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Class: Dental Histology

Please be prepared to discuss, creating a small PPT to lecture on your topic: Basic tissue: Blood. Please use the textbook below as a resource and break it down to make the easiest way for classmates to understand and learn about the blood in basic tissue.

Textbook:

BLOOD PROPERTIES

The blood is a fluid connective tissue that serves as a transport medium for cellular nutrients, such as respiratory gases like oxygen and carbon dioxide as well as metabolites for the entire body. Blood is carried in endothelium-lined blood vessels and its medium consists of plasma with blood components (Table 8.4).

Plasma

The plasma (plaz-muh) is the fluid substance in the blood vessels that carries the plasma proteins, blood cells, and metabolites. It is more consistent in composition than tissue fluid and lymph, yet it contains most of the same materials with the addition of red blood cells (see Chapter 7). Serum, another fluid product, is distinguished from the plasma from which it is derived due to the removal of clotting proteins.

If a sample of blood is treated with an agent to prevent clotting and is spun in a centrifuge, the plasma fraction is the least dense and will float as the top layer.

Blood Components

Blood cells and associated derivatives are also considered the formed elements of the blood. Most blood cells develop from a common stem cell in the bone marrow (Fig. 8.16). The formed elements of the blood include the numerous red blood cells. Not only are these cells present in the blood and its associated vessels but certain related components are also present in surrounding connective tissue.

Thus the most common cell in the blood is the red blood cell

(RBC) or erythrocyte (ih-rith-ruh-sahyt) (see Table 8.4). An RBC is a biconcave disc that contains hemoglobin, which binds and then transports the oxygen and carbon dioxide. It has no nucleus and does not undergo mitosis because it is directly formed from the bone marrow's stem cells. There are 5 to 6 million per cubic milliliter of blood and are more common than other blood cells. In centrifuged blood, the RBCs settle to the bottom because they are also denser than the rest; this fraction is the hematocrit.

The blood also contains platelets (pleyt-litz) or thrombocytes (throm-buh-sahyts), which are smaller than RBCs, disc-shaped, and also have no nucleus. However, these formed elements are not considered true blood cells but instead fragments of bone marrow cells (or megakaryocytes) and platelets are also found in much lesser numbers than RBCs at 250,000 to 400,000 per cubic milliliter. Platelets function in the clotting mechanism.

In even smaller numbers in the blood is the white blood cell (WBC) or leukocyte (loo-kuh-sahyt) (see Tables 8.4 and 85). Like RBCs, WBCs form from bone marrow stem cells. The WBCs later mature in the bone marrow or in various lymphatic organs. They are involved in the defense mechanisms of the body, including the inflammatory and immune responses. Therefore WBCs are also usually found in both eithelium and connective tissue after they migrate from the blood by moving through openings between the cell junctions of the endothelial lining of the vessel to participate in defense mechanisms. The WBCs differ from RBCs because they possess a nucleus, have more cytoplasm, and have the power of active amoeboid movement in order to migrate from the blood to the tissue; thus, unlike RBCs, WBCs perform their functions not only in the blood but also in other tissue.

They are also even less numerous than platelets at only 5000 to 10,000 per cubic milliliter. There are five main types based on their microscopic structure, the neutrophils, lymphocytes, monocytes, eosino-phils, and basophils. The fraction of centrifuged blood that settles on the surface of the hematocrit consists of the WBCs along with platelets, forming the intermediately placed buffy coat with the plasma fraction superior to it.

The most common WBC in the blood is the neutrophil (noo-truh-fil) or polymorphonuclear (PMN) leukocyte (pol-ee-mawr-fuh-noo-kee-er) (Fig. 8.17). These are the first cells to appear at an injury site when the inflammatory response is triggered; thus large numbers of the PMNs can be present in the suppuration or pus, which in certain cases forms locally at the injury site. The PMNs constitute 54% to 62% of the total blood WBC count. They have a short lifespan, contain lysosomal enzymes, are active in phagocytosis, and respond to chemotactic factors (see Chapter 7). One important difference between the two divisions remains the B-cell lymphocytes divide during the immune response to for One important difference between the two divicions remains. the B-cel lymphocytes divide during the immune response to form The second most common WBC in the blood is the lymphocyte (lim-fuh-sahyt), which makes up 25% to 33% of the count. There are three functional types of lymphocytes, the B cell, T cell, and natural killer (NK) cell. The B cells mature in the bone marrow and gut-asso. ciated lymphoid tissue such as lymph nodes (see Fig. 11.16), whereas the T cells mature in the thymus gland (see Fig, 8.16). The NK cells also mature in the bone marrow; they are large cells that are involved in the first line of defense against tumor- or virally infected cells by killing them and thus are not considered part of the immune response.

Cytokines are produced by both B and T cells and are one of the major chemical mediators of the immune response (see the discussion in Chapter 14 related to periodontal disease). Thus, both of these types of lymphocytes are involved in the immune response (see Table 8.5).

In the past, the immune response was broken into two strict divisions, the humoral immune response with B cells and cell-mediated immune response with T cells. However, the distinction between the two divisions is now considered less important because they are so strongly related

One important difference between the two divisions remains the B-cell lymphocytes divide during the immune response to form plasma celis. Once mature, plasma cells produce an immunoglobulin (Ig) (im-yuh-noh-glob-yuh-lin), which is also considered an antibody (an-ti-bod-ee) and one of the blood proteins. There are five distinct dasses of immunoglobulins: IgA (including serum or secretory types), IgD, IgE, IgG, and IgM (Table 8.6). Each plasma cell produces only one specific class of immunoglobulin in response to a specific immunogen (th-myoo-nuh-juhn) or antigen (an-ti-juhn). Immunogens are mostly proteins that are seen by the body as foreign and are capable of triggering an immune response.

Although immunoglobulin structure overall is very similar, a small region at the tip of the protein (hypervariable region) is extremely vari-able, allowing generation of an infinite number with slightly different tip structures or antigen-binding sites to exist. An immunoglobulin, along with its specific immunogen (at epitope variable region), often forms an immune complex in an effort to render the immunogen unable to cause disease. Immunoglobulins can be extracted from the blood of recovering patients and used for passive immunization against certain infectious diseases.

However, the most common WBC in the connective tissue proper is the macrophage (mak-ruh-fey), which is considered a monocyte (mon-uh-sahyt) before it migrates from the blood into the tissue. They have a longer lifespan than PMNs but constitute only 2% to 10% of the WBC count. After migration, macrophages arrive at the site of injury later and in fewer numbers than PMNs when the inflammatory response is triggered. Macrophages contain lysosomal enzymes, are involved in phagocytosis (as are PMNs), are actively mobile, and have the ability to respond to chemotactic factors and cytokines (see Fig. 7.4). Macrophages also assist in the immune response to facili-late immunoglobulin production. In certain disease states, numbers of macrophages may fuse together, forming giant cells with multiple nuclei. In bone connective tissue, these are then considered osteoclasts that will resorb bone (discussed earlier). The eosinophil (ee-uh-sin-uh-fil) is usually only 6% of the WBC count, but its percentage is increased during a hypersensitivity response (or allergy) and in parasitic diseases because its primary function is the phagocytosis of immune complexes.

The basophil (bey-suh-fil) is usually found to be less than 1% of the

WBC count and is also involved in the hypersensitivity response releasing bioactive products. Other WBCs located in the connective tissue include the mast cell, which is similar in structure to the basophil.

Mast cells are involved in a type of primitive hypersensitivity response that also releases bioactive products but are not involved with immunoglobulins such as IgE. However, even though both cells are derived from the bone marrow, they may originate from different stem cells within the bone marrow. Mast cells have been implicated in the progression of periodontal disease due to their bioactive products as well as many confounding systemic diseases. Dental professionals must understand certain laboratory procedures that patients may have undergone when viewing the medical record These procedures include a complete blood count (CBC), which is an evaluation of both RBC and WBC types to detect infections, anemia, or leukemia. A platelet count can also be performed to determine the number of platelets if bleeding problems are a consideration due to past medical history; a coagulation (bleeding) test can also be performed to test platelet function. These procedures may also be recommended to the dental patient if there is clinical evidence or history of bleeding difficulties, especially before periodontal surgery, tooth extraction, or dental implant placement as well as if they have an unusual level of periodontal disease, such as an aggressive periodontitis with its uncontrolled loss of periodontal support. Also these tests can be done if there is failure to form a clot after any dental surgical procedures.

There is now an increase in the use during dental surgery of plate-let-rich plasma (PRP), which is an autologous conditioned plasma that is a concentrate of PRP protein derived from whole blood centrifuged to remove RBCs. This is used to support both soft and hard tissue healing (i.e., osteoid, blood vessels, and even collagen), a process already well known postsurgically in medicine. This increased healing level occurs because the PRP contains vast amount of growth factors as well as having other various healing mechanisms along with the high concentration of platelets. The PRP is used to coat dental implants and is also placed within the soft tissue flaps created following periodontal surgery to promote repair of bony defects as well as with graft placement. Another use of blood-related products within a dental setting is with the use of postexposure prophylaxis of dental healthcare personnel (DHCP) by a passive injection of hepatitis B immunoglobulin

(HBIG). It is given if there is evidence that the person is without seroconversion after the usually required vaccination for the infection. It is made from human plasma containing immunoglobulins made in response to the type B form of hepatitis.