in place the tuna externa also has nerve fibers lymphatic vessels and in the biggest vessels the protein elastin to make things really wild some huge vessels have a tunic externa that's so thick that it needs its own blood supply so there are tiny blood vessels called the Vasa vasorum which means vessels of the vessels that creep along the tuna externa to bring nutrients to specifically that layer of the blood vessel
12:51
wall so the largest arteries closest to the heart which are the aorta its main branches in the pulmonary arteries have so much elastin in their tuna externa and tuna media that they're called elastic arteries these guys are really stretchy kind of like Spandex and this is what allows these arteries to keep their shape as well as absorb and even out the systolic and diastolic pressures these arteries eventually Branch into the arterials the smallest of the arteries in the arterials the
13:21
tunic media is bulky and can contract in response to hormones in the autonomic nervous system which is called vasoconstriction where the Lumin gets a lot smaller which decreases the blood to a capillary bed and ultimately the organ or tissue IT Supplies also though these vessels can relax or vasod dilate and the lum's diameter increases which allows more blood flow this process can also help with temperature control or Thermo regulation because blood carries a lot of heat with
13:52
it and when it gets close to the surface of the skin more of that heat gets lost so with Vaso dilation of the arterials more heat gets lost which therefore helps to lower body temperature likewise if you wanted to raise body temperature vasil constriction reduces blood flow which means less heat gets lost through the surface of the skin finally the capillary walls are generally only one cell thick just the tuna intimate layer with some larger vessels that also have a subendothelium
14:22
basement membrane layer which is a layer of protein just outside of the endothelial cells that provides extra support in addition to allowing oxygen and carbon dioxide to flow back and forth capillaries are also where nutrients like glucose can get delivered and where fluid can move out of the blood vessel and into the interstitial space which is the space between the blood vessels and cells water soluble substances like ions cross the capillary wall through either
14:49
water-filled spaces called cfts between the endothelial cells or through large pores in the walls of fenestrated capillaries meanwhile lipid or fat soluble molecules like oxygen and carbon dioxide can dissolve and then diffuse across the endothelial cell membranes on the other end of the capillary bed there's a venil and the arterial and venil are usually directly connected by a vessel called The Met arterial all right as a quick recap the pulmonary circulation starts with the
15:21
right ventricle which delivers blood to the lungs which then sends fresh oxygenated blood to the left atrium at which point it enters the systemic circulation starting with the left ventricle which pumps blood to the body and then deoxygenated blood comes back to the right atrium and it all starts over
15:42
again what is happening guys thanks for watching um that was an absolutely monstrous video so hopefully you made it through and learned a thing or two along the way huge huge props are going to go to everyone involved in making it uh Andrea wrote the script and Rishi edited the script and ye went through my hours and hours of illustrating and turned it into a coherent video so thanks guys I think it turned out really well and for you viewers um if you want to do a
16:09
deeper dive into this content you should definitely head over to osmosis.org we have a ton of quiz questions and the ability to make and uh look at flashcards as well so if you're interested in that you should definitely head over to osmosis.org and make an account um other than that you can always help support us by donating on patreon and you know subscribing to our Channel and following us on social media all right guys till next time see you
16:53
later
Here to help you learn
Sign in to keep a private conversation with your course tutor.
Ask me anything about the material…
Sign in to chat