Blood Cells PDF

# Blood Cells ## Intended Learning Objectives (ILOs) - Define what blood is. - Outline the major plasma proteins and all of the formed elements. - Describe in detail the morphology and structure of the RBCs. - Describe the hemoglobin structure. - Classify the white blood cells in general. - Descri...

# Blood Cells ## Intended Learning Objectives (ILOs) - Define what blood is. - Outline the major plasma proteins and all of the formed elements. - Describe in detail the morphology and structure of the RBCs. - Describe the hemoglobin structure. - Classify the white blood cells in general. - Describe in detail the morphology and structure of the different types of WBCs. - Describe in detail the origin, morphology, and structure of platelets. - Know the life span and fate of the blood cells. - List in brief the main functions of blood cells. ## Blood Blood is a specialized type of connective tissue consisting of cells and fluid extracellular material called plasma. Propelled mainly by rhythmic contractions of the heart, about 5 L of blood in an average adult moves uni-directionally within the closed circulatory system. ### Composition of Blood - Plasma (55%) - White blood cells and platelets (4%) - Red blood cells (41%) ### Functions of the Blood - Transmission of nutrients from the GIT system to all of the cells and then delivering the waste products to specific organs for elimination. - Carry hormones, electrolytes, and signaling molecules. - Oxygen is carried by hemoglobin, also CO2. - Adjust body temperature and to maintain the acid-base and osmotic balance. - Pathway for migration of WBCs between various connective tissue components. - Responsible for coagulation, the process which is mediated by platelets and clot. ## Plasma - Plasma is an aqueous solution with pH (7.4). - Consisting of: 93% water and 7% low or high molecular weight substance. - The dissolved components are mostly plasma proteins, but they also include nutrients, respiratory gases, nitrogenous waste products, hormones, and inorganic ions collectively called electrolytes. - The major plasma proteins include the following: - Albumin, the most abundant plasma protein, is made in the liver and serves primarily to maintain the osmotic pressure of the blood. - Globulins (α- and β-globulins), made by liver and other cells. ## Staining of Blood Film - Blood smear or film prepared by spreading a drop of blood in a thin layer on a microscope slide. - When erythrocytes are seen in a film of blood spread out on a slide, they appear yellow (or pale red) in color. - Their rims (being thicker) appear darker than the central parts. - Type of stains: Giemsa's, Wright's, Leishman's ### Giemsa's Stain - **Methylene blue (basophilic):** Stains DNA, RNA (blue-grey, violet). - **Eosin (esinophilic):** Stains hemoglobin, eosin granules (orange-red). - **Azurophilic (red purple):** Stains lysosomal enzymes. ## Blood Cells ### Red Blood Corpuscle (RBC) - The average RBCs count: - In males: 4.1–6 (5) million cells microliter (mcL). - In females: 3.9–5.5 (4.5) million mcL. - **Life span:** 100–120 days. - Old and deformed RBCs are destroyed by the macrophages of the spleen, bone marrow, and liver. #### LM picture of RBCs - **Size (diameter):** 7.5 µm in, 2.6 µm in the rim, and 0.8 µm thick in the center. - **Shape:** Esinophilic biconcave disks without nuclei (↑ surface: volume). - **Cytoplasm:** Mostly occupied by hemoglobin. - In small vessels red blood cells also often stack up in aggregates called rouleaux formation (stickec coins). #### EM picture of RBCs - **Shape:** Membranous electron dense biconcave. - **Cell organelles:** No nucleus &no organelles. #### RBC membrane - **Typical lipid bilayer (50% protein, 40% lipids, and 10% carbohydrates).** - Most of the proteins are transmembrane proteins, principally glycophorin A, ion channels, and the anion transporter protein. - **From outside:** By well-developed glyccalyx which is responsible for the blood grouping. - **From inside:** It is supported by well-developed cytoskeleton, which is responsible for flexibility of RBSs >>> It is formed of microfilaments (actin & spectrin) that are attached to a peripheral membrane protein >>> Ankyrin. ### Hemoglobin Structure - About 95% of the dry weight of the red blood cell consists of hemoglobin, the substance necessary for oxygen transport. - Hemoglobin is a protein; a molecule contains four polypeptide chains (tetramer): - **Hemoglobin A (adult hemoglobin) (2 α & 2 β).** - **Hemoglobin F (fetal hemoglobin) (2 α & 2 γ).** - To each chain is attached a chemical structure known as a heme group. - Heme is composed of a ring-like organic compound known as a porphyrin, to which an iron atom is attached. - The hemoglobin in the cell allows a single cell to carry 4 molecules of oxygen. ### Function of RBCs - Hemoglobin is a metalloprotein, acting as a transporter of gases, especially transporting 97% O2 and 7–10% CO2. - Hemoglobin carrying O2 is known as oxyhemoglobin. - Hemoglobin carrying CO2 is known as carbamino hemoglobin. - Exchange of O2 & CO2 in the body is aided by simple diffusion using the difference in pressure gradient. #### How erythrocytes can adapt its function? - **Biconcave disk:** Increase the surface area to allow more oxygen to be absorbed efficiently. - **Have a thin outer membrane:** To let oxygen diffuse through easily. - **Cytoskeletone & membrane structure:** Permits the RBCs to be passed through the narrowest blood capillaries. - **Absence of nucleus & organelles:** This allows the cells to contain more hemoglobin that is involved in the transportation of oxygen molecules. - **Selective permeability to O2 and CO2.** - **Carrying of NO:** Neurotransmitter substance that causes dilatation of blood vessels. ## Clinical Point ### Complete Blood Count (CBC) - A valuable screening test in medical practice that is used to diagnose and manage many conditions and diseases. - It measures the number of erythrocytes (RBCs) and leukocytes, the total amount of blood hemoglobin, and the fraction of blood composed of RBCs - the hematocrit. - The CBC also includes other information about RBCs such as mean corpuscular hemoglobin (MCH) and mean corpuscular hemoglobin concentration (MCHC) as well as the platelet count. ### Polycythemia or erythrocytosis - An increased number of RBCs. ### Anemia - Deficiency of RBCs and/or hemoglobin, with many different types of anemia existing. - **Causes:** - Blood loss >>> Hemorrhage. - Insufficient intake >>> Iron deficiency anemia. - Production of RBCs >>> Chronic diseases. - ↑ Destruction of RBCs >>> Hemolytic anemia. ### Sickle Cell Anemia - An autosomal recessive disorder leading to faulty synthesis of the b-globin chain of hemoglobin. - Resulting hemoglobin S causes RBC deformities. - Instead of biconcave discs, they become crescent-shaped sickle cells, which lose malleability and malfunction. ## Leukocytes (White Blood Cells - WBCs) - Leukocytes (white blood cells or WBCs) leave the blood and migrate to the tissues where they become functional and perform various activities related to immunity. - They are called leukocytes because they are colorless (No Hb). - Normal total number of leukocytes: 4,000 – 11,000/mm³. - Leukocytes are divided into two major groups, granulocytes and agranulocytes, based on the density of their cytoplasmic granules. ### Granulocytes - Possess two major types of abundant cytoplasmic granules: - Lysosomes (often called azurophilic granules in blood cells) and specific granules that bind neutral, basic, or acidic stains and have specific functions. - Have polymorphic nuclei with two or more distinct lobes. - Their Golgi complexes and rough ER are poorly developed, and with few mitochondria. - Have short life span, most granulocytes undergo apoptosis in the connective tissue. - Subdivided into 3 types: - **Neutrophils:** Their specific granules are neither markedly acidophilic nor basophilic. - **Eosinophils:** Their specific granules are stained by acidic dyes (e.g., Eosin). - **Basophils:** Their specific granules are stained by basic dyes (e.g., methylene blue). | Type | Nucleus | Specific Granules | Differential Count | Lifespan | | :---------- | :---------- | :----------------------------- | :----------------- | :----------- | | Neutrophils | 3-5 lobes | Faint/light pink | 50-70 | 1-4 days | | Eosinophils | Bilobed | Red/dark pink | 1-4 | 1-2 weeks | | Basophils | (S)shaped | Dark blue/purple | 0.5-1 | 1-2 months | #### Neutrophils - **L/M:** - The lobes of their multilobed nucleus are connected to each other by slender chromatin threads. - They possess very small specific granules. - **E/M:** - **Nucleus:** Lobulated with chromatinthread. - **Golgi complex:** Small. - **Mitochondria& RER:** Few. - **Two types of granules:** - The small, pale specific granules and the larger, dense azurophilic granules. ##### Neutrophil Granules - **Specific granules:** The more abundant granules, they are small (0.1 µm in diameter). Have: collagenase, alkaline phosphatase and phagocytins (bactericidal proteins). - **Azurophilic granules:** They are lysosomes (0.5 µmin diameter). Have: hydrolytic enzymes such as Acid phosphatase and peroxidase. - **Glycogen granules:** Glycogen is broken down into glucose to yield energy via the glycolytic pathway. The ability of neutrophils to survive in an anaerobic environment is highly advantageous, since they can kill bacteria and help clean up debris in poorly oxygenated regions, eg, inflamed or necrotic tissue. ##### Functions of Neutrophil: - Neutrophils are inactive and spherical while circulating but become amoeboid and highly active during adhering to ECM substrates such as collagen. - **Neutrophils are usually the first leukocytes to arrive at sites of infection** - Phagocytosis of micro-organisms (microphage) especially bacteria. - Secretion of proteolytic enzymes which cause lysis of the bacteria. - Release of macrophage chemotactic factor that stimulate attraction ofmacrophage at the site of inflammation. - Attraction of monocytes to the site of infection. ### Neutropenia - Is an abnormal decrease in neutrophil numbers in peripheral blood so that too few cells are available to defend against bacterial infection. - This may be caused by genetic, drug-induced or with autoimmune diseases. ### Pus Cells: - Under inflammatory conditions, neutrophils degranulation, releasing their contents including inflammatory mediators, antibacterial enzymes and tissue matrix breakdownenzymes. - Massed neutrophils, their debris and dead bacteria in tissue are visually recognized as pus. #### Eosinophils - **L/M:** - Closely packed eosinophilic granules fill the cytoplasm. - The usually bilobed nucleus has an irregular shape. - This granular leukocyte has a larger diameter 1350x. Wright's. - **E/M:** - **Nucleus:** Lobulated with chromatin thread. - **Cytoplasm:** Eosinophilic granules: - **Specific granules:** Has a disk-shaped electron-dense crystalline core (internum) that appears surrounded by a matrix enveloped by a unit membrane (externum). - The internum contains: A protein-called the major basic protein. Act to kill parasitic worms such as schistosomes. - **Also possess other enzymes:** Acid phosphatase, Arylsulfatase, Glucuronidase, Cathepsin, Phospholipase, RNase & Eosinophilic peroxidase. - **Azurophilic granules:** They are lysosomes containing hydrolytic enzymes similar to those found in neutrophils. ##### Functions of Eosinophil: - Phagocytize antibody-antigen complexes (Limited phagocytic power). - **Antiallergic:** By release of histaminase enzyme (destroy histamine) and sulphatase enzyme (destroy sulphate substances) at the site of allergic reactions, therefore slows down inflammation caused by basophils. - **Antiparasitic:** Attack parasitic worms: Leave capillaries to enter tissue fluid → The proteins is their specific granules → Act on the surface of the parasitic worm forming pores → Releasing toxic molecules from their specific granules to the parasite → Death of parasite. #### Basophils - Constitute less than 1% of the total leukocyte population. - Basophils have several surface receptors on their membrane, including immunoglobulin E (IgE) receptors. - Life span: Several months. - Diameter: They are about the same size as neutrophils i.e. 10–12 µm. - **L/M:** - They are round cells and have an S-shaped nucleus, which is commonly masked by the large dark blue to black specific granules present in the cytoplasm. - **Metachromasia:** When stained with toluidine blue (the specific granules appear red instead of blue because of their content of heparin). - **E/M:** - **Nucleus:** The lobulated nucleus (N) appearsas three separated portions. - **Cytoplasm:** Basophilic granules: - **Specific granules:** Are few, very large and irregularly shaped. They contain heparin, histamine, eosinophilic chemotactic factor and Peroxidase. - **Azurophilic granules:** They are lysosomes containing hydrolytic enzymes similar to those found in neutrophils. ##### Functions of Basophil: - Release of eosinphil chemotactic factor. - Release of heparin (anticoagulant). - Release of histamine (initiates allergic reaction). - They have limited phagocytic power. ### Clinical Point: Basophilia - Increase basophil counts in peripheral blood, basophils and mast cells alsoare central to immediate or type 1 hypersensitivity. - In some individual's substances such as certain pollen proteins or specific proteins in food are allergenic, that is, elicit production of specific IgE antibodies, which then bind toreceptors on mast cells and immigrating basophils. ### Agranulocytes - Don't have specific granules, but they do contain azurophilic granules (lysosome). - This group includes lymphocytes and monocytes. - The nucleus is round or indented but not lobulated. | Type | Nucleus | Count (%) | Life Span | | :---------- | :---------- | :-------- | :----------------------- | | Lymphocytes | spherical | 20-40 | Hours to many years | | Monocytes | Indented or C- | 2-8 | Hours to years | | | shaped | | | #### Monocytes - Are agranulocytes that are typically much larger than lymophocytes and less abundant. - About 5% of circulating leukocytes. - Diameter: 12–20 µm. - **Life span:** hours-years. - **L/M:** - **Nucleus:** Large, deeply indented than that of a lymphocyte, generally eccentrically placed and frequently shows a horseshoe, or kidney shaped. - **Chromatin:** Is less condensed than that in lymphocytes. Because of their delicate chromatin distribution, the nuclei of monocytes stain lighter than do those of large lymphocytes. - **Cytoplasm:** Is basophilic and frequently contains very fine azurophilic granules. - **EM:** - One or two nucleoli are seen in the nucleus. - Small quantity of rough endoplasmic reticulum, polyribosomes, and many small mitochondria is observed. - Golgi complex involved in the formation of the lysosomal granules is present in the cytoplasm. - Many microvilli and pinocytotic vesicles are found at the cell surface. ##### Function: - Monocytes are precursor cells of macrophages, osteoclasts, microglia, and other cells of the mononuclear phagocyte system in connective tissue which phagocytose tissue debris, apoptotic cells, bacteria, and other extraneous material. - They are stimulated by growth factors, such as macrophage colony-stimulating factor (M-CSF), granulocyte-macrophage colony-stimulating factor (GM-CSF) orIL-3. - When adequately stimulated, macrophages may increase in size and fuse to form **multinuclear giant cells**, usually found only in pathologic conditions. - Macrophages can secrete numerous chemokines, cytokines and growth factors involved in inflammation, immunity, tissue healing and repa #### Lymphocytes - About 20–30% of circulating leukocytes. - A family of spherical cells with similar morphological characteristics. - They can be classified into several groups according to distinctive surface molecules (markers), which can be distinguished by immunocytochemical methods. - They also have diverse functional roles, all related to immune reactions. - Life span: For several months. The memory cells can live for several years. - **According to their diameter, lymphocytes are classified into:** - **Small lymphocytes:** 6-8 µm (the predominant) - **Medium-sized lymphocytes:** 12 µm - **Large lymphocytes (Natural Killer):** 18 µm (present only in the lymphatic tissues). ##### Types of small lymphocytes: - According to the site of differentiation and function, small lymphocytes are classified into: - **B-Lymphocytes:** Precursor cells of lymphocytes originate in the bone marrow in the late fetal life. Some of them will stay in the bone marrow to differentiate into B-lymphocytes. Other will migrate from the bone marrow to the thymus to differentiate into T-lymphocytes. - **15% of circulating small lymphocytes.** Have short life span (3 months). - **Function:** B-Lymphocytes are concerned with **humoral immunity.** - When stimulated by specific antigen, some of B-lymphocytes differentiate into plasma cell (in connective tissue), which then produce antibodies. - **T-lymphocytes:** - **80% of circulating small lymphocytes.** - They have long life span as they can live for years. - **Function:** They are concerned with the **cellular immunity (cell mediate immunity).** - **Note:** There are few lymphocytes in the blood (about 5%) that have neither T-nor B-lymphocyte surface antigens and are called **null cells (or natural killer cells).** - **L/M:** - **Cytoplasm:** Of the small lymphocyte is scanty, and in blood smears it appears as a thin rim around the nucleus. Slightly basophilic. - **Nucleus:** Slightly indented, dense, round nucleus that occupies most of the cell. - **EM:** - Have a few azurophilic granules. - Few mitochondria and a small Golgi complex; it contains free polyribosomes. ##### Lymphadenopathy - (enlarged lymph nodes) → Infectious mononucleosis (viral infection due to Epstein-Barr virus). ##### Chronic Lymphocytic Leukemia (CLL) - Increased uniform-appeаring small lymphocytes → Chronic lymphocytic leukaemia (CLL), a common disease in the elderly. ##### Lymphomas - Are a group of disorders involving neoplastic (malignant) proliferation of lymphocytes. ### Platelets (Thrombocytes) - Normal count: 250,000 and 400,000 platelets per mm3 of blood. - Life span: Less than 14 days. - Structure: Small, disk-shaped, non-nucleated cell fragments derived from megakaryocytes in the bone marrow. - **LM:** Are about (2 to 4µm) in diameter in blood smears. They display a peripheral clear region (hyalomere) and a central darker region (granulomere). - **Blood platelets are concerned with the process of thrombus formation (blood clot) in response to any vascular endothelial injury to prevent excessive blood loss.** #### EM: - **Platelets membrane (Cell Coat):** Covered by well-developed glycocalyx, helps in platelets adhesion. - **Hyalomere:** - **Membrane Zone:** - **Open canalicular system:** Small canaliculi that open on the platelet surface, thus facilitating the liberation of active molecules stored in platelets. - **Dense tubular system:** The remnant of megakaryocyte's endoplasmic reticulum. - **Structural Zone:** - **Marginal bundle of microtubules:** Helpsto maintain the platelet's ovoid shape. - **Actin and myosin molecules:** Can assemble to form a contractile system that functions in platelet movement and aggregation. - **Granulomere:** - **OrganelleZone:** Possesses a variety of membrane-bound granules, mitochondria and glycogen particles. - **Alpha granules:** Are a little larger. Contain fibrinogen, platelet-derived growthfactor. - **Delta granules (Dense bodies):** Contain calcium ions, ADP, ATP, and serotonin. - **Lambda granules: Small vesicles.** Contain only lysosomal enzymes. ##### The role of platelets in controlling hemorrhage - **Primary aggregation:** injury → Break in the endothelium → Platelet aggregation to the exposed collagen, via collagen-binding protein in platelet membrane → Platelet plug. - **Secondary aggregation:** Platelets in the plug → An adhesive glycoprotein and ADP (Both are potent inducers of platelet aggregation) → Increasing the size ofthe platelet plug. - **Blood coagulation:** Many factors from (blood plasma, damaged blood vessels, and platelets) boost the serial interaction cascade of about 13 plasma proteins → Fibrin that forms a network of fibers trapping RBCs, WBCs, and platelets toform a blood clot (thrombus). - **Clot retraction:** The clot contracts because of the interaction of platelet actin, myosin, and ATP. ##### Clot removal: - By the proteolytic enzyme plasmin through the activation of the plasma proenzyme plasminogen, by endothelium-produced plasminogen activators. And enzymes released from formed a granules also contribute to clot removal. ### Megakaryocytes - **LM:** - Shape: Giant cells (50–150 Mm) - Nucleus: Large, lobulated containing the polypoid number of the ordinary DNA sets. - Cytoplasm: Basophilic contains many organelles together with the alpha, delta and lambda granules. - **EM:** - The cytoplasm shows membranous demarcation lines surrounding groups of granules. - Megakaryocytes are located near the bone marrow sinusoids; they extend their processes to release the platelets in bloodstream. ### Clinical Notes - **Thrombocytopenia:** Reduced platelet numbers which associated with spontaneous small vessel bleeding petechial usually in skin and in the bowelwall. - **Von Willebrand disease:** Mutations in various proteins affecting platelet function which is due to defects in von Willebrand factor (FVIII-VWF), a complex adhesion molecule produced in endothelium and megakaryocytes. - **Some drugs can affect platelet function like Aspirin (acetylsalicylic acid) which blocks the enzyme cyclooxygenase, inhibiting thromboxane production, and thereby impairing platelet function.** ## References - Junqueira's Basic Histology Text and Atlas, 13th Edition - Ross atlas and txt of histology, 4th Edition. - Gartner Color Textbook of Histology, 3rd Edition.