Lymphatic System Structures
The lymphatic system relies on two semi-independent parts:
lymphatic vessels and lymphoid tissues/organs.
lymphatic vessels and lymphoid tissues/organs.
Excess tissue fluid and plasma proteins, known as lymph are carried by lymphatic vessels. Lymphatic vessels pick up lymph and return it to the blood. If fluids are not picked up, edema occurs as fluid accumulates in the tissues. Edema impairs the exchange of materials within the tissue.
Lymphatic vessels form a one-way system towards the heart. Lymph capillaries weave between tissue cells and blood capillaries. Fluid leaks into the lymph capillaries and overlapping walls form flap-like mini-valaves, higher pressure inside the filled lymph capillaries keeps the flaps from allowing fluid to leak back out, forcing the fluid along the vessel. |
Lymphatic collecting vessels collect lymph from lymph capillaries, carry lymph to (afferent) and away (efferent) from lymph nodes and return fluid to circulatory veins near the heart. The right lymphatic duct drains the lymph from the right arm and the right side of the head and thorax while the thoracic duct drains lymph from the rest of the body. |
Lymphatic vessels are similar to veins of the cardiovascular system as they both are thin-walled, larger vessels have valves and operate under lower-pressure.
Lymph transportation is possible by:
Lymph nodes filter lymph before it is returned to the blood. They filter out harmful materials such as bacteria, viruses, cancer cells and cell debris. The lymph nodes are also home to some immune cells such as macrophages and lymphocytes. Macrophages work by engulfing (eating) and destroying foreign substances such as bacteria, viruses and foreign cells.
Lymph transportation is possible by:
- contraction of skeletal muscles, creating a milking action
- pressure changes in the thorax during breathing
- smooth muscle contractions in the walls of the vessels
Lymph nodes filter lymph before it is returned to the blood. They filter out harmful materials such as bacteria, viruses, cancer cells and cell debris. The lymph nodes are also home to some immune cells such as macrophages and lymphocytes. Macrophages work by engulfing (eating) and destroying foreign substances such as bacteria, viruses and foreign cells.
Spleen
Located on the left side of the abdomen, tucked behind the stomach the spleen filters blood. It destroys worn-out blood cells and returns some of the products to the liver. It also is active in forming blood cells in the fetus during development. It also stores platelets and acts as a blood reservoir.
Thymus Gland
Located in the mediastinum, the thymus gland rests anterior and superior to the heart. It functions at peak levels through adolescence and then begins to shrink. It produces hormones such as thymosin to program lymphocytes and is the site of T-lymphocyte cells maturation.
Tonsils
Small masses of lymphoid tissues surround the pharynx. They function to trap and remove bacteria and other foreign materials. Tonsillitis is caused by congestion with bacteria.
Peyer's Patches
Located in the wall of the small intestine and appendix, Peyer's patches resemble tonsils in structure. Their function is to capture and destroy bacteria in the intestine.
Bone Marrow (Red)
Found inside of flat bones and the epiphysis of long bones, this is the site of blood cell production. Lymphocytes that mature here are known as B-Lymphocytes.
Located on the left side of the abdomen, tucked behind the stomach the spleen filters blood. It destroys worn-out blood cells and returns some of the products to the liver. It also is active in forming blood cells in the fetus during development. It also stores platelets and acts as a blood reservoir.
Thymus Gland
Located in the mediastinum, the thymus gland rests anterior and superior to the heart. It functions at peak levels through adolescence and then begins to shrink. It produces hormones such as thymosin to program lymphocytes and is the site of T-lymphocyte cells maturation.
Tonsils
Small masses of lymphoid tissues surround the pharynx. They function to trap and remove bacteria and other foreign materials. Tonsillitis is caused by congestion with bacteria.
Peyer's Patches
Located in the wall of the small intestine and appendix, Peyer's patches resemble tonsils in structure. Their function is to capture and destroy bacteria in the intestine.
Bone Marrow (Red)
Found inside of flat bones and the epiphysis of long bones, this is the site of blood cell production. Lymphocytes that mature here are known as B-Lymphocytes.