What is Feces?
Feces or human excrement is the waste material remaining after the digestion of food and absorption of nutrients which is passed out through the anus. It also contains water, some breakdown products of normal metabolic activity, indigestible material and residual nutrients that have not been absorbed. Feces or fecal matter is also referred to as stool or poo.
Feces (UK ~ faeces) is the waste material passed out from the bowels through the anus. It is usually solid to semi-solid in consistency but can be hard in constipation or watery with diarrhea. Fecal matter is also referred to as stool and the process of passing feces is known as defecation or bowel movement.
Formation of Feces
Fluid to Solid Feces
Fecal matter is the remaining material after food is digested along with water, bacteria and other substances secreted into the gastrointestinal tract. About 1.5 liters of fluid chyme passes from the small intestine into the large intestine each day. Most of the nutrients from the food has been absorbed at this stage.
As the chyme moves through the first half of the colon, large amounts of water and electrolytes are absorbed. Despite this, water makes up about 70% of the fecal weight. Water absorption transforms the fluid chyme into a mush-like consistency by the time it passes through the transverse colon. It solidifies further along its passage down the descending colon.
The bacteria in the colon play integral roles in nutrient absorption and the formation of feces. Colonic bacteria digest cellulose thereby releasing residual nutrients which are absorbed by the colon. In addition, the action of colonic bacteria contribute to the formation and absorption of vitamin B12, thiamin, riboflavin and vitamin K. The bacteria also produce the gases, carbon dioxide, hydrogen and methane, which make up flatus.The action of the bacteria plays a major part in determining the color and odor of fecal matter.
Water and Electrolytes in the Colon
Electrolytes like bicarbonate are secreted by the wall of the large intestine into the lumen. This helps to neutralize any acidic byproducts of bacterial metabolism. At the same time sodium and chloride are absorbed by the intestinal wall which creates a concentration gradient to facilitate water absorption.
However, the large intestine can only absorb about 8 liters of water in a day. Any extra fluid will remain in the colon, giving a liquid consistency to the feces (loose stool). It also creates additional bulk and increases defecation frequency by triggering the local defecation reflex. This is seen as watery diarrhea. Excess or a deficiency of water will also change the consistency of the stool as outlined in the Bristol Stool Chart which features the different types of feces.
Composition of Feces
About 75% of fecal weight is made up of water. The other 25% is composed of solid matter which contains :
- Undigested fiber and solidified components of digestive juices (30%)
- Bacteria (30%)
- Fat (10% to 20%)
- Inorganic matter (10% to 20%)
- Protein (2% to 3%)
Color of Feces
Feces usually has a brown color, ranging from a tan hue to a darker-brown color. Bilirubin is passed out in the bile and the action of bacteria and air in the gut breaks it down into stercobilin and urobilin, which gives stool its typical color. Additionally, certain foods with a strong colorants or other staining agents may also influence the color of feces.
Odor of Feces
The odor of feces may differ among people and is influenced significantly by the foods that are consumed. The gas byproducts of bacterial action in the colon largely accounts for the odor of the feces. Hydrogen sulphide is one of the most prominent odoriferous compounds responsible for the characteristic smell of the stool. Other compounds like indole, skatole and mercaptans are also responsible for the odor.
Types of Stool
Understanding the shape and consistency of stools is important to identify any changes which may be indicative of gastrointestinal disorders, nutritional disturbances and other systemic diseases which may affect bowel movements.
The Bristol Stool Chart is a convenient method to assess the consistency of stool and identifying normal or healthy stool forms from those that may be indicative of an underlying disorder. This scale identifies seven types of stool forms. Refer to the picture below for a graphical representation of the types of stool.
- Separate hard lumps, like nuts.
- Hard to pass.
- Sausage shape but lumpy.
- Like a sausage but with cracks on the surface.
- Like a sausage or snake, smooth and soft.
- Soft blobs with clear cut edges.
- Passed easily.
- Fluffy pieces with ragged edges.
- A mushy stool.
- Watery with no solid pieces.
- Entirely liquid.
Source : Wikimedia Commons
Bristol Stool Chart developed at the University of Bristol, United Kingdom
Hard Bowel Movements
Hard stool may be related to constipation. The stool is very firm to hard, passes out with difficulty (discomfort, pain, straining) and is not passed out frequently. The fecal matter becomes hard due to a low water content and may have been in transit through the bowels for too long. It is often linked to low fluid consumption and low fiber intake and associated with types 1 and 2.
Other gastrointestinal, nutritional and systemic disorders may cause hard bowel movements and constipation.
Normal Bowel Movements
A normal bowel movement is the evacuation of feces anywhere between once daily to 3 times a week. As long as the stool consistency and form is normal (type 3 and 4), it may not be a problem if a person does not pass stool on a daily basis. The color varies from tan to brown to dark brown,
Loose Bowel Movements
Loose stool may be related to diarrhea. The stool is very soft to watery, passes out easily and more frequently than normal. Blood and mucus may sometimes be found in the stool. The fecal matter becomes hard due to poor absorption of water from the bowels, malabsorption syndromes, rapid movement through the gut, the presence of pathogenic bacteria (“bad bacteria”) or low populations of normal intestinal flora(“good bacteria”).
Other gastrointestinal, nutritional and systemic disorders may cause loose bowel movements and diarrhea.
Constipation and Hard Stool
- What is Constipation?
- What Causes Constipation?
- Types of Constipation
- Chronic Constipation
- Foods that Cause Constipation
Diarrhea and Loose Stool
- Definition of Diarrhea
- Causes of Acute Diarrhea
- Causes of Chronic Diarrhea
- HIV Diarrhea
- Antibiotic Associated Diarrhea
- Diarrhea Induced by Drugs, Remedies or Other Medication
- Foods Causing Diarrhea
Different Colors of Stools and Diarrhea
- Black Bowel Movement
- Green Bowel Movement
- Orange Bowel Movement
- Pale, Clay, Gray or White Bowel Movement
- Yellow Bowel Movement
Last updated on 9 August 2018.