Science Fair Project Encyclopedia
Feces (also spelled faeces in British English, or fæces) are the waste products from the digestive tract expelled through the anus during defecation. In humans, defecation may occur (depending on the individual and the circumstances) from once every two or three days to three times a day. Prolonged interruption in the usual routine is called constipation.
The distinctive odor of feces is due to bacterial action. Bacteria produce compounds such as indole, skatole, and mercaptans, which are rich in sulfur, as well as the inorganic gas hydrogen sulfide. These are the same compounds that are responsible for the odor of flatulence.
The word faeces is the plural of the Latin word faex meaning "dregs".
Feces are also known as scat and scatology is the study of feces. Excrement is also another word for feces.
Feces are generally a taboo subject (see toilet humour). This is probably because of the need to keep feces well away from food, for health reasons. The word shit is a vulgar term for feces in English.
Meconium (also spelled merconium) is a newborn baby's first feces, and is normally passed post-partum. There is a danger that aspiration (inhalation) of meconium can occur if it is passed during labor and delivery. Inhaled meconium can cause a partial or complete blockage of the newborn's airways, and the severity depends on the amount of meconium the baby aspirates. Meconium aspiration affects around 20 percent of all newborn babies worldwide.
Laboratory testing of feces
In the medical profession, feces are referred to as stools. This comes from the Anglo-Saxon word stol, which means "seat". The word stool was originally used to describe the seat one sat on to defecate. So, the expression was that they were "going to stool." By the end of the 16th century, the word stool was used to mean the same thing as feces.
Feces will usually be required for microbiological testing, looking for an intestinal pathogen .
It is recommended that the clinician correlate the symptoms and submit specimens according to laboratory guidelines to obtain results that are clinically significant. Formed stools often do not give satisfactory results and suggest little of actual pathologic conditions.
Three main types of microbiological tests are commonly done on feces:
- Antibody-antigen type tests, that look for a specific virus (e.g. rotavirus).
- Microscopic examination for intestinal parasites and their ova (eggs).
- Routine culture.
Routine culture involves streaking the sample onto agar plates containing special additives, such as MacConkey's Agar , that will inhibit the growth of Gram-positive organisms and will selectively allow enteric pathogens to grow, and incubating them for a period, and observing the bacterial colonies that have grown.
Yellowing of feces can be caused by an infection known as giardia. Giardia are tiny parasitic organisms. If giardia infects the intestines it can cause severe yellow diarrhea. This is a dangerous communicable infection and must be reported.
Another cause of yellowing is a condition known as Gilbert's Syndrome. This condition is characterized by jaundice and hyperbilirubinemia. Hyperbilirubinemia occurs when too much bilirubin is present in the circulating blood.
Feces can be black if dried blood is present in them from a bleed. More active bleeding can lead feces to be red in color.
In children with certain illnesses, feces can be blue or green. Babies also produce green feces when they are given food for the first time.
The main pathogens that are commonly looked for in feces include:
- Salmonella and Shigella
- Yersinia (this tends to be incubated at 30°C, which is cooler than usual.)
- Campylobacter (incubated at 42°C, in a special environment.)
- Candida (if the person is immunosuppressed e.g. cancer treatment.)
- E. coli O157 (if blood is visible in the stool sample.)
External links and references
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