 Normal count of red blood cells at birth is around 6-7 million per cubic millimeter while in adult males it is 5-5.5 million per cubic millimeter and adult females it is still lesser that is 4.5-5 million per cubic millimeter. So you see why the count in adult males is more compared to the females because of the reproductive hormone testosterone which actually stimulates the erythropoiesis and it also causes release of erythropoietin so that also increases the erythropoiesis. On the other hand female hormone that is estrogen it inhibits erythropoiesis that is why the RBC count is less in females compared to males but you see at birth the count is much more so at birth and in infants the RBC count is much more compared to that in adults. Why is it so? Well infants have a hemoglobin that is hemoglobin F and this hemoglobin F has much higher affinity for oxygen. So this hemoglobin by virtue of having higher affinity for oxygen there is a decrease in release of oxygen to the tissues. So you may ask that why then hemoglobin F is present in uterus and after at birth? Well this hemoglobin F increase affinity is useful for carrying oxygen from the maternal blood to the fetal blood so that is why that is important but because of this virtue only it is releasing less oxygen into the tissues. So that means this compensation is brought about by increased RBCs because there will be hypoxia to the tissues right so it will lead to increase in synthesis of the RBC. So you should remember that at birth RBC count is much more compared to that in adults. Then life span in adults the RBC life span is 100 to 120 days basically approximately 4 months. While in infants the life span of RBC is approximately 60 to 80 days so that is approximately 2 to 2 and a half months and this is because that in infants the RBCs are susceptible to oxidative damage. Coming to shape and size of RBCs you see the diameter of RBC so this diagram is showing the RBC and the full axis right so this is the diameter diameter of RBC is approximately 7.5 microns. Central thickness is 1 microns while peripheral thickness is 2 microns so centrally you see thickness is less it is only 1 microns while peripherally it is more this is 2 microns and this is the biconcave shape of the RBCs which we talk about. Then volume of a single RBC is 90 micrometer cube so fundamentally in cross section of RBC we are seeing the biconcave shape of RBC and what are the advantages of this biconcave shape what is the need and how it is helping the physiology. First of all if surrounded by a hypotonic solution where water will start moving from the hypotonic solution into the cell in that case RBC can swell quite a bit before bursting and basically this concept is used in one test known as osmotic fragility where RBCs are placed in different solutions with different hypotonicity and we see that in which solution the RBCs have started bursting more so that gives the osmotic fragility of the cells and as the RBCs age there is increase in the osmotic fragility with age of the RBCs because of the loss of this membrane of the RBCs and that there is change in the shape so this biconcave shape is best suited for squeezing through the narrow spaces and you see the size of the capillaries is around 5 to 6 micrometers while the diameter of RBCs is 7.5 micrometers so how do they pass through the capillaries that is because of this biconcave shape then due to this biconcave shape they have a large surface area to volume ratio so for a particular volume the surface area of the RBC is quite large and due to this there is increase in the efficiency of O2 transfer so more membrane is available for the diffusion of the oxygen across the RBC membrane now RBCs do not have any nucleus or any cell organ as such there is no mitochondria no ribosome no endoblasmic etc why is it important first of all they are the mature cells and they are not going to divide so there is no need of nucleus but other cell organ is not also present so since mitochondria is not there the source of energy for RBC it is mainly going to be anaerobic metabolism so that is important since mitochondria is not there but why is it so that there are no cell organ is how does it help RBC well RBC is basically carrying hemoglobin hemoglobin is a very big protein okay and RBC is basically carrying this hemoglobin so basically RBC is a bag of hemoglobin so if these RBC is filled with other cell organelles and there would be very less space for carrying of the hemoglobin so that's how by getting rid of all the organelles RBC is most efficient in carrying the hemoglobin and remember that hemoglobin cannot increase more the percentage the volume the amount of volume which is occupying in the RBC it cannot increase more and on the other hand if hemoglobin formation is impaired then the size of the cell also decreases that's why we get in iron deficiency where hemoglobin synthesis is impaired it is decreased the size of the cell also decreases because there is no need why the size should be more so that leads to micrositic hypochromic anemia so basically RBCs are fully saturated with hemoglobin and when we say fully saturated that means 34 percent of the volume of the RBC is occupied by hemoglobin and that is basically this value is represented as MCHC mean or particular hemoglobin concentration so 34 percent of the volume of RBC is occupied by hemoglobin and if we say weight wise actually hemoglobin is responsible for 90 percent of the dry weight of the RBC now let's move on to little bit more intricacies on a structure of mature red cell now what is any membrane made up of it is made up of lipids proteins and carbohydrates and this kind of diagram you might have seen anywhere right so there is this lipid membrane is there and there are a lot of proteins are there right so this is a integral protein which is basically traversing the membrane integral protein is there on the other hand these are like peripheral proteins they are not passing through the entire membrane like this integral membrane protein integral membrane protein also known as trans membrane protein these are just peripheral proteins present on one leaflet of the membrane so basically like any other membrane RBC membrane also consists of lipid bilayer there is carbohydrate and there are membrane proteins and you see proteins are much more than the lipid and it is true for most of the membranes of the various cells right so membrane proteins it is 52 percent and in this the important ones which we should know is that there are integral membrane proteins or transmembrane proteins which include band 3 protein glycophorin aquaporin right then there are outer peripheral proteins that is lecithin and sphinxomyelin and there is inner peripheral proteins including spectrum and chyrin actin protein 4.1 let's see these in little bit diagrammatic manner so you can understand little bit here you see that this is the inner part okay cytoplasmic part and this is the outer part and these are the membrane and you see this glycophorins these are the transmembrane proteins these are transmembrane proteins and here they are also having carbohydrate moieties attached to them then inner peripheral proteins you see what are the inner peripheral proteins here there is band 4.1 protein and here there is band 4.2 proteins there is chyrin and these proteins are attached intracellularly to cytoskeletal elements and what are these cytoskeletal elements you see tropomycin is there there is actin so this you might have heard the name actin in the skeletal muscle contraction right tropomycin is not the cytoskeletal protein sorry it is actin and these are the actin filaments right so they are kind of holding the cell membrane and attaching them to the inner contents and that is mostly the hemoglobin so these proteins are very important in maintaining the shape of RBCs suppose there is problem in these proteins ankyrin or 4.2 4.1 band protein then the actin will not be able to attach to the membrane of the RBC and there will be change in the shape of the RBC and that happens in a disease known as hereditary spherocytosis so in this defects in the genes that code for certain proteins like spectrum ankyrin so ankyrin is the most common then band 3 protein protein 4.2 and other etrocyte membrane proteins also that will lead to change in the shape of the RBCs and it will change from biconcave to spherical so our RBCs which were like this they will become like this so what will be the problem see we told you the advantages of biconcave shape so once the RBCs become spherical those advantages will be lost they will have very much difficulty in traversing through the capillaries and especially in spleen actually spleen is a graveyard of RBCs so the cells which have aged and become less deformable they cannot pass through the spleenic sinusoids now with the change in shape of the RBCs to spherical there will be too much destruction of RBCs especially in a spleen and what is this basically too much destruction of RBCs is known as destruction of RBCs basically is known as a hemolysis and too much destruction will lead to hemolytic anemia okay and because of hemolysis there will be excess production of bilirubin due to the metabolism of the hemoglobin and ultimately it will lead to jaundice spleen also increases in size so this is the classical triad of hereditary spherocytosis that is hemolytic anemia right jaundice and spleenomegaly so for the treatment of hereditary spherocytosis because too much hemolysis is taking place blood transfusion may be required and depending on the size of the spleen and how much hemolysis is being going on suppose in moderate to severe cases spleenomegaly is also done to prevent excessive hemolysis now let's talk about the functions of RBCs so RBC functions are basically same as that of the function of hemoglobin so RBC actually transports hemoglobin which in turn transports oxygen and carbon dioxide and since hemoglobin is a protein so like most proteins it acts as a buffer also so these are the basically functions of the hemoglobin and since hemoglobin is enclosed in RBCs these are the functions of the RBCs then RBCs also transport nitric oxide in blood so that is a novel function which you should remember but you see we are telling that mainly the function of RBC is to carry hemoglobin and hemoglobin is a protein so my question is that why hemoglobin is not directly present in circulation then also it can do its job isn't it what is the need that hemoglobin should be carried in RBC well if hemoglobin is present only in blood then it is such a large protein that there will be increase in blood viscosity and osmotic pressure so it is going to increase the resistance through the flow and there will be too much increase in the blood pressure so it is better to be carried within a cell second it also prevents leakage through the capillary membrane into the tissue spaces or through the glomerular membrane of the kidney each time the blood passes through the capillaries so this hemoglobin can actually filter in the kidney and it happens when excessive hemolysis occurs and hemoglobin is present in the circulation there is a protein known as hemopexin okay so this hemoglobin binds with hemopexin so this prevents the leakage of hemoglobin into the circulation but when there is too much hemoglobin then this hemopexin gets used up right then this hemoglobin is free in the circulation in that case it starts appearing in the tubules