Free Biology NEET Video Lectures for Body Fluids And Circulation

00:00:41 Hello everyone. So today's lecture is going to be about body fluids and circulation. This is the first part of the lecture on this topic. So the first question that you can possibly ask is why do we need a circulatory system? So as you know that we have a circulatory system in our body through which blood flows and this is very important for the following reason. It is important to maintain a proper environment for the functioning of the tissues. Now how does the circulatory system actually do this? The circulatory

00:01:16 system does this through the following two methods. By supplying tissues with nutrients. You know the food that we eat has to be converted and broken down into the constituents which are the nutrients for all the cells for example carbohydrate, lipids and proteins and and also the cells need oxygen a constant supply of oxygen. So this constant supply of oxygen and other various necessary substances for example hormones and other proteins which need to need to be supplied to the cells are all carried through the blood. The other

00:01:53 very important and critical function that is performed by the blood is the taking away of the waste that is created as a result of the metabolic processes that happen inside the cell all the time. So the metabolic waste consists of carbon dioxide and other breakdown products of the nutrients that are consumed by the cells and these have to be removed in a regular manner otherwise the buildup of these toxic substances is going to lead to uh uh harmful effects on the cells. So then let's see how does the

00:02:28 body do this. So there is a uh conduit through which this uh oxygen, nutrients and waste products are carried. These are called special fluids in the body. So in human body the special fluids that are used to distribute these substances are of two kinds. They are blood which you all have heard of and there might be something else which you have not really heard of that is called lymph. So we are going to today talk about both lymph and blood and try to understand their functions in the circulatory

00:03:01 system. So first we will talk about blood and you may have already heard this before but the blood consists of a fluid component which is about 55% of the total volume and the rest of it comprises of cells which are the 45% of the total volume. So in very uh quick uh way if we list the constituents of the blood we can see that the plasma is comprised of largely water, various proteins, many minerals and nutrients and clotting factors. What about the cells? What kind of cells are there in the blood? So in the blood you can see

00:03:41 that there are ithroytes which are called red blood cells or RBC's in short. Then there are the luccoytes which are also known as white blood cells or WBC's in short. And lastly there are the thrombocytes which are also known as platelets. So today we are going to learn about each of these constituents of blood namely the plasma as well as each of the cell types that we have listed here and we will understand what is the function of each of each and every component of the blood. So first let us begin with

00:04:13 plasma. So plasma is what remains if you remove all the cellular components or the formed components of the blood. So if if you are able to put a little bit of your blood in a machine called a centrifuge which spins it at a very high speed, what remains at the bottom is the cells and what is remaining at the top is a clear liquid which is called as a plasma. Now the plasma just does not comprise of liquid. It also has some proteins and other substances dissolved in it which I'm going to describe now.

00:04:46 So this is a straw colored liquid and it is comprised of about 90 to 92% of water and then it has a lot of proteins which make up about 6 to 8% of the total volume. So this is mainly made up of fibbrronogen. It is made up of globulin and albumin. Fibbrronogen is needed for blood clotting. We will discuss this in the later part of this lecture today. Globulin is a very important component of certain molecules that you may have heard of which are known as antibodies. So antibodies are a type of globulins

00:05:26 called imunoglobulins. So globulins are therefore needed for defense mechanism of the body. Then the third category of proteins that are present in the plasma are known as albumins. These albumins are needed to maintain the osmotic balance in the uh body fluids. So now let us look at the next component which is minerals. So among the minerals that are present in the plasma the very important ones are sodium ions, calcium ions, magnesium ions, bicarbonate ions and chloride ions. So other than this

00:05:59 the plasma also contains various nutrient factors. For example, the breakdown products of the food that we eat, which is glucose, the amino acids, which are the constituents of the proteins that are part of our diet. And lastly, the lipids, which are the components of the fat that is present in the food that we eat. And then last but not the least, there are these factors which are known as clotting factors. Whenever there is a break in the blood vessel or in the circulatory system, the blood will tend to flow out of the

00:06:30 broken end of the blood vessel. But to prevent loss of blood there is a process which is known as clotting. So this clotting produces a clot that acts like a plug to block the blood vessel. So this requires a lot of factors to be activated for this clot to happen. So these factors are known as the clotting factors and they are also normally present in the plasma of the blood. Now moving on to the cells. So this is an image that shows you all the major components of the cells that are present within the blood. So you can see

00:07:04 here that there are the RBCs which are the red blood cells. There are the platelets which are also known as the thrombocytes and then you have a whole lot of cells which are known as the white blood cells together. But the white blood cells are of various kinds. So we have eosinophils, we have basopils, we have neutrfils and we also have monocytes and lymphocytes which are of two kinds Tlymphosytes and Blymphosytes. So now what we are going to do is one by one we will go and look at what each of these

00:07:39 cells are required for in the blood and what their normal function is. So we'll start with first uh the RBCs. But before I begin that I want to introduce you to a concept. This concept is about where do these blood cells come from. So the blood cells come from the bone marrow. The bone marrow has hematopoetic stem cells which are also in short form known as HSC's. So these hematopoetic stem cells look somewhat like this. So stem cells are those that are capable of self renewal. Meaning when they divide they

00:08:15 can produce more cells that are exactly copies of themselves. So the hematopoitic stem cell just does that. It copies itself and at one point of time when the need arises it decides to give rise to two cells. One of which will remain a heopoetic stem cell and the other one is going to become differentiated into what is known as a lympho site precursor cell. Now this hematopoetic stem cell which uh again will undergo another round of division. And now what it will produce is known as a iththroidid stem cell. Now this

00:09:12 eriththroidid stem cells then will differentiate further into a throid precursor and finally into an RBC red blood cell. So now you know where red blood cells come from. Then what about other cell types? So similarly this hematopotic stem cell can also differentiate into another kind of stem cell which is known as a colony forming unit. So this colony forming unit is a precursor to all the white blood cells other than the lymphocytes. So this colony forming unit will then again divide into two kinds of cells.

00:09:55 One of them is going to be a precursor for all the WBC's that I have talked about before the basoils the neutrfils the monocytes other than the lymphocytes and the third cell is going to be a precursor for what is known as a megaarioite. This megaarioite will ultimately give rise to small fragments which will form the platelets. Then the lymphosy precursor cell will actually further differentiate into the T- cell and the B cell. So in other words in the bone marrow you have the hematopotic stem

00:10:50 cell which is capable of copying itself multiple times and it amplifies itself in this manner and not only that at as and when required it can give off daughter cells which will differentiate into different kinds of precursor cells that can give rice to all the mature cell types that are present in the blood including the RBC's the platelets and all the WBC's. So why uh is this important to know? So you can uh think of it in the context of certain diseases. When uh you have a disease that affects your blood

00:11:26 cells, then you may need to replace the blood cells. So normally the blood cells have a finite life. They die after a certain period and the bone marrow continues to produce new blood cells throughout your life. But what if you have a disease in the bone marrow because of which there is a problem with your own production of blood cells then a process called bone marrow transplantation can be used and this in under this process your own defective cells are killed off by a very high dose of radiation and this is followed by

00:11:58 transplantation of bone marrow from a donor. This donor has to be matched with you of course and the matching donor will donate their bone marrow and the bone marrow will come with all the hematopotic stem cells and they can be then used to replenish all the blood cell types that are present in your in your body and this is a very uh useful uh method for curing any diseases that affect your blood cells. So now let us move on to studying each of these cell types. So we begin with the ariththraittes or as they're

00:12:31 called the red blood cells in short RBCs. So RBC's are the most abundant of all the cells in the blood. There are about 5 to 5.5 million of them in every cubic millm of blood. Not only that they are very interesting because they are not really a classical cell. They look somewhat like this. They are a flattened disc like in shape and if you look at them sideways you can see that they have a by concave shape. It is almost as if you took a ball which is a typical cell represented like a sphere and you

00:13:13 applied force from two sides so that you flatten it and now it becomes by concave in shape. So later on we will come to the uh uh reason why this uh cell is by concave in shape. So it looks like a frisbee or you know a disk. Then they don't have a nucleus but they have several other features. For example, they contain a protein called hemoglobin and they're completely full of many many molecules of hemoglobin. Now why is hemoglobin present? The only type of uh cell in our body that has hemoglobin is the red blood cell. So the

00:13:52 hemoglobin is there because hemoglobin can bind to oxygen. And one of the very important functions of the blood that I talked to you about before is the transport of oxygen to the tissues. Because in the lungs when we breathe in air there is an exchange of gases that takes place. So the oxygen from the air diffuses in uh into our blood and it is taken up by the hemoglobin that is present in the RBCs and it binds to the hemoglobin and it forms oxyhemoglobin and in this way when the blood flows into different tissues the

00:14:28 oxygen is carried along with the hemoglobin and distributed all over the body and the normal concentration of hemoglobin that is present in a normal individual is about 12 to 16 g per deciliter. What about the RBC's? Where are they born? I already told you that they are born in the bone marrow and their life is about 120 days after which they die in this organ known as the spleen. So spleen is a very important organ which is present behind the liver and this is the place where a lot of the uh immune

00:15:00 system uh related functions are carried out and one of the important functions that the spleen also uh performs. It is called as the graveyard for the RBCs. The dead RBCs are all removed from the circulation over there and then they are replaced from new RBCs which are born in the bone marrow. So the next kind of cells that make up the blood are as I said the white blood cells. So the white blood cells are also known as luccoytes or WBC's for short but they are a heterogeneous population unlike what I told you for the red blood

00:15:34 cells which are all the same. The white blood cells comprise of many different kinds of cells but they have certain characteristics which are the base uh basis for calling themselves white blood cells. So these are colorless due to the absence of hemoglobin. They are nucleated unlike the RBC's that we discussed before and they're much lesser in number than the RBCs. There are about 6,000 to 8,000 of them every cubic mm of blood. So this is again a picture that shows you the different kinds of white

00:16:05 blood cells that are present. And you can see that they have very distinct features on the basis of which they have been named. And I will explain the names of each of these white blood cells. and why they have been given those names in a bit. So the first uh cell type is known as the eosinophil and then there is the basopil and then there is something called the neutrfil and there is something called the monocy and then the two kinds of lymphocytes which are called the B and the T- cells. I'll I'll

00:16:34 provide you with an explanation of what uh the names really mean. So let us first uh look at how these can be classified into two big classes. So the eosinophils and the basopils and the neutrfils are together called granulosytes and the other cells which are the monocytes and the lymphocytes are called arranulosytes. Now why this name? The granulosytes mean they are cells which have granules or particles that can be seen inside them. So these granules are actually minute groups of um chemicals

00:17:11 which are present within these cells and they are used for their function which I will explain in the next few slides. So let us look at the first two cell types which are the neutrfils and the monocytes. So the neutrfil is the first one that we're going to talk about. The neutrfil is the most abundant kind of uh WBC that is present. About 60 to 65% of the WBC's are neutrfils. And what do they do? They are known as fagosytes. Now let me explain to you what fagosite means. So the fagosite word comes from

00:17:50 the word fa fage which means eating and sites are of course meaning cells. So cells that eat are called as fagosytes. So what do they eat? So WBC's or neutrfils that are fagocytes eat any foreign organism or any foreign substance that can enter into your body. For example, a bacterial cell. So if your body is invaded by a bacterial cell, this fagosite looks much like an amoeba and it can actually move along like a amoeba. So it swims along and then it chases the bacteria and what it does is that it has

00:18:30 these protrusions of the cytoplasm which is bound by membrane which are called the feet or pseudopodiaike structures that are present in an uh in the amoeba and two of these projections will surround the bacteria and eventually it will end up in engulfing the bacteria completely. ly within the space here and then it forms a vesicle inside the cell which is known as the fagosome which has the bacteria inside it. Now this fagosome will fuse with another organal known as the lossome and the lossome has a lot of

00:19:14 enzymes which will chew up the bacteria and completely destroy it. So in this way the fagosytes can get rid of lot of bacteria or other foreign organisms that enter into your body and prevent them from humming. What about the next cell type which is a monocy? Now a monocy is also a kind of a fagosite and it works in pretty much the same way as I explained to you right now but it is a much lesser abundant uh cell. only six to eight% of the WBC's are monocytes and they have a very short time which they spend in the

00:19:51 blood. So they spend a few hours in the blood and what they do is they enter into different tissues and there they undergo a metamorphosis or they undergo a change in shape they become much bigger and they are known as macro phasages or big eaters. So these macrofasages become resident in the tissues that they are present in and they serve as the guardians of those tissues preventing those tissues from being harmed by any foreign organism that can enter your body for example bacteria or fungus or viruses or what be

00:20:28 it. So these macrofasages are then called as tissue resident macrofages and as you can predict from that the one of the functions of the monocy is also fagocytosis. Now we are going to move on to the next kind of cells the WBC's that are the granulosytes. So we'll talk about two of them that are left which are the eosinophils and the basopils. So first the basoils. So why the name basopil? The name basopil is because they are stained. Although they are colorless naturally in order to see

00:21:04 them people use lots of dyes to look at them. So basoils particularly like basic dyes. So they get stained blue with basic dyes and therefore they're called as basoofil. Phil means liking. So baso means like basic stuff. So it is called as a basopil. These are the least abundant kind of WBC's that are present in the blood. Only 0.5 to 1% of WBCs are basoils. Now what kind of uh function do they perform? So they secrete a lot of substances for example histamine, serotonin these two are primarily

00:21:40 involved in the process of inflammation. So what is inflammation? Inflammation is the reaction of your body to an injury or trauma that has happened. So usually at a site where there is some kind of injury to the tissue or uh or to the skin what happens is there is a reaction which creates a redness, swelling and heat and also there is a lot of chemical factors which are secreted from that tissue and this tends to attract a lot of the basopils and other cells the neutrfils to the site of action and this is what

00:22:19 constitutes the activates the immune system to defend the body against the uh invasion of foreign organisms that may enter through a cut that is present on your body. So the histamine and serotonin forms a part of the process which is involved in inflammation and heperin is another molecule which is also secreted by the basopil. So this heperin molecule is actually acting as an anti-coagulant. If you remember in the previous uh part of this talk I actually mentioned that there is a process called blood uh clotting which

00:22:54 takes place to prevent the loss of blood when there is a break in a blood vessel. That process is also called as coagulation and those things that prevent coagulation from happening are called heperin. So heperin is very important because it prevents your blood from clotting when it is not necessary. If such anti-coagulants were not present in your blood, there would be a tendency for your blood to clot more and that would really hamper the process of circulation. So heperin is a natural anti-coagulant which is present in your

00:23:28 blood. Now the next type of cells is the eosinophils. So again where does the name eosinophil come from? Eosinophil means acidic loving cells. So eosin is a kind of acidic dye which is used to stain these cells. So since these cells get stained red with eosin they are called as eosinophils. They are of low abundance. Only 2 to 3% of the WBC's are eosinophils and they are also involved in the process of um resistance to infections and they're often associated with allergic reactions. All right. So

00:24:06 now we are going to go to the last kind of WBC's that are left which are known as lymphocytes. So they are residents of a structure called lymph nodes. Hence they are called as lymphocytes. And why they are called as T and B lymphocytes I will tell you in a bit. But first let me tell you what are the common characteristics of these lymphocytes. They are the second most abundant type of WBCs. About 20 to 25% of the cells are lymphocytes. Of the two types, there are B and T cells. The B cells refer to the place of

00:24:47 their uh differentiation which is the bone marrow. Al although lymphocytes are all produced in the bone marrow, they finally mature into different organs. The B cells mature in the bone marrow and therefore they are called as the belymphosytes and the T- cells migrate onwards to a structure called as the thymus gland. So the T stands for the thymus gland. So therefore the T- cells are called as uh the thymus uh lymphocytes. So both the B cells and the T cells are together responsible for carrying out all the immune responses of

00:25:22 the body. If I tell you in some more details, the tlymphocytes actually produce a lot of uh proteins called as cytoines. These cytoines are very useful for activating the immune system and many other substances are also produced by the tlymphosytes which actually help the immune system to destroy foreign organisms. The belymphosytes on the other hand are very specialized. They produce a molecule which is known as an antibbody. So I will come to what an antibbody is a little bit later and then I will tell you exactly what the

00:25:59 function of an antibbody is. But for right now what you need to know is that antibodies are used to provide protection from foreign organisms by helping to destroy them. Finally we move on to the last kind of cellular component that is present in blood other than the RBC's and the WBC's which are the platelets. The platelets are also known as thrombocytes. So the blood contains about uh 150,000 to 350,000 platelets per millm cube of blood volume. The platelets are not really cells. So they

00:26:37 are similar to the RBC's but the RBCs are just whole cells which have lost their nucleus and they have lost many other components that are present in a normal cell. But platelets are actually fragments of a cell. So if you remember from the previous part of the talk where I was talking about the bone marrow and how the hematopoetic stem cell forms the different types of blood cells. So there there was this cell called the meggaarioite which also comes from one of the hematopoetic stem cells and this

00:27:08 megaarioite is the precursor for the platelets. So the megaarioite kind of fragments into little bits and these little bits of membrane bound uh fragments of a cell don't really contain any nucleus but they have lot of proteins and other factors that are present inside them. So these little packets are called platelets and they are known to release a variety of substances which are known to be involved in the process of blood clotting. So I will tell you more about the process of blood plotting in the

00:27:40 later part of this lecture. Now I would like to introduce a concept called blood groups. So I'm sure most of you have already heard of uh blood groups and uh you will know what what uh actually blood groups are. But let me tell you that there are two kinds of blood groups that we will be talking about today. one is the type of blood group and the second is the RH type of blood group. So first let us talk about the type of blood group. So the blood group is decided based on the presence of two proteins on the

00:28:20 surface of red blood cells. These proteins are called A or B and they are known as antigens. Usually antigens are referred to as those substances which can bind to an antibbody. Okay. So any protein or other kind of molecule can be known as an antigen because usually there is an antibbody which can bind to it or recognize it very specifically. So these two types of antigens depending on whether they are present on the surface of the red blood cell or not. They are grouped into four kinds of blood groups.

00:28:56 A B A B and O. Now let me explain to you what this really means. So if this is a typical red blood cell, this is the cell membrane and usually there are proteins that are stuck in the cell membrane like this. So if I show you a blow up of this, it will look like this. So if the red blood cell membrane has a protein called a which is stuck into it then this will be known as the the people who have this uh blood group will be known as a blood group. The other kind of people who have another protein called B that is present in the

00:29:42 cell membrane of the RBC but no A protein will be known as B blood group. The third kind of people may be there who have both A and B proteins stuck in the membrane of their RBCs. So they are predictably called the AB blood group. And the third uh sorry the fourth kind of people who do not have any of these no A no B are called the O blood group. So this explains to you the four different kinds of blood groups and in the next uh slide I'm going to show you what this actually means and why do we

00:30:28 need to know this blood groups. So if you look at this table here which shows you that there are the four different blood groups A, B, AB and O. Now as I told you there are different antigens which are present on the surface of the RBCs of the people that belong to each of these blood groups. The people who belong to blood group A have an antigen A and the people who have B antigen belong to B blood group. AB people have both A and B and O blood group people have none. What about antibodies in the

00:31:05 plasma? Now normally we do not carry antibodies in our body that can recognize our self proteins or proteins that belong to our own body. This is because antibodies are a defense mechanism against foreign organisms. So it would be very counterproductive to have antibodies that can recognize your own proteins that are present in your own cells. Therefore, this means that a person who has an A blood group, because he has the A protein already, he will not have the anti-A antibbody. But because he never had the

00:31:46 B protein in his cells, so B is recognized as a foreign protein and so he will have the anti-B antibbody. Similarly, the person of the B blood group because has never seen the A protein will have an anti- A antibbody in his blood. And the person who has both A and B proteins will therefore not have any antibodies either to A or to B. Lastly, the person with the O blood group has anti- both anti-A and anti-B antibodies because that person never had any A or B antigens to begin with. So they have produced both antibodies A and

00:32:26 B because it recognizes both these pro proteins as being foreign. Now the last column is really really important. So you know that when there is a blood loss either due to some kind of a disease or due to some kind of a trauma or injury or accident there's a lot of blood that can flow out before the clotting mechanism can take care of it. So what happens when there's a lot of blood loss? If there's a lot of blood loss, we need to replenish the blood. And the way this can be done is through

00:32:58 a blood transfusion. So but if you want to transfuse blood from a person to another person, you have to do a matching of the blood group. And this is the reason why you need to know the blood group of the person. So why is it necessary to know the blood group of the person who is going to donate blood to you? The reason is the following. For example, let's take this person who is of a blood group and he has lost a lot of blood but his cells had the RBCs had the A protein on their surface. So he

00:33:33 did not have any anti- A antibbody but had a lot of anti-B antibbody present. Now what happens if a person who is of blood group B donates blood to this person? This person's blood will have lot of red blood cells bearing the B antigen on the surface. So the anti-B antibodies that are present in the recipient will go and immediately bind to the B antigen on the surface of the red blood cells and this will cause the red blood cells to clump together because an antibbody is usually a Yshaped molecule and it has these two

00:34:25 ends of the Y which are the sides that recognize the antigen. So the antigen can bind to two spots on the Y-shaped molecule. So one arm of the Y will bind to one RBC, the other one will bind to another RBC bearing the Btype antigen. And similarly you can also have uh antibodies that can simultaneously bind to two different RBCs and in this way they will cause clumping of the RBCs and ultimately this is a signal for the body to destroy such clumps of cells. So what will happen is the blood donor cells will all be

00:35:04 destroyed and the transfusion will not at all be useful. On the other hand, if he were to receive a blood from a person who belongs to the A blood group, no such problem would be there because the RBC's would only have the A antigen on them and this person does not have any anti-A antibodies. So there would be uh no problem with accepting the RBC's from a person of the A blood group. Similarly, a person from the AB blood group cannot donate blood to this person because he will have both antigen A and

00:35:42 antigen B on the RBCs which will be recognized by the antibb antibbody present in the person with the A blood group. But the person with the O blood group is a very safe donor. So the person with the O blood group has RBCs which don't have either A or B antigens. So they can easily donate blood to um anybody to a A blood group to a B blood group to a AB blood group and also to an O blood group. So therefore O is often known as the universal donor. But AB has the opposite problem. AB can receive blood from everyone from

00:36:28 the A blood group, from the B blood group and of course from the AB and the O blood group. So AB is therefore known as the universal recipient and it is also called as the selfish blood group for that reason. O on the other hand although it can donate blood to everyone it cannot receive blood from anybody except an O blood group otherwise there will be the clumping of the RBCs. So now I hope you have understood why it is very important to match the blood group before you uh undergo a blood transfusion. So this was the AB blood

00:37:11 grouping system that I talked about. So now there is another system which is present which is known as the Rh blood group. So this Rh blood group is based on the presence of another antigen again on the surface of the RBCS. So this antigen is known as the Rh factor. So this Rh factor uh is also present in recess monkeys. So these reesus monkeys uh since they are uh their first two letters of their name are Rh therefore the name of this antigen is Rh. Those people who carry the Rh antigen on their cells are called

00:37:53 Rh positive and predictably those that don't carry the Rh antigen on their cells are known as Rh negative. So now is this a problem? So Rh antigens do not normally u incite a immune response if there's a transfusion immediately. So if a person who is Rh negative is given a blood transfusion which is Rh positive, it requires some time for the immune system to produce antibodies against the Rh positive donor RBCs. So this will create an immune reaction but it will take some time. However, this is a very important factor

00:38:36 to be bear in mind during the pregnancy of a woman who is Rh negative. So if this is a first pregnancy for an Rh- negative woman, the fetus if by chance has uh is Rh positive what will happen? So normally the placenta is a barrier between the blood of the mother and the baby. So there is no chance that the mother's blood is going to be exposed to the Rh positive blood cells of the fetus. However, at the end of uh pregnancy when the baby is delivered at that time there is a possibility that the mother's blood

00:39:23 can be mixed with the fetal blood and at that point of time there is often this little exposure to the RH antigen will lead to production of anti- Rh antibodies from in the mother and this is a danger in the next pregnancy. So in the second pregnancy again if the fetus is Rh positive now the mother has a lot of anti- Rh antibodies present in the blood. So unlike the RBCs which cannot travel across the placenta antibodies can pass through the placenta. So these antibodies will get into the fetal

00:40:08 circulation and they will attack the RH bearing cells of the fetus and this causes a particular disease which is known as ariththro blastosis fetalis and what happens is a lot of the RBC species of the fetus or the baby are destroyed and then the baby can have jaundice or the baby can have very severe anemia. So how would you cure this? So prevent this from happening what is done is right after the first delivery of the first Rh- positive baby the mother is given a heavy dose of anti- Rh antibodies. Now if there are

00:40:59 any fetal red blood cells which are present in the mother at this point of time those RH antibodies will take care of those and will not allow the mother's immune system to develop anti- Rh antibodies against the next fetus. So the next pregnancy will be safe. Now we are going to move on to another topic and that is the coagulation of blood. So this has to do with the third cell type that is present in the blood which is known as the thrombocytes or the platelets. So before that let me explain to you what is the

00:41:37 clotting of blood. So if you imagine this is a blood vessel. It is like a pipe through which blood is flowing. Now there is a cut or a break in this pipe for some reason. And what will happen as a result of this? blood will start to ooze out and this blood will eventually form what is called as a clot and this clot serves the purpose of blocking the blood vessel the break in the blood vessel so that there is not too much blood loss. So this clot is made up of certain elements. So if you look at it in high magnification

00:42:22 what you can see it looks like this meshwork of a particular protein which is called as fibbrin and embedded in this meshwork are a whole lot of platelets and other dead and destroyed components of the cellular components of the blood. So this forms a like a plug and it literally blocks the capillary that was broken through which the blood was flowing out and now there is no loss of blood. Now how does this process actually take place? So the components that make up the clot are this fibrin network and this fibrin network is

00:43:06 present in a inactive form within the blood known as the protein fibbrinogen. So now something has to convert the uh fibbrinogen into fibrin. So fibbrinogen is a big molecule and this broken up into small bits which are called as fibbrin monomers. Now these fibrin monomers will all line up together like this and form really long fibers which will be the fibrin fibers that constitute the meshwork of the uh clot. Now the fibbrinogen to fibrin conversion takes place by the action of another protein which is known as

00:43:49 thromben. Thromben is also not present in this form in the blood normally. But thrombin is present in the form of a precursor which is known as proth thrombin. Now the conversion of proth thrombin to thrombin takes place only in the presence of what is known as a thrombocynise. This is a complex of enzymes. This complex of enzymes together uh makes the proth thrombin convert to thrombin and this thrombin then can convert the inactive form of fibbrin which is fibbrronogen to fibbrin and that starts the process of the clot.

00:44:30 Now what leads to the formation of this thrombocynise. The thrombocynise is formed whenever there is an injury or when there is some kind of trauma that causes a breach in the blood vessel or there's a tissue damage. So many many chemicals are released at the site of this injury and that leads to an activation of what is known as a cascade. So there are many components which I will not name because they are numerous in number and also very complicated. So a protein say A will get activated as a result of this

00:45:07 which will convert B from its inactive form to its active form which will then convert C to its active form and finally this will result in after multiple steps into the production of this thrombocynase complex which will then produce the fibrin. So this is triggered by the process of the breach and the same process also activates the platelets. So some of the components of the blood clotting cascade are also produced by the platelets. And not only this, the platelets play a very important role as the plug which makes

00:45:46 up uh the fibrin which is embedded in the mesh of the fibbrin and that physically helps in blocking the blood vessel the breach in the blood vessel. So now you know what is the role of blood clotting and how thrombocytes are very important for this process. Lastly I want to talk to you about uh lymph tissue. So this lymph is a fluid. It is known as the tissue fluid. So we have only been talking about blood and its components so far. And in the very beginning I told you there are two kinds of body fluids that

00:46:22 are used in the circulatory system. One is the blood which flows through the blood vessels which we are all aware of and the other one which we are not so much aware of is the lymph and it also has its own system of vessels which are known as the lymphatic drug uh ducts and the lymph flows through the lymphatic system. So how is the lymph produced as the blood passes through the capillaries in the tissues. So imagine that this is a blood vessel and the walls of the blood vessel are actually made up of

00:46:57 cells. So these cells are called as endothelial cells. But these endothelial cells are not very tightly attached to each other. There are certain gaps between these endothelial cells and the blood that is flowing through as a result of this it is coming in contact with lot of tissues in the surrounding region. Right? So these are the surrounding areas outside the blood vessel. The important constituents of the blood need to get to the tissues. So what are the important constituents? the gases such as oxygen, the

00:47:38 nutrients as well as other components of the blood such as hormones and other growth factors and proteins. So all of these can actually pass through by uh through the gaps that are present between the capillaries. Oxygen can itself diffuse through the membrane of the cell. it it doesn't have a problem. But the other nutrients can be transported through the gaps between the capillaries. The ions can also be transported. But what cannot be transported are really high molecular weight proteins like the albumins and globulins

00:48:13 that I talked about that are present normally in the plasma. Now what is this space that is present outside the blood vessel in between the tissues? It is known as the interstitial space and the fluid that is present in this space is called as the interial fluid. Now this interial fluid has all the components that have diffused from the blood out out of the capillaries into this space and sometimes if there is a breach there is often proteins that also accumulate here. Now these proteins cannot be absorbed back into the

00:48:55 capillaries because of the barrier that is present. Now they have to be removed from the system and the way that they can be removed from the system is through a drainage system that is present here which is known as the lymphatic system. So this whole intestial area is drained by the lymphatic ducts which carry the lymph in them. So the lymph vessel just like the blood vessel is also lined by cells but the gap between the cells in the wall of the lymph vessels is much larger because the gap is so large.

00:49:38 Therefore, big molecular weight proteins can also get into the lymphatic system and in this way a lot of cellular debris that is accumulated in the intestial fluid can actually be drained into the lymph and the lymph then goes and drains into the veins that are present in the circulatory system. So this is a very good scavenging mechanism to get rid of the waste. So now let me tell you u what is the composition of the lymph. The lymph is very close in its composition therefore to the intersticial fluid. Okay. And

00:50:17 this uh thus the process of gaseous exchange and all of the nutrients that have reached the tissues are then metabolized and then they lead to the release of uh carbon dioxide which goes back into the uh circulation and it also releases various other waste products some of which get into the capillaries but the others are removed from the system through the lymphs. So this elaborate network of vessels called the lymphatic system collects this fluid and drains it back into the major veins and this is the

00:50:50 very important function that it performs. It is also a colorless liquid much like plasma and it is responsible for the immune responses of the body because it also has the lymphocytes and it is an important carrier of nutrients and hormones etc. So with this we have finished the part one of this lecture but before I go I would like to leave you with certain questions that you might want to think about. So for example you have learned about blood groups. So let's try to answer this question. A person who has a

00:51:25 blood group A can receive blood transfusions from donors belonging to which blood group. So to answer this question you will have to think about what is there in the blood of a person who has the blood group A. He has the antigen A present on the RBCs but he has the antibodies which are present which are anti- B. So obviously he cannot get blood group B to give blood to A. That is not allowed. AB again not allowed because the B antigen is present which will be recognized by the antiBB antibbody. So

00:52:10 now what is left? O which I told you is an universal donor can give blood to A and also A can be a donor for the A blood group. So the answer to this question would be blood groups O and blood groups A. So another question that I would like to ask you is when a blood clot is formed after some time there is a pale liquid that comes out the clot kind of retracts and there's a pale liquid that is extruded from the clot and this is called serum. So the question is is there any difference between the plasma and the

00:52:51 serum because they look very similar. You would think that there is no difference but actually there is a lot of difference. The serum is like the plasma except it does not contain the platelets. Along with that it does not contain the clotting factors because all of them have been used up and most of them have been trapped in the clot and therefore are not present in the serum. The third question that I would like to ask you is is the lymph fluid more similar to the plasma or to the interstial

00:53:29 fluid. To answer this question, you have to think about where is the lymph present. So the lymph as I told you is present outside the circulation the blood vessels. So it is a drainage system for the interstatial fluid. So whatever that is present in the interial fluid around the tissues is the same as what is present inside the lymphatic ducts and which is the lymph. So the lymph would be very similar in composition to the inter intersticial fluid. Another question that I would like to ask you if you

00:54:17 remember the RBC if you look at it sideways is by concave in shape. Why is the RBC by concave in shape? And a related question to that would be why does it not have a nucleus? The reason it doesn't have a nucleus is to so that it can acquire this by concave shape. And what is the advantage of having this by concave shape is that it can have a larger surface area to volume ratio as compared to a spherical cell. Why does it need a larger surface area to volume? so that it can readily absorb oxygen and

00:54:54 gaseous exchange between oxygen and carbon dioxide can readily take place and this can therefore carry the gases very easily in large quantities to the desired destination. Now I will ask you a question that requires a little bit of general knowledge or general awareness about the conditions right now. So if I ask you which mosquito-born disease do people have a decreased ability to form blood clots. You might have heard about this already in the newspapers that denu what happens when you get denu when

00:55:32 you get denu your platelet counts go down. So remember there were normally about 350,000 platelets per cubic millm of blood. But very often if you are unfortunate enough to have a person in your family who has this disease you would know the platelet count can go down to 3,000 or even less. So what will happen? The ability to form blood clots will be seriously compromised and such people will die because they will have lot of small breaks that happen normally in your blood which are not even blood

00:56:07 vessels which are not even aware of are repaired immediately because your blood clots and forms blockers blocks but if you have dingo then this ability to form these clots is not there. Hence you will have internal bleeding and you can die from that. And the last question that I wanted to ask you is how is the blood that is stored in the blood banks prevented from clotting? See if I draw some blood from your body right now and put it into a tube, it will clot after some time and you will see the clot forming and what

00:56:40 will be left is the serum. Now think about this. A lot of blood is collected from people who uh participate in blood donation camps. So how is that blood prevented from actually clotting? The answer is uh that a lot of uh the steps in the blood clotting process are dependent on calcium on the presence of calcium. So if you add to the blood a substance that will remove the calcium or precipitate the calcium then the blood clotting cascade that steps that I told you A to B to C which ultimately lead to the production of fibrin will

00:57:21 not take place. So therefore if you remove calcium from the blood you can store it and prevent it from clotting. So with this we will end today's lecture and I'll see you again when I tell you about part two of the uh same topic which will be about the circulatory system which will be the heart and the blood vessels. Thank you. [Music]