Lymphatic System Anatomy

• The lymphatic system functions essentially as a drainage system.
• There is no circulation in the lymphatic system.
• It is critical for immunologic defenses against bacteria and viruses.
• It assists in the absorption and transport of dietary fat.
• Lymphatic or lymphoid tissues consist of connective tissue and large quantities of lymphocytes.
• Sites that produce lymphocytes include the thymus, lymph nodes, spleen, lymphatic nodules aggregated in walls of digestive track and myeloid tissue in red bone marrow.
• Lymphatic vessels are tubes that help the cardiovascular system remove tissue fluid from body tissue and bring the fluid back to the blood.
• Lymphatic vessels are in all tissues and organs except the central nervous system, eyeball, internal ear, epidermis of the skin, cartilage, and bone.
• Lymph is tissue fluid once it enters a lymphatic vessel.

Lymph Capillaries

• Fine vessels drain lymph from the tissues.
• They drain into small lymph vessels that unite to form large lymph vessels.
• Lymph vessels have a beaded look because of the presence of several valves during their passage.

Lymph Nodes

• These are small lymphatic tissue masses along the lymphatic vessel course.
• Lymph passes through it, which is then filtered on its way to the venous system.
• Lymph nodes filter lymph as it moves to the venous system.
• Afferent lymph vessels carry lymph to a lymph node.
• Efferent lymph vessels transport lymph out of a lymph node.
• The right lymphatic trunk drains into the junction of the right venous angle.
• The right lymphatic trunk drains lymph from body's the right upper quadrant.
• The thoracic duct releases lymph from the rest of the body.
• The thoracic duct ends into the left venous angle formed between the left internal jugular vein and left subclavian vein.
• The thoracic duct is about 45 cm long.
• It contains many valves and has a beaded look.
• It is the main lymphatic duct of the body.
• The thoracic duct drains all lymph vessels in the body except from the right side of the head and neck, right upper limb, right side of the chest, and the upper surface of the right lobe of the liver.
• The thoracic duct begins in the abdomen, behind the right crus of diaphragm, as a dilated sac, called cisterna chyli, at the level of L1, 2.
• The thoracic duct ascends through the aortic opening of the diaphragm on the right side of descending thoracic aorta.
• The thoracic duct crosses the median plane behind esophagus to reach its left border.
• It happens at the lower border of the body of the 4th thoracic vertebra (sternal angle).
• It runs upwards along the left edge of esophagus to enter the root of neck.
• It bends laterally behind carotid sheath and in front vertebral vessels.
• This happens at level of 7th cervical vertebra.
• It turns downward in front of phrenic nerve.
• It crosses the 1st part of the left subclavian artery.
• It ends in the neck.
• It begins in the left brachiocephalic vein.
• At the neck root, the thoracic duct receives the left jugular lymph trunk, the left subclavian lymph trunk, and the left bronchomediastinal lymph trunk.
• The thoracic duct takes to blood lymph from the lower limbs, pelvic cavity, abdominal cavity, left side of the thorax, left side of head and neck, and the left upper limb.
• The right lymphatic trunk is about 1½ inch (1.25 cm) long.
• It forms by union of the right jugular lymph trunk, the right subclavian lymph trunk, and right bronchomediastinal lymph trunk.
• The right lymphatic trunk drains the right side of the head and neck, the right upper limb, and the right side of the thorax.
• It ends as the beginning of the right brachiocephalic vein.

Spleen:

• Measuring 1 inch thick, 3 inches wide, 5 inches long, and weighing 7 ounces, with ribs 9-11 in relation.
• It has a reddish color.
• It is the body's largest lymphoid tissue mass.
• It is oval in shape.
• It lies just below the left half of the diaphragm close to 9th, 10th, and 11th ribs.
• The long axis lies along the shaft of the 10th rib.
• Its lower pole stretches forward only to the mid-axillary line.
• It cannot be felt on clinical examination.
• It features a notched anterior border.
• It is surrounded by peritoneum, which passes from its hilum as a gastrosplenic ligament to the greater stomach curvature, carrying short gastric and left gastroepiploic vessels.
• Peritoneum also passes to the left kidney as a lienorenal ligament, carrying splenic vessels and the tail of the pancreas.
• The anterior or visceral surface relates to the stomach, tail of the pancreas, left colic flexure, and left kidney.
• The posterior or diaphragmatic surface relates to the diaphragm, left pleura, left lung, and left 9th, 10th, and 11th ribs.
• The splenic artery enters the spleen at the hilum and is a branch off the celiac trunk.
• The splenic vein leaves the hilum and runs behind the tail and body of the pancreas to meet the superior mesenteric vein behind the neck of the pancreas to form the portal vein.
• Lymph vessels emerge from the hilum and pass through lymph nodes along the splenic artery, draining into celiac nodes.
• Nerves accompany the splenic artery and are derived from celiac plexus.

Thymus Gland

• It is the primary lymphoid organ.
• It has a flattened, bilobed shape with no main hilum.
• It sits between the sternum and pericardium in the front mediastinum.
• It has the biggest relative size of the body in a newborn child.
• It stretches into the superior mediastinum in front of great vessels into the neck root.
• It continues to grow until puberty, but later it undergoes involution.
• The thymus gland shows a pink, lobulated look.
• It is a site for forming T (thymic) lymphocytes (immunity).
• The thymus gland's arterial supply includes the inferior thyroid artery, internal thoracic artery, and superior thyroid artery sometimes.
• Venous drainage of thymus gland is done by left brachiocephalic vein, internal thoracic veins and inferior thyroid veins.
• There are no afferent lymphatics.
• Efferent vessels end into the brachiocephalic, tracheobronchial and parasternal nodes.
• The thymus gland is supplied by the sympathetic chain via the cervico-thoracic or stellate ganglion and vagus nerve (ANS).
• Branches from phrenic and descending cervical nerves go to its sensory capsule.

Lymph Nodes

• These are encapsulated areas of antigen presentation plus lymphocyte activation, differentiation, and proliferation.
• Lymph nodes produce mature, antigen-primed, B and T cells. They also filter particles, including microbes, from the lymph by the action of numerous phagocytic macrophages.
• A normal young adult body has around 450 lymph nodes, with 60-70 in the head and neck, 100 in the thorax, and up to 250 in the abdomen and pelvis.
• Lymph nodes are mainly found in the neck, mediastinum, back abdominal wall, abdominal mesenteries, pelvis, and nearby limb regions.
• The most reside near the internal organs, mainly in mesenteries.
• Lymph nodes are small, oval or kidney-shaped bodies between 0.1 and 2.5 cm long.
• Each has a hilum, where blood vessels enter and exit and efferent lymphatic vessels leave.
• Several afferent lymphatic lines go into the capsule all around the periphery.
• Their highly cellular cortex and the medulla contains tiny lymphatic canals where lymph passing the afferent lymphatics gets filtered, to be collected at the hilum by the efferent lymphatic.
• The arteries and veins travel through the hilum, emitting straight branches which cross deep inside the medulla, and delivering smaller branches.
• The cortex is absent at the hilum, with the medulla reaching the surface.
• Lymphatic vessels that transport lymph to a lymph node through the cortex are regarded as afferent vessels, and those transporting it out of a node via the hilum are efferent vessels.
• Veins remove a node through its primary trabeculae and capsule, draining them and the nearby connective tissue.
• Lymph nodes may enlarge from metastases or a primary tumor.
• For that reason, the lymphatic drainage of all major body organs, including the skin, must be known.