The lymphatic system, or lymphoid system, is an organ system in vertebrates that is part of the circulatory system and the immune system. It is made up of a large network of lymphatic vessels, lymphatic or lymphoid organs, and lymphoid tissues. The vessels carry a clear fluid called lymph towards the heart.
A lymph node, or lymph gland is a kidney-shaped organ of the lymphatic system, and the adaptive immune system. A large number of lymph nodes are linked throughout the body by the lymphatic vessels. They are major sites of lymphocytes that include B and T cells. Lymph nodes are important for the proper functioning of the immune system, acting as filters for foreign particles including cancer cells, but have no detoxification function.
In human anatomy, the thoracic duct is the larger of the two lymph ducts of the lymphatic system. It is also known as the left lymphatic duct, alimentary duct, chyliferous duct, and Van Hoorne's canal. The other duct is the right lymphatic duct. The thoracic duct carries chyle, a liquid containing both lymph and emulsified fats, rather than pure lymph. It also collects most of the lymph in the body other than from the right thorax, arm, head, and neck. The thoracic duct usually starts from the level of the twelfth thoracic vertebrae (T12) and extends to the root of the neck. It drains into the systemic (blood) circulation at the junction of the left subclavian and internal jugular veins, at the commencement of the brachiocephalic vein.
The periaortic lymph nodes are a group of lymph nodes that lie in front of the lumbar vertebrae near the aorta. These lymph nodes receive drainage from the gastrointestinal tract and the abdominal organs.
The cisterna chyli is a dilated sac at the lower end of the thoracic duct in most mammals into which lymph from the intestinal trunk and two lumbar lymphatic trunks flow. It receives fatty chyle from the intestines and thus acts as a conduit for the lipid products of digestion. It is the most common drainage trunk of most of the body's lymphatics. The cisterna chyli is a retro-peritoneal structure. In humans, it is located posterior to the abdominal aorta on the anterior aspect of the bodies of the first and second lumbar vertebrae. There it forms the beginning of the primary lymph vessel, the thoracic duct, which transports lymph and chyle from the abdomen via the aortic opening of the diaphragm up to the junction of left subclavian vein and internal jugular veins. In dogs, it is located to the left and often ventral to the aorta; in cats it is left and dorsal; in guinea pigs it runs to the left and drains into the left innominate vein.
The midgut is the portion of the embryo from which most of the intestines develop. After it bends around the superior mesenteric artery, it is called the "midgut loop". It comprises the portion of the alimentary canal from the end of the foregut at the opening of the bile duct to the hindgut, about two-thirds of the way through the transverse colon.
The external iliac lymph nodes are lymph nodes, from eight to ten in number, that lie along the external iliac vessels.
The tracheobronchial lymph nodes are lymph nodes that are located around the division of trachea and main bronchi.
The preaortic lymph nodes lie in front of the aorta, and may be divided into celiac lymph nodes, superior mesenteric lymph nodes, and inferior mesenteric lymph nodes groups, arranged around the origins of the corresponding arteries.
The inferior mesenteric lymph nodes consist of:
The internal iliac lymph nodes surround the internal iliac artery and its branches, and receive the lymphatics corresponding to the distribution of the branches of it, i. e., they receive lymphatics from all the pelvic viscera, from the deeper parts of the perineum, including the membranous and cavernous portions of the urethra, and from the buttock and back of the thigh. The internal iliac lymph nodes also drain the superior half of the rectum, above the pectinate line.
The lumbar trunks are formed by the union of the efferent vessels from the lateral aortic lymph nodes.
The intestinal trunk receives the lymph from the stomach and intestine, from the pancreas and spleen, and from the lower and front part of the liver, and empties lymph into the cisterna chyli, which in turn drains into the thoracic duct.
The mastoid lymph nodes are a small group of lymph nodes, usually two in number, located just beneath the ear, on the mastoid insertion of the sternocleidomastoideus muscle, beneath the posterior auricular muscle.
Supraclavicular lymph nodes are lymph nodes found above to the clavicle, that can be felt in the supraclavicular fossa. The supraclavicular lymph nodes on the left side are called Virchow's nodes.
The intercostal lymph nodes occupy the posterior parts of the intercostal spaces, in relation to the intercostal vessels.
The celiac lymph nodes are associated with the branches of the celiac artery. Other lymph nodes in the abdomen are associated with the superior and inferior mesenteric arteries. The celiac lymph nodes are grouped into three sets: the gastric, hepatic and splenic lymph nodes.
The splenic lymph nodes are found at the splenic hilum and in relation to the tail of the pancreas.
The gastric lymph nodes are lymph nodes which drain the stomach and consist of two sets, superior and inferior:
The scrotum is an anatomical male reproductive structure located caudal to the penis that consists of a suspended dual-chambered sack of skin and smooth muscle. It is present in most terrestrial male mammals. The scrotum contains the external spermatic fascia, testes, epididymis, and ductus deferens. It is a distention of the perineum and carries some abdominal tissues into its cavity including the testicular artery, testicular vein, and pampiniform plexus. The perineal raphe is a small, vertical, slightly raised ridge of scrotal skin under which is found the scrotal septum. It appears as a thin longitudinal line that runs front to back over the entire scrotum. In humans and some other mammals the scrotum becomes covered with pubic hair at puberty. The scrotum will usually tighten during penile erection and when exposed to cold temperature. One testis is typically lower than the other to avoid compression in the event of impact.
