BIO 240: Condensed Review
“Run this by me One More Time”
The Lymphatic System
Major lymphatic ducts. (Courtesy of NIH/NCI)
- The lymphatic system aids the immune system in removing and destroying waste, debris, dead blood cells, pathogens, toxins, and cancer cells.
- The lymphatic system absorbs fats and fat-soluble vitamins from the digestive system and delivers these nutrients to the cells of the body where they are used by the cells.
- The lymphatic system also removes excess fluid, and waste products from the interstitial spaces between the cells.
Arterial blood carries oxygen, nutrients, and hormones for the cells. To reach these cells it leaves the small arteries and flows into the tissues. This fluid is now known as interstitial fluid and it delivers its nourshing products to the cells. Then it leaves the cell and removes waste products.
After this task is complete, 90% of this fluid returns to the circulatory system as venous blood.
WHAT IS LYMPH?
The remaining 10% of the fluid that stays behind in the tissues as a clear to yellowish fluid known as lymph.
- Unlike blood, which flows throughout the body in a continue loop, lymph flows in only one direction within its own system. This flow is only upward toward the neck. Here, it flows into the venous blood stream through the subclavien veins which are located on either sides of the neck near the collarbones.
- After plasma has delivered its nutrients and removed debris, it leaves the cells. 90% of this fluid returns to the venous circulation through the venules and continues as venous blood.
- The remaining 10% of this fluid becomes lymph which is a watery fluid that contains waste products. This waste is protein-rich due to the undigested proteins that were removed from the cells.
The lymph is moved through the body in its own vessels making a one-way journey from the interstitial spaces to the subclavian veins at the base of the neck.
- Since the lymphatic system does not have a heart to pump it, its upward movement depends on the motions of the muscle and joint pumps.
- As it moves upward toward the neck the lymph passes through lymph nodes which filter it to remove debris and pathogens.
- The cleansed lymph continues to travel in only one direction, which is upward toward the neck.
- At the base of the neck, the cleansed lymph flows into the subclavian veins on either side of the neck.
Lymph returning to the
THE ORIGIN OF LYMPH
Lymph originates as plasma (the fluid portion of blood). The arterial blood, which flows out of the heart, slows as it moves through a capillary bed. This slowing allows some plasma to leave the arterioles (small arteries) and flow into the tissues where it becomes tissue fluid.
- Also known as extracellular fluid, this is fluid that flows between the cells but is not into the cells. This fluid delivers nutrients, oxygen, and hormones to the cells.
- As this fluid leaves the cells, it takes with it cellular waste products and protein cells.
- Approximately 90% of this tissue fluid flows into the small veins. Here it enters the venous circulation as plasma and continues in the circulatory system.
- The remaining 10% of the fluid that is left behind is known as lymph.
In order to leave the tissues, the lymph must enter the lymphatic system through specialized lymphatic capillaries. Approximately 70% of these are superficial capillaries located near, or just under, the skin. The remaining 30%, which are known as deep lymphatic capillaries, surround most of the body’s organs.
Lymphatic capillaries begin as blind-ended tubes that are only a single cell in thickness. These cells are arranged in a slightly overlapping pattern, much like the shingles on a roof. Each of these individual cells is fastened to nearby tissues by an anchoring filament.
The lymphatic capillaries gradually join together to form a mesh-like network of tubes that are located deeper in the body.
- As they become larger, and deeper, these structures become lymphatic vessels.
- Deeper within the body the lymphatic vessels become progressively larger and are located near major blood veins.
- Like veins, the lymphatic vessels, which are known as lymphangions, have one-way valves to prevent any backward flow.
- Smooth muscles in the walls of the lymphatic vessels cause the angions to contract sequentially to aid the flow of lymph upward toward the thoracic region. Because of their shape, these vessels are previously referred to as a string of pearls.
Lymph nodes kill pathogens and cancer cells. They also
There are between 600-700 lymph nodes present in the average human body. It is the role of these nodes to filter the lymph before it can be returned to the circulatory system. Although these nodes can increase or decrease in size throughout life, any nodes that has been damaged or destroyed, does not regenerate.
- Afferent lymphatic vessels carry unfiltered lymph into the node. Here waste products, and some of the fluid, are filtered out.
- In another section of the node, lymphocytes, which are specialized white blood cells, kill any pathogens that may be present. This causes the swelling commonly known as swollen glands.
- Lymph nodes also trap and destroy cancer cells to slow the spread of the cancer until they are overwhelmed by it.
- Efferent lymphatic vessels carry the filtered lymph out of the node so that it can continue its return to the circulatory system.
Lymphatic system drainage is organized into two separate, and very unequal drainage areas. The right drainage area clears the right arm and chest. The left drainage area clears all of the other areas of the body including both legs, the lower trunk upper left of the chest, and the left arm.
Lymphatic Drainage Areas