Blood Cells and Hematopoiesis (PDF)

## Récepteurs nucléaires et pathologies - A certain number of pathologies are linked to the mutation of these receptors. They are capable of self-renewal and differentiation into non-multipotent progenitors in response to an exogenous signal. - Some deregulations exist in certain cancers. The the...

## Récepteurs nucléaires et pathologies - A certain number of pathologies are linked to the mutation of these receptors. They are capable of self-renewal and differentiation into non-multipotent progenitors in response to an exogenous signal. - Some deregulations exist in certain cancers. The therapy in the treatment of these cancers is to block nuclear receptors. ## ÉLÉMENTS FIGURÉS DU SANG ### I. Le sang, généralités - The blood is a specialized fluid connective tissue, included in the cardiac cavities and blood vessels. The blood volume is approximately 5 liters in humans, containing 45% of this tissue. This is mainly red blood cells (= red blood cells). The hematocrit corresponds to the volume occupied by the red blood cells in the blood in relation to the total blood volume. - **Composition:** Blood is composed of cells (= blood cells) and of the liquid extracellular matrix (= plasma). - **ATTENTION +++:** - The plasma is the total liquid phase (therefore without cells). - The serum is plasma without fibrin or coagulation factors. - **Functions of the blood:** - **The transport and exchange of gases** (O2 brought to the tissues by the arteries, and the CO2 recovered by the veins) as well as ions, nutrients (glucose, amino acids derived from proteins and lipids), hormones, cytokines (= inflammatory or anti-inflammatory factors), medications and metabolic wastes that are sent to be processed (filtered and excreted) to the kidneys, liver and lungs (for gas exchange). - **The cellular circulation** (of blood cells) - **The immunological and cellular purification** via the spleen. - **The coagulation.** - **Functions of the blood cells:** - **Red blood cells (erythrocytes)** ensure gas exchange. - **Platelets (thrombocytes)** maintain the integrity of the circulatory system by closing endothelial breaches. - **White blood cells (leucocytes)** belong to the body's various defense systems. - All blood cells and immune cells originate from multipotent hematopoietic stem cells, located mainly in the bone marrow. - **Do not confuse multipotent cells with totipotent cells:** - **Totipotent cells** = typically embryonic cells, which will be able to produce any cell type. - **Multipotent cells** = unable to differentiate into cells belonging to another tissue (for example, hematopoietic stem cells will produce blood cells but not liver cells). ### II. Hematopoiesis - Hematopoiesis is a physiological process that allows the creation and renewal of blood cells. It allows the production of 10^11 to 10^12 hematopoietic cells per day. This is done from multipotent hematopoietic stem cells (or HSPC), which are at the origin of all blood cells. - This regeneration is done from multipotent stem cells. The primordial stem cells can produce all blood cell lineages, while specialized progenitor cells produce, after the first division, only one blood cell lineage (red blood cells, platelets, leukocytes, etc...) - **No blood cell divides in the cardiovascular cavities +++** - Blood cells originate from: - **The hematopoietic tissue** found in the child and adult in the bone marrow, and in the fetal period in the liver, spleen and bone marrow (which will lose their hematopoietic function). - **The lymphoid tissue** for lymphocytes, with the primary lymphoid tissue, which is the bone marrow and the thymus, and the secondary lymphoid tissue, which are the lymph nodes, the spleen and the lymphoid tissues associated with mucous membranes, called MALT (= mucosa-associated lymphoid tissue, such as the lymphoid tissues associated with the digestive system or the respiratory system). - The thymus is a very active organ during childhood that atrophies later in adulthood. - **Three pathways of differentiation are then possible for differentiated HSPCs (= specialized progenitor cells):** - **Erythropoiesis (=CFU-E)** producing erythrocytes (= red blood cells = red blood cells). - **Leucopoiesis**, producing leukocytes, which is divided into two distinct processes: - - **Granulopoiesis (=CFU-GM or CFU-Eo or CFUBaso)** producing neutrophils and monocytes, eosinophils and basophils, respectively. - - **Lymphocytic leucopoiesis**, that is, the formation of lymphocytes which only reach their maturity (acquire their functions) after passing through the primary lymphoid tissues, which are the thymus for T lymphocytes (T=Thymus) and the bone marrow for B lymphocytes (B-Bone). - **Thrombopoiesis (=CFU-Mk)** forming megakaryocytes, which themselves produce platelets. - Red blood cells and platelets are said to be specific to the blood, that is to say, they do not leave the vascular system under physiological conditions, but only under pathological conditions (in case of hemorrhage), unlike leukocytes which circulate in the blood but also in other tissues (where they acquire their functional properties). ### III. Coagulation - Coagulation corresponds to the complex process leading to the formation of blood clots (this is physiological !!!). This is essentially but not exclusively +++ a clot of insoluble fibrin, obtained by transformation of fibrinogen, which is soluble. It begins almost instantaneously after a breach of the endothelial wall of blood vessels. This blood clot will allow to fill the created breach. The exposure of blood to tissue factors such as collagen, will initiate certain modifications in platelets and fibrinogen, to allow the formation of the clot. - This reaction can be divided into 2 main parts: - **The first is primary hemostasis**, where platelets will form a plug (= platelet plug) to block bleeding. - **The second is secondary hemostasis**, involving coagulation factors which, in a complex cascade, transform fibrinogen into fibrin, thus strengthening the platelet plug. It is called secondary but begins at the same time as primary hemostasis. - **Coagulation is therefore a step in hemostasis, +++** - **Hemostasis is a physiological process that intervenes in response to a pathological process, such as bleeding, to prevent hemorrhage.** - The regulation of coagulation is complex. There are physiological inhibitors of coagulation (mostly in physiological situations) as well as activators of coagulation (in pathological cases such as a cut). There is a very fine balance between these two types of actors, to avoid for example intravascular coagulation when it is not necessary (thrombosis can lead to ischemia), or conversely a too great fluidity preventing a correct coagulation (hemophilic individuals). - **So the goal of coagulation: +++** - fibrinogen (soluble) ------ fibrin (insoluble) - **The two major pathways for regulating coagulation are:** - The intrinsic pathway, with intravascular factors. These factors are therapeutic targets for heparin (a widely used anticoagulant), and its derivatives (examples: low molecular weight heparin and unfractionated heparin) - The extrinsic pathway, linked to the exposure of blood via vascular breaches, leading to contact with collagen from the basement membrane of connective tissue. This contact between blood and collagen will activate coagulation. - Many factors in these pathways depend on the presence of calcium ions +++ for their activation. Coagulation is then said to be dependent on calcium ions and can be limited by calcium chelators (chelators = chemical molecules that trap calcium here). When blood samples are taken, vials with purple stoppers are therefore often used, which contain EDTA, a chelator of all divalent ions (therefore calcium in particular), preventing intra-tube coagulation. - The professor shows you the entire factor cascade that is not to be memorized, he just tells you that there are many different factors to have many control points, they are very important to avoid intravascular coagulation in a physiological situation (risk of stroke, etc.) ### IV. Blood count and other types of cell quantification. - The blood count consists of counting the number of red blood cells (erythrocytes), white blood cells (leukocytes) and platelets per unit volume of blood. The numbers are to be known by heart! +++ ### A. Normal results and averages in adults | | **Male** | **Female** | | ----- | ----- | ----- | | **Red Blood Cells **|5 000 000 ± 500 000/µL |4 500 000 ± 500 000/µL | | **White Blood Cells** | 7000 ± 3000/μL | | | **Platelets** | 150 000 to 450 000/μL | | ### B. Cell count and blood formula (NFS) - The count allows for the evaluation of the number of each of the different populations of leukocytes. It is carried out by automatons (flow cytometers), but the identification of cell anomalies is done on smears spread on slides, which are then colored; there is therefore a human verification by microscope. These results are expressed in absolute numbers per microliter or in percentage. However, it is more judicious to rely on the absolute value than on the percentage. | Cell Type| Absolute Count| %| | ----- | ----- | ----- | | **Polymorphonuclear leukocytes (one single nucleus formed of several lobes, and not several nuclei) = granular leukocytes** | | | | **Neutrophil granulocytes** | 1800 to 8 000/μL | 50 à 70% | | **Eosinophil granulocytes** | 50 to 500/μL | 1 to 3% | | **Basophil granulocytes** | <100/μL | 0 to 1% | | **Mononuclear leukocytes (no different lobes) = agranular leukocytes** | | | | **Lymphocytes** | 1 500 à 4 500/μL | 20 to 50% | | **Monocytes** | 100 to 1000/µL | 2 to 20% | ### C. Cell count of lymphocyte sub-populations - This cell count is performed by immunostaining (Ac-Ag reaction) on slides or by flow cytometry. It gives, normally, the following results for a total of 1000 lymphocytes per microliter: - Lymphocytes B: 150 - Lymphocytes NK: 150 - Lymphocytes T: 700, of which: - Lymphocytes T4: 500 - Lymphocytes T8: 200 - (T4/T8 ratio= 2) ### V. Blood cells ### A. Red blood cells or erythrocytes - They are anucleate cells (without a nucleus or DNA) in the form of a biconcave disc about 8 micrometers in diameter and 2 micrometers in thickness. They are very deformable to allow for passage through small diameter capillaries and are often stacked. - In certain pathologies, such as sickle cell anemia, red blood cells are sickle-shaped (sickle-shaped) and therefore lose this deformable phenotype, which can lead to infarctions or ischemia. - Mature erythrocytes have neither a nucleus, nor mitochondria, nor ER, nor ribosomes. #### 1. Formation - Red blood cells form in the bone marrow during erythropoiesis under the influence of multiple molecules such as erythropoietin (EPO), androgens (hormones mainly male, therefore more red blood cells in men than in women). - If you inject EPO you will produce a lot of red blood cells and your endurance will increase. The formation of these cells by erythropoiesis takes about one week, for a lifetime of about 120 days (4 months). - Their destruction is ensured by phagocytosis by macrophages in the liver and spleen mainly ++. #### 2. Role - Red blood cells have as their main role the transport of O2 and CO2 thanks to hemoglobin, containing an iron nucleus (heme), the site of gas fixation. The normal hemoglobin concentration in the blood is: - 13 to 18g/100 mL in men. - 12 to 16 g.100 mL in women. - Hemoglobin is a major constituent of red blood cells (about 1/3 of its weight). - The red color of hemoglobin is due to the oxidation of the iron nucleus by the oxygen coming to bind to the complex (it's rust!). - It provides 3 functions: - The transport of O2 from the lungs to the tissues. - The transfer of part of the CO2 from the tissues to the lungs. - The buffering of H+ ions released by the tissues: metabolic reactions produce waste products including high concentrations of protons that acidify the environment. - **The professor explains that hemoglobin is an iron atom to which oxygen will bind. Iron with oxygen on it is called oxidized iron, hence rust, basically our blood is rust, hence the red color.** - The plasma membrane of the red blood cell carries antigens that determine blood groups (A, B, O, Rh). - **The professor specifies that, obviously, the blood group is not limited to ABO and Rh groups which are, moreover, independent. There are many other blood groups such as the KELL group, which are studied for organ transplants in particular. However, for blood transfusions, the most important ones are A, B, O, and Rh, explaining their popularity.** - Glucose is the main source of energy for the red blood cell, which is consumed by the process of anaerobic intra-erythrocytic glycolysis because, due to the absence of mitochondria, there can be no aerobic reactions (no Krebs cycle). ### B. Platelets or thrombocytes - Platelets are fragmented cells of megakaryocytes that have exploded. They are anucleate, 2 to 5 micrometers in diameter, and lenticular in shape. - **The professor does not consider platelets as cells per se, but as entities of megakaryocytes.** - They contain mitochondria, dense-core vesicles, and a cytoskeleton rich in contractile proteins (they must be able to stick together to form the platelet plug in hemostasis). Their lifespan is 8 to 12 days. - They originate from the cytoplasmic fragmentation. - **Attention, they are medullary, therefore there are no megakaryocytes in the blood under physiological conditions. Megakaryocytes are of normal size, with a large single monolobed nucleus, often off-center (picture opposite).** - Platelets play a key role in the processes of hemostasis and coagulation with the phenomenon of platelet aggregation. This is a consequence of the adhesion of platelets to each other and to the collagen of the connective tissue, under the effect of the ADP released by platelets. It constitutes the initial step of hemostasis. ### C. White blood cells or leukocytes - White blood cells defend the body against pathogens and non-self. To perform this function, they leave the blood to go to other tissues. - White blood cells are classified according to the presence or absence of cytoplasmic granules: they are called agranular or granular. They are also classified according to the shape of their nucleus: they are called mononuclear (massive nucleus) or polymorphonuclear (lobed nucleus): - Mononuclear leukocytes are agranular and monocytes and lymphocytes are distinguished. - Polymorphonuclear leukocytes are granular and neutrophils, eosinophils and basophils are distinguished. #### 1. Mononuclear/agranulocytic cells ##### a. Monocytes - Monocytes are the largest blood cells with a diameter of 15 to 20 micrometers. - They are rounded cells with a horseshoe-shaped (reniform, kidney-shaped) central nucleus. - In the agranular cytoplasm, there are a few azurophilic grains: lysosomes. - Monocytes are the undifferentiated form of the macrophage and leave the blood to migrate into the tissues and differentiate into macrophages. ##### b. Macrophages - Macrophages are scattered throughout the body and differ from monocytes by their larger size and the considerable development of their vacuolar apparatus, comprising endocytosis vesicles, endosomes, primary lysosomes, phagosomes and phagolysosomes. - Macrophages are involved in the digestion of extracellular waste (phagocytosis). They have cytoplasmic extensions forming true pseudopods: they are extremely mobile cells with a high secretory capacity. - They secrete fractions of complement, pro (IL1, IL6, TNF-α) and anti-inflammatory cytokines, hematopoietic factors, proteases, prostaglandins, as well as a large amount of free radicals that participate in the destruction of bacterial membranes, viruses and dead cells. They play a key role in the body's defense with non-specific cleaning, which explains their name of "trash" cells. They play an important role in inflammatory and immune reactions. - Monocytes and macrophages are regulated in their functions by different cytokines, such as interferon γ produced by T lymphocytes. It is in particular T lymphocytes CD4 that modulate the action of monocytes and macrophages. ##### c. Lymphocytes - They can be recognized under the microscope by their nucleus-to-cytoplasm ratio: the nucleus is very large compared to the total size of the cell. - They are poorly represented in the blood (compared to the total number of leukocytes), and their functions are mainly outside the blood. They are cells of the immune system. Their location is mainly tissue in the primary and secondary lymphoid organs. ### 2. Polymorphonuclear/granulocytic cells - They belong to the granulocytic lineage and have a single multilobed nucleus. The cytoplasm of granulocytes contains numerous cytoplasmic granules allowing them to be divided into 3 categories: neutrophils. - **Attention: the nucleus is single, but multilobed. They are therefore not multinucleated cells!** ##### a. Neutrophils - Neutrophils are neither acidophilic nor basophilic, so they do not pick up a specific stain with MGG. - They are the most numerous polymorphonuclear leukocytes and they represent 50 to 70% of leukocytes. - They act locally in the tissues where they eliminate pathogens and cells or molecules that have become abnormal (cancer cells for example). They release bactericidal substances that lead to the partial destruction of bacteria, the process being completed by macrophages which end up eliminating all the debris. Due to their high activity, they have a very short lifespan, of the order of 24 hours. ##### b. Basophils - Under the microscope, with MGG staining, they take up lots of blue spots. (see picture below) - They are easy to identify with their large cytoplasmic granules that are dense and violet.. They represent 1% of all white blood cells and have a lifespan of a few days. - They circulate in the blood, and go into the tissues in case of allergic reactions (in the skin, nose, lungs...). They are therefore involved in immediate hypersensitivity reactions of allergic reactions, working in conjunction with tissue mast cells (seen in the course on connective tissue). Degranulation of mast cells releases histamine which intervenes in the process of allergy. ##### c. Eosinophils - These are the main cells of antiparasitic immunity (worms, agents responsible for toxoplasmosis or malaria for example). They also play a role in tumor resistance. - Their granules contain numerous proteins, some of which cause degranulation of mast cells, and therefore the release of histamine (a molecule responsible for urticaria, whose release is blocked by antihistamines). Eosinophils also contain peroxidase which has the ability to destroy many microorganisms, including parasites, but also tumor cells. - After a half-life of only a few hours in the bloodstream. - **The professor does a recap: Blood is composed of blood cells suspended in plasma, the whole is contained in blood vessels and the total blood volume of an adult is around 5 liters. Blood cells represent 45% of the total volume, this is called the hematocrit. The hematocrit is often considered as the amount of red blood cells by abuse of language because red blood cells are the majority.** <start_of_image> schematic diagram: ``` THE HUMAN BODY ( 8% ) ____________ | | | BLOOD | |____________| | | _____________________ | | | PLASMA | | | |___________________| | | | ________________ __________________ | | | | | OTHER LIQUIDS | ( 92% ) | OTHER TISSUES | | AND TISSUES | | | |___________ | |__________________| | | | WATER (1.5%) | |___________| | SOLUTES | ( 0.5% ) |___________| | _____________________ | | | BLOOD CELLS | ( 45% ) |___________________| | | _______________________ __________________________ | | | | | RED BLOOD CELLS | | WHITE BLOOD CELLS | |_______________________| | | | | | _________________________ _____________________ | | | | | PLATELETS | | BLOOD PROTEINS | (7% ) |_________________________| |___________________| | | | ____________________ ____________________ | | | | | OTHER SOLUTES | ( 1.5% ) | OTHER | |____________________| | SOLUTES | | | | - Nutrients | | - Hormones | | - Lipids | | - Gases | | - Electrolytes | | - Nitrogenous | substances | | - Vitamins | | - Metabolic wastes | |______________ | | | | - Fibrinogen | | - Globulins | | - Albumins | | - Hormones | | - Proteins | - Enzymes |______________ | | | ____________________ | | | WHITE BLOOD CELLS | |____________________| | | ___________________ | | | - Basophils | | - Neutrophils | | - Eosinophils | | - Lymphocytes | | - Monocytes | |___________________| ``` ### ++ENDOMEMBRANE SYSTEM++ This system is typical of eukaryotic cells. It is not present in prokaryotic cells. - **A. Definitions** - The endomembranous system is specific to eukaryotic cells (not in bacteria). There is no compartmentalization in prokaryotes, everything is loose in the cytosol. - It is a complex system composed of several intracellular cavities (compartments): - Each compartment is delimited by a membrane, that is to say by a lipid bilayer with TM proteins and peripheral proteins (similar to the plasma membrane). - These compartments are differentiable by their morphology but especially by their functional properties which are specific to them. - Even if these compartments have different functionalities, are named differently, and seem to be separated in different regions of the cell, there is nevertheless a permanent intercommunication between these compartments. This communication will take place through two networks: - Network of tiny channels = canaliculi: not always visible under the microscope - Circulating vesicles that go from one compartment to another.