What does a soap and water enema do physiologically to relieve constipation?

In normal intestinal function, the body pulls in fluids into the small intestines so the contents in that section becomes like mush. (A consistency like mashed up soup, or putting soup through a blender. But the body cannot permit all that fluid to stay, or every human would have constant diarrhea.

So when the mush reaches the large intestines, it must shuttle the fluid portion to the kidneys to filter. This comes out when we urinate. But the body must keep a balance in how much fluid it pushes to the kidneys, and how much it leaves in the large intestines. With the right balance, the mush changes to more firm stool, but soft because it has the right amount of fluid in it.

But lots of things can disrupt this balance. Most people do not drink enough water and fluids. We don't eat enough fiber or roughage, like vegetables. Fiber and roughage attracts more fluids in the intestines, so without it, when the body takes fluid from the large intestines, it makes stool harder and causes constipation. Also, not going to the bathroom to excrete stool on a regular basis (several times a week) means the body will continue to remove fluids and compact the stool.

All enemas, but especially soap and water enemas, cause the cells to move more fluids into the large intestine. This begins to soften the outer edge of the formed stool, to make it easier to pass or excrete. However, using any enema too frequently can cause the intestines to stop using their usual transport of fluids into and out of the intestines. A person could begin to have more frequent cramping, gas, and alternating diarrhea and hard stool. So it is important to ask your doctor how often you can use an enema. Also, it is absolutely essential to know how much soap to mix with the water, to prevent negative side effects.