Final answer:
The venous cannula drains deoxygenated blood from the superior and inferior venae cavae into a cardiopulmonary bypass machine during surgeries. It is crucial for procedures requiring the temporary cessation of heart function. Interstitial fluid is drained by the lymphatic system and enters the venous bloodstream near the right atrium.
Step-by-step explanation:
The venous cannula is a medical device used during surgeries to drain deoxygenated blood from the patient and return it to a cardiopulmonary bypass machine. The blood primarily drains from two major systemic veins, the superior and inferior venae cavae. The inferior vena cava drains blood from areas below the diaphragm, including the lower body and limbs, while the superior vena cava drains regions above the diaphragm such as the head, neck, upper limbs, and thoracic region.
The drained blood is then oxygenated and returned to the patient's body. This process is critical in heart surgeries where the heart needs to be stopped. Moreover, interstitial fluid, which is fluid between cells, may sometimes collect excess fluid, proteins, and waste products from the cells. This fluid is often drained into the lymphatic system, filtered through lymph nodes, and eventually returned to the bloodstream near the junction of the venae cavae and the right atrium of the heart.