. This explains why defecation is frequently accompanied by urination, and why urination is frequently accompanied by flatulence.

Defecation may be involuntary or under voluntary control. Young children learn voluntary control through the process of toilet training. Once this has been achieved, loss of control causing fecal incontinence may be caused by physical injury (such as damage to the anal sphincter that may result from an episiotomy), intense fright, excessive pressure placed upon the abdomen, inflammatory bowel disease, impaired water absorption in the colon (see diarrhea), and psychological or neurological factors.

The loss of voluntary control of defecation is experienced frequently by those undergoing a terminal illness.Joanne Lynn, MD. Merck.  October 2007.  Symptoms During a Fatal Illness.  Uploaded 3/1/09. 

Posture aspects

The positions and modalities of defecation are culture-dependent. The natural and instinctive method used by all primates, including humans for defecation, is the squatting position. Squat toilets, sometimes referred to as 'natural-position toilets', are still used by the vast majority of the world, including most of Africa, Asia and the Middle East.Kira A. The Bathroom. Harmondsworth: Penguin, 1976, revised edition, pp.115,116.  The widespread use of seated-position toilets in the Western World is a recent development, beginning in the 19th century with the advent of indoor plumbing.A History of Technology, Vol.IV: The Industrial Revolution, 1750-1850. (C. Singer, E Holmyard, A Hall, T. Williams eds) Oxford Clarendon Press, pps. 507-508, 1958

Bockus Gastroenterology, the standard textbook on the subject, states:
"The ideal posture for defecation is the squatting position, with the thighs flexed upon the abdomen. In this way the capacity of the abdominal cavity is greatly diminished and intra-abdominal pressure increased, thus encouraging expulsion ..."Bockus. Gastroenterology. p. 754 2nd ed. Saunders, Philadelphia and London, 1964

Other considerations
The anus and buttocks may be cleansed with toilet paper, similar paper products, or other absorbent material. In some cultures water is used (e.g. as with a bidet or Lota (vessel)) either in addition or exclusively. In Japan and South Korea, some toilets known as washlets are designed to wash and dry the anus of the user after defecation (see anal cleansing).

References

Deeb, Benjamin (2004).  "Healthy to the Core: How to Measure Effective Defecation."  Greenwood Press.
Widmaier, Raff, Strang (2006). "Vanders Human Physiology, the mechanisms of body function. Chapter 15. McGraw Hill.

Category:Digestive system
Category:Medical signs
Category:Proctology

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