Question

Thoracic duct in humans is associated with
A. Aorta
B. Hepatic duct
C. Purkinje fibre
D. Innominate vein

Answer 1

Thoracic duct in humans is the largest lymphatic duct of the lymphatic system. It collects most of the lymph in the body, its transportation is mainly due to the action of breathing. The other large duct which comes after the thoracic duct is the right lymphatic duct which has its role in transporting lymph.

Complete answer:
The thoracic duct in humans originates in the abdomen from the junction of the right and the left lumbar trunks and the intestinal trunk, it forms a pathway upward called the cisterna chyli. It is normally 38-45 cm in length and with a diameter of 5mm. It generally starts with the twelfth thoracic vertebrae and extends to the root of the neck. Its main function is to drain into the blood circulation. On the right side of the neck the right lymphatic duct passes the lymph from head and neck, the upper extremity and the right side of the thorax to the right innominate vein.

Lymphatic ducts empty the fluid which is called lymph into the venous system. The wall of thoracic duct is made up of three layers and those are : The intima, the media and the adventitia it also consist of basement membrane. The middle layer which is called the media is made up of smooth muscle and connective tissue. The contraction of these smooth muscles is responsible for flow of lymph forward.

Hence, the correct answer is option (D).

Note: It is to be noted that about 75% of lymph is passed through lymphatic duct. It is also known as the principal channel for lymph transportation. The thoracic duct drains the lymph from both the lower limbs, abdomen, left face and neck, left hemithorax.