The process of (i)______ is modulated by long powerful waves of contractions of the (ii)______. Once the rectum is filled to 25% of its capacity, a (iii)______ stimulates the desire to defecate. In response to this, we voluntarily relax the external (iv)______ to allow feces to pass from the rectum into the anal canal and out through the anus.
i. Egestion or Defecation ii. Colon iii. Neural reflex iv. Anal sphincter