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Lymphatic System Lab

About 10% of the plasma leaves the bloodstream in capillaries and enters the lymph vessels, which run one-way back toward the right atrium of the heart. A few proteins also are returned to blood through lymph. Lymphatic vessels, like small veins, have valves that keep the lymph flowing in the right direction.

Major lymphatic trunks and the two collecting ducts (Right lymphatic duct and Thoracic {left} duct).

Details of lymph drainage showing subclavian veins, where both left and right ducts enter the blood circulation. Note the Cisterna chyli, which is the enlarged region where lymph from the digestive system carries lipids from the lacteals into the thoracic duct.

Detail of axillary lymph nodes and drainage from the breast into the junction of the right subclavian and internal jugular veins.

Photo of lymphatic vessels associated with a lymph node.

Be able to identify each of these structures on a microscopic view of a lymph node. As with some other organs, the outer portion of the node containing the germinal centers is the cortex, while the deeper portion (center) is the medulla. The trabeculae are composed of connective tissue, while the medullary sinuses (not labeled) are light areas, and the medullary cords (also not shown) are darker staining cells leading from germinal centers. 

Notice that the structure of the thymus is similar to that of lymph nodules. What are the functions of the thymus? Tonsils are similar to the thymus in structure.

The spleen is the largest lymph organ. Be able to identify structures of the spleen. The connective tissue within the spleen forms trabeculae and contains trabecular veins.

At the center of each area of white pulp, lies a branch of the splenic artery. The red pulp is filled with venus sinuses, which drain into trabecular veins, which are surrounded by connective tissue trabeculae, much like those in the lymph nodes.

The lymphatic system is sometimes divided into an immune system, as immunity is a major portion of its function. What are the functions of the B cells (also referred to as GALT - gut associated lymphatic tissue), and the T cells? Distinguish between non-specific immunity and specific immunity, between antigens and antibodies.

Nonspecific defenses: The illustrations below show general body defenses.

Killer cells (T cells) form holes in the membrane of target cells, thus killing them. The protein "perforin" perforates the plasma membrane of invading target cells.

Detail of a membrane attack complex. Complement proteins forming the "holes" allow water to enter the cell, and also allows cellular contents to flow out, thus killing the attacked cells.

Inflammation and fever. Upon injury, cells release histamines (and other chemicals), which attract phagocytic leukocytes, dilate arterioles, which will allow more blood to flow into the area, thus causing swelling and redness. The increased pressure of the fluids also adds pressure to nerve endings, which cause pain. Relate these processed to margination and diapedesis of the leukocytes.

The following two illustrations show and label the different cells of the immune system.

MHC (Major histocompatibility complex) proteins.

T cells and MHC proteins.

Immune defense of T cell lymphocytes. Where are these cells developed?

Cytotoxic T cell (orange) and cancer cell (purple).

Specific immunity (antibodies) from B cell lymphocytes: Each type of antibody attacks only one specific type of antigen (disease causing organism). Helper T cells aid the B cells.

Roles of helper T cells. 

Two different types of antibodies: IgM and IgG (immunoglobulins). Correlation between levels of each antibody and time from onset of infection. Gamma globulin (IgG) reaches a peak in about three weeks.

The variable portion (yellow) reacts with a specific antigen.

Several genes on a chromosome are condenses in the mRNA that codes for the antibody receptor.

Overview of the specific immune response.

Blood typing by immune response. The top row is Type A, the middle is Type B, and the lower row is Type AB. In type O blood, neither drop of blood agglutinates.

Evolution of the immune system. Many invertebrates and primitive chordates have only phagocytic cells to protect them. The first lymphocytes appear in lambreys (jawlwss fishes). T and B cells are found in all other classes of vertebrates.

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