Also contains specialized structures known as Hassall's corpuscles - function unknown. Blood supply. Branches from the internal thoracic and inferior thyroid arteries that penetrate the capsule surrounding the thymus.
Capillaries branch into the cortico-medullary junction area and extend into the cortex. Blood-thymus barrier is present as described above. These eventually arch into the medulla where they drain into venules. Venules connect to veins that exit thymus along connective tissue septa.
Cells entering thymus from bone marrow arrive via the circulatory system and enter in the medullary zone from which they can move to the cortical areas. There are no afferent lymphatic vessels in thymus. So it does not act as filter for lymphatic fluids. Only a few efferent lymphatic vessels are present, and these are associated with the blood vessels.
Physiology of thymus relative to immune system. Recall that T-lymphocytes are responsible for cell-mediated immune responses and also for interacting with B-lymphocytes to cause those cells to produce antibodies against certain antigens. The thymus can be considered a proliferation and maturation center for T-lymphocytes. Precursor cells migrate from bone marrow to thymus entering the organ via blood vessels in medullary zone.
These cells undergo mitosis and maturation in cortical zone and then leave thymus through blood vessels of medullary zone to go about their various activities. General characteristics. Largest piece of lymphatic tissue in body. Site of formation of activated lymphocytes that enter the circulatory system. Also important in recycling of components of worn-out blood cells. Can be said to act as filter of blood both in an immunologic sense that is it mediates components of immune response , but also in the sense of removing worn out erythrocytes from circulation.
Surrounded by a dense connective tissue capsule that extends processes trabeculae into lymphatic tissue of this organ. There are no lymph vessels in the pulp. Color designations have to do with appearance in freshly cut open organ. Red pulp. Cells can enter or leave spleen through large spaces between endothelial cells lining sinusoids. White pulp. Central artery is identifying characteristic. Mainly T-lymphocytes in periarterial lymphatic sheath PALS sheath surrounding central artery, B-lymphocytes in lymphatic tissue of white pulp surrounding sheath i.
The B-lymphocytes and associated cells are organized into typical lymphatic nodules. Blood circulation in spleen. Arteries enter pulp via trabeculae. Branches of arteries extend into white pulp forming the central arteries of the white pulp. These arteries are surrounded by a sheath of lymphocytes mainly T-lymphocytes that form the periarterial lymphatic sheath PALS extending along the length of the artery.
Branches of central artery extend into white pulp. Some of these leave white pulp and then loop back toward it emptying into sinusoids that form part of marginal zone of loose lymphoid tissue that surrounds white pulp.
Other branches of central arteries extend into red pulp to form the pulp arteries that empty into various sinusoids of this tissue. Blood from the sinusoids is collected into red pulp veins.
These trabecular veins combine to form the spleenic vein that leaves the spleen through the hilus. Blood circulation is probably both open blood empties into tissue of pulp that is percolates through and is later collected into sinusoids that connect to venules and closed blood from arterioles empties into sinusoids that are directly connected to venules.
Functions of the spleen. Production of blood cells. This stops about the time of birth. Destruction of erythrocytes. Recycling of ferritin from worn out erythrocytes for synthesis of hemoglobin. Immune response. Storage of erythrocytes that can be released into circulatory system when needed. What is the lymphoid system? The lymphoid system consists of 2 major components, A. The lymph vascular network that permeates all tissues of the body and has two functions, 1.
This group of organs and non-organ lymphatic tissue serves at least two roles: a. Tissues of lymphoid organs consist of two major cell types, A. There are 2 major types of lymphoid tissue, A.
Unencapsulated, sub-epithelial, aggregations of lymphocytes that can occur anywhere in the body 2. Non-nodular parenchyma of lymphoid organs such as the thymus, lymph nodes and spleen B. Nonencapsulated lymph nodules 2. Encapsulated lymph nodes 3. Spleenic white pulp 4. Immune system functions of the lymphoid system A. Immune response : 1. Some examples of nodules are lymph nodules, thyroid nodules, breast nodules, synovial nodules, etc.
Generally, lymph nodules are the small, localized collection of lymphoid tissue present within the loose connective tissue beneath the wet epithelial tissue. They occur in the respiratory system, digestive system, and urinary bladder.
Also, thyroid nodules are the lumps developed in the thyroid gland. One can have a single thyroid nodule or several nodules in the thyroid gland. Also, they can be either solid or fluid-filled compartments. Furthermore, breast nodules are the movable fluid-filled sacs or fibroadenoma tumors containing glandular tissue that are not attached to the chest wall. Majority of them are benign and resemble breast lumps that are hard and immovable.
Moreover, synovial nodules are the abnormal, cartilaginous growth of the synovium, the thin tissue which surrounds joints. They lead to osteoarthritis by damaging the smooth articular cartilage. A node refers to a small individual structure within the connective tissue while a nodule refers to a swelling or aggregation of cells in the body, especially an abnormal one.
Thus, this is the main difference between nodes and nodules. Moreover, size is a major difference between nodes and nodules. Nodes are small while nodules are comparatively large. Identify and discuss the flow of lymph through the lymph node from the afferent to the efferent lymphatic vessels. Identify the red and white pulp of the spleen and understand their role in splenic function.
Describe and understand the functional significance of blood flow through the spleen. Identify the palatine tonsil and understand its function. Slide 55 Appendix. Here the lamina propria and submucosa are heavily infiltrated with lymphatic tissue.
Look near the lining epithelium for individual lymphoid cells. Slide 53 Ileum. Scattered cells and lymphoid tissue, as well as slightly more organized lymph nodules, are commonly found in the mucosa of the GI tract.
Lymph nodules in the ileum are referred to as Peyer's patches. Again, examine the lymphoid cells mostly lymphocytes and plasma cells. Slide 59 Lymph node. Lymph nodes are more organized organs than are nodules. They have a capsule , subcapsular sinus , hilus , supporting connective tissue trabeculae , and trabecular sinuses.
Arteries, veins, and efferent lymphatics are all located at the hilus. Afferent lymphatics enter the capsule.
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