The Complement System: A Decisive System in Body Defence. This article will discuss the complement system's role in the body's defense mechanisms, including its site of origin and mechanism of action. Keywords: cellular immunity| humoral| Mannose-binding lectin (MBL)| Histamine|Body defense system|WBC| Classical Pathway| Lectin Pathway| Properdin or Alternative P athway Introduction The complement system is crucial in the body's defense against invading pathogens and tumor cells. The complement system is a system of plasma enzymes. The liver synthesizes enzymes of the complement system. It comprises over 30 enzymes circulating in the blood and is responsible for cell killing by humoral and cellular immunity. These enzymes are inactive and become active when stimulated by an antigen-antibody complex or other pathways. When in active form, they work in a sequence of cascade reactions to remove pathogens, kill pathogens, initiate and promote inflammation, an...
Thrombopoiesis
Thrombocyte formation is known as thrombopoiesis. You will learn about structure, formation, and thrombocytes in this article. Thrombocytes are also called platelets.
Keywords
Multipotent stem cells
Myeloid stem cells
CFU-Meg
megakaryoblast
promegakaryocyte
megakaryocyte
platelets
PF4
CXCL5
CXCL7
CCL5
Table of contents
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1. |
Introduction |
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2. |
Developments |
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3. |
Stimulants and inhibitors |
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4. |
Structure |
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5. |
Clinical |
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Introduction
Platelets are the smallest blood cells, with a diameter of only 2 to 3 microns. The average diameter of a Red blood cell is 7 to 8 microns, and that of a White blood cell is 10 to 14 microns.
Platelets are rod-shaped biconvex cells. They are colorless, non-nucleated, and very complex. Like red blood cells, platelets are non-nucleated but contain organelles and granules like white blood cells.
Platelets are found only in mammals.
The average diameter is 2 to 3 microns.
The average count is 1.5 lakhs to 4 lakhs per cubic milliliter of blood.
The average life span is 8 to 12 days.
The site of formation is bone marrow.
The site of destruction is the reticuloendothelial system-especially that of the spleen.
Development
Multipotent stem cells in the narrow sinusoids can produce all blood cells. Multipotent stem cells form Myeloid stem cells stimulated by thrombopoietin form CFU-Meg (colony forming unit-megakaryocyte)-that will form megakaryoblast -> promegakaryocyte megakaryocyte and finally, platelets are formed.
Megakaryocyte is the immediate precursor of platelets.
Megakaryocyte =megalokaryocyte=megakaryocyte.
[Mega=large,karyo=cell nucleus, cyte=cell.]
A megakaryocyte is a large cell with a lobated nucleus in bone marrow. Megakaryocyte produces thrombocytes (platelets).
Megakaryocytes are large cells with an average diameter of 50 to 100 microns. During maturation, they increase in size and replicate their DNA without cytokinesis. This process of development is known as endomitosis. Due to growth, the nucleus becomes very large, giving the false impression of several nuclei.
The megakaryocyte's cytoplasm contains cellular organelles such as mitochondria, endoplasmic reticulum, Golgi bodies, microtubules, lysosomes, large granules (alpha granules), and small, dense granules.
Stimulants of plaelet formation
Thrombopoietin is the primary stimulant for megakaryocyte production. Other signals are GM-CSE,IL-3, IL-6, IL-11, chemokines like SDF-1, and erythropoietin.
Erythropoietin is the primary stimulant of erythropoiesis(red blood cell formation).
Inhibitors of platelet formation
Some factors, for example, PF4, CXCL5, CXCL7, and CCL5, reduce and inhibit platelet formation.
Steps of thrombopoiesis
Megakaryocytes lose their ability to divide, but they replicate their DNA and continue to become polyploid. The cytoplasm and DNA amount increase. The maturation occurs by endomitotic synchronous replication. Whereby cytoplasm enlarges and the number of chromosomes multiplies without cellular division. The cell stops growing, and granules appear in the cytoplasm. Now, the megakaryocyte is mature and starts platelet production.
Platelet production
Microtubules are formed in the cytoplasm, which joins and forms Platelets. Megakaryocytes form small proto-platelet processes containing platelets. These proto-platelet processes break to create and release platelets. One megakaryocyte forms about 3000 to 5000 platelets. About 2/3rd of these produced platelets will remain in circulation, and one-third will go to the spleen.
After platelets form, the megakaryocyte cell nucleus crosses the bone marrow barrier into the blood and is consumed in the lung by alveolar macrophages.
Structure of platelets
Platelets have no nucleus; they have cytoplasm with organelles like mitochondria, Golgi bodies, endoplasmic reticulum microtubules, and lysosomes. In addition small
dense granules and large granules -alpha granules are present.
.
Platelets are biconvex structures. Its diameter is about 2 to 3 microns.
Usually, about 10 to the power eleven platelets are produced daily in a healthy individual.
The cytoplasm of platelets can be divided into four zones from peripheral to innermost
1. Peripheral zone is rich in glycoproteins
2. The Sol-gel zone is rich in microtubules and microfilaments, which help maintain platelets' shape.
3.Organelle zone is rich in platelet granules.
Alpha granules contain clotting factors like factor V, Factor
VIII, fibrinogen, platelet-derived growth factor, and chemotactic agents.
Dense granules contain ADP, calcium, and serotonin.
The Membranpus zone contains a smooth endoplasmic reticulum and forms a dense tubular system connected to the surface platelet membrane to help thromboxane A2 release.
Clinical conditions
The normal count is 1.5 lakhs to four lakhs per cubic milliliter of blood.
Thrombocytopenia is a condition in which platelet count is less than 1.5 lakhs per cubic milliliter of blood.
Thrombocytosis is a condition in which platelet count is more than four lakhs per cubic milliliter of blood.
Congenital amegakaryocytic thrombocytopenia is a rare inherited disorder in which megakaryocytes are absent in the bone marrow.
Hashtags:
Multipotent stem cells#Myeloid stem cells # CFU-Meg# megakaryoblast#promegakaryocyte # megakaryocyte #platelets #PF4 #CXCL5 CXCL7#CCL5
Internal Links:
https://blog.totalphysiology.com/2021/01/plateletsthrombocytes.html
https://blog.totalphysiology.com/2021/01/white-blood-cellleucocytes.html
https://blog.totalphysiology.com/2022/05/purpura-bleeding-disorder-physiology.html
https://blog.totalphysiology.com/2022/10/red-blood-cell-formation-destruction.html
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