23 Lymphatic organs and lymphatic circulation Flashcards
Well developed in newborns and younger children. However, when you hit adolescence, this organ involutes (shrinks and is gradually replaced with adipose tissue)
Thymus
The lymphatic tissue found in the walls of the gut
Mucosa associated lymphoid tissue (MALT)
o Principal site of hematopoiesis (production of the formed elements: RBCs, leukocytes, platelets aka thrombocytes)
o Islands of stem cells that replace lost cells
o Stem cells surrounded by a branching, leaky capillary network (aka a sinusoid)
o Site of macrophage breakdown of worn-out erythrocytes and iron storage (stored as ferritin for future recycling of erythrocytes)
Bone marrow
The lumen is lined by simple squamous epithelium. Sits on a basal membrane (basal lamina). There are adventitial cells in the outer layer.
Sinusoid
o Gives rise to myeloblast and lymphoblast cell lineages
Myeloblasts: Turn into
• RBCs
• Eosinophils
• Neutrophils
• Basophils
• Monocytes: turn into macrophages upon entry into tissues
• Megakaryocytes: pieces break off to form platelets
Lymphoblasts: turn into
• B lymphocytes: mature into plasma cells in the lymph nodes
• T lymphocytes
Pluripotent hematopoietic stem cells
Found only in lymph nodes and the spleen
Reticular fibers
Found in lymph nodes, spleen, thymus, and all other lymphatic organs
Reticulocytes
Consists of lymphatic cells and extracellular matrix. Always surrounded by a connective tissue capsule (dense irregular connective tissue)
Lymphatic organs
o Consist of multiple germinal centers and have invaginated outer edges (with crypts: or crevices). Help trap material and facilitate its identification by lymphocytes
o Several groups form a protective ring around the pharynx
Pharyngeal
Palatine
Lingual: posterior-most aspect of the tongue
Tonsils
Clusters of calcified material that form in the tonsillar crypts (i.e. the crevices of the tonsils). Contain volatile sulfur compounds (VSCs)
Tonsillolith
o Lobulated organ w/ dark cortex, light medulla
o Immature lymphocytes mature into immunocompetent T-cells: i.e. helpers & cytotoxic T cells
o Sends mature T cells to target organs
o Hormones are produced by epithelioreticulocytes, which make up much of the cellular population of this gland.
Thymus
Thymulins Thymosins THF (thymic humoral factor) Thymopoietins Interferons (INFs) Interleukins
Hormones of the Thymus
Cells of the thymus that produce hormones
Epithelioreticulocytes
aka hassal’s corpuscle. These epithelioreticulocytes have flattened nuclei, twist around each other, they are large, and they are keratinized
Type 6 epithelioreticulocyte
o Small, round, or oval structures o Range in length: 1 to 25 mm, typically found in clusters o Clusters: axillary, inguinal, cervical o Individually throughout the body tissues o Composed of Capsule Cortex Medulla
Lymph nodes
o Contains proliferating B-lymphocytes and some macrophages in this region of the nodule (lighter in staining)
Germinal center
o T-lymphocytes are located deep to the follicles. It is in the ___ of the lymph nodes that aggregates of t-lymphocytes are found (as opposed to the nodules in which B cells are found)
Paracortex
The cells of the lymphatic nodules that are mainly responsible for attacking antigens
Follicular dendritic cells
o Contains proliferating B-lymphocytes and some macrophages in the germinal center of the nodule (lighter in staining)
o T-lymphocytes are located deep to the follicles. It is in the paracortex of the lymph nodes that aggregates of t-lymphocytes are found (as opposed to the nodules in which B cells are found)
o Filter and attack antigen. Follicular dendritic cells are the cells mainly responsible for attacking antigens
Lymphatic nodules (or follices)
o Largest lymphatic organ
o Blood reservoir (of RBCs) and filter
o White pulp: immune component
o Red pulp: filtering component (filters blood). Everything outside the orb-shaped white pulp regions is red pulp
Spleen
The regions of the spleen surrounding an arteriole. They contain T-lymphocytes
PALS (periarteriole lymphatic sheath)
Cells found in the connective tissue capsule of the spleen. These are present so that the spleen can contract when blood or RBCs are needed
Myofibroblasts
o Initiates an immune response when antigens are found in the blood (white pulp)
o Serves as a reservoir for erythrocytes & platelets (red pulp)
o Phagocytizes defective erythrocytes & platelets (red pulp)
o Phagocytizes foreign materials
Functions of the spleen
o Detects antigens and initiates an immune response
o Prominent in the mucosa (of the gut tube)
o Includes Peyer’s patches, that are prominent in the ileum
MALT (mucosa associated lymphatic tissue)
o Closed-ended tubes that are found in most blood capillary networks
o Similar to a blood capillary, larger in diameter
o No basement membrane
o Overlapping endothelial cells
Lymphatic capillaries
A worm that takes residence in capillaries. Symptoms are elephantiasis (lymphedema, or accumulation of interstitial fluid in the tissues)
Wuchereria bancrofti
o Special types of lymphatic capillaries
o Pick up interstitial fluid, dietary lipids, and lipid-soluble vitamins
o Transport chyle
Lacteals
Name for lymph that is found in the lacteals. It is more viscous than normal lymph
Chyle
Unfiltered lymph enters lymphatic organs through these vessels
Afferent vessels
Afferent vessels deliver lymph into these structures
Sinuses
create a mesh in lymphatic channels, which filter lymph
Reticular fibers
Filtered lymph exits through these vessels
Efferent vessels
When lymphocytes can leave circulation and become assimilated into the lymphocyte population of lymphatic organs. This only occurs in the high endothelial venules
Homing
The only location at which homing can occur
high endothelial venules
Interstitial fluid that has accumulated in tissue beds. The interstitial fluid leaked out of capillaries
Lymph
