Lecture 15

• Blood Cells, Cont.
  
  • Hematopoietic Stem cells, cont...
    
  • An HSC cell can become 1.) another HSC cell, 2.) a Colony-Forming Unit (CFU-L) of Lymphocytes (dedicated to become a lymphocyte), or 3.) a CFU-GEMM cell (from this cell we get all the other cells possible)
    
  • From the CFU-GEMM cell we can get:
    
    • BFU-E  Burst Forming Unit (BFU-E) (E = erythroblast), it makes a red blood cell.
      
    • CFU-GM becomes a Monocyte or a Neutrophil.
      
    • CFU-Eo becomes an Eiosinophil.
      
    • CFU-Ma  becomes a Basophil (Mast cell = Ma  these are the majority of basophils and they circulate and crawl into the tissues, but a true basophil stays in circulation)
      
    • CFU-Meg  forms Platelets (Meg = Megakaryoblast – a huge cell that a platelet is made from – platelets are a piece of a cell)
      
  • At any one time in your life, the majority of the blood cells in your body came for a single HSC cell.
    
    • When the body decides it needs to produce blood, it only stimulates one HSC cell.  This is called Colonal Succession
      
    • Colonal Succession – the majority of your blood at any one time can be traced back to a single cell.
      

   
   

  Chemical Regulators of Hematopoiesis (there are many regulators that are causing this to happen)
  

  • You can tell if something is a stimulating factors b/c the abbreviation is on the other side.
    
  • EPO – (Erythropoietin) – causing the production of RBC's or Erythrocytes.
    
  • G-CSF – (Colony Stimulating Factor) – it makes Neutrophils (G = neutrophil)
    
  • M-CSF – makes Monocytes (M = monocyte)
    
  • Interleukin-2 (IL-2) – stimulates the production of Lymphocytes.
    
  • Interleukin-5 (IL-5) – stimulates the production of Eiosinophils
    
  • TPO – (Thrombopoietin) – it is a hormone and it makes Platelets
    
    • These are all cytokines and produced by cells and released.
      
  • Some of these factors are not very good a making blood, and they need the help of a synergist.
    
  • Synergist – it enhances the ability of these compounds to create blood cells.
    

   
   

  We are going to follow Erythropoiesis (The production of RBC's).
  

  • CFU–GEMM cell  becomes BFU–E (Burst Forming Unit Erythoid (E)) – the BFU-E is committed to becoming a CFU–E (Colony Forming Unit Erythroid) (this is less prolific and is a storage form), which will become a RBC.
    
    • The BFU is extremely prolific (need lots of RBC's), and there is lots of multiplying/reproducing going on. The RBC has to go through this stage b/c we have to make so many of them, but it is committed to becoming a RBC.  So they undergo a period where they go through a lot of mitotic cell division in the burst form. Then the cell division starts to calm down and it goes to the CFU-E (less prolific, but still multiplying). This is a storage form, waiting to get to the maturation process of becoming a RBC.
      
  • CFU-E cannot continue any farther without stimulation by Erythropoietin (EPO). 
    
  • If CFU-E does not get stimulated by EPO it will die a natural cell death and its DNA will denature.
    
  • If CFU-E gets stimulated by EPO then it becomes a Proerythroblast.
    
    • A Proerythroblast is going to go through a committed maturation process to make it a RBC and it cant be stopped.
      
      • Proerythroblasts have Pherotin (which is a storage form of iron) but no hemoglobin
        
    • The Proerythroblast will change to a Basophilic Erythroblast.
      
      • The nuclei in the nucleolus will disappear and chromatin material will condense and Hemoglobin production begins.  These cells are still multiplying, and they will become a Polychromatophyllic Erythroblast
        
    • Polychromatophyllic Erythroblasts – are the last cells capable of cell divisions at all.
      
      • Hemoglobin production starts to occur at full blast, and pink areas will appear.
        
      • It is pink because we are dealing with much larger areas than a normal red blood cell.  But when the cell shrinks, it becomes more red.
        
      • The Polychromatic Erythroblast becomes an Orthochromic Erythroblast.
        
        • Hemoglobin production slows greatly.
          
        • This cell has lost most of its cell organelles but it still has a nucleus.
          
        • At the very end of this stage, it expels the nucleus, and the nucleus will be consumed by a Macrophage.
          
        • The second that the nucleus is gone, it is called a Reticulocyte.
          
        • 3 to 5 days have elapsed since it transitioned from a Proerythroblast to this Reticulocyte stage.  This is a range, not an average.
          
        • The day range depends on the amount of EPO stimulating the CFU-E cells
          
          • The more EPO stimulating, the faster it will mature (3 days)
            
          • The less EPO stimulating, the slower it will mature (5 days).
            
        • The Reticulocyte has Ribosomes, Mitochondria (b/c Krebs cycle is occurring), and Small amounts of Hemoglobin are being produced.
          
        • It is the Reticulocyte that will enter into the circulation and it matures to a RBC in 2 days (from the time of Proerythroblast to where it becomes a Reticulocyte).
          
        • There are 250 billion Reticulocytes produced every day
          
        • The Reticulocyte has to mature to become a RBC/erythrocyte
          
        • It then becomes little more than just a sac of Hemoglobin in 2 days – an Erythrocyte.
          
        • The average lifespan of an erythrocyte is 100-200 days.
          
        • The maturation mostly took place in the Spleen, but some goes to Bone marrow, and some goes to the Circulation and matures there.
          
          • The cells die in the spleen after 100 days b/c they become Fragile
            
        • Instead of Erythroblast it can be called a Normoblast – this is okay (ex. Polychromatic Normoblast).
          
        • Normoblast is a physiological normal erythroblast.
          
          • There is no pathological condition.
            

   
   

  WBC's – Leukocyte Ontongeny – life according the Leukocyte
  

  • Neutrophils – mature in bone marrow, as immature cells they are bands, they stay there for 5 days as part of a large reserve pool (that is with the understanding that you are not having a major immune response at the time – the pool will start to empty out when you have an immune response). After the 5 days, the Neutrophils enter the circulation, they will only live for about 12 hours, and then they will die a programmed cell death. This is the most prevalent type of WBC.
    
    • 100 billion Neutrophils are made each day.
      
    • Neutrophils do not go through a Burst Forming Unit stage (where we are creating lots of these cells), and b/c of this we have to have a lot of area creating these neutrophils. 
      
    • 60% of the Red Marrow (the zones) in surface area is creating Neutrophils.
      
    • 250 billion RBC's are made each day.
      
    • 25% of Red Marrow is making RBC's.
      
  • Monocytes – will mature in Red Bone Marrow – circulate for about 1 day, and get stored in tissue for about 2 to 4 months and become a variety of cells.
    
  • Eosinophils – will mature in Red Bone Marrow in about 2 to 6 days, and they will circulate in the blood with a half-life of about 6-12 hours. However, if they crawl into the connective tissue, they can live there for few days (live longer).
    
  • Basophils and Mast Cells – Basophils are distinct from Mast Cells
    
    • Mast Cells – will circulate as a Basophilic fraction of the blood but it is not the same.  Mast cells travel through the circulation for a few days and then enter the tissues and live weeks or months (they have a long life), it releases a different set of chemical compounds when it is called upon in the immune response.
      
    • Basophils – remain in circulation living just a few days (short life).
      

   
   

   
   

   
   

  We have different types of Lymphocytes:
  

  • B-lymphocytes (they were created in the bone marrow) – they mature in the red bone marrow and they become immunocompetent, meaning that they are going to be able to destroy an antigen, and in the mean time self-killers are suppressed (those that say kill self, are killed). They have an antigen that they will be up and do nasty things to.
    
    • Once we have immunity a Memory cell is created, which does not have to go back to lymphoid tissue.
      
    • Naïve B-lymphocyte – are B-lymphocyte that have not found its antigen, and they travel to the lymphoid tissue through circulation.  These will die a few days after release.
      
      • The body is constantly making B-cells.
        
    • NK – Lymphocyte (Natural Killer) – are made in Red Bone Marrow, are not programmed for any specific antigen (unlike B and T cells), are released to circulation, and after it gets to the circulation it concentrates on areas of intake such as the Lungs, GI tract, and Liver (where we take in air, food and water, etc).
      
      • They are the first line of defense against antigens.
        
    • T-lymphocytes – originate in Red Bone Marrow during fetal life, and for the first few years of your life, they travel to the Thymus gland and begin to proliferate there.  The Thymus gland is the main source of the Bone marrow for T-lymphocytes.  They also become immunocompetent. 
      
      • The Thymus gland start to fill with fat (sometime after puberty).
        
      • Naïve T-lymphocytes migrate to the lymphoid tissue, and they can live an extremely long time. They can live as long as you can live. But they have to come in contact with an MHC Class I Protein in order to live for a long time.  But if they don't bump into an MHC class 1 protein they will die a programmed cell death in a few days – This is called Tickling.
        
      • Diestche's father was 93 years old when he died, and he had a cell that was a T-lymphocoyte that had been living in him for 91 years. 
        

   
   

  Platelets (are only thrombocytes in submamallian species, but in humans they are NOT thrombocytes) – they are pieces of a much larger cell.
  

  • Thrombopoiesis: starts with a CFU-GEMM cell  becomes a CFU-Meg (termed a Megakaryoblast)  becomes a Promegakaryocyte  becomes a Megakaryocyte.
    
    • The Promegakaryocyte enters into many mitotic cell divisions but it doesn't end in cytokinesis (cell splitting). The nuclei from the mitotic divisions all clump together, and we get thousands of small compartments of cytoplasm. When it is all ready to go it is called a Megakaryocyte.
      
  • This was occurring in the 1.) Bone marrow, but not it has to enter into the circulation. 
    
  • As it enters into the circulation, the blood going by quickly, and the bone marrow will be breaking off platelets from the Megakaryocytes because it is very fragile.
    
  • Platelet formation starts at the bone marrow, but once it gets into the blood cell, it starts to move at the same speed as the blood and it is not going to create any more platelets (i.e. break up anymore) until it gets to the first set of capillaries
    
  • The first set of capillaries that it gets to is in the 2.) Lungs.  This is the second place for platelet formation.
    
    • We start with Megakaryoctyes and then we get lots of platelets breaking off. This is the second place for platelet formation.
      
  • All that is left is the clump of nuclei because the cytoplasm broke up, and the clump is what a Macrophage likes to eat.
    
  • Circulation platelets exist for 10 days in circulation; their job is blood clotting.
    
  • The 2 areas of platelet formation are the Bone marrow and the Lungs
    

   
   

  • The way that the cells enter the circulation is through 2 impermeable membranes.
    
    • The blood cells get to the endothelial cell, they push on the edge of the endothelial cell, as soon as the inner membrane touches the other membrane a 4um hole will open, and everything has to crawl through it with a big squeeze.
      
      • A RBC is 8.6um in diameter (squeezing through this hole)
        
    • When one of the membranes recognizes something that needs to go through, the two impermeable membranes will merge together and a hole will form between them to allow the thing to pass through.
      
    • The Reticulocytes have problems, they have lost a lot of weight and they have problems getting out. 
      
      • In the zones where Reticulocyte formation (producing RBC's) is occurring, there will be surges in pressure so they can get the RBC's into the circulation.
        
  • Cells entering the tissues from the circulation (they pretty much have to go through the Pericytic Venules).
    
    • They are pretty much preset for where they are going to go, they are only going to enter the lymphoid tissue through Pericytic Venules (they are also called Post-Capillary Venules).
      
      • They have been programmed with a sensor knowing which tissue they are going for, and the sensor will bounce against the wall of the tissue that it should be going to and then it will stick out Adhesion Molecules.
        
      • It will bounce and keep sticking out more Adhesion Molecules; it keeps bouncing until it gets stuck.
        
      • Margination – occurs when the cell tumbling stops and it adheres to the endothelium.
        
      • Then it will find a space to crawl between the endothelial cells to get into the tissues– this is called Diapedesis.
        
      • It enters the tissues from the circulation using Margination and Diapedesis.
        
      • If it wants to get back into the circulation and go somewhere else, it will follow the lymphatic system and re-enter the circulation.
        

         
         

  • There are approximately 3500ml of plasma in a 70kg man.
    
  • Plasma is 90% water
    
    • 2% everything else (consists of nutrients, electrolytes, respiratory gases, and the waste products of metabolism (such as lactic acid, urea, ammonia salts etc.) – you don't have to know these
      
    • 8% protein
      
      • 60% of the plasma proteins is Albumin (the major protein that we find in blood)
        
        • It is created by the liver and it functions as a buffer
          
        • It maintains the osmotic gradient of the plasma (most of the time we think that Sodium is in this case Sodium can get in and out of the blood), but what maintains the gradient is the Albumin.
          
        • Albumin is a Blood Volume Expander – only used in emergencies when short of blood
          
          • People can be allergic to it. It used to be commonly carried in the battlefield in WWI and WWII.
            
        • Albumin doesn't leave the blood unless there is an immunological response where we have inflammation, and then albumin will go out through open venules
          

   
   

  • The Globulins:
    
    • We name the Globulins by their Electrophoresis bands.
      
      • Electrophoresis is where you take some medium and you put a drop of some group of proteins on one end, and then you run an electrical current through it, and each of the proteins will move at a different speed, thus separating the proteins out.  Today we use gels and vary the amount of electricity that we are putting through the medium.
        
      • We put a drop of a group of different types of proteins on paper or a gel.  Then we apply an electrical charge to it, so the proteins can separate.
        
      • Variations in how fast these proteins will travel are based on the type of gel or paper and the amount and length the electricity is applied for. These are all variables for the electrophoresis bands that these proteins will end up in.
        
    • There are 5 different Globulins: Alpha 1, Alpha 2, Beta 1, Beta 2, and Gamma (use Greek letters)
      
      • Alpha 1- ₁
        
        • ₁ – Lipoprotein – has to do with HDL (High Density Lipoprotein  this is the Good Cholesterol), we will explain this more during digestion and absorption of fats
          
        • ₁ - Anti-trypsin Factor – this is a protease inhibitor
          
        • ₁ – Anti-chymotrypsin Factor – another powerful digestive enzyme that is secreted by the pancreas.
          
          • Trypsin and Chymotrypsin are two powerful protein digesters that are being kicked out by the pancrease into the GI tract for digestion. Should chymotrypsin or Trypsin get to the blood stream, there are things (the Anti- from above) that will get rid of it, b/c we do not want it digesting things in the bloodstream digesting blood proteins.
            
        • Inter- -trypsin factor inhibitor (is between bands ₁ and ₂) – is a protease inhibitor.
          
      • Alpha 2- ₂
        
        • ₂ – Prothrombin – is an integral protein for blood clotting
          
        • ₂ – HS – Glycoprotein – it is a carrier (HS – is a person's initials – Dietsche Syndrome, it does not carry HS).
          
        • ₂ – Macroglobin – is a protease inhibitor
          
        • ₂ – Haptoglobin – binds free hemoglobin – when Hb is outside of a RBC it can be extremely toxic – as soon as it binds to Hb it is picked up by the liver.
          
        • Pre-Beta Lipoprotein – (is between ₂ and ₁) is a (VLDL) Very Low Density Lipoprotein.