What are the lymphatic vessels?
The lymphatic vessels are a part of the human’s circulatory system. They drain the fluid called the lymph from around the cells and carry it through the system of the lymph nodes and lymphatic ducts into the venous blood.
Afferent lymphatic vessels drain the lymph from the tissues toward the lymph nodes.
Efferent lymphatic vessels leave the lymph nodes and carry the lymph toward the subsequent lymph nodes or toward the lymphatic trunks and ducts and subsequently to the subclavian veins.
The deep lymphatic vessels usually follow the course of the arteries and the superficial ones the course of veins .
Lymphatic vessels do not drain the bone marrow, cartilage, teeth, epidermis, subcutaneous tissues, nails, hair, splenic pulp, eye sclera, cornea, retina and lens, joint spaces and the spaces between the two layers of the lung membrane (pleura), heart sac (pericardium) and abdominal membrane (peritoneum) [12,13,15,16].
It has been long believed that central nervous system does not have lymphatic vessels, but they have been recently discovered in the walls of the sinuses of the dura mater (the hard membrane of the brain) .
Healthy lymphatic vessels are not visible or palpable on the surface of the body. Inflamed lymphatic vessels can appear as tender red streaks on the inner (medial) sides of the legs or arms or on the lateral sides of the neck.
Lymphatic vessels :
- Return the interstitial fluid and proteins from around the cells in the form of lymph back to the blood
- Deliver the lymph to the lymph nodes, which remove foreign particles, microbes and cancer cells from it
- Transport lymphocytes from one node to another
- Transport the chyle–a mixture of the lymph and chylomicrons (made of triglycerides, cholesterol and protein absorbed from food in the small intestine)–to the venous blood
The smallest lymphatic vessels–lymphatic capillaries–begin as dead-end ducts. They have porous walls, so they can absorb the fluid from around the cells – the lymph .
Most lymph vessels are less than 1 mm thick. They have smooth muscles in the walls, which can contract and thus exhibit peristalsis, which results in the flow of the lymph from the tissues toward the subclavian veins . The contraction of the skeletal muscles in the limbs (muscle pump) and breathing (respiratory pump) probably also stimulate lymph flow . Like the veins, the lymphatic vessels have the valves that prevent the back-flow of the lymph .
Lymphatic Trunks and Ducts
The lymphatic trunks are smaller and the ducts are larger tubes that collect the lymph from the lymphatic vessels.
The jugular trunks are located on each side of the neck, laterally to the internal jugular veins . They collect the lymph from the lymph nodes in the head and neck, including the pharynx, larynx, thyroid and the upper part of the trachea and esophagus .
The left jugular trunk opens into the thoracic duct and the right one into the subclavian vein [1,10].
The subclavian trunks are located under the clavicles in front of the subclavian veins . They collect the lymph from the arms, chest and upper back wall and from the axillary nodes in the armpits .
The subclavian trunks open into the subclavian veins on each side .
The lumbar trunks are located on each side of the lumbar spine behind the aorta and ascending vena cava . They collect the lymph from the legs, genitalia, buttocks, prostate, testicles, uterus, ovaries, Fallopian tubes, bladder, abdominal wall bellow the belly button, the kidneys, adrenal glands and from the inguinal nodes in the groin .
The lumbar trunks open into the cisterna chyli .
The intestinal trunk opens into the cisterna chyli .
The bronchomediastinal trunks lie in the chest cavity (thorax) on each side of the upper thoracic spine. They collect the lymph from the lungs, pleura, heart, pericardium, esophagus, trachea, bronchi and the tissues between the lungs (mediastineum) .
The right bronchomediastinal trunk opens into the right lymphatic duct and the left bronchomediastinal trunk into the thoracic duct .
The cisterna chyli is a dilated sac, which represents the lower end of the thoracic duct. It lies vertically in front of the 2nd lumbar vertebra, behind the aorta and is 5-7 cm long . It receives the lymph from the lumbar and intestinal trunks, which drain the legs, pelvis and most of the abdominal organs .
The cisterna chyli can be detected by a CT and MRI; it is absent in more than 50% of individuals [5,8,11].
The thoracic duct is the largest lymphatic vessel, which lies in the thoracic cavity behind the aorta. It starts at the 1st to 3rd lumbar vertebra as a continuation of the cisterna chyli, travels up in front of the spine and then–from the 5th thoracic vertebra on–along the left border of the thoracic spine toward the root of the neck. Then it travels behind the aortic arc and opens into the junction of the left subclavian and internal jugular vein [7,8]. In adults, it is 38-45 cm long and 2-3 mm thick [8,10]. In some individuals, the thoracic duct can be partially doubled . Rarely (in ~4%) it lies on the right side of the aorta .
The thoracic duct drains the left part of the head and neck (via the left jugular trunk), the left side of the thoracic cavity–the left lung and heart–(via the left bronchomediastinal trunk) and the left arm (via the left subclavian trunk) .
The thoracic duct opens into the left subclavian vein.
Right Lymphatic Duct
The right lymphatic duct, which is about 1.2 cm long, opens into the right subclavian vein . It collects the lymph from the right jugular, bronchomediastinal and subclavian trunks, which drain the right part of the head and neck, the right lung and right arm .
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