In the United States, the carriers have effectively exited the tower business. Most sold their towers to companies like American Tower (AMT) and Crown Castle. These companies construct, maintain and operate the towers, and lease space to the carriers. Tower operators such as AMT actively seek to lease the same tower to multiple carriers, and this is a key metric of their financial success. A best-in-class tower operator will have 2-3 carrier tenants per tower.
The descending aorta is the part of the aorta beginning at the aortic arch that runs down through the chest and abdomen. The descending aorta anatomically consists of two portions or segments, the thoracic and the abdominal aorta, in correspondence with the two great cavities of the trunk in which it is situated.
The function of the aorta is to pump this new oxygen-rich blood from the left ventricle of the heart, where the oxygenated blood is deposited, and circulate it back into the body. The shape of the aorta assists with blood circulation. It has four main sections: the ascending aorta, the aortic arch, the descending thoracic aorta and the abdominal aorta. The ascending aorta begins at the semilunar valve of the left ventricle and connects to the coronary arteries.