The wall of the lymph capillary is composed of endothelium in which the simple squamous cells overlap to form a simple one-way valve. This arrangement permits fluid to enter the capillary but prevents lymph from leaving the vessel.
The microscopic lymph capillaries merge to form lymphatic vessels. Small lymphatic vessels join to form larger tributaries, called lymphatic trunks , which drain large regions. Lymphatic trunks merge until the lymph enters the two lymphatic ducts. Most of the fluid is reabsorbed into the capillaries and the rest is drained into the lymphatic vessels, which eventually return it to the veins.
Lymph also contains many other substances including. Damaged cells, cancer cells, and foreign particles such as bacteria and viruses that may have entered the tissue fluids. Lymph nodes are tiny bean-shaped organs that serve as collection centers for lymph.
All lymph passes through strategically placed lymph nodes, which filter damaged cells, cancer cells, and foreign particles out of the lymph. Lymph nodes also contain specialized white blood cells for example, lymphocytes Lymphocytes One of the body's lines of defense immune system involves white blood cells leukocytes that travel through the bloodstream and into tissues, searching for and attacking microorganisms and Thus, important functions of the lymphatic system are to remove damaged cells from the body and to provide protection against the spread of infection and cancer.
Some lymph nodes are clustered under the skin, particularly in the neck, armpits, and groin. Other lymph nodes are deep within the body, for example inside the abdomen. The lymphatic vessels drain into collecting ducts, which empty their contents into the two subclavian veins, located under the collarbones. These veins join to form the superior vena cava, the large vein that drains blood from the upper body into the heart.
Blockage obstruction : Obstruction in the lymphatic system leads to an accumulation of fluid lymphedema Lymphedema Lymphedema is the accumulation of lymph in tissues, resulting in swelling. When lymphatic vessels are injured or obstructed, lymph fluid cannot drain and accumulates in tissues, causing swelling Obstruction may result from scar tissue that develops when the lymph vessels or nodes are damaged or removed during surgery, by radiation therapy, by injury, or in tropical countries, by infection with a threadworm filariasis Lymphatic Filariasis Lymphatic filariasis is infection of the lymphatic system caused by one of three species of roundworms.
The lymphatic capillaries conduct the fluid into larger lymphatic vessels, which carry it toward lymph nodes and lymphoid organs. The nodes and organs filter the lymph and eliminate harmful substances. Filtered lymph then moves toward major lymphatic ducts—namely, the thoracic duct and right lymphatic duct, located at the junction between the subclavian and internal jugular veins. These ducts empty the filtered lymph into the veins to rejoin the bloodstream. See more from our free eBook library.
A description of the lymphatic system from the edition of Gray's Anatomy of the Human Body. Lymphatic Immunity: The Great Protectors. When you select "Subscribe" you will start receiving our email newsletter.
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The capillaries have external valves but no internal valves or smooth muscle, so the pressure of lymph accumulation itself must propel the fluid forward into the larger vessels. Because lymphatic capillaries have a closed end and minivalves normally prevent backflow into tissues, the pressure of lymph becomes higher as more lymph is collected from the tissues, which sends the lymph fluid forward. Multiple capillaries converge in collecting vessels, where the internal valves and smooth muscle start to appear.
This moves lymph further along the system despite the fall in pressure that occurs when moving from the higher-pressure capillaries to the lower-pressure collecting vessels. The lymph trunks drain into the lymph ducts, which in turn return lymph to the blood by emptying into the respective subclavian veins. After filtration by the lymph nodes, efferent lymphatic vessels take lymph to the end of the lymphatic system. The final goal of the lymphatic system is to recirculate lymph back into the plasma of the bloodstream.
There are two specialized lymphatic structures at the end of the lymphatic system, called the lymph trunks and ducts.
Lymphatic Ducts : The thoracic duct and right lymphatic duct. A lymphatic trunk is any large lymph vessel that forms from the convergence of many efferent lymph vessels. There are four sets of of lymph trunks that are paired with a right and left half, and one unpaired trunk:. Lymphatic trunks then drain lymph fluid into the lymph ducts, the final part of the lymphatic system.
Two lymph ducts receive lymph from the lymph trunks. These are the largest lymph vessels and contain three layers, similar to those of great veins. The thoracic duct drains into to the left subclavian vein while the right duct drains into the right subclavian vein, both at the junction between the respective vein and the jugular vein.
The two subclavian veins then merge into the vena cava, the large vein that brings deoxygenated blood to the heart. The lymph ducts each have internal valves at their junction with the subclavian vein. These function similarly to other lymphatic valves and prevent venous blood from flowing into the lymph duct.
Privacy Policy. Skip to main content. Lymphatic System. Search for:. Lymphatic Vessels. Lymphatic Vessel Structure The lymphatic structure is based on that of blood vessels.
Learning Objectives Describe lymphatic circulation and the structure of lymphatic vessels. Key Takeaways Key Points Lymph or lymphatic vessels are thin-walled valved structures that carry lymph. Lymph vessels are lined by endothelial cells and have a thin layer of smooth muscles and adventitia that bind the lymph vessels to the surrounding tissue.
Lymph movement occurs despite low pressure due to smooth muscle action, valves, and compression during contraction of adjacent skeletal muscle and arterial pulsation.
When the pressure inside a lymphangion becomes high enough, lymph fluid will push through the semilunar valve into the next lymphangion, while the valve then closes.
Lymph vessels are structurally very similar to blood vessels. Valves prevent backwards flow of lymph fluid, which allows the lymphatic system to function without a central pump. Key Terms lymphagion : The space between two semilunar valves of the lymphatic vessels that forms a distinct functional unit for the forward flow of lymph.
ISF : Interstitial or tissue fluid, a solution that bathes and surrounds the cells of multicellular animals. It is the main component of extracellular fluid, which also includes plasma and transcellular fluid. Distribution of Lymphatic Vessels The lymphatic system comprises a network of conduits called lymphatic vessels that carry lymph unidirectionally towards the heart.
Learning Objectives Describe the structure of the lymphatic system and its role in the immune system and blood circulation. Key Takeaways Key Points The lymph system is not a closed system. Lymph nodes are most densely distributed toward the center of the body, particularly around the neck, intestines, and armpits. Lymph vessels and nodes are not found within bone or nervous system tissue. Afferent lymph vessels flow into lymph nodes, while efferent lymph vessels flow out of them.
Lymphatic capillaries are the sites of lymph fluid collection, and are distributed throughout most tissues of the body, particularly connective tissue. Key Terms lymph : A colorless, watery, bodily fluid carried by the lymphatic system, consisting mainly of white blood cells. Efferent : A type of vessel that flows out of a structure, such as lymph vessels that leave the spleen or lymph nodes and arterioles that leave the kidney.
Afferent lymphatic vessels flow into a lymph node and carry unfiltered lymph fluid.
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