Final answer:
Venous cannulae include venules, small vessels leading from capillaries, and veins, larger blood vessels with valves that carry blood toward the heart. The pulmonary veins are exceptional as they carry oxygenated blood to the heart.
Step-by-step explanation:
Two main types of venous cannulae are used in medical procedures: venules and veins. Venules are small vessels that lead away from capillaries and join to form larger veins. Veins, on the other hand, are larger blood vessels that carry blood toward the heart and are equipped with valves to prevent backflow, ensuring unidirectional blood flow. A specific example of veins that carry oxygenated blood instead of deoxygenated blood are the pulmonary veins. There are four pulmonary veins, which are unique as they carry oxygenated blood from the lungs to the left atrium of the heart.
The two largest veins in the body are the superior vena cava and the inferior vena cava, which carry deoxygenated blood from the upper and lower parts of the body, respectively, to the right atrium. These large veins are an essential part of the complex venous system, which includes the smallest veins, or venules, that lead from capillaries to the heart.