hello all welcome to let's do to get more such videos do subscribe to our channel and also press the bell icon to never miss an update from us we also have courses from different subjects do check them out on our website www.let's so let's start with today's session we started off with the human circulatory system and the three components of it the pumping organ heart the network of tubes the blood vessels and blood in our previous session we studied about the heart in detail in today's session let's learn more about the other components of the circulatory system the network of tubes that circulate the blood throughout the body are called blood vessels these blood vessels are of different types the ones that carry oxygen-rich blood away from the heart are called arteries the blood vessels that carry carbon dioxide rich blood from different body parts back to the heart are called veins the tiny blood vessels that connect the arteries and the veins are called capillaries if we lay out the blood vessels in a line they would stretch for nearly 62 000 miles that's enough to circulate the earth almost three times that's how vast the network is let's compare some of their features of all the three blood vessels the arteries have the thickest wall can you think why is it so it is to withstand the pressure of the blood pumped by the heart veins are thin walled and capillaries are the thinnest talking about the lumen arteries have a narrow lumen the vein has a comparatively large or wide lumen and capillaries have an extremely narrow lumen it is just a single cell wide we know the veins carry blood towards the heart and to prevent the backward flow of the blood they have valves valves ensure unidirectional flow of the blood arteries and capillaries do not have valves arteries are situated deep inside the body whereas the veins are superficially present the bluish blood vessel that we see beneath our skin are the veins capillaries are situated in the terminals of the artery or a vein let's now talk about blood blood is a fluid that constantly circulates in a human body transporting nutrients different gases to each and every cell of the body it also carries waste from different parts of the body but did you know that blood is actually a tissue a fluid connective tissue just like any other tissue it is made up of different types of cell but its matrix is fluid to study the composition of blood let's carry out a small experiment we collect some amount of blood from a person in a tube and allow it to stand still for few hours we can see that the cells deposit at the bottom and the fluid is there on the top this yellowish white fluid is called plasma 55 of the blood is composed of plasma the remaining 45 is the cellular component which includes the red blood cells rbcs or the erythrocytes the white blood cells or wbcs or the leukocytes and platelets but what gives blood its red color to find the answer to this watch our video on why is blood red in color the link for the same is added in the description box below do watch it now let's find out the functions of each of these components plasma is the main component of the blood and contains water nutrients ions protein and waste mixed in it the rbcs are responsible for carrying oxygen and carbon dioxide the rbcs contain a pigment called hemoglobin which bind with oxygen and carbon dioxide molecules the wpcs are part of the body's defense system and helps to fight infections and diseases the platelets helps in the clotting of the blood all right friends that is it for today's session we have now completed the major components of the circulatory system but there's another system that runs parallely in the body and is a part of both circulatory and immune systems to find out what that is do tune in to our next session i hope this session was informative and you like it if yes please give us a thumbs up before you leave take a look at the online courses hosted on our platform www.letstude.com see you next time until then keep watching keep learning and subscribe to let's do we make it easy [Music]