Lymphatic System Flashcards
What is the immune system?
A cell population that inhibits all organs and defends the body from agents of disease.
What is the lymphatic system?
Network or organs and vein-like vessels that recover fluid - unrecovered from capillary filtrate.
What are the 3 functions of the lymphatic system?
1) Fluid Recovery
2) Immunity
3) Lipid Absorption
What is lymph?
Fluid, similar to plasma, has very little protein; essentially extracellular
fluid
What does a lymphatic vessel do?
Transport the lymph; mechanisms of flow similar to venous return.
Characteristics of lymphatic tissues.
Composed of aggregates of lymphocytes and macrophages that
populate many organs in the body.
Characteristics of lymphatic organs.
Defense cells are especially concentrated in these organs; Separated from surrounding organs by connective tissue capsules
Examples of lymphatic organs.
Lymph nodes. red bone marrow, spleen, etc.
Describe fluid recovery.
Fluid continually filters from the blood capillaries into the tissue spaces. The capillaries reabsorb about 85% of it on average. The other 15% (2 to 4 L/day) is reabsorbed by the lymphatic system and returned to the blood.
Describe immune surveillance (immunity).
Excess-filtered fluid picks up foreign cells and chemicals from the
tissues. Fuild passes through the lymph nodes, where immune cells are always on the lookout for foreign matter. When they detect anything potentially harmful, they activate an immune response.
Describe lipid absorption.
In the small intestine, special lymphatic vessels called lacteals absorb dietary lipids that are not absorbed by the blood capillaries.
Describe lymphatic capillaries.
They penetrate nearly every tissue of the body but are absent from cartilage, bone, bone marrow, and the cornea. They are closely associated with blood capillaries but unlike them, they’re closed at one end and there is no through flow of fluid.
How do lymphatic endothelial cells differ from the endothelial cells of blood capillaries?
They have intercellular clefs between them so that bacteria, lymphocytes, and other cells and particles can enter along with the fluid tissue.
Describe the relationship between tissue pressure and the endothelial valves.
When the tissue pressure is high, it pushes the flaps open (inward) and fluid flows into the capillary. When the pressure is higher in the lymphatic capillary than in the tissue fluid, the flaps are pressed outward (closed).
What is the route from the tissue fluid back to the bloodstream?
Lymphatic capillaries → collecting vessels → 11 lymphatic trunks → two collecting ducts → subclavian veins.
Describe the flow of lymph.
Lymph is moved along by rhythmic contractions of lymphatic vessels. Stretching of vessels stimulates contraction and flow is aided by skeletal muscle pump. Exercise significantly increases lymphatic return.
Neutrophils
Respond to bacterial infections.
Natural killer (NK) cells
Large lymphocytes that attack and destroy bacteria, transplanted tissue, host cells infected with viruses or that have turned cancerous
T lymphocytes (T cells)
Lymphocytes that mature in the thymus and later depend on thymic hormones.
B lymphocytes (B cells)
Lymphocytes that differentiate into plasma - connective tissue cells that secrete antibodies.
Macrophages
Phagocytotic cells of the connective tissues. They arise from monocytes that have emigrated from the bloodstream and other macrophages. Phagocytize foreign matter. Process foreign matter and display antigenic fragments of it to certain T cells.
Dendritic cells
Branched, mobile APCs found in the epidermis, mucous membranes, and lymphoid organs. Alert immune system to pathogens that have breached the body surface.
Reticular cells
Branched stationary cells that contribute to the stroma of a lymphatic organ.
Macrophages
Develop from monocytes or other macrophages; Phagocytize debris, bacteria, dead neutrophils, and foreign matter; Antigen-presenting cells
