Anatomy & Physiology I and II

Anatomy & Physiology Study Guide which supplies the frontal and parietal lobes of the brain; and (3) a middle cerebral artery, which supplies the mesencephalon and lateral surfaces of the cerebral hemispheres. The brain is extremely sensitive to modifications in blood supply. An interruption of blood flow for several seconds will produce unconsciousness, and after four minutes some permanent neural damage can occur. Such circulatory crises are rare because blood reaches the brain through the vertebral arteries as well as by way of the internal carotid arteries. The left and right vertebral arteries arise from the subclavian arteries and ascend within the transverse foramina of the cervical vertebrae. The vertebral arteries enter the cranium at the foramen magnum, where they fuse along the ventral surface of the medulla oblongata to form the basilar artery. The vertebral arteries and the basilar artery supply blood to the spinal cord, medulla oblongata, pons, and cerebellum before dividing into the posterior cerebral arteries, which in turn branch off into the posterior communicating arteries. The Descending Aorta The descending aorta is continuous with the aortic arch. The diaphragm divides the descending aorta into a superior thoracic aorta and an inferior abdominal aorta. The Thoracic Aorta The thoracic aorta starts at the level of vertebra T5 and penetrates the diaphragm at the level of vertebra T12. It travels within the mediastinum, on the posterior thoracic wall, slightly to the left of the vertebral column. This vessel supplies blood to branches that service the tissues and organs of the mediastinum, the muscles of the chest and the diaphragm, and the thoracic spinal cord. The divisions of the thoracic aorta are anatomically separated as either visceral or parietal: • Visceral branches supply the organs of the chest. The bronchial arteries supply the tissues of the lungs not involved in gas exchange, the pericardial arteries supply the pericardium, the esophageal arteries supply the esophagus, and the mediastinal arteries supply the tissues of the mediastinum. • Parietal branches supply the chest wall. The intercostal arteries supply the chest muscles and the vertebral column area, and the superior phrenic arteries deliver blood to the superior surface of the diaphragm, which separates the thoracic and abdominopelvic cavities. The Abdominal Aorta The abdominal aorta, which begins immediately inferior to the diaphragm, is a continuation of the thoracic aorta. Descending slightly to the left of the vertebral column, but posterior to the peritoneal cavity, the abdominal aorta is commonly surrounded by a cushion of adipose tissue. At the level of vertebra L4, it splits into two major arteries—the left and right common iliac arteries—that supply deep pelvic structures and the lower limbs. The region where the abdominal aorta splits is called the terminal segment of the aorta. The abdominal aorta delivers blood to all the abdominopelvic organs and structures. The abdominal aorta gives rise to three unpaired arteries: • The celiac trunk takes blood to the liver, stomach, and spleen. The celiac trunk divides into three branches: the left gastric artery, which supplies the stomach and the inferior portion of the esophagus; the splenic artery, which supplies the spleen and arteries to the stomach (left ©2018 Achieve Test Prep Page 269 of 367