Anal Sphincter

Two sets of muscles separate the colon from the outside world. One is the internal anal sphincter muscle. The other is the external anal sphincter muscle. Known as the anus. As feces collects in the rectum it puts pressure on the internal anal sphincter muscle, where nerve endings send a message to the brain signaling its time to move your bowels. Ignoring the signal will generally end up causing constipation. Constipation can be from mild to severe depending upon how long you ignore the signal to have a bowel movement.

Anus

External Sphincter

anus,external anus sphincter

Remember that the anus has literally thousands upon thousands of nerve endings, and if you injure it, it is likely to be very painful. So great care must be taken whenever inserting anything into the anus. Anything with a sharp edge can scratch or cut the delicate anal tissue. Dealing with an anal fissure can be a long and very painful experience. You need to inspect, anything that you're going to insert into the anus for sharp or ragged edges to avoid injury.
The people that are most susceptible to anal injury are people with hemorrhoids. Hemorrhoid tissue is thinner and more susceptible to injury.

Many of us as we get older tend to have less muscle control than when we were younger. This holds true for the anus (anal sphincter muscle). Especially when have intestinal problems like diarrhea or taking an enema, trying to hold the nozzle and or the enema solution in. However, there are some products that can help us with this. One is the retention nozzle or a balloon catheter and the other is a retention plug.