Blood and Immune System PDF

Blood  General characteristics of the Blood Specialized connective tissue: composed of blood cells (erythrocytes, leukocytes and platelets) and a liquid matrix – plasma Dark, viscous and slightly alkaline shiny liquid that circulates within the circulatory system Transport of s...

Blood  General characteristics of the Blood Specialized connective tissue: composed of blood cells (erythrocytes, leukocytes and platelets) and a liquid matrix – plasma Dark, viscous and slightly alkaline shiny liquid that circulates within the circulatory system Transport of substances, nutrients (from the digestive system to the rest of the body) and waste products (to other organs for disposal) Transport of hormones and other signaling molecules between cells, respiratory gases (O2 and CO2) and immune cells Helps regulate body temperature and osmotic balance of tissues  Plasma Yellowish liquid in which cells, platelets, organic compounds and electrolytes are dissolved or suspended. Composition: 54% plasma - 90% water - 9% proteins - 1% nutrients and respiratory gases 1% platelets The plasma proteins maintain the + leukocytes osmotic pressure of the blood and thus maintain normal blood volume. 45 % The plasma leaves the blood erythrocytes capillaries and infiltrates in the connective tissue as tissue fluid (similar composition).  Erythrocytes (red blood cells) Most abundant formed elements of the blood (5 million cells) Absence of nucleus or organelles but contains numerous enzymes that will participate in obtaining ATP to cover the energy needs of the erythrocyte Lifespan of 120 days, then they are destroyed in the liver, spleen or bone marrow  Biconcave disc shape that gives them a high surface-volume ratio: Provides a large surface to facilitate gas exchange (transport O2+CO2) Adaptation to pass through narrow capillaries without breaking. This shape is maintained and adapted thanks to actin filaments of the cytoskeleton, which will spend ATP after contraction, hence the important energy needs of these cells.  Transport of O2 and CO2 Erythrocytes carry hemoglobin (protein formed by 4 chains), each linked to a heme group (contains iron). This is what gives erythrocytes and blood their red color. This heme group protects iron from being oxidized, while allowing this molecule to bind oxygen to transport it through the blood. Oxygen (O2) transport: In the lungs, where there is abundant O2, hemoglobin binds to 4 molecules of O2 - oxyhemoglobin. Carbon Dioxide (CO2) transport: When it reaches the tissues, where there is little O2 and abundant CO2, O2 is released, and hemoglobin Heme group binds CO2 - carbaminohemoglobin. Leukocytes (white blood cells) Leukocytes are larger than erythrocytes, much less numerous, have nuclei and organelles and are not functional in the blood, but they use it as a means of transport to reach the tissues where they will perform their immune function. These cells are classified into two large groups: - Granulocytes or polymorphonuclear cells: present specific granules in their cytoplasm. Neutrophils (55-70%) Eosinophils (1-4%) Basophils (0.2-1.2%) - Agranulocytes: do not present specific granules. Monocytes (2-8%) Lymphocytes (17-45%)  Neutrophils Most common type of leukocytes Multilobed nucleus and specific granules that do not stain with usual dyes Actively phagocytic: they engulf bacteria and other microorganisms and microscopic particles. The granules contain enzymes with antibacterial functions. They also contain nonspecific granules that are enzymes. NEUTROPHILS Phagocytosed Bacteria (cocos) Eosinophils Bilobed nucleus and specific granules that are stained with acid dyes (eosin). In its membrane they have receptors for IgG, IgE and for the complement. Specific granules: contain the major basic protein to fight parasites Nonspecific granules: lysosomes with hydrolytic enzymes. Histamine, leukotrienes or eosinophil chemotactic factor attract them to the site of the allergic, inflammatory or parasitic infection. There they pour their major basic protein that attacks parasitic worms. Basophils S-shaped nucleus usually masked by specific granules, which stain with basic dyes just like the nucleus. Granules contain heparin, histamine, eosinophil chemotactic factor, neutrophil chemotactic factor, proteases and peroxidase. Inflammatory response: Basophils have IgE receptors on their membrane. Upon the first exposure to an antigen, specific IgE antibodies for that antigen are synthesized and bind to the basophil's membrane. On a second exposure, the antigen binds directly to the membrane-bound IgE on the basophil, which then releases the content of its granules. An inflammatory response is initiated, attracting neutrophils and eosinophils. Histamine causes vasodilation, increased capillary permeability, and bronchoconstriction, while heparin improves blood flow Leukocytes They are classified into two large groups: - Granulocytes or polymorphonuclear cells: present specific granules in their cytoplasm. Neutrophils (55-70%) Eosinophils (1-4%) Basophils (0.2-1.2%) - Agranulocytes: do not present specific granules. Monocytes (2-8%) Lymphocytes (17-45%) Both cell types have nonspecific granules that are lysosomes. Monocytes Largest blood cells, agranulocytes Large eccentric and kidney-shaped nucleus Remain in the blood for a few days and then migrate to tissues where they differentiate into macrophages. Lymphocytes Smallest leukocytes, agranulocytes Rounded cells, with a round nucleus and scarce cytoplasm. Three types of lymphocytes: T, B and NK cells, which are morphologically equal but with different functions and surface markers: T lymphocytes are formed in the bone marrow, then migrate to the thymus to mature and acquire immunocompetence. B lymphocytes and NK cells are formed in the bone marrow and go directly to the tissues where they will act. When activated, B lymphocytes differentiate into plasma cells that secrete antibodies (Ig) against the specific antigen. T lymphocytes can be cytotoxic, which attack foreign cells or cells altered by viruses and destroy them, or they can be helpers, which activate B lymphocytes. The NK lymphocytes attack foreign cells, or cells altered by viruses, and destroy them.  Immune system General characteristics System responsible for the defense of the organism. It is composed of: - Isolated cells: macrophages, granulocytes, lymphocytes, mast cells. - Primary lymphoid organs: are those that participate in the development of immune cells. - Bone marrow - Thymus - Secondary lymphoid organs: are those where the immune cells exert their action. - Lymph nodes - Spleen - Lymphoid tissue  Types of immunity The first line of defense of the organism is the epithelial barrier of the skin and mucous membranes. If this barrier breaks, or if foreign substances penetrate, the second and third lines of defense are activated: Innate (natural) or cellular immune system: it does not need previous contact with antigens. It is composed of immune cells and a system of molecules transported by the blood - complement. Adaptive (acquired) or humoral immune system: reacts against specific antigens, so it requires prior contact with said antigen. The ability to react to that particular antigen improves with every confrontation the body has with it. Innate immunity. It responds Adaptive immunity. It responds more slowly than rapidly in a non-specific manner innate immunity, but it is specific, has immunological and has no immunological memory. memory and great diversity. Main components: complement, Main components: T and B lymphocytes. These cells macrophages, neutrophils and communicate with each other and also with the NK lymphocytes. components of innate immunity in the presence of an antigen.  Platelets Smallest formed elements of the blood Disc-shaped fragments of another larger cell formed in the bone marrow (megakaryocyte). They have no nucleus, but many granules. The peripheral zone of the platelet is lighter - hyalomere, whereas the central zone is darker and that is where the granules are - granulomere. Granules of the platelets: α (alpha) granules: more abundant, they contain fibrinogen, coagulation factors and thrombospondin. δ or dense granules: they contain Ca2+, serotonin, ATP and ADP. λ granules: lysosomes. Hemostasis Introduction to Hemostasis | JoVe Platelets are involved in hemostasis: set of physiological processes that aim to prevent blood leakage, repair damaged vessels, keep blood flowing, and restore circulation once the vessel has been repaired. 1. Vascular injury: The endothelium of the vessels, when it suffers an injury, stops producing prostacyclins and ON, which inhibit platelet aggregation, and thrombomodulin that blocks coagulation. Von Willebrand factor (vWF) and a vasoconstrictor are released to reduce blood flow. 2. Platelet adhesion: Platelets attach to vWF and this in turn binds to subendothelial collagen. 3. Platelet aggregation: When platelets adhere, they release the content of their granules, Ca2+, ADP and thrombospondin, this causes more platelets to be added and form a plug that blocks bleeding. The coagulation cascade is activated, the final step of which activates fibrinogen, giving rise to fibrin, which binds to platelets forming a denser and more stable clot that also traps erythrocytes and leukocytes. 4. Thrombus removal: Endothelial cells release enzymes that initiate thrombus clearance when the vessel has repaired. Hematopoiesis Physiological process of blood cells formation. All blood cells have a limited life and must be renewed continuously. This process begins in the second week of embryonic development and will first occur in the liver and spleen. From the sixth month of development, when the skeletal system develops, it will occur in the bone marrow. After birth, the liver and spleen do not have hematopoietic activity, but they could recover it if necessary. All blood cells originate from pluripotent stem cells. These cells will give rise to multipotential stem cells that will be either common lymphoid progenitors, which give rise to all types of lymphocytes, or common myeloid progenitors, which give rise to erythrocytes, granulocytes, monocytes and megakaryocytes (platelet precursor).