Lecture – 11 (20) Sept. 28, 2011
[16:45] pg.752
Lymphatic System
 Lymphatic Vessels
 Lymphatic Nodes
 Lymphoid Cells (Lymphoid = tissue type) o Lymphocytes (T&B cells) macrophages; dendritic cells
 Lymphoid Organs o Spleen o Thymus o Tonsils o Peyer’s Patches o Appendix
Function of Lymphatic
 Return interstitial fluid lost by capillaries back to the blood
 Filters interstitial fluid
 Absorb lipids in small intestines (Lacteals)
 Provide places for patrolling lymphatic cells to hang out and operate
Lymphatic Vessels
 Blind-end vessels that pick up interstitial fluid
 Flaps (one-way) valves
 Interstitial fluid pressure loads vessels
 Lymphatic vessels lead to lymph nodes where they bottle-neck, resulting in filtration
 Leukocytes hang out in lymph nodes
Lymph Transport pg.754
The lymphatic system lacks an organ that acts as a pump. Under normal conditions, lymphatic vessels are low-pressure conduits, and the same mechanisms that promote venous return in blood vessels act here as well – the milking action of active skeletal muscles, pressure changes in the thorax during breathing, and valves to prevent backflow.
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Lymphoid Cells pg.756
Lymphocytes are the main warriors of the immune system; arise in red bone marrow (along with other formed elements). They then mature into one of the two main varieties of immunocompetent cells Tcells or B-cells that protect the body against antigens (anything the body perceives as foreign).
Activated T-cells manage the immune response, and some of them directly attack and destroy infected cells. B-cells protect the body the body by producing plasma cells, daughter cells that secrete antibodies into the blood (or other body fluids). Antibodies mark antigens for destruction by phagocytes or other means.
Lymphoid macrophages play a crucial role in body protection and in the immune response by phagocytizing foreign substances and by helping to activate T-cells. So do the spiny-looking dendritic
cells that capture antigen and bring them back to the lymph nodes. The reticular cells are fibroblastlike cells that produce the reticular fiber stroma, which is the network that supports the other cell types in the lymphoid organs and tissues.
Lymphoid Tissue pg.756
Lymphatic tissue is an important component of the immune system, mainly because it:
1.
House and provides a proliferation site for lymphocytes
2.
Furnishes an ideal surveillance vantage point for lymphocytes and macrophages
Lymph Nodes (pg.756)
 Principal lymphoid organs of body
 Hundreds hidden in connective tissue (Lymphoid = connective tissue making up lymphatic sys.)
 Large clusters of superficial lymph nodes in neck, armpit, groin, and mesenteric.
 Anatomically comprised of cortex and medulla
 Several afferent (more in) vessels & few efferent (less out) vessels into nodes (bottle-neck)
Each node (bean shaped) is surrounded by a dense fibrous capsule from which connective tissue strands called trabeculae extend inward to divide the node into a number of compartments. A lymph node has two histologically distinct regions, the cortex and the medulla. Cortex contains germinal centers heavy with dividing B-cells and deeper cortex contains dendritic cells, which primarily houses Tcells in transit. Medullary cords are thin inward extensions from the cortical lymphoid tissue, and contain both types of lymphocytes plus plasma cells.
Node circulation – lymph enters the convex side of the node through numerous afferent lymphatic vessels; through large bag-like sinuses through the cortex to the medulla; finally exiting via the hilum via the less numerous efferent lymphatic vessels and eventually towards the heart. This feeding system into the lymph node slows down circulation allowing time for lymphocytes to carry out their functions.
Lymph passes through several nodes before it is completely cleaned.
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Other Lymphoid Organs pg.758
Except for the thymus, the common feature of all these organs is their tissue makeup: all are composed of reticular connective tissue. Although all lymphoid organs help protect the body, only the lymph nodes filter lymph. The other lymphoid organs and tissues typical have efferent lymphatic vessels draining them, but lack afferent lymphatic vessels.
Spleen
 Large lymphatic organ – Fist Size
 Located on left side – abdominal cavity
 Site of lymphatic proliferation
 Removes aged erythrocytes & platelets from blood
 Stores iron from blood recycling
 Stores blood platelets
 Site of erythrocyte production in fetuses. WHY? Stem cells do not have a place to live yet as red bone marrow has not formed, so they use the spleen as temporary housing.
Pg.758
The spleen provides a site for lymphocyte proliferation and immune surveillance and response. But perhaps even more important are its blood-cleansing functions. Besides extracting aged and defective blood cells and platelets from the blood, its macrophages remove debris and foreign matter from blood flowing through its sinuses.
If the spleen is removed, the liver and bone marrow take over most of its functions. In children younger than 12, the spleen will regenerate if a small part of it is left in the body.
Thymus
 Overlays the superior-anterior portion of the heart
 Allows for the immune-competency of T Lymphocytes
 Large in newborns & infants; atrophies beginning at puberty
 Does not directly fight (foreign) antigens since it is sealed off from the blood
 Sealed off from antigen entry
Tonsils
 Simplest lymphoid tissue
 Palatine tonsils are largest and most often infected
 Pharyngeal tonsils – Adenoids
 Lingual tonsils
 Ambush tactic of invite & destroy
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Miscellaneous Adenoid Follicles
 Peyer’s Patches – Distal portion of small intestine
 Appendix – beginning of large intestine (Cecum)
 Both guard the intestine & intestinal wall
 Aid in Memory
Right side of head/chest plus right arm drain into the R. lymphatic duct  R. subclavian vein
L. side of head/chest, L. arm and both lower extremities drain into L. lymphatic duct  L. subclavian
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