Food is digested in the stomach, mainly through various digestive enzymes. The colon does not produce enzymes, only bacteria can digest them. There are many kinds of bacteria in the colon, including Escherichia coli 70%, anaerobic bacteria 20%, streptococcus, Proteus, staphylococcus, lactobacillus, spores and yeast. There are few protozoa and spirochetes. The important function of intestinal bacteria is to produce substances needed by physiology. For example, vitamin K, vitamin B 1, B2, vitamin H, vitamin B 12, B6, tretinoin, folic acid, racemic pantothenic acid, etc. can be synthesized in the intestine in the absence of vitamins in food. It can also produce indole, fecal odorant and hydrogen sulfide, which makes feces stink. If antibiotics are used for a long time, it is not easy to synthesize vitamins and cannot be absorbed, resulting in vitamin deficiency. Chyme passes through ileocecal valve to cecum every 24 hours, about 500~ 1000 ml. It is mainly absorbed in the right colon, mainly absorbing water and sodium, and can absorb 460 milliequivalents of sodium and 350~2000 ml of water every day. It also absorbs a small amount of potassium, chlorine, urea, glucose, amino acids, cholic acid and drugs. The rectum can also absorb water, a small amount of glucose, amino acids, milk and drugs. Intestinal dysfunction, enteritis and infection will all affect absorption. When diarrhea occurs, intestinal peristalsis increases, absorption decreases, and in severe cases, a lot of vitamins, water and electrolytes can be lost. If normal, feces will form in the sigmoid colon, waiting for excretion. [ 1]
The composition of feces is the same. Contains undigested cellulose, connective tissue and upper digestive tract secretions in food, such as mucus, bile pigment, mucin, digestive juice, digestive tract mucosal fragments, epithelial cells and bacteria. If you don't eat vegetables, the composition of coarse grain manure is often the same, that is, 65% moisture and 35% solid. The solid part of bacteria can reach up to 50%, but most of them are dead when they are discharged. The other 2-30% is nitrogen-containing substance, and10-20% is inorganic salt (calcium, iron and magnesium). Fat accounts for 10~20%, and there are two kinds. The decomposed fat is not absorbed by food, and the neutral fat comes from bacteria and epithelial debris. There are cholesterol, purine groups and a small amount of vitamins. Normal feces are cylindrical, with a length of 10 ~ 20cm, a diameter of 2 ~ 4cm and a weight of100 ~ 200 g. Protein's feces are brown or yellow, smelly, hard and lumpy, and contain many Gram-positive bacteria. The feces of edible carbohydrates are brown-green, smelly, soft or semi-liquid, acidic and contain many gram-negative bacteria. Normal feces are slightly brown, which is due to the existence of fecal bile and urinary bile. The color of feces varies with food, and some drugs can change the color. Normal is alkaline, and its level is directly proportional to the length of stay in the colon.
The gas in the colon is about 100 ml, 60% nitrogen, 10% carbon dioxide, 25% methane, 5% hydrogen sulfide and a little oxygen. The smell varies with the composition of food and gas. For example, excessive hydrogen sulfide can cause thiohemoglobin, and cyanosis is enterogenous cyanosis. The source of these gases is mainly air swallowed with diet and breathing, accounting for 70%. In addition, bacteria ferment carbohydrates, beans, Chinese cabbage and onions to produce more gas. Some gases produced by bacterial fermentation can be burned, with hydrogen up to 20.9% and methane up to 7.2%. Pay attention to the explosion caused by electrocautery. Intestinal gas can slightly dilate the colon and help peristalsis. The more gas there is, the more active the intestine is, and there is a slight crackling sound in the abdomen. Excessive gas will dilate the intestinal wall, pull the nerve and cause pain. Continued expansion will press the blood vessels in the intestinal wall, hinder absorption, further flatulence, and form a vicious circle. Intestinal gas burps upward from esophagus and downward from anus, and is sucked into the blood circulation in intestine. There are goblet cells in rectal mucosa, which secrete alkaline mucus to protect mucosa, lubricate feces and help defecation. The more distal secretions, the more rectal secretions. Chemical and mechanical stimulation can increase mucus secretion, such as rectal villous papilloma, which often secretes a lot of mucus. The anal gland also secretes glandular body fluids, which remain in the anal sinus and are squeezed out from the unobstructed stool during defecation, which is convenient for excretion. Some cells secrete hormones such as vasoactive intestinal peptide, which can stimulate the secretion of intestinal fluid and relax intestinal muscles.
Normally discharged feces are cylindrical, with a length of 10 ~ 20cm, a diameter of 2 ~ 4cm and a weight of100 ~ 200 g. Normal feces are alkaline, and its alkalinity is related to the length of stay in the colon. The longer the time, the higher the alkalinity. On the contrary, thin feces have a short retention time and are often acidic, which can stimulate the skin around the anus. Generally, normal feces are brown, because feces contain fecal bile pigment and urobilin. Due to different foods, feces have also changed. For example, the feces rich in food in protein are smelly, slightly hard, lumpy, slightly yellowish brown or yellowish in color, and most of them contain Gram-positive bacteria; Feces that eat carbohydrate-rich foods are brown-green, smelly, soft or semi-liquid, acidic, and most bacteria are gram-negative. Some drugs can also change the color of feces. [ 1]
Food residues are in the large intestine, and some water and electrolytes are absorbed by the mucosa of the large intestine. After the bacteria ferment and rot, they turn into feces and are excreted. Feces contain undigested cellulose in food, epithelial cells shed from digestive tract, mucosal fragments and a large number of bacteria, as well as undigested digestive tract secretions, such as mucus, bile pigment, mucin and digestive juice. If you don't eat vegetables and miscellaneous grains, the composition of feces is always the same, that is, 65% water and 35% solid. The bacteria in solid part are the most, accounting for 1/3- 1/2 of the total. When the feces are discharged, most of the bacteria have died. There are also 2%-3% nitrogen-containing substances and 10%-20% inorganic salts, such as calcium, iron and magnesium salts. Fat accounts for 10%-20%, one is decomposed fat that is not absorbed, the other is neutral fat from bacteria and epithelial debris, and there are a small amount of cholesterol, purine groups and vitamins. Generally, normal feces are brown, because feces contain fecal bile pigment and urobilin.