20 WBC structure and functions^J Students 24-25-1.pdf

WBC Structure and Function Dr Nahid Ahmed Mohammed Physiology department College of Medicine University of Bisha Date: August, 31, 2024 1 Our Objective By the successful completion of this...

WBC Structure and Function Dr Nahid Ahmed Mohammed Physiology department College of Medicine University of Bisha Date: August, 31, 2024 1 Our Objective By the successful completion of this presentation, you are expected to: Specific Learning 1. Demonstrate understanding of the differences between structure and functions of various WBCs Outcomes 2. Describe the lifespan and functions of WBCs 3. Explain the physiologic variations in WBCs count 4. Explain the clinical significance of differential and absolute WBCs counts 5. Describe the structure of the granulocytes and monocytes 2  Introduction White blood cells (WBCs) or leucocytes are colourless  so the named These are nucleated cells which play an important role in the defence mechanism of the body.  Types of white blood cells 1/ Granulocytes 2/ Agranulocytes nongranulocytes Depending upon the colour These are of two types: of granules, are further – Lymphocytes and divided into three types: – Monocytes. neutra – Neutrophils: They contain granules which take both acidic and basic stain. – Eosinophils: They contain granules which take acidic stain. – Basophils: They contain granules which take basic stain  Total leucocyte count (TLC) Varies with age as: – Adults: 4000–11,000/mm3 of blood. – At birth, in full-term infant: 10,000–25,000/mm3 of blood. – Infants up to 1 year of age: 6000–16,000/mm3 of blood. – Children, 4–7 years of age: 5000–15,000/mm3 of blood. – Children, 8–12 years of age: 4500–13,500/mm3 of blood.  Clinical significance of differential and absolute counts In different diseases, one type of cells shows an increase or decrease in its numbers. The differential count is done in 100 or 200 cells. For example, an increase in the percentage of neutrophils would be associated with a decrease in percentage of lymphocytes, thus giving an impression of lymphocytopenia. If the TLC is taken into account, the absolute lymphocyte count could be within a normal range. Therefore, DLC alone is not of much importance and so is never done as an isolated test, but always it is part of full blood counts  Morphology of WBCs Morphological features of various types of WBCs, as studied under microscope with Leishman’s staining and haematoxylin- eosin stain  Neutrophils (polymorphonuclear leucocytes): Nucleus: Nucleus of a mature neutrophil is multilobed (2–6 lobes) and purple in colour. The lobes are connected by chromatin filaments. Cytoplasm: is pale bluish in colour, full of fine (pinpoint) granules Granules: – Take both acidic and basic stain and look violet–pink in colour. – Lysosomal in origin and contain a variety of enzymes (glycosidases, sulphatases, phosphatases, nucleases and proteolytic enzymes)  They can lyse any type of substance. – Liberate histamine and peroxidase enzyme which help in killing the ingested bacteria  Neutrophils (polymorphonuclear leucocytes Life span: Functions: Remain in circulating blood for 8–10 h The neutrophils along with monocytes  enter the tissues  either constitute the first line of defence against destroyed during phagocytosis or die microorganisms, viruses and other due to senescence after 4–5 days. injurious agents that enter the body. The dead neutrophils are taken up by Neutrophils subserve this role by the the macrophages. following mechanisms: In cases of severe infection, lifespan of 1. Phagocytosis: The neutrophils engulf the neutrophils may become as short as foreign particles or bacteria, digest them few hours. and ultimately may kill them. 2. Reaction of Inflammation: The neutrophils also release leucotrienes, prostaglandins, thromboxanes, etc. that bring about the reactions of inflammation like vasodilatation and oedema. 3. Febrile Response: The neutrophils contain a fever-producing substance called endogenous pyrogen, which is an important mediator of febrile response to the bacterial pyrogens.  Eosinophils Morphological features Nucleus: Nucleus is bilobed in 85% of the cells and trilobed in the 15% and is purple in colour Cytoplasm: Cytoplasm is acidophilic and appears bright pink in colour. Granules: – Coarse, deep red-staining granules (not cover the nucleus). – Contain basic protein (react with acidic dye like eosin) – Contain histamine, lysosomal enzymes and eosinophil chemotactic factor of anaphylaxis (ECF-A).  Functions of eosinophils 1. Mild phagocytosis. 3. Role in allergic reaction. Not very motile and thus The eosinophils increase in have very mild phagocytic number in allergic activity. conditions like bronchial 2. Role in asthma and hay fever. parasitic infestations. 4. Role in immunity. They play an important role The eosinophils are present in the defence mechanism in abundance in the mucosa of body, especially in of respiratory tract, parasitic infestations gastrointestinal tract and Important ralu of those als urinary tract, where they Most probably provide mucosal immunity  Eosinophils act through the following lethal substances present in their granules: Major basic protein (MBP) makes up about 50%of the mass of large granules. It is a highly larvicidal polypeptide  are able to damage the parasitic larvae, which are large to be engulfed by phagocytosis Eosinophil cationic protein (ECP) is a potent bactericidal and major destroyer of helminths.. Eosinophil peroxidase is capable of destroying helminths, bacteria and tumour cells. Eosinophil-derived neurotoxin is capable of destroying the nerve fibres.  Basophils Nucleus: – Is irregular, may be bilobed or trilobed, – Its boundary is not clearly defined because of overcrowding with coarse granules Cytoplasm: is slightly basophilic and appears blue. It is full of granules. Granules: – are very coarse and stain deep purple or blue with basic (methylene) dye. – are in plenty and completely fill the cell and overload the nucleus. – contain heparin, histamine and 5-HT.  Functions 1. Mild phagocytosis. – Have very mild phagocytic function. 2. Role in allergic reaction. most important role ingallg – Enter into the tissue  release cytokine and inflammatory mediators such as histamine, bradykinin, slow-reacting substances of anaphylaxis (SRS-A) and serotonin (5HT). – These substances, in turn cause local vascular and tissue reactions that cause allergic manifestations by binding of specific antigen to cell-fixed IgE molecules 3. Role in preventing spread of allergic inflammatory process. – Release eosinophil chemotactic factor that causes eosinophils to migrate towards the inflamed allergic tissue. – Eosinophils then phagocytose and destroy the antigen–antibody complexes and prevent spread of local inflammatory process. 4. Release of heparin. – Release heparin in the blood which: Prevents clotting of the blood and Activates the enzyme lipoprotein lipase which removes fat particles from the blood after a fatty meal.  Mast cell Mast cells – Mast cells are large tissue cells resembling the basophils. – These are present in bone marrow and immediately outside the capillaries in the skin. – Mast cells are granulated cells of connective tissue; their granules contain proteoglycans, histamine and many proteases. Functions. Mast cells play role in allergic reactions similar to the basophils.  When allergens bind to the surface of mast cell coated with Ig G molecules, the degranulation of mast cells occurs and thus involved in inflammatory responses.  Mast cells also play an important role in acquired immunity; they release TNF-α in response to bacterial product by antibodyindependent mechanism.  Agranulocytes Lymphocytes – Two types large and small (almost similar structure. – Majority of lymphocytes in peripheral blood are small. Monocytes  Lmphocytes Nucleus: a large round, single nucleus which almost completely fills the cell. It stains blue very deeply giving ink-spot appearance. Cytoplasm: is scanty  its amount is always less than that of the nucleus. Cytoplasm does not contain visible granules  Functional subtypes: 1. B lymphocytes: are processed in the bone marrow  concerned with the humoral immunity. 2. T lymphocytes: are processed in the thymus  concerned with cellular immunity. 3. Natural killer (NK) cells: are lymphocyte-like cells that non-specifically kill any cell that is coated with immunoglobulin IgG. This phenomenon is called antigendependent cell- mediated cytotoxicity (ADCC). Thus NK cells provide innate immunity.  FUNCTIONS Lymphocytes play an important role in immunity. – B lymphocytes as well as their derivatives, the plasma cells are responsible for the development of humoral immunity (antibody-mediated immunity). – T lymphocytes are responsible for the development of cellular immunity, (cell-mediated immunity or T cell immunity)  Monocytes Nucleus: large, single and eccentric in position, i.e. present on one side of the cell (horseshoe or kidney shaped). Cytoplasm: is abundant, pale blue and usually clear (no granules); sometimes, it may contain fine purple, dust-like granules called azure granules which may be few or numerous.  Monocytes LIFE SPAN AND FATE OF MONOCYTES Release from the bone marrow  remain in circulation for 10–20 to over 40 h  enter the extravascular tissues  converted to macrophages (form part of tissue macrophage system (reticuloendothelial system). In the tissues, they can live for months or even years unless destroyed while performing the phagocytic function  Monocytes FUNCTIONS: 1. Role in defence mechanism: The main function is phagocytosis 2. Role in tumour immunity: Monocytes may also kill tumour cells after sensitization by the lymphocytes 3. Synthesis of biological substances: Monocytes synthesize complement and other biologically important substances.  References Medical Physiology for undergraduate Students. Indu Khurana. (Elsevier) Chapter 3.3, pp.121-131 25 THANK YOU