The cisterna chyli is a dilated sac-like structure at the lower end of the thoracic duct, where lymph from the intestinal trunk and lumbar lymphatic trunks is collected before being transported to the thoracic duct. It acts as a reservoir for lymph, particularly lymph rich in fats, known as chyle, absorbed from the digestive system. The cisterna chyli plays a crucial role in the lymphatic system by draining lymph from the lower half of the body.
Location
The cisterna chyli is located in the retroperitoneal space, anterior to the bodies of the first and second lumbar vertebrae (L1 and L2). It lies just to the right of the aorta and behind the right crus of the diaphragm. From this location, it continues superiorly as the thoracic duct, which ascends through the diaphragm into the thoracic cavity.
Structure and Anatomy
The cisterna chyli is an important structure in the lymphatic system, serving as the origin point for the thoracic duct. It functions as a collecting reservoir for lymph from the lower part of the body, especially lymph rich in fat (chyle) from the gastrointestinal tract. The cisterna chyli is relatively small, sac-like in appearance, and forms a crucial conduit for the flow of lymph upwards into the thoracic duct. Below is a detailed description of the anatomical features of the cisterna chyli.
Shape and Structure
The cisterna chyli is a dilated sac-like structure that marks the beginning of the thoracic duct, the largest lymphatic vessel in the body. It typically measures about 5 to 7 cm in length, though its size and shape can vary between individuals. It is a thin-walled, elongated, or bulbous structure that serves as a confluence point for lymph from several major lymphatic trunks.
Sac-like Dilatation
The cisterna chyli appears as a dilated or saccular portion of the lymphatic system. It can be oval, cylindrical, or funnel-shaped depending on individual anatomical variations. The sac can expand and contract slightly based on lymphatic flow, especially after meals when lymph rich in fat (chyle) is absorbed from the intestines.
Lymphatic Input
The cisterna chyli serves as a collecting chamber for lymph from the lower half of the body. It receives lymph from several major lymphatic trunks, including:
Lumbar Lymphatic Trunks
The right and left lumbar lymphatic trunks drain lymph from the lower limbs, pelvis, kidneys, adrenal glands, and deeper regions of the abdominal wall. These trunks converge on the cisterna chyli to transport lymph from the lower body into the thoracic duct.
Intestinal Lymphatic Trunks
The intestinal lymphatic trunks carry lymph from the gastrointestinal tract, primarily the small intestine, and are rich in dietary fats absorbed during digestion. This lymph, known as chyle, gives the cisterna chyli its characteristic milky appearance. The intestinal trunk drains lymph from the stomach, intestines, pancreas, spleen, and liver.
Other Lymphatic Contributions
In addition to the lumbar and intestinal trunks, the cisterna chyli may also receive lymph from smaller lymphatic vessels and channels that drain lymph from surrounding abdominal and retroperitoneal structures.
Anterior to the Vertebral Bodies
The cisterna chyli lies directly in front of the first and second lumbar vertebrae (L1 and L2). It is located slightly to the right of the midline of the body, just behind the abdominal aorta and inferior vena cava.
Posterior to the Right Crus of the Diaphragm
The cisterna chyli sits posterior to the right crus of the diaphragm, the muscular band that extends from the lumbar vertebrae to the diaphragm. This position is significant because the thoracic duct passes through the diaphragm via the aortic hiatus at the T12 vertebral level as it ascends from the cisterna chyli into the thoracic cavity.
Close to Major Blood Vessels
The cisterna chyli is situated near the abdominal aorta and the inferior vena cava, two major blood vessels that run through the retroperitoneal space. Its proximity to these vessels highlights its central location in the abdomen.
Relationship to the Thoracic Duct
The cisterna chyli is the origin point of the thoracic duct, the main conduit for lymph drainage from the majority of the body.
Beginning of the Thoracic Duct
The cisterna chyli continues superiorly as the thoracic duct, which is the largest lymphatic vessel in the body. The thoracic duct ascends through the aortic hiatus of the diaphragm into the thoracic cavity and eventually drains into the venous system at the junction of the left subclavian and internal jugular veins.
Path of the Thoracic Duct
From the cisterna chyli, the thoracic duct passes upward through the diaphragm at the level of T12, travels along the vertebral column, and enters the thorax. It continues to transport lymph from the lower half of the body and the left side of the upper body into the venous circulation.
Lymph Composition
The lymph collected in the cisterna chyli is typically rich in chyle, a milky white lymph that contains a high concentration of lipids absorbed from the small intestine.
Chyle Composition
Chyle is a mixture of lymph and emulsified fats that are absorbed from the intestines during digestion. It is carried to the cisterna chyli through the intestinal lymphatic trunks. Chyle contains triglycerides, fatty acids, and fat-soluble vitamins, which give it a distinctive milky appearance.
Lymph from the Lower Body
In addition to chyle, the cisterna chyli collects standard lymph from the lower limbs, pelvis, and other abdominal structures. This lymph contains immune cells (lymphocytes), waste products, and fluid that has been filtered out of the blood.
Variations in Anatomy
The size, shape, and location of the cisterna chyli can vary between individuals.
Absence or Smaller Size
In some individuals, the cisterna chyli may be absent, or it may be much smaller than usual. In such cases, the thoracic duct begins directly from the convergence of the lumbar and intestinal trunks without a well-defined cisterna chyli.
Accessory Lymphatic Vessels
In some cases, there may be accessory lymphatic vessels that drain into the cisterna chyli or bypass it entirely. These anatomical variations can alter the pattern of lymph flow but typically do not interfere with the overall function of the lymphatic system.
Function
The cisterna chyli plays a crucial role in the lymphatic system, acting as a collection point for lymph from the lower part of the body and the gastrointestinal tract before transporting it into the thoracic duct and eventually into the venous system. Its functions are integral to maintaining fluid balance, fat absorption, and immune surveillance. Below is a detailed description of the various functions of the cisterna chyli.
Collection of Lymph
The primary function of the cisterna chyli is to collect lymph from the lower half of the body. It serves as a reservoir where lymph from multiple lymphatic trunks converges before being transported to the thoracic duct.
Lymph from the Lower Limbs
The cisterna chyli receives lymph from the lumbar lymphatic trunks, which drain the lower limbs, pelvis, and associated structures. This lymph contains excess fluid, proteins, and waste products that are collected from tissues and returned to the circulatory system.
Lymph from the Gastrointestinal Tract
The cisterna chyli also collects lymph from the intestinal lymphatic trunks, which drain the stomach, intestines, pancreas, and other digestive organs. This lymph is rich in absorbed fats (chyle) from the small intestine, making the cisterna chyli a key component in fat absorption and transport.
Transport of Chyle (Fat-Rich Lymph)
The cisterna chyli plays an essential role in transporting chyle, a lymphatic fluid rich in fat, which is absorbed from the intestines during digestion.
Absorption of Dietary Fats
After fats are broken down in the digestive system, they are absorbed by specialized lymphatic vessels in the intestines called lacteals. These lacteals transport the fat-rich lymph (chyle) to the intestinal lymphatic trunks, which drain into the cisterna chyli.
Chyle Storage and Release
The cisterna chyli acts as a temporary storage chamber for chyle. When chyle enters the cisterna chyli from the intestinal trunks, it is held there until it is transported through the thoracic duct into the venous circulation. This ensures the efficient transport of dietary fats to the bloodstream, where they can be distributed throughout the body for use or storage.
Drainage of the Lower Body
The cisterna chyli is responsible for collecting and draining lymph from the lower limbs, pelvis, and abdominal organs, ensuring that excess interstitial fluid is returned to the bloodstream.
Lymph from the Lumbar Region
The cisterna chyli receives lymph from the right and left lumbar lymphatic trunks, which drain the lower back, kidneys, adrenal glands, and deeper structures of the abdominal wall. This ensures that the lymphatic system can effectively manage fluid balance and remove waste products from tissues.
Fluid Balance
By collecting lymph from the lower body and returning it to the circulation via the thoracic duct, the cisterna chyli plays a critical role in maintaining overall fluid balance in the body. It prevents the buildup of interstitial fluid (which can lead to edema) by transporting excess fluid back to the blood.
Pathway for Lymph Transport
The cisterna chyli is the starting point for the thoracic duct, the largest lymphatic vessel in the body, which transports lymph into the venous system.
Beginning of the Thoracic Duct
The cisterna chyli marks the origin of the thoracic duct, which ascends through the thorax and drains lymph into the venous system at the junction of the left subclavian and internal jugular veins. This pathway is essential for returning lymph to the bloodstream, ensuring proper fluid circulation.
Movement of Lymph
Lymph moves from the cisterna chyli into the thoracic duct through a combination of smooth muscle contractions in the walls of the lymphatic vessels and valves that prevent the backflow of lymph. The cisterna chyli plays an important role in ensuring that lymph flows smoothly from the lower body into the thoracic duct and then into the venous circulation.
Immunity and Immune Cell Transport
The cisterna chyli, like other lymphatic structures, plays a role in immune function by transporting immune cells and aiding in the removal of foreign particles from the body.
Transport of Immune Cells
Lymph passing through the cisterna chyli contains lymphocytes and other immune cells. These immune cells are critical for identifying and fighting infections or other foreign invaders. The cisterna chyli helps transport these cells from the lower body and gastrointestinal tract to the rest of the lymphatic system, where immune responses can be initiated.
Filtering of Lymph
Although the cisterna chyli itself is not a filtering organ like the lymph nodes, it collects lymph that has already passed through lymph nodes in the lower body. These lymph nodes filter out pathogens, debris, and foreign particles before the lymph reaches the cisterna chyli and is transported to the thoracic duct.
Fat Absorption and Distribution
The cisterna chyli plays a pivotal role in the absorption and distribution of dietary fats. This function is essential for transporting fats from the digestive system into the bloodstream.
Chyle Transport
Chyle, which is lymph rich in triglycerides, fatty acids, and fat-soluble vitamins, enters the cisterna chyli from the intestinal lymphatic trunks. The fats absorbed by the intestinal lacteals are crucial for energy storage and metabolism.
Distribution of Fat to the Bloodstream
After chyle is collected in the cisterna chyli, it travels through the thoracic duct and enters the bloodstream. From there, the fats are distributed to various tissues in the body, where they can be used for energy or stored for later use. This process is critical for maintaining proper nutritional status and metabolic function.
Lymphatic Fluid Circulation
The cisterna chyli is a critical point in the circulation of lymphatic fluid throughout the body, particularly in connecting the lower body lymphatics to the central lymphatic system.
Connection to Central Circulation
The cisterna chyli serves as the central collection point for lymph from the lower body, linking the peripheral lymphatic system with the thoracic duct, which connects to the central venous system. This connection ensures that lymph from the lower body, rich in immune cells, fats, and waste products, is efficiently returned to the bloodstream.
Flow Regulation
The cisterna chyli helps regulate the flow of lymph through its reservoir-like structure. It stores lymph temporarily, allowing for a smooth, controlled flow into the thoracic duct. This regulation prevents backflow and ensures that lymph moves steadily toward the venous system.
Response to Dietary Fat Intake
The cisterna chyli plays a significant role in responding to increased dietary fat intake by processing and transporting chyle from the gastrointestinal tract.
Postprandial Increase in Lymph Flow
After a meal high in fat, the volume of chyle entering the cisterna chyli increases. The cisterna chyli adapts to this by expanding slightly to accommodate the increased volume of lymph. This allows for efficient transport of the absorbed fats from the intestines to the bloodstream.
Nutrient Transport
The fats absorbed and transported through the cisterna chyli are essential for delivering fat-soluble vitamins (such as vitamins A, D, E, and K) to the body’s tissues. This function is important for maintaining proper nutritional balance and overall health.
Clinical Significance
The cisterna chyli is a crucial structure in the lymphatic system, as it serves as the main reservoir for lymph collected from the lower body and gastrointestinal tract before being transported to the thoracic duct. Clinically, conditions that affect the cisterna chyli or the thoracic duct can lead to significant health issues.
Chylous disorders, such as chylothorax (accumulation of chyle in the chest cavity), can occur due to damage or obstruction of the cisterna chyli or thoracic duct, often following trauma or surgery. This can result in the leakage of fat-rich lymph (chyle) into surrounding spaces, leading to respiratory distress or nutritional deficiencies. Lymphatic obstruction, which may be caused by tumors, infections, or surgical trauma, can lead to swelling (lymphedema) in the lower body due to impaired lymph drainage.
