Chapter 81: Vascular & Lymphatic Systems Anatomy

Vascular & Lymphatic Systems Anatomy anatomical chapter details the vascular and lymphatic systems throughout the body, beginning with the arterial supply of the head and neck primarily via the common carotid arteries, which typically bifurcate at the thyroid cartilage into the external carotid, supplying the face and external head, and the internal carotid, supplying cranial and orbital contents. Specialized structures at this bifurcation include the carotid sinus, functioning as a baroreceptor (pressure sensor), and the carotid body, a chemoreceptor that regulates ventilation in response to blood gas changes. The internal carotid artery proceeds through cervical, petrous, cavernous, and cerebral segments, giving rise to the ophthalmic artery and its crucial branches, such as the central retinal artery, which is an end-artery supplying the inner retina. Intracranially, circulation to the cerebral hemispheres is managed by the large anterior and middle cerebral arteries (terminal branches of the internal carotid), complemented by the vertebrobasilar system (vertebral and basilar arteries), which supplies the brainstem and cerebellum. The anterior and posterior circulation pathways are interconnected via the circulus arteriosus (Circle of Willis), although anatomical variations mean this collateral route is rarely functionally complete. The spinal cord receives supply longitudinally from the anterior and posterior spinal arteries, reinforced segmentally by vessels like the essential Great Anterior Radiculomedullary Artery of Adamkiewicz, which, if compromised, threatens perfusion to the lower cord (T4–T9 critical zone). Moving inferiorly, the aortic arch branches into the brachiocephalic trunk, left common carotid, and left subclavian arteries, while the ascending aorta gives rise to the coronary arteries supplying the myocardium, noted for their numerous congenital variations and anastomoses. The abdominal aorta provides crucial visceral branches, including the coeliac trunk (supplying the foregut derivatives), the superior mesenteric artery (midgut), and the inferior mesenteric artery (hindgut). Paired lateral branches, such as the renal arteries, are critical systems providing roughly 20% of cardiac output to the kidneys. The lower extremity is supplied primarily by the femoral artery, with the profunda femoris artery being the main supply to the thigh musculature via its perforating and circumflex branches, participating in important collateral circuits like the cruciate anastomosis. Venous drainage of the brain occurs via the valveless dural venous sinuses (e.g., superior sagittal, cavernous), which connect to the extracranial circulation through emissary veins, posing a risk for infection spread, such as cavernous sinus thrombosis. Systemic venous return for the trunk is primarily through the superior and inferior vena cavae (SVC/IVC). The azygos, hemiazygos, and accessory hemiazygos systems provide a vital collateral path in IVC obstruction. The hepatic portal system, formed by the splenic and superior mesenteric veins, collects blood from the abdominal viscera for processing in the liver, and its obstruction can lead to clinically significant porto-systemic shunts, resulting in varices and caput medusae. Finally, the lymphatic system drains interstitial fluid, starting with superficial and deep networks, feeding into collecting vessels that eventually form the thoracic duct. This duct typically originates from the cisterna chyli (L1/L2 level), ascends through the thorax, and drains into the left venous circulation. Regional lymph node groups, such as the surgically classified deep cervical nodes (Levels Ia–VI) and the axillary nodes (draining the breast), reflect predictable pathways for metastatic disease dissemination, underlining the clinical importance of understanding vascular and lymphatic anatomy.