Lymphatic System: Structure, Function, Lymphedema

  • The immune system is a complex collection of cells and organs that works together to destroy or neutralize germs that would otherwise cause disease or death. The lymphatic system is a network of tubes, cells, and organs that filters pathogens from the blood and transports surplus fluids to the bloodstream.

Lymphatic System Structure

  • Lymphatic vessels start off as open-ended capillaries that feed into larger and larger lymphatic vessels before emptying into the bloodstream through a succession of ducts. The lymph passes through lymph nodes along the way, which can be located in the groin, armpits, neck, chest, and abdomen. 
  • There are around 500–600 lymph nodes in the human body. The lymphatic and cardiovascular systems in humans are distinguished by the fact that lymph is not actively pumped by the heart, but is instead forced through the vessels by body movements, skeletal muscle contractions during body movements, and breathing.
Lymphatic System

Structure of the Lymphatic System

Lymphatic Capillaries

  • Lymphatic capillaries, also known as terminal lymphatics, are vessels that allow interstitial fluid to enter the lymphatic system and turn into lymph fluid. These vessels are interlaced among the arterioles and venules of the circulatory system in the soft connective tissues of the body and can be found in almost every tissue. 
  • The central nervous system, bone marrow, bones, teeth, and the cornea of the eye are the only exceptions, as they do not contain lymph vessels. Lymphatic capillaries are formed by a single cell-thick layer of endothelial cells and serve as the system’s open end, allowing interstitial fluid to flow into them via overlapping cells. When interstitial pressure is low, the endothelial flaps close to prevent “backflow.” As interstitial pressure increases, the spaces between the cells open up, allowing the fluid to enter.

Lipid Transport

  • Lacteals, a type of lymphatic capillary found in the small intestine, are important for transporting dietary lipids and lipid-soluble vitamins into the bloodstream. Dietary triglycerides interact with other lipids and proteins in the small intestine and enter the lacteals to generate chyle, a milky fluid. The chyle then travels via the lymphatic system until it reaches the liver, where it enters the bloodstream.

Larger Lymphatic Vessels

  • The lymphatic capillaries discharge into bigger lymphatic vessels, which have a three-tunic structure and have valves, similar to veins. The superficial and deep lymphatics eventually join to produce lymphatic trunks, which are bigger lymphatic tubes. The right lymphatic duct drains lymph fluid into the right subclavian vein from the right sides of the head, thorax, and right upper limb on the right side of the body. 
  • The remaining components of the body drain into the bigger thoracic duct, which drains into the left subclavian vein on the left side of the body. The thoracic duct starts directly behind the diaphragm in the cisterna chyli, a sac-like chamber that receives lymph from the lower belly, pelvis, and lower limbs through the left and right lumbar trunks, as well as the intestinal trunk. Only lymph from the upper right side of the body enters the right lymphatic duct. The rest of the body’s lymph reaches the bloodstream via the thoracic duct and the remaining lymphatic trunks.

Functions

  1. The lymphatic system’s primary job is to drain and return bodily fluids to the bloodstream. Blood pressure promotes fluid leakage from capillaries, leading in fluid accumulation in the interstitial space, which is the space between individual cells in tissues. Capillary filtration releases 20 litres of plasma into the interstitial space of the tissues per day in people. Interstitial fluid is what happens when the filtrate leaves the circulation and enters the tissue gaps. 17 litres is directly reabsorbed by the blood vessels.
  2. A system of arteries, trunks, and ducts drain the surplus fluid and return it to the bloodstream. Interstitial fluid that has entered the lymphatic system is referred to be lymph. Protein-rich interstitial fluid accumulates in the tissue gaps when the lymphatic system is disrupted in some way, such as by cancer cells blocking it or by injury. Lymphedema is the abnormal build-up of fluid that can have major medical effects. The network of lymphatic capillaries became ideal pathways for transferring immune system cells as the vertebrate immune system evolved. This pathway is also used to transfer dietary fats and fat-soluble vitamins absorbed in the stomach.

Further Readings

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