Identify the lymph node, spleen, thymus, and palatine tonsil based on their histological arrangement. 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. Immune response :. Involves the recognition of foreign antigens by certain lymphatic cells. An immune response results in changes in the metabolism and chemical programming of lymphocytes that allows them to act in destroying the foreign substance or organism. An immune response may be either humoral or cell-mediated.
Without the activities of cells of the lymphoid system, your life on earth after birth would be brief indeed. This fact is evident in babies that are born lacking a functional immune system. Unless extraordinary measures, such as total sterile isolation, are taken they die shortly after birth. This results in the body not being able to efficiently and effectively cope with infectious organisms via a cell-mediated immune response.
Without treatment, the patient will soon succumb to a mortal disease. Structure and function of lymphoid organs. Free lymphatic nodules lymphatic follicles. Mainly found in the lamina propria of the digestive tract, the respiratory tract, and urinary passages.
Lamina propria - layer of loose connective tissue that underlies the epithelia lining the lumens of internal organs. No connective tissue capsule surrounds free lymphatic nodules. The fixed and free cells of a lymphatic nodule are organized into a densely packed and more or less spherical structure. When the nodule is active in an immune response, it has a cortex and a more or less central germinal center a medullary structure.
Lymphoid tissue consists of:. Fixed cells — reticulocytes in cortex and follicular dendritic cells in germinal center.
Free cells - B-lymphocytes, immunoblasts clonally dividing B-lymphocytes , plasma cells, macrophages, A few eosinophils and mast cells. Lymph nodes. Present along the course of lymphatic vessels. Multiple lymph vessels may connect to a lymph node. Oval or bean shaped bodies surrounded by a dense connective tissue capsule. Septa or trabeculae extend from capsule into lymph node. Filled with stroma consisting of reticular fibers and cells.
Stroma provides a support network for large numbers of lymphocytes. Node consists of:. Many lymphocytes, macrophages, other antigen presenting cells APCs , plasma cells and reticulocytes are present. Follicular dendritic cells are found in the germinal centers of lymph nodules that are in the cortex. A less dense medulla consisting of lymphocytes arranged in strands called medullary cords. Between the cortex and medulla is the paracortical region or thymic dependent zone of the node that contains densely packed cells that are mainly T-lymphocytes.
This region lacks lymphocytes in animals that have had the thymus removed at birth. Cells outside the paracortical region are mostly B-lymphocytes. Tonsils - 3 types that are defined by their structure and their location in mouth and pharynx. Palatine tonsils. On left and right in rear area of oral cavity. Dense lymphoid tissue that forms a band of lymphatic nodules that lie just below a non-keratinized, stratified, squamous epithelium lining the oral cavity in this region.
Overlying epithelium forms invaginations called multiple crypts that penetrate into the band of nodules. These crypts act as collecting places for cellular debris and bacteria as well as some living lymphocytes that have migrated into the crypts. The band of lymph nodules is separated from underlying tissues by a partial capsule of dense connective tissue. Pharyngeal tonsils. Diffuse lymphoid tissue containing nodules, but no crypts. Mostly lie beneath a typical pseudostratified ciliated columnar respiratory epithelium in rear roof of pharynx.
Some areas of the covering epithelium may be stratified squamous. A thin partial capsule of dense connective tissue separates the lymphoid tissue from underlying tissue.
Lingual tonsils. Situated in the root of tongue. Each lingual tonsil consists of numerous. The crypt is lined by a non-keratinized , stratified, squamous epithelium. Location - situated above the heart where the great vessels connect. Importance - during early life when the cellular mediated component of the immune system develops. Undergoes atrophy in later life, at which time it loses its functional significance.
The thymus consists of multiple lobes each containing characteristic cortical and medullary structure; however, these are not lymphatic nodules i. A connective tissue capsule surrounds the thymus. Embryologically, the thymus has a dual origin. These epithelial tissues are invaded by lymphoblasts immature T-lymphocytes that originate from stem cells in the bone marrow. The invading cells organize themselves into the cortical and medullary portions of lobules.
Other cell types found in the thymus are:. Cortical layer of thymus. Site of lymphocyte production - divisions of lymphoblast cells. Lymphatic vessels form an alternative channel by means of which the following are removed from the connective tissue spaces: fluid, particulate matter, protein that escapes from blood capillaries, ingested fats absorbed across the intestinal surface, disease microorganisms, other antigenic material which may penetrate the skin and other protective surfaces, and cells both normal and cancerous.
This proteinaceous fluid, variably rich in particles and cells, is termed lymph and is filtered and cleansed in lymph nodes before being returned via the thoracic duct and the right lymphatic duct to the circulating blood in the great veins. Lymphoid Tissues Learning objectives: Know the structure and function of the lymphoid tissues and organs: including afferent and efferent flow and specialized vasculature t tonsil diffuse lymphatic tissue and lymph nodules lymph nodes thymus spleen Components of the Lymphatic System Lymphoid tissue is not one of the primary or basic tissue types of the body but is a variety of connective tissue or, in the case of the thymus, epithelial tissue.
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