What is feces?
Feces are unabsorbed food residues.
For unabsorbed residues, the digestive tract passes through the large intestine and is discharged from the anus in the form of feces.
Formation of feces
Food is digested in the stomach and small intestine mainly by 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.
Fecal composition
The formation of feces has no important relationship with food, and there is no significant difference between fasting and normal feeding animals, but the amount of feces is reduced. 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 loose stool is acidic, which will irritate the skin around the anus and cause pain. Eating Chili or drinking alcohol can cause anorectal reactive congestion, which can lead to an acute attack of hemorrhoids.
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 compress 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 for easy 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.
clarify
After the feces are formed, the peristalsis of the colon shrinks all parts of the colon and pushes the feces to the distal colon. This kind of peristalsis often starts from the liver curvature, 2~3 times a day, and advances to the left colon at a speed of 1~2 cm per minute, and then stores in the sigmoid colon. However, after eating or getting up in the morning, the total peristalsis of the colon is caused by gastrocolonic reflex or posture reflex, which advances at the speed of 10 cm per hour. If there is feces in the sigmoid colon, it can make feces enter the rectum, and when it accumulates enough (about 300 grams), it will cause defecation reflex.
Defecation reflex is a complex comprehensive action, including involuntary low-level reflex and involuntary high-level reflex activity. Usually the rectum is empty. When feces fills the rectum, it stimulates the intestinal wall receptors, sends an impulse to the low-level defecation center in the lumbosacral spinal cord, and at the same time uploads it to the cerebral cortex to produce defecation. If the environment permits, the cerebral cortex sends out impulses to make the defecation center excited and enhance, resulting in expulsion reflex, which makes the sigmoid colon and rectum contract and the anal sphincter relax. At the same time, we should consciously inhale deeply, close the glottis, increase chest pressure, reduce diaphragm contraction of abdominal muscles, increase intra-abdominal pressure, and promote fecal excretion. If the environment does not allow, there will be impulses from the lower abdominal nerve and pudendal nerve to contract the external sphincter of anal canal at will to prevent feces from being discharged. The contraction force of external sphincter is 30%-60% greater than that of internal sphincter, so it can prevent feces from being discharged from anus and antagonize defecation reflex. After a period of time, the feces in the rectum return to sigmoid colon or descending colon, which is a protective inhibition. However, if defecation is often inhibited, the rectum will gradually lose its sensitivity to fecal pressure stimulation and lose its sense of defecation. In addition, if the feces stay in the large intestine for too long, the water will become dry and hard, which will lead to difficulty in defecation, which is also one of the reasons for constipation. Defecation can be delayed at will, so we should also develop the habit of regular defecation. Both the standing reflex when people get up in the morning and the gastrocolon reflex after breakfast can promote the peristalsis of colon group and produce defecation reflex. Therefore, regular defecation in the morning or after breakfast meets the physiological requirements and is of great significance to prevent anorectal diseases. It is necessary to form a normal reflex of defecation after getting up or after meals, and do not consciously inhibit defecation unless the environment does not allow it. When a link of defecation reflex arc is destroyed, such as cutting off the intestinal segment of 4~5 cm on the tooth line, damaging the lumbosacral spinal cord or pudendal nerve, and breaking the anorectal ring, it will lead to defecation reflex disorder and fecal incontinence.
Normal people's rectum has a certain threshold for the pressure stimulation of feces. When this threshold is reached, defecation will occur. It can occur when 100ml feces fills the rectum by 25%, or when the pressure in the rectum reaches about 2.4kPa. In order to reach the point where defecation is needed, the rectal contents and pressure must be tripled. However, defecation depends on whether the function of the superior defecation center to the lower defecation center is inhibited or enhanced.
The frequency and habit of defecation vary from person to person, generally one day/kloc-0 times, defecation after breakfast. There is 1 time for 3 ~ 5 days or longer, but I don't feel difficult to defecate. Feel comfortable and happy after defecation. Therefore, the change of constipation, diarrhea or defecation law can not be determined only by the number of defecation, but by everyone's defecation habits.
How is defecation controlled?
Because human defecation reflex is controlled by cerebral cortex, consciousness can control defecation. The anus keeps a certain tension, so that the anus can be closed and feces, liquid and gas can be prevented from leaking out. This function is called defecation control. The function of defecation control is completed by sensation, reflex and muscle activity, which is a complex reflex activity. Can be summarized into two types.
(1) Reservoir control function (colon control function):
The control function of colon is independent of sphincter function. Colon, especially sigmoid colon, has adaptive response, which can adjust the volume and pressure in intestinal cavity. The pressure changes with the volume of intestinal cavity, which can prevent the pressure from being too high and delay the passage of intestinal contents. The resistance, bending and folding at the junction of rectum and sigmoid colon can delay the entry of feces into rectum and make rectum in a state of emptying and deflation at ordinary times. The left colon can accumulate a certain amount of feces. If it exceeds a certain amount, it can stimulate the colon and make feces enter the rectum. Patients with sigmoidostomy can form the habit of defecation if they eat properly and enema every day, which is due to the control function of colon.
The rectum is a sensory and expandable reservoir, which has the greatest tolerance to volume and can accumulate feces and liquids. The rectal flap can make feces spiral in the rectum, make the pressure of feces equal, prevent feces from accumulating in the lower part of the rectum, and prevent it from going straight through the rectum, thus playing a corresponding role in controlling feces discharge.
(2) Sphincter control:
It is the function of anal sphincter to resist colon peristalsis and push forward. The contraction force of sphincter must be better than the propulsion force of colon to control it. If you can't beat the push, it's anal dysfunction. Internal sphincter is the most important factor to resist defecation, and it is often in a state of continuous tension and contraction to control defecation activities; The external sphincter is also in a state of contraction, and the anal canal is closed. The contraction force of external sphincter is 30% ~ 60% higher than that of internal sphincter, so it can prevent feces from flowing out of anus. If the external sphincter loses tension, anal dysfunction will occur.
In defecation control activities, the functions of voluntary external sphincter, puborectal muscle and levator ani are interrelated and combined with the functions of voluntary internal sphincter and longitudinal muscle. For example, the contraction of external sphincter can inhibit the reflex relaxation of internal sphincter on detrusor contraction, which is called random inhibition. At the same time, levator ani's gastric fundus loop contracts and tightens, which inhibits the contraction of longitudinal muscle. The contraction of puborectal muscle reduces the right angle of anus, increases the pressure of lower rectum, prevents feces from entering anal canal, and plays a role in controlling defecation.
Because consciousness can control defecation, normal people also have the ability to control defecation. If the environmental conditions do not allow, when defecation is impossible, the downward impulse of the defecation center at the higher level inhibits the defecation center at the lower level, which makes the sphincter contraction strengthen, the anus closes like a non-return door, which reflexively relaxes the sigmoid colon, and the feces in the rectum flow back to the sigmoid colon, so that defecation temporarily disappears. However, if defecation is inhibited frequently or for a long time, the sensitivity of rectum to fecal stimulation can be reduced or disappeared, and the feces will stay in the large intestine for too long, which may lead to constipation.
What factors will affect defecation reflex?
There are many factors that affect defecation reflex, mainly in the following aspects:
(1) The amount of feces entering the rectum is too small, and the pressure on the rectal wall is insufficient, so that the receptors in the rectal wall are not impulsive, so there is no defecation reflex. This situation is more common in people who eat too little and eat too carefully.
(2) The rectum has lost its normal sensitivity to the pressure stimulation in the intestinal cavity, so it can't produce impulse. This situation can be seen in people who do not defecate in time for a long time, often enema or abuse laxatives.
(3) Nerve or spinal cord injury, such as polyradiculitis, paraplegia and other diseases, damages the nerve that conducts impulses and cannot produce defecation reflex.
What are the factors that affect the defecation process?
Although there are many factors that affect the defecation process, there are two kinds in summary. One is the factors that affect defecation, and the other is the factors that affect rectal emptying. The former has been introduced in the topic "Factors affecting defecation reflex" and will not be repeated here. Factors affecting rectal emptying are as follows:
(1) The inhibitory effects of the cerebral cortex on defecation, such as work stress, travel, changes in life patterns, depression and overwork, will all inhibit defecation. In addition, local rectal lesions such as hemorrhoids and anal fissure can cause defecation pain and inhibit brain defecation.
(2) Defecation is weak, such as the elderly and people who have been ill for a long time. Because the contraction of diaphragm, abdominal muscle and intestinal smooth muscle is weak, they lack the motivation to promote feces.
What is the difference between normal defecation?
The defecation situation of normal people is very different, which is related to individual differences, living habits, especially eating habits. Under normal circumstances, normal people defecate 1 ~ 2 times a day, some defecate once every 2 ~ 3 days (as long as there is no discomfort such as difficulty in defecation), but most people (about 60%) defecate once a day.
Chinese medicine also discusses the defecation frequency of normal people: "The stomach is a sea of water and valleys, and it is normal to be exposed to its new changes every day."
What diseases can different characteristics of stool reflect?
It is of great significance to know the frequency and time of defecation, the quantity, color, quality, smell, feeling and accompanying symptoms of defecation.
★ Constipation with high fever and irritability is intestinal heat syndrome;
★ Those with pale complexion and deep pulse are cold and secret, which is intestinal cold;
★ Constipation and thready pulse in the elderly belong to spleen yin deficiency;
★ Diarrhea of stool, less abdominal distension is spleen-yang deficiency;
★ Abdominal pain is diarrhea, the pain is relieved after diarrhea, and nausea and decay are eating disorders;
★ Emotional depression, abdominal pain, poor defecation, liver depression affected by spleen;
★ Abdominal pain and diarrhea before dawn are spleen and kidney yang deficiency;
★ When defecating, the anus is burning, which is damp and hot in the large intestine;
★ Acute internal tightening is followed by severe internal tightening, which is seen in dysentery and proctoptosis. It belongs to damp evil or spleen deficiency and qi stagnation in the large intestine, and bloody stool is close to blood, which is large intestine bleeding or hemorrhoids.
★ Dark or tar-like blood is distant blood, mostly bleeding from esophagus, stomach and duodenum.
★ Irritable bowel syndrome is characterized by stool as hard as sheep dung, accompanied by paroxysmal abdominal pain, which can be temporarily relieved after defecation, with mucus in the stool and no purulent blood;
★ The fecal shape of colorectal cancer continues to become thinner, and there may be blood on the fecal surface;
★ Congenital Hirschsprung's disease is more common in newborns, characterized by decreased fetal feces after birth, or persistent constipation and abdominal distension.
Food is digested in the stomach and small intestine mainly by 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.
The formation of feces has no important relationship with food, and there is no significant difference between fasting and normal feeding animals, but the amount of feces is reduced. 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 loose stool is acidic, which will irritate the skin around the anus and cause pain. Eating Chili or drinking alcohol can cause anorectal reactive congestion, which can lead to an acute attack of hemorrhoids.
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.
clarify
After the feces are formed, the peristalsis of the colon shrinks all parts of the colon and pushes the feces to the distal colon. This kind of peristalsis often starts from the liver curvature, 2~3 times a day, and advances to the left colon at a speed of 1~2 cm per minute, and then stores in the sigmoid colon. However, after eating or getting up in the morning, the total peristalsis of the colon is caused by gastrocolonic reflex or posture reflex, which advances at the speed of 10 cm per hour. If there is feces in the sigmoid colon, it can make feces enter the rectum, and when it accumulates enough (about 300 grams), it will cause defecation reflex.
Defecation reflex is a complex comprehensive action, including involuntary low-level reflex and involuntary high-level reflex activity. Usually the rectum is empty. When feces fills the rectum, it stimulates the intestinal wall receptors, sends an impulse to the low-level defecation center in the lumbosacral spinal cord, and at the same time uploads it to the cerebral cortex to produce defecation. If the environment permits, the cerebral cortex sends out impulses to make the defecation center excited and enhance, resulting in expulsion reflex, which makes the sigmoid colon and rectum contract and the anal sphincter relax. At the same time, we should consciously inhale deeply, close the glottis, increase chest pressure, reduce diaphragm contraction of abdominal muscles, increase intra-abdominal pressure, and promote fecal excretion. If the environment does not allow, there will be impulses from the lower abdominal nerve and pudendal nerve to contract the external sphincter of anal canal at will to prevent feces from being discharged. The contraction force of external sphincter is 30%-60% greater than that of internal sphincter, so it can prevent feces from being discharged from anus and antagonize defecation reflex. After a period of time, the feces in the rectum return to sigmoid colon or descending colon, which is a protective inhibition. However, if defecation is often inhibited, the rectum will gradually lose its sensitivity to fecal pressure stimulation and lose its sense of defecation. In addition, if the feces stay in the large intestine for too long, the water will become dry and hard, which will lead to difficulty in defecation, which is also one of the reasons for constipation. Defecation can be delayed at will, so we should also develop the habit of regular defecation. Both the standing reflex when people get up in the morning and the gastrocolon reflex after breakfast can promote the peristalsis of colon group and produce defecation reflex. Therefore, regular defecation in the morning or after breakfast meets the physiological requirements and is of great significance to prevent anorectal diseases. It is necessary to form a normal reflex of defecation after getting up or after meals, and do not consciously inhibit defecation unless the environment does not allow it. When a link of defecation reflex arc is destroyed, such as cutting off the intestinal segment of 4~5 cm on the tooth line, damaging the lumbosacral spinal cord or pudendal nerve, and breaking the anorectal ring, it will lead to defecation reflex disorder and fecal incontinence.
References:
What is the composition of feces?
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 the solid part are the most, accounting for one-third to one-half 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.
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.
How is the defecation process completed?
Defecation is a nerve reflex activity. The reflex arc of defecation includes receptor, afferent nerve, nerve center, efferent nerve and effector. Normally, the rectum is empty, but when the mass moves to push feces into the rectum, if the volume reaches 150 ~ 200 ml, the pressure in the rectal cavity will rise to 7.3kPa, which can stimulate the receptors in the rectal wall and its vicinity to generate nerve impulses, which will reach the lower defecation center of S2 ~ 4 through the pelvic nerve and hypogastric nerve, and the impulses from this center will spread along the parasympathetic nerve fibers of the pelvic nerve, causing descending colon, sigmoid colon and sigmoid colon. At the same time, the impulse from the lower central nervous system is reduced, the external anal sphincter is relaxed, and feces are excreted.
Under normal circumstances, the lower reflex center is controlled by the upper center. The impulses generated by rectal receptors not only spread to the lower center, but also to the spinal cord and thalamic tract, upward to the thalamus, and finally to the cerebral cortex, and enter the defecation reflex high center of the central accessory lobule, hypothalamus and brain stem, causing defecation. The higher defecation reflex center can strengthen the activity of the lower defecation center, and also make the abdominal muscles and diaphragm contract, increase the intra-abdominal pressure and help defecation. Then, the abdominal muscles relax, the anal sphincter contracts, and a piece of feces breaks, which naturally falls due to the weight of feces. After that, the anal canal is closed again, the anal plica muscles contract, and the residual feces around the anus are removed. After the feces are discharged, the internal sphincter relaxes, and the skin folds around the anus become shallow, which can also remove the residual feces in the skin folds. After this defecation activity is completed, another defecation activity can be started. During normal defecation, the descending colon, splenic flexure of colon or upper colon can be emptied. Some people cannot completely empty the contents of the rectum, but rarely can they empty all the contents of the colon.
During defecation, the contraction of longitudinal muscles of large intestine is very important. Contraction of longitudinal muscles of the large intestine can shorten the large intestine and eliminate the angle between the distal colon and rectum. At this time, the pressure in the rectum increases, the internal and external sphincter of anus relaxes, the diaphragm shrinks and the abdominal muscles contract, which can increase the intra-abdominal pressure as high as 13.3 ~ 26.7 kPa and promote fecal excretion. When defecating, the pelvic diaphragm striated muscle supports abdominal organs, which can prevent rectal and anal prolapse.
The feeling of defecation is caused by various impulses, mental or organic. In addition, there is a false feeling of defecation caused by external pressure on the rectal wall, such as prostate tumor, bladder stones, and the pressure of the delivery head on the rectum.
Normal people's rectum has a certain threshold for the pressure stimulation of feces. When this threshold is reached, defecation will occur. It can occur when 100ml feces fills the rectum by 25%, or when the pressure in the rectum reaches about 2.4kPa. In order to reach the point where defecation is needed, the rectal contents and pressure must be tripled. However, defecation depends on whether the function of the superior defecation center to the lower defecation center is inhibited or enhanced.
The frequency and habit of defecation vary from person to person, generally one day/kloc-0 times, defecation after breakfast. There is 1 time for 3 ~ 5 days or longer, but I don't feel difficult to defecate. Feel comfortable and happy after defecation. Therefore, the change of constipation, diarrhea or defecation law can not be determined only by the number of defecation, but by everyone's defecation habits.
How is defecation controlled?
Because human defecation reflex is controlled by cerebral cortex, consciousness can control defecation. The anus keeps a certain tension, so that the anus can be closed and feces, liquid and gas can be prevented from leaking out. This function is called defecation control. The function of defecation control is completed by sensation, reflex and muscle activity, which is a complex reflex activity. Can be summarized into two types.
(1) Reservoir control function (colon control function): Colon control function is independent of sphincter function. Colon, especially sigmoid colon, has adaptive response, which can adjust the volume and pressure in intestinal cavity. The pressure changes with the volume of intestinal cavity, which can prevent the pressure from being too high and delay the passage of intestinal contents. The resistance, bending and folding at the junction of rectum and sigmoid colon can delay the entry of feces into rectum and make rectum in a state of emptying and deflation at ordinary times. The left colon can accumulate a certain amount of feces. If it exceeds a certain amount, it can stimulate the colon and make feces enter the rectum. Patients with sigmoidostomy can form the habit of defecation if they eat properly and enema every day, which is due to the control function of colon.
The rectum is a sensory and expandable reservoir, which has the greatest tolerance to volume and can accumulate feces and liquids. The rectal flap can make the feces spiral in the rectum, make the feces pressure equal, prevent the feces from accumulating in the lower part of the rectum, and prevent it from going straight through the rectum, thus playing a corresponding role in controlling the excretion of feces.
(2) Sphincter restraint: it is the function of anal sphincter to resist colon peristalsis and push forward. The contraction force of sphincter must be better than the propulsion force of colon to control it. If you can't beat the push, it's anal dysfunction. Internal sphincter is the most important factor to resist defecation, and it is often in a state of continuous tension and contraction to control defecation activities; The external sphincter is also in a state of contraction, and the anal canal is closed. The contraction force of external sphincter is 30% ~ 60% higher than that of internal sphincter, so it can prevent feces from flowing out of anus. If the external sphincter loses tension, anal dysfunction will occur.
In defecation control activities, the functions of voluntary external sphincter, puborectal muscle and levator ani are interrelated and combined with the functions of voluntary internal sphincter and longitudinal muscle. For example, the contraction of external sphincter can inhibit the reflex relaxation of internal sphincter on detrusor contraction, which is called random inhibition. At the same time, levator ani's gastric fundus loop contracts and tightens, which inhibits the contraction of longitudinal muscle. The contraction of puborectal muscle reduces the right angle of anus, increases the pressure of lower rectum, prevents feces from entering anal canal, and plays a role in controlling defecation.
Because consciousness can control defecation, normal people also have the ability to control defecation. If the environmental conditions do not allow, when defecation is impossible, the downward impulse of the defecation center at the higher level inhibits the defecation center at the lower level, which makes the sphincter contraction strengthen, the anus closes like a non-return door, which reflexively relaxes the sigmoid colon, and the feces in the rectum flow back to the sigmoid colon, so that defecation temporarily disappears. However, if defecation is inhibited frequently or for a long time, the sensitivity of rectum to fecal stimulation can be reduced or disappeared, and the feces will stay in the large intestine for too long, which may lead to constipation.