BBS2001 Threats and Defenses - Cases and Consolidation Assignments - BBS2001 (BBS2001) - Stuvia US

1) Which types of blood cells are there and what are their structure and function? And how does this affect the coagulation? First it would be important to note that there exist two types of immune systems, the innate immune system (up to a few hours), which mainly plays a role in the coagulation, blood clotting and general healing of wounds for this case, while it activates immediately and has been acquired via inheritance. And the adaptive immunity which takes up to several days to start and makes specific antigens/cells to destroy the bacteria that entered the body, and has to be acquired by the organism itself. The innate immune system kills of more general bacteria and normally mainly protects the body due to physical barriers, if one of those barrier brakes the innate immune system at first will try to fight of the foreign organisms entering the body. The innate immune system consists out of epithelia cells, cells in the circulation and tissues and several plasma proteins, these cells play complementary roles in preventing microbes to enter the body. The Multipotential Hematopoietic stem cell (Hemocytoblast) is the stem cell for all blood cells, it separates its division into the common lymphoid progenitor, of which its Natural Killer Cells and Lymphocytes do not play a role in the innate immune system, and the common myeloid progenitor. The common myeloid progenitor is the precursor of the megakaryocyte (and therefor thrombocytes), erythrocytes, mast cells, and myeloblasts, which can be subdivided later into basophils, neutrophils, eosinophils and monocytes and macrophages.

• Erythrocytes are blood cells with a red colour, they do not contain a nucleus nor mitochondria and have a

biconcave disc (a donut shape with a closed hole); They do not contain most of the organelles so that they cannot use the oxygen they transport themselves and have maximum carrying capacity for haemoglobin and thus oxygen. These erythrocytes take up oxygen in the lungs and release carbon dioxide, travel via the blood vessels towards the remaining parts of the body where they release this oxygen and take up carbon dioxide from these surrounding tissues. The erythrocytes function for oxygen and carbon dioxide uptake and release is for 98% based on the haemoglobin found within the erythrocytes; the haemoglobin takes up oxygen in a high oxygen environment causing the chemical equilibriums to alter in such way that carbon dioxide will be released; in high carbon dioxide environments the opposite occurs (H2O + CO2 ⇋ H2CO3 ⇋ H+ + HCO3- ⇋ H+ + HbO2 ⇋ HHb + O2). Haemoglobin molecules consist out of two α- and two β-chains and four haemoglobin molecules.

• Thrombocytes/Platelets are parts of blood cells that are the first to form a plug at the site of injury in a blood

vessel, these platelets accumulate at the damaged site. This accumulation causes a temporary plug which prevents blood from flowing out of the vessel, the platelets also secrete certain substances which signal more platelets to come and Thromboxane A2 from their phospholipid bilayer. Granulocytes

• The polymorphonuclear neutrophil (its name derived of the fact that its nucleus contains multiple

lobes) is the dominant white blood cell in the blood stream (50%-70%) and structure wise are closely related to eosinophils and basophils; also granulocytes. The granules found within the neutrophil are mainly the primary azurophil granules, which has the typical lysosomal morphology and filled with substances as myeloperoxidase and nonoxidative antimicrobial effectors; and secondary specific granules containing lactoferrin and much of the lysozyme. Neutrophils have a sort lifespan, from several hours up to several days. These neutrophils are active in phagocytosing bacteria and are found in large amounts in the pus of wounds, the neutrophils phagocytose multiple bacteria and are non-specific up to a certain point. Another reason that pus has high levels of neutrophils is while they can capture multiple bacterial organisms, however their lysosomal storage is limited, eventually causing the neutrophils to die while killing of the pathogens.

• Eosinophils (1%-4%), just like basophils and neutrophils originate from the myeloblast and mainly

roam through the blood itself, they contain granules filled with enzymes that can break down the cells walls of pathogens, however these enzymes can also affect the cells of the host itself. Eosinophils have a bilobed nucleus and can be stained with eosin. , - Basophils (<1%), the third type of granulocyte, also have a high amount of granulocytes, filled with fairly similar mediators as mast cells and are activated by IgE, in theory they could be seen as mast cells that swim in the blood vessels, however their concentration in the human body is too low and actual defence mechanisms are uncertain.

• Mature Mast cells will normally not be found in the blood stream, but only the tissue itself (mainly in

the skin, around the lips, blood vessels and nerves and other sites with potential injury), these mast cells are filled with granules with acidic proteoglycans, which will be released if the mast cell’s high affinity IgE membrane receptors are activated. Included in the acidic proteoglycans is histamine, which when released causes surrounding blood vessels to vasodilate, and therefore increase the blood flow to an injured site and allow more white blood cells to enter the tissue. Mast cells also release cytokines which signal leukocytes to come to the site of injury itself. Phagocytes

• Monocytes (12%), or Macrophages when they have left the blood stream, share a slightly similar

function with neutrophils, as in phagocytosing the bacteria encountered, but there the similarity ends. Monocytes are the biggest white blood cells in the human body, and live much longer than neutrophils, on top of that the macrophages are able to present pieces of the killed pathogen to T-lymphocytes to start creating antigens. The macrophages of course have the same job, while they are essentially the same cell, however in the tissue they quite often also phagocytose debris and dead cells of the human body itself.

• Both T and B Lymphocytes (20%-40%) are small cells who have a relative large nucleus, and only a

small amount of cytoplasm and poorly developed organelles. B Lymphocytes can be produced in bone marrow tissue, originating the Common Lymphoid Progenitor, as where the T lymphocytes only can mature/be produced in the Thymus. For both types of lymphocytes the same set of rules apply where they are actually non-functional as mature lymphocytes in the blood stream, but can be activated by antigens in “Secondary Lymphoid Organs” such as the spleen and the lymphoid nodes. + Both subtypes of lymphocytes can be further divided into general groupings of lymphocytes; T Lymphocytes can majorly be subdivided into T-helper cells, which on their own do not kill pathogens, but by producing cytokines or via direct contact they can activate other cells which do have a direct function in killing pathogens. The second main group are the T-cytolytic cells which release granules filled with cytotoxic substances if in contact with a foreign cell. Both types of T cells express T-Cell-Receptors, however the T-helper cells also express CD4 next to that, which recognizes cells from the same organism via the MHC II molecules, as where T- cytolytic cells recognize foreign cells by their MHC I Molecules/cells that need to be destroyed via the CD8 proteins on the cell membranes. + However not all foreign cells have a nucleus, and in general there are exceptions on the rules that nucleated cells have MHC proteins, where the “Large Granular Lymphocytes” play a role, although better known as Natural Killer Cells due to the fact that they are no lymphocytes actually, which kill organisms without MHCs. + B Lymphocytes on the other hand mainly find their function in killing pathogens by producing antibodies which can bind onto these pathogens; the B cells can be subdivided into the multi-pathogen reactive antibody producing B-1 cells and the mono-reactive antibodies of the B-2 cells. (Naïve Lymphocytes have to be activated by encountering an antigen of a bacteria, without ever encountering an antigen, either actively on its own or displayed by Antigen Presenting Cells, are rather functionless)- Antigen-Presenting Cells (APCs) are cells that capture microbials and other antigen and display the antigens to lymphocytes, which can use this information to produce antibodies, but the APCs also can provide signals that stimulate differentiation and proliferation of lymphocytes. There are multiple Antigen-presenting cells, such as; + Dendritic Cells play an important role in linking the innate immune system to the adaptive immune system, which is based on the fact that they have phagocytotic capabilities and present parts/antigen of these captured microbes to the T lymphocytes. They also have membrane receptors which can respond on microbe molecules and start secreting cytokines themselves. These roles mainly are for the “Conventional Dendritic Cells”, the Plasmacytoid DCs on the other hand can also produce soluble Type I Interferons and reorganize nucleic acids in such ay that they can attack viruses on their own. + Follicular Dendritic Cells find and bind, and display, protein antigens for T and B lymphocytes to read, these FDCs are no real DCs and mainly only found around the spleen and lymphoid nodes. + Also Macrophages and B Lymphocytes can present antigens to T lymphocytes. , 2) How does the haemostasis work and its function? And then mainly zoom into the coagulation process. A damaged blood vessel needs to be repaired while still allowing blood to flow through, however this blood flow normally has to be decreased (by factors like vasoconstrictors which lower the blood flow and therefore pressure) whilst otherwise the platelet plaques will wash away. Platelets do not contain a nucleus, the cytoplasm however contains the normal mitochondria and sooth endoplasmic reticulum, on top of that they contain high amounts of granules filled with clotting proteins and cytokines.