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Anatomy of the anus and rectum

Defecation is the final act of digestion, by which organisms eliminate solid, semisolid, or liquid waste material from the digestive tract via the anus.

Humans expel feces with a frequency varying from a few times daily to a few times weekly.[1] Waves of muscular contraction (known as peristalsis) in the walls of the colon move fecal matter through the digestive tract towards the rectum. Undigested food may also be expelled this way, in a process called egestion.

Open defecation, the practice of defecating outside without using a toilet of any kind, is still widespread in some developing countries.[2]

Description

digestion, by which organisms eliminate solid, semisolid, or liquid waste material from the digestive tract via the anus.

Humans expel feces with a frequency varying from a few times daily to a few times weekly.[1] Waves of muscular contraction (known as Humans expel feces with a frequency varying from a few times daily to a few times weekly.[1] Waves of muscular contraction (known as peristalsis) in the walls of the colon move fecal matter through the digestive tract towards the rectum. Undigested food may also be expelled this way, in a process called egestion.

Open defecation, the practice of defecating outside without using a toilet of any kind, is still widespread in some developing countries.[2]

The rectum ampulla stores fecal waste (also called stool, or poo) before it is excreted. As the waste fills the rectum and expands the rectal walls, stretch receptors in the rectal walls stimulate the desire to defecate. This urge to defecate arises from the reflex contraction of rectal muscles, relaxation of the internal anal sphincter, and an initial contraction of the skeletal muscle of the external anal sphincter. If the urge is not acted upon, the material in the rectum is often returned to the colon by reverse peristalsis, where more water is absorbed and the faeces is stored until the next mass peristaltic movement of the transverse and descending colon.

When the rectum is full, an increase in pressure within the rectum forces apart the walls of the anal canal, allowing the fecal matter to enter the canal. The rectum shortens as material is forced into the anal canal and peristaltic waves push the feces out of the rectum. The internal and external anal sphincters along with the puborectalis muscle allow the feces to be passed by muscles pulling the anus up over the exiting feces.[citation needed]

Voluntary and involuntary control

Defecation may be involuntary or voluntary. Young children learn voluntary control through the process of toilet training. Once trained, loss of control, called fecal incontinence, may be caused by physical injury, nerve injury, prior surgeries (such as an episiotomy), constipation, diarrhea, loss of storage capacity in the rectum, intense fright, inflammatory bowel disease, psychological or neurological factors, childbirth, or death.[3]

Sometimes, due to the inability to control one's bowel movement or due to excessive fear, defecation (usually accompanied by urination) occurs involuntarily, soiling a person's undergarments. This may cause significant embarrassment to the person if this occurs in the presence of other people or in a public place.

Posture

The positions and modalities of defecation are culture-dependent. Squat toilets are used by the vast majority of the world, including most of Africa, Asia, and the Middle East.[4] The use of sit-down toilets in the Western world is a relatively recent development, beginning in the 19th century with the advent of indoor plumbing.[5]

Disease

Regular bowel movements determine the functionality and the health of the alimentary tracts in human body. Defecation is the most common regular bowel movement which eliminates waste from the human body. The frequency of defecation is hard to identify, which can vary from daily to weekly depending on individual bowel habits, the impact from the environment and genetic.[6] If defecation is delayed for a prolonged period the fecal matter may harden, resulting in constipation. If defecation occurs too fast, before excess liquid is absorbed, diarrhea may occur.[7] Other associated symptoms can include abdominal bloating, abdominal pain, and abdominal distention.[8] Disorders of the bowel can seriously impact quality of life and daily activities. The causes of functional bowel disorder are multifactorial, and dietary habits such as food intolerance and low fibre diet are considered to be the primary factors. [9]

Constipation

Constipation, also known as defecatory dysfunction, is the difficulty experienced when passing stools. It is one of the most notable alimentary disorders that affects different age groups in the population. The common constipation is associated with abdominal distention, pain or bloating.[10] Researches revealed that the chronic constipation complied with higher risk of cardiovascular events such as 'coronary heart disease and ischemic stroke', while associating with an increasing risk of mortality.[11] Besides the dietary factors, the psychological traumas and 'pelvic floor disorders' can also cause the chronic constipation and defecatory disorder respectively.[10] Multiple interventions, including physical activities, 'high-fibre diet', probiotics [12] and drug therapies can be widely and efficiently used to treat constipation and defecatory disorder.

Inflammatory bowel diseases

Inflammatory disease is characterized as a long-lasting chronic inflammatory throughout the gastrointestinal tract. Crohn's disease (CD) and ulcerative colitis (UC) are the two universal type of inflammatory bowel diseases that have been studied over a century, and they are closely related to different environmental risk factors, family genetic and people's lifestyle such that smoking is considered highly associated with these diseases.[13] Crohn's disease is discovered to be related to immune disorders particularly .[14] Different level of cumulative intestinal injuries can cause different complications, such as 'fistulae, damage of bowel function and symptoms reoccur, disability' etc.[15] The patient group can vary from children to adults. The newest research revealed that immunodeficiency and monogenic are the causes of young patients with inflammatory bowel diseases.[16] The onset rate keeps updating each year with dramatically increased number and the pathogen of the bowel disease are also complicated due to the complexity of the bowel organs, bowel diseases are diverse in terms of the small and big bowel.

Common symptoms for inflammatory bowel diseases differ by the infection level, but may include severe abdominal pain, diarrhoea, fatigue and unexpected weight loss. Crohn's disease can lead to infection of any part of the digestive tract, including ileum to anus.[17] Internal manifestations include diarrhoea, abdomen pain, fever, chronic anaemia etc. External manifestations include impact on skin, joints, eyes and liver. Significantly reduced 'microbat diversity' inside the gastrointestinal tract can also be observed. Ulcerative colitis mainly affects the function of the large bowel, and its incidence rate is three times larger than the Crohn's disease.[18] In terms of clinical features, over 90% of patients exhibited constant diarrhoea, 'rectal bleeding, softer and mucus in the stool, tenesmus and abdomen pain'.[18] At the same time, patient also reported to be having 'arthralgia, episcleritis and erythema nodosum'.[18] The symptoms can continue for around 6 weeks or even more than that.

The inflammatory bowel diseases could be effectively treated by 'pharmacotherapies' to relieve and maintain the symptoms, which showed in 'mucosal healing' and symptoms elimination.[19] However, an optimal therapy for curing both inflammatory diseases are still under research due to the heterogeneity in clinical feature.[19] Although both UC and CD are sharing similar symptoms, the medical treatment of them are distinctively different.[19] Dietary treatment can benefit for curing CD by increase the dietary zinc and fish intake, which is related to mucosal healing of the bowel.[14] Treatments vary from drug treatment to surgery based on the active level of the CD.

When the rectum is full, an increase in pressure within the rectum forces apart the walls of the anal canal, allowing the fecal matter to enter the canal. The rectum shortens as material is forced into the anal canal and peristaltic waves push the feces out of the rectum. The internal and external anal sphincters along with the puborectalis muscle allow the feces to be passed by muscles pulling the anus up over the exiting feces.[citation needed]

Defecation may be involuntary or voluntary. Young children learn voluntary control through the process of toilet training. Once trained, loss of control, called fecal incontinence, may be caused by physical injury, nerve injury, prior surgeries (such as an episiotomy), constipation, diarrhea, loss of storage capacity in the rectum, intense fright, inflammatory bowel disease, psychological or neurological factors, childbirth, or death.[3]

Sometimes, due to the inability to control one's bowel movement or due to excessive fear, defecation (usually acc

Sometimes, due to the inability to control one's bowel movement or due to excessive fear, defecation (usually accompanied by urination) occurs involuntarily, soiling a person's undergarments. This may cause significant embarrassment to the person if this occurs in the presence of other people or in a public place.

The positions and modalities of defecation are culture-dependent. Squat toilets are used by the vast majority of the world, including most of Africa, Asia, and the Middle East.[4] The use of sit-down toilets in the Western world is a relatively recent development, beginning in the 19th century with the advent of indoor plumbing.[5]

Disease

Regular bowel movements determine the functionality and the health of the alimentary tracts in human body. Defecation is the most common regular bowel movement which eliminates waste from the human body

Regular bowel movements determine the functionality and the health of the alimentary tracts in human body. Defecation is the most common regular bowel movement which eliminates waste from the human body. The frequency of defecation is hard to identify, which can vary from daily to weekly depending on individual bowel habits, the impact from the environment and genetic.[6] If defecation is delayed for a prolonged period the fecal matter may harden, resulting in constipation. If defecation occurs too fast, before excess liquid is absorbed, diarrhea may occur.[7] Other associated symptoms can include abdominal bloating, abdominal pain, and abdominal distention.[8] Disorders of the bowel can seriously impact quality of life and daily activities. The causes of functional bowel disorder are multifactorial, and dietary habits such as food intolerance and low fibre diet are considered to be the primary factors. [9]

ConstipationConstipation, also known as defecatory dysfunction, is the difficulty experienced when passing stools. It is one of the most notable alimentary disorders that affects different age groups in the population. The common constipation is associated with abdominal distention, pain or bloating.[10] Researches revealed that the chronic constipation complied with higher risk of cardiovascular events such as 'coronary heart disease and ischemic stroke', while associating with an increasing risk of mortality.[11] Besides the dietary factors, the psychological traumas and 'pelvic floor disorders' can also cause the chronic constipation and defecatory disorder respectively.[10] Multiple interventions, including physical activities, 'high-fibre diet', probiotics [12] and drug therapies can be widely and efficiently used to treat constipation and defecatory disorder.

Inflammatory bowel diseases