Human feces


Human feces or faeces, commonly and in medical literature more often called stool, are the solid or semisolid remains of food that could not be digested or absorbed in the small intestine of humans, but has been further broken down by bacteria in the large intestine. It also contains bacteria and a relatively small amount of metabolic waste products such as bacterially altered bilirubin, and the dead epithelial cells from the lining of the gut. It is discharged through the anus during a process called defecation.
Human feces have similarities to the feces of other animals and varies significantly in appearance, according to the state of the diet, digestive system, and general health. Normally, human feces are semisolid, with a mucus coating. Small pieces of harder, less moist feces can sometimes be seen impacted in the distal end. This is a normal occurrence when a prior bowel movement is incomplete, and feces are returned from the rectum to the large intestine, where water is further absorbed.
Human feces together with human urine are collectively called human waste or excretion. Containing human feces and preventing spread of pathogens from human feces by the fecal–oral route are the main goals of sanitation.

Characteristics

Classification

The Bristol stool scale is a medical aid designed to classify the form of human feces into seven categories. Sometimes referred to in the UK as the Meyers Scale, it was developed by K.W. Heaton at the University of Bristol and was first published in the Scandinavian Journal of Gastroenterology in 1997. The form of the stool depends on the time it spends in the colon.
The seven types of stool are:
  1. Separate hard lumps, like nuts
  2. Sausage-shaped but lumpy
  3. Like a sausage but with cracks on the surface
  4. Like a sausage or snake, smooth and soft
  5. Soft blobs with clear-cut edges
  6. Fluffy pieces with ragged edges, a mushy stool
  7. Watery, no solid pieces. Entirely liquid
Types 1 and 2 indicate constipation. Types 3 and 4 are optimal, especially the latter, as these are the easiest to pass. Types 5–7 are associated with increasing tendency to diarrhea or urgency.
Meconium is a newborn infant's first feces.

Color

Human fecal matter varies significantly in appearance, depending on diet and health.

Brown

Black or red

Orange

Yellow

Green

Blue

Violet or purple

Pale or gray

Silver

Odor

Feces possesses physiological odor, which can vary according to diet and health status. For example, meat protein is rich in the amino acid methionine, which is a precursor of the sulfur-containing odorous compounds listed below. The odor of human feces is suggested to be made up from the following odorant volatiles:
is the most common volatile sulfur compound in feces. The odor of feces may be increased when various pathologies are present, including:
Attempts to reduce the odor of feces are largely based on animal research carried out with industrial applications, such as reduced environmental impact of pig farming. See also: Flatulence#Management, odor. Many dietary modifications/supplements have been researched, including:
On average, healthy humans eliminate 128 g of fresh feces per person per day with a pH value of around 6.6 as indicated by a Fecal pH test. Fresh feces contains around 75% water and the remaining solid fraction is 84–93% organic solids along with some insoluble phosphate salts.
These organic solids consist of: 25–54% bacterial biomass, 2–25% protein or nitrogenous matter, 25% carbohydrate or undigested plant matter, and 2–15% fat. Protein and fat come from the colon due to secretion, epithelial shedding, and gut bacterial action. These proportions vary considerably depending on many factors but mainly diet and body weight. The remaining solids are composed of insoluble calcium and iron phosphate salts, intestinal secretions, small amounts of dried epithelial cells, and mucus.

Undigested food remnants

Sometimes undigested food may make an appearance in feces. Common undigested foods found in human feces are seeds, nuts, and corn, mainly because of their high fiber content. Beets may turn feces different hues of red. Artificial food coloring in some processed foods, such as highly colorful packaged breakfast cereals, can cause an unusual coloring of feces if eaten in sufficient quantities.
Undigested objects such as seeds can pass through the human digestive system, and later germinate. One result of this is tomato plants growing where treated sewage sludge has been used as fertilizer.

Analytical tools

Stool analysis (stool sample)

Clinical laboratory examination of feces, usually termed as stool examination or stool test, is conducted for the sake of diagnosis; for example, to detect the presence of parasites such as pinworms and their eggs or to detect disease-spreading bacteria. A stool culture—the controlled growth of microbial organisms in culture media under laboratory conditions—sometimes is performed to identify specific pathogens in stool. The stool guaiac test is conducted to detect the presence of blood in stool that is not apparent to the unaided eye.
The main pathogens that are commonly looked for in feces include:
  • Bacteroides species
  • Salmonella and Shigella
  • Yersinia tends to be incubated at, which is cooler than usual
  • Campylobacter incubated at, in a special environment
  • Aeromonas
  • Candida if the person is immunosuppressed
  • E. coli O157 if blood is visible in the stool sample
  • Cryptosporidium
  • Entamoeba histolytica
Intestinal parasites and their ova can sometimes be visible to the naked eye.

Fecal markers

Feces can be analyzed for various markers that are indicative of various diseases and conditions. For example, fecal calprotectin levels indicate an inflammatory process such as Crohn's disease, ulcerative colitis, and neoplasms.
Also, feces may be analyzed for any fecal occult blood, which is indicative of a gastrointestinal bleeding.

Analysis of ''E. coli'' bacteria in water sources

A quick test for fecal contamination of water sources or soil is a check for the presence of E. coli bacteria performed with the help of MacConkey agar plates or Petri dishes. E. coli bacteria uniquely develop red colonies at temperature of approximately overnight. Although most strains of E. coli are harmless, their presence is indicative of fecal contamination, and hence an increased possibility of the presence of more dangerous organisms.
Fecal contamination of water sources is highly prevalent worldwide, accounting for the majority of unsafe drinking water. In developing countries most sewage is discharged without treatment. Even in developed countries events of sanitary sewer overflow are not uncommon and regularly pollute the Seine River and the River Thames, for example.

Diseases and conditions

Diarrhea

Diarrhea is the condition of having three or more loose or liquid bowel movements per day. This condition can be a symptom of injury, disease, or foodborne illness and is usually accompanied by abdominal pain. There are other conditions which involve some but not all of the symptoms of diarrhea, and so the formal medical definition of diarrhea involves defecation of more than 200 grams per day.
It occurs when insufficient fluid is absorbed by the colon. As part of the digestion process, or due to fluid intake, food is mixed with large amounts of water. Thus, digested food is essentially liquid prior to reaching the colon. The colon absorbs water, leaving the remaining material as a semisolid stool. If the colon is damaged or inflamed, however, absorption is inhibited, and watery stools result.
Diarrhea is most commonly caused by a myriad of viral infections but is also often the result of bacterial toxins and sometimes even infection. In sanitary living conditions and with ample food and water available, an otherwise healthy patient typically recovers from the common viral infections in a few days and at most a week. However, for ill or malnourished individuals diarrhea can lead to severe dehydration and can become life-threatening without treatment.

Constipation

Constipation refers to bowel movements that are infrequent or hard to pass. Constipation is a common cause of painful defecation. Severe constipation includes obstipation and fecal impaction, which can progress to bowel obstruction and become life-threatening.

Others

overload is very rare, and not a health threat. Problems as simple as serious diarrhea may cause blood in one's stool. Black stools caused by the presence of blood usually indicate a problem in the intestines, whereas red streaks of blood in stool usually are caused by bleeding in the rectum or anus.

Uses

Use as fertilizer

Human feces has historically been used as fertilizer for centuries in the form of night soil, fecal sludge, and sewage sludge. The use of untreated human feces in agriculture poses significant health risks and has contributed to widespread infection with parasitic worms—a disease called helminthiasis, affecting over 1.5 billion people in developing countries.
There are methods available to safely reuse human feces in agriculture as per the "multiple barrier concept" described by the World Health Organization in 2006. The approach to "close the loop" between human excreta and agriculture is also called ecological sanitation. It may involve certain types of dry toilets such as urine-diversion dry toilets or composting toilets.