Immune Systems Summary Notes PDF

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Immune Systems Summary NotesThe Immune System (also called lymphatic system) consists of a network of vessels, called lymphatic vessels, and several organs and structures made up largely of lymphatic tissue. These include:  Bone marrow  Thymus  Spleen  Lymph nodes  Tonsils  Nodules of lymphati...

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Immune Systems Summary Notes The Immune System (also called lymphatic system) consists of a network of vessels, called lymphatic vessels, and several organs and structures made up largely of lymphatic tissue. These include:  Bone marrow  Thymus  Spleen  Lymph nodes  Tonsils  Nodules of lymphatic tissue in the wall of the alimentary canal, respiratory passages, and genitourinary tract BONE MARROW  Is the tissue comprising the center of large bones, "Long bones" are tubular in structure, and the hollow middle is filled with yellow marrow. While the majority of long bones are formed of cortical ("compact") material; at the ends are the epiphysis, which is generally composed of cancellous ("spongy") material and red marrow  Bone marrow contains two types of stem cells: o Hematopoietic (which can produce blood cells). Hematopoietic stem cells give rise to the three classes of blood cell that are found in the circulation: leukocytes, red blood cells (erythrocytes), and platelets (thrombocytes). o Stromal (which can produce fat, cartilage and bone).Stromal stem cells have the capability to differentiate into many kinds of tissues, such as nervous tissue.

Thymus (encapsulated)  Is a lympho-epithelial organ located in the mediastinum  The thymus is active in children, but at the start of puberty, until old age, it starts to atrophy, producing fewer T-cells. The thymus also produces thymic hormones that support the growth and differentiation of T-cell progenitors.  It has two lobes divided up into many lobules. The outer, more darkly staining region is the cortex, and this is highly cellular. The inner lighter staining region is the medullar, and this region is less cellular. It has an outer connective tissue capsule and septa.  It has a connective tissue capsule that penetrates the parenchyma and divides it into lobules. Each lobule contains a dark zone known as the cortex and a central light zone known as the medulla.

Thymus The cortex stains more darkly (is more basophilic) than the medulla, because it contains more lymphocytes than the medulla. The epithelial network in the cortex is more finely branched than in the medulla - and this gives this network the name 'reticular'.

SPLEEN (encapsulated) • located between the stomach and diaphragm • (contains the largest collection of lymphoid tissue in the body • Function: performs the same function for blood that lymph nodes perform for lymph; the spleen filters the blood and is involved with:  removal of abnormal blood cells and other blood components by phagocytosis  storage of iron from recycled RBCs  initiation of immune responses by B cells and T cells in response to antigens in circulating blood  the spleen also acts as a blood reservoir Microanatomy  Encapsulated lymphoid organ – The spleen is covered by a dense capsule, and there are connective tissue trabeculae, which provide internal support for the spleen, and carry the blood vessels into the spleen.  In addition to large numbers of lymphocytes, it contains specialized vascular spaces, a meshwork of reticular cells and reticular fibers, and a rich supply of macrophages.  There are two main types of tissue in the spleen • red pulp - area of the spleen that contains large numbers of RBCs; the structural framework of the red pulp consists of a network of reticular fibers; it is rich in macrophages; red pulp is mainly concerned with disposing of worn-out red blood cells and bloodbourne pathogens • white pulp - area of the spleen that resembles lymphoid nodules; it is composed mostly of lymphocytes suspended on reticular fibers, and is involved with the immune functions of the spleen

Spleen

LYMPH NODES  Are encapsulated spherical or kidney-shaped organs composed of lymphoid tissues that are distributed throughout the body along the course of the lymphatic vessels.  They are found in the axilla and the groin; along the great vessels of the neck, and in large numbers in the thorax and abdomen, especially in the mesenteries.  They have a convex side and a concave depression, the hilum through which arteries and nerves enter and veins and lymphatic vessels leave the organ.

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afferent lymphatic vessel - lymph vessel that carries lymph to the lymph node; as lymph flows through the lymph node it is exposed to B and T cells and macrophages; at least 99% of the pathogens in the lymph are removed  efferent lymphatic vessel - lymph vessel that carries lymph away from the lymph node Capsule –dense fibrous connective tissue that surrounds the lymph node, sending trabeculae into its interior.  Trabeculae, provide support for blood vessels entering into the nodes. Each lymph node contains: a cortex and a medulla The cortex is divided into an outer and an inner cortex.  The outer cortex has lymphatic nodules that mostly contain B-cells. Small lymphocytes sit in the spaces between the reticular fibre meshwork in the cortex. (see the picture below). The lighter staining areas are germinal centres, where the B-cells proliferate into antibody secreting plasma cells (see B-and T-lymphocytes). Macrophages are also present in these regions, together with dendritic cells, and some T-cells. Both the

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macrophages, and the dendritic cells trap antigens and present them on their surfaces to B-cells. The inner cortex contains mostly T-cells.

The deep cortical, and medullary cords contain B-cells and plasma cells.

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they filter the lymph, removing bacteria and antigens lymphocytes congregate, function, and proliferate in the lymph nodes

Lymph Node

TONSILS • Tonsils are large non-encapsulated (or partially encapsulated) masses of lymphoid tissue that lie in the walls of the pharynx and nasopharynx and at the base of the tongue. • The luminal surfaces of the tonsils are covered with a stratified squamous epithelium (in common with the oral epithelia). • The tonsils have many invaginations which form blind crypts.

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Below the epithelium, there are many lymphoid follicles beneath which have germinal centres like lymph nodes. o The epithelial cells are able to phagocytose bacteria, and transfer them to macrophages, which then present the foreign antigens to B-cells, which are activated (with the help of T cells). Like the MALT, the activated cells mostly secrete IgA type antibodies, which are secreted locally palatine tonsils - a pair of tonsils located at the posterior margin of the oral cavity along the border along its boundary with the oropharynx lingual tonsil - located under the attached base of the tongue

'Mucosa associated lymphoid tissue' (MALT) • The mucosa of the digestive, respiratory and urinary tracts often contains small aggregations of lymphocytes called lymphoid follicles. • In some cases, these aggregations are large, and confluent. This happens in the tonsils, peyers patches and appendix.

PEYER’S PATCHES • Peyer's patches are clusters of lymphoid nodules deep to the epithelial lining of the small intestine • contain lymphocytes and macrophages which remove microorganisms, debris, and antigens from the digestive tract

Peyer’s patches in the ileum

APPENDIX -The most characteristic property of the appendix is the presence of masses of lymphoid tissue in the mucosa and submucosa. There are often follicles containing paler germinal centres similar to the follicles of Peyers patches in the small intestine.

The cross section of appendix shows a slit-like lumen, mucosa made up of many glands, a lamina propria containing several lymphocytic nodules, and a peripheral muscularis and serosa....