Embodiments of a surgical access port system that comprises a retractor that is adapted for being coupled to a cap and that is particularly useful in natural orifice surgery are described. The retractor comprises an outer ring, wherein the outer ring is configured to be disposed proximate the natural orifice of the patient and substantially surround the orifice; a tubular body; a funnel segment extending between and coupling the outer ring and the tubular body, wherein the funnel segment provides a diametric reduction between the relatively large diameter of the outer ring and the relatively smaller diameter of the tubular body, which is sized to fit within a natural orifice with minimal distention of the orifice; and an inflatable member disposed around the distal end of the tubular body, the inflatable member sized and configured to fit snugly around the tubular body in the deflated condition and to expand against the wall of the natural orifice in the inflated state to thereby stabilize and retain the retractor within the orifice.