Humans and pigs have the same types of jugular veins, which total three pairs. The external jugular veins collect blood from the neck, face and the outer parts of the cranium. They are linked to the subclavian veins, which branch out to the arms in humans and front limbs in pigs. A pair of internal jugular veins are also connected to the subclavian veins, and mainly collect blood from the brain.
Jugular veins play an important role in systemic circulation, which is responsible for the collection of carbon dioxide from cells. Although jugular veins do not transport deoxygenated blood directly into the heart, they provide a vital link within the systemic circulatory system; they connect the brain and other organs located in the head with the heart and the lungs, the final destination of the carbon dioxide dissolved in the blood.
Jugular veins of humans and pigs are made of an outer layer of connective tissue, which is called tunica externa. Muscle tissue or tunica media is a deeper and thinner constitutive layer present in jugular veins. The innermost layer or tunica intima is made of endothelial cells, a specialized cell type only found in blood vessels.
In humans, pigs and most mammals, infections and tumors in the head and neck can lead to thrombosis of the internal jugular, a life-threatening complication. Thrombosis is the formation of blood clots, which can obstruct the blood flow and cause hypoxia or lack of oxygen in the body tissues. The condition is difficult to diagnose, especially in animals. Sometimes, a sharp pain in the neck is the only symptom.