Lymphatic System Outline PDF

# Outlines of the lymphatic system Prepared by Dr. Ahmed A. Morsi Assist. Prof of Histology & Cell Biology ## Learning objectives: - By the end of this lecture, you will be able to: - Classify the lymphatic organs - Describe the structure of lymph node - Describe the structure of sple...

# Outlines of the lymphatic system Prepared by Dr. Ahmed A. Morsi Assist. Prof of Histology & Cell Biology ## Learning objectives: - By the end of this lecture, you will be able to: - Classify the lymphatic organs - Describe the structure of lymph node - Describe the structure of spleen - Define mucosa associated lymphatic tissue (MALT) ## The lymphatic system includes: - Lymphatic vessels - Lymphatic organs: - Primary lymphatic organs (maturation sites): bone marrow & thymus - Secondary lymphatic organs: Spleen, lymph nodes, and MALT (mucosal associated lymph tissue) - BALT (bronchus associated lymph tissue) - GALT (gut associated lymph tissue) - Tonsils (palatine, pharyngeal, and lingual) ## Structures of the Lymphoid Tissues and Organs ### I. Mucosa-associated lymphoid tissue - Gut-associated lymphoid tissue: Lymphatic tissue in the mucosa of the digestive tract, such as Peyer patches in ileum and nodules in the appendix. - Bronchus-associated lymphoid tissue: Lymphatic tissue in the mucosa of the respiratory tract, such as lymphatic tissue in bronchi, bronchioles. - Tonsils - Palatine tonsils - Pharyngeal tonsils (adenoids) - Lingual tonsils ### II. Lymphoid organs - Bone marrow - Thymus - Cortex - Medulla - Lymph nodes - Afferent lymphatic vessels - Efferent lymphatic vessels - Cortex - Paracortex - Medulla - Spleen - White pulp - Red pulp ## Lymph Node - Bean-shaped small-sized structures located in groups along the course of lymphatics. They could be palpable or non-palpable. - Histologically, lymph node is composed of stroma & parenchyma. ### I. Stroma 1. **Capsule:** thick CT; receives multiple afferent lymphatic (3-5) through the convex surface & gives rise to a single efferent lymphatic vessel through the concave surface (hilum). 2. **Trabeculae:** CT septae divide it into compartments. 3. **Reticular CT:** ### II. Parenchyma: cortex, paracortex & medulla **- Cortex:** is the outermost region just beneath the capsule - It is densely packed by lymphocytes which are aggregated in the form of oval or rounded lymphatic nodules. Each nodule has a pale-stained central region (germinal centre) surrounded by a dark zone of densely packed lymphocytes. The nodules are separated from the capsule by a space called subcapsular sinus (ScS). **- **Medulla**:** is the innermost central region of the lymph node - It contains medullary cords (anastomosing branching cords of lymphocytes) & medullary sinuses inbetween the cords. **- Paracortex:** is the deep part of the cortex just prior to the medulla. - It contains T lymphocytes & high endothelial venules (HEVs). ## Spleen - A large hemolymphatic organ situated in the left hypochondrium - Histologically, spleen is composed of stroma & parenchyma: ### I. Stroma: 1. **Fibromuscular capsule** (Ca) 2. **Trabeculae** (T): are rich in smooth muscle fibers. 3. **Reticular CT** ### II. Parenchyma: white pulp & red pulp **a)White pulp (Malpighian bodies):** - rounded or oval aggregations of lymphocytes surrounding central arteriole: - Central arteriole (CA): called central although eccentric in position - Periarteriolar lymphatic sheath (PALS): mainly T lymphocytes - Germinal center(GC) - Marginal zone (arrow): mainly B lymphocytes **b) Red pulp:** space located in between the white pulp and filled with loose reticular CT: - **Splenic cords (cords of Billroth):** loose reticular CT rich in blood cells, plasma cells, reticular cells, and macrophages. - **Splenic sinusoids:** supported by reticular CT. It show all features of discontinuous capillaries. ## Mucosa associate lymphatic tissue (MALT) - It is also called mucosal immune system as it is present in close association with the lining mucosa of common systems e.g. GIT & respiratory system. Subsequently, MALT is subdivided into GALT, BALT, and tonsils. - In addition to lymphocyte, the MALT includes other cells e.g. plasma cells, dendritic cells and antigen presenting cells (APCs). - It includes 2 distinct forms: 1. **Diffuse lymphatic tissue (transient):** scattered lymphocytes throughout the CT lamina propria either singly or in small nodules (1mm). They represent temporary response to antigenic stimulation (infection). 2. **Lymphatic nodules (permanent):** Noncapsulated, sharply defined localized concentrations of lymphocytes. They are large enough that extend to the submucosa. They are permanent aggregates in the lamina propria of the wall of the GIT e.g. tonsils, Peyer's patches of ileum, appendix. ## Clinical correlation - **Tonsilitis:** acute bacterial inflammation of the palatine tonsils. - **Adenoiditis:** acute bacterial inflammation of the pharyngeal tonsils. - **Appendicitis:** acute inflammation of the appendix. ## Reference: - Junqueira's Basic Histology: Text and atlas, 13th Edition, 2013. Anthony L. Mescher