Final answer:
The epithelial lining above the pectinate line is primarily composed of simple columnar epithelium and is innervated by visceral sensory fibers, making it less sensitive to pain and suited for absorption. Below the pectinate line, the epithelium is stratified squamous and innervated by somatic sensory fibers, giving it increased sensitivity and a protective function.
Step-by-step explanation:
The epithelial lining of the gastrointestinal tract varies significantly above and below the pectinate line. Above the pectinate line, the epithelium is primarily composed of a sensitive simple columnar epithelium, which is less sensitive to pain due to innervation by visceral sensory fibers. This area of the epithelial lining is typically involved in the absorption of nutrients and production of mucus to facilitate the movement of feces.
Below the pectinate line, the epithelium changes to stratified squamous epithelium, which is much more sensitive due to somatic sensory fibers providing innervation. This region has to withstand more mechanical stress and therefore requires a more robust type of epithelial tissue. Additionally, the presence of sensory nerves makes this area quite sensitive to pain.
Thus, the epithelial tissue above the pectinate line is specialized for secretion and absorption, with reduced pain sensitivity, while the epithelium below is adapted to a protective role, with increased pain sensitivity.