As the blood vessels divide, they eventually get converted into fine blood capillaries.
Red blood cells cannot pass through these blood capillaries, instead, they are filtered out of the plasma and white blood cells. For this reason, blood vessels do not reach the blood of all the cells of the body. The fluid (plasma) without red blood cells filtered from these capillaries is called lymph which is found in our lymphatic system. It is through this lymph that the exchange of nutrients, oxygen, carbon dioxide, and excretory substances from the tissue cells.
Parts of Lymphatic System
In humans, lymph capillaries, lymph vessels, lymph nodes, and lymph organs are found under the lymphatic system.
1. Lymph capillaries
These are soft vessels with very thin walls. Their last branches located in the intestinal villi are called lacteals. They absorb fatty acid and glycerol from the intestinal tract of the alimentary canal, creating emulsified fat. This is called chyle. It is a milky-colored liquid.
2. Lymphatic vessels
The lymph capillaries join together to form a luteous vessel with valves, which contains a fluid substance called lymph. They can be divided into the following two parts.
a. Left Thoracic Lymph Duct
The lymph vessels of the left hand, both legs, the left parts of the head and neck, the alimentary canal, thoracic, and other parts of the abdominal cavity, open into a large left thoracic lymph duct located below the body wall. This lymph duct is attached to a large sac called Cisterna Chyli present in the abdominal cavity. It subsequently opens into the left subclavian vein.
b. Right Thoracic Lymph Duct
The right hand, and the lymph vessels of the right, cervical, and thoracic parts of the head, form a large right thoracic lymph duct that opens into the right subclavian vein.
3. Lymphatic Nodes or Glands
Lymphatic ducts swell in some places to form lymph nodes or glands. It is a kidney-shaped organ of the lymphatic system and the adaptive immune system. A large number of lymph nodes are linked throughout the body by the lymphatic vessels. Lymph nodes or glands become inflamed or enlarged in various diseases.
4. Lymph Organs
a. Bone marrow
This is the soft, spongy tissue located in the center of major bones that makes RBC, WBC, and platelets.
It is the largest lymphatic organ located under the left side ribs and above the stomach. It filters and stores blood and produces white blood cells to avoid foreign invaders.
c. Thymus Gland
It is located in the upper chest beneath the breast bone. Within the thymus, lymphocytes or T cells mature. T cells are critical to the adaptive immune system.
d. Tonsils and Adenoids
These lymphoid organs trap pathogens such as bacteria or viruses, that enter your mouth or nose from the food you eat and air you breathe. They are your body’s first line of defense against foreign organisms.
e. Peyer’s Patches
These are small masses of lymphatic tissue in the mucous membrane that lines your small intestine. Peyer’s patches play an important role in the immune surveillance of materials within the digestive system.
Major Works of Lymphatic System
The lymph nodes and organs perform the following functions:
1. Producing lymphocytes to build the immune system.
2. Filter and clean the lymph.
3. Synthesis of antibodies to improve immunity
4. Destroying bacteria and other foreign invaders.
5. Maintains fluid levels in the body.
6. Absorbs fats from the digestive tract.
7. Transports and removes waste products and abnormal cells from the lymph.
Differences in Blood and Lymph
1. RBCs are found in the blood whereas those in the lymph are not.
2. Blood is a thick, red, and viscous liquid substance while lymph is colorless and thinner than blood.
3. The number of soluble plasma proteins and neutrophils in the blood is high while the number of insoluble plasma proteins and lymphocytes in the lymph is high.
4. Oxygen and nutrients are high in the blood while the amount of excretory substances in the lymph is high.
5. Blood is transmitted only in the blood vessels whereas the lymph material is also found in the extravasation of lymph vessels as tissue fluid.