Lymphatic System



Lymphatic System


-To filter extracellular fluid by bringing it into the lymphatic system and running it through the lymph nodes or accessory organs and exposing it to the lymphocytes.
-To produce new lymphocytes in organs, especially the thymus
-To Circulate other materials around, by way of the extracellular fluid, things like hormones and lipids.

General Structure

*Begins as a lymphatic capillaries
-small vessels made of simple squamous epithelium tissue
-"dead end" capillaries- begin blindly near regular capillary beds.
- Epithelial cells create one way valves, so extracellualr fluid thats released from the arterial end of regular capillaries can be forced into the lymph capillaries and stay in so theres no backflow.

*One in the capillaries, lymph has a one way flow into lymphatic vessels
-walls become a little more substantial but not too much
- lymphatic vessels have valves to prevent "backflow"

*In the process of heading back to the venous system, the lymphatic vessels enter and leave a series of lymph nodes. Which are acutally clusters of lymphocytes, both B and T cells and also contain macrophages and plasma cells.

The flow direct is as follows:

Afferent vessels -> subcapsular space or sinus -> outer cortex -> inner cortex -> medulla -> and out the efferent vessels

*Eventually the lymph vessels coalesce towards two major ducts:

-thoracic duct- drains entire LOWER half of the body and UPPER LEFT quadrant, dumps into the LEFT subclavian vein.
-right lymphatic duct- drains UPPER RIGHT quadrant, dumps into RIGT subclavian vein.

Accessory Lymphatic Tissues

*Diffuse lymphatic tissue.- May or may not have a capsule and found many places in the body, but usually in connective tissue under surface epithelium. Sometimes referred to as MALT (mucous associated lymphatic tissue). Or GALT (Gastric associated lymphatic tissue)

1. Things suchs as:

A. Lymph nodules- Scattered throughout the body, cluster of lymphocytes with germinal center where new lymphocytes are being produced by mitosis.

B. Tonsils- Cluster of lymphocytes in pharyngeal area, pharyngeal (adnoids), palatine and lingual

C. Peyer's Patch- found in small intestines under epithelium

2. Discrete Organs

a. Lymph nodes (see above)

b. Thymus- Found just superior and anterior to the superior heart. Very large proportionally in children and involutes (very important in children and decreases in size as age progresses past puberty). Some lymphocytes produced in the bone marrow go to the thymus to become fully developed. This is helped along by Thymosins, now considered to be a family of chemicals. Once the cells are fully mature they are called T-Lymphocytes. Several different types of T-Cells such as cytotoxic, helper and suppressor types.
-Once matured they can then migrate and "Seed" other organs such as lymph nodes.
a. two main lobes subdivided into lobules by connective tissue
b. each lobule has an outer cortex and innr medulla. Cells originate in the cortex and exit from the medulla.

C.Spleen- Found in abdomen high on left side under the diaphragm.
a. Functions
1. Red blood cell graveyard- Iron and hemoglobin recycled
2. immunity- White pulp- like lymph nodules

**Side note (free of charge) All lymphocytes are born in bone marrow.