Final Answer:
The venous drainage above the pectinate line is to the systemic circulation, while below the pectinate line, it is to the portal circulation.
Step-by-step explanation:
In the anatomy of the an-al canal, the pectinate line demarcates a significant transition in venous drainage. Above the pectinate line, the venous blood drains into the systemic circulation. The superior rectal vein, a branch of the inferior mesenteric vein, is an example of a vessel draining above the pectinate line. Below the pectinate line, the venous blood drains into the portal circulation.
The inferior rectal veins, which drain into the internal iliac veins and eventually into the portal vein, are examples of vessels draining below the pectinate line. This difference in venous drainage is crucial clinically, as it influences the management of conditions such as hemorrhoids and an-al fissures.