Final answer:
A venous plexus includes multiple veins draining the same body region, such as the internal iliac vein draining into the common iliac vein. It applies to veins like ovarian or testicular ones linked to reproductive organs or lumbar veins draining into the inferior vena cava or azygos system.
Step-by-step explanation:
A venous plexus includes two or more veins draining the same body region. For example, the internal iliac vein drains the pelvic organs and integument and is formed from several smaller veins in the region, eventually flowing into the common iliac vein. A venous plexus can also refer to a generic term for a vein draining a reproductive organ; depending on the sex of the individual, this may be either an ovarian vein or a testicular vein. Additionally, major veins of the abdominal region involve large systemic veins such as the inferior vena cava, which drains blood from areas inferior to the diaphragm and empties into the right atrium. The lumbar veins, which drain the lumbar portion of the abdominal wall and spinal cord, flow into either the azygos vein on the right or the hemiazygos vein on the left, with remaining lumbar veins draining directly into the inferior vena cava.
The upper thoracic region's drainage into the superior vena cava is managed by a pair of veins that result from the fusion of the external and internal jugular veins with the subclavian vein. These include contributions from the subclavian, external and internal jugulars, vertebral, and internal thoracic veins.