The Human Digestive Tract Organs and Functions

What is Digestive tract?

The digestive tract is a long, muscular duct from the mouth that continues into the pharynx, esophagus, stomach, small intestine, large intestine, and finally the anal canal, including the mouth, pharynx, esophagus, stomach, small intestine (duodenum, jejunum).

The digestive gland has two small digestive glands and one large digestive gland. The small digestive glands are scattered in the wall of each part of the digestive tract.

The large digestive glands have three pairs of salivary glands (the parotid gland, submandibular gland, sublingual gland), liver and pancreas, all of which are drained into the digestive tract by means of a catheter.

Upper digestive tract function

The upper digestive tract is composed of the mouth, pharynx, esophagus, stomach, and duodenum.

(1) Oral: consists of the lips, cheeks, palate, teeth, tongue and oral glands. After the mouth is stimulated by food, the glands in the mouth secrete saliva, and the chewed food is mixed with saliva. The saliva is passed through the esophagus. The amylase in the saliva can partially decompose the carbohydrates.

(2) Pharynx: It is a common channel between the respiratory tract and the digestive tract. According to the passages of the nasal cavity, the mouth and the throat, the pharynx can be divided into three parts: the nasopharynx (part), the oropharynx (part), and the hypopharynx (part). The main function of the pharynx is to complete the complex reflex action of swallowing.

(3) Esophagus (esophagus): The esophagus (channel) is a long strip of muscular duct with a total length of about 25 to 30 cm. The esophagus (dao) has three stenosis parts, which are easy to retain foreign bodies and are also a good site for esophageal cancer.

The main function of the esophagus (channel) is to transport food into the stomach, followed by preventing air from entering the esophagus when breathing, and preventing the stomach contents from flowing back into the esophagus (channel).

(4) Stomach: divided into four parts: cardia, fundus, stomach and antrum. The total volume of the stomach is about 1000-3000 ml. The gastric mucosa contains a large number of glands, which can secrete gastric juice. The gastric juice is acidic. The pH value (pH) usually fluctuates between pH 2.0 and pH 3.0, and sometimes it may reach pH 1.0.

The main components of gastric acid are hydrochloric acid, sodium, potassium chloride, digestive enzymes, mucin, and the like. The role of gastric juice is many. Its main function is to digest food, kill bacteria in food, protect gastric mucosa and lubricate food, and make food easy to pass in the stomach.

The main function of the stomach is to contain and digest food. The esophagus enters the stomach in the stomach, and undergoes mechanical digestion (Mechanical Digestion) and chemical digestion (Chemic Digestion) to form a chyme (Chyme). The chyme is successively discharged into the duodenum by the movement of the stomach.

(5) Duodenum: the initial segment of the small intestine. The length is equivalent to the finger width of my twelve fingers (about 25 to 30 cm), hence the name.

The duodenum is C-shaped and wraps around the head of the pancreas and can be divided into four parts: the upper part, the lower part, the lower part and the ascending part. Its main function is to secrete mucus, stimulate the secretion of pancreatic digestive enzymes and bile, and is an important digestive site for proteins.

Lower digestive tract function

The lower digestive tract consists of the jejunum, ileum and large intestine.

(1) jejunum, ileum: jejunum from the duodenum jejunum, lower ileum, ileum connected to the cecum. There is no obvious limit in the jejunum and ileum.
The length of the jejunum accounts for 2/5 of the total length and the ileum accounts for 3/5. Both of them belong to the small intestine. The main function of the jejunum and ileum is to digest and absorb food.

(2) Large intestine: The large intestine is the lower part of the digestive tract, including the cecum, appendix, colon and rectum. The adult large intestine is 1.5 meters in length and starts from the ileum. The whole process is shaped like a box and surrounds the jejunum and ileum. The main function of the large intestine is to further absorb water and electrolytes to form, store and excrete feces.

The basic function of the digestive system is the digestion and absorption of food, the substances and energy required for the body. The nutrients in the food can be directly absorbed and utilized except for vitamins, water and inorganic salts.

Proteins, fats and sugars cannot be used. It is directly absorbed and utilized by the body and needs to be decomposed into small molecular substances with simple structure in the digestive tract to be absorbed and utilized.

The process by which food is broken down into small molecules that are simple in structure and can be absorbed in the digestive tract is called digestion.

The process by which small molecules pass through the digestive tract mucosal epithelial cells into the blood and lymph is absorbed. For the portion of the residue that is not absorbed, the Alimentary Canal is excreted in the form of feces through the large intestine.

Digested form

In the digestion process, there are two forms of mechanical digestion (Mechanical Digestion) and chemical digestion (Chemical Digestion).

Food is chewed through the mouth, the teeth are grinded, the tongue is stirred, swallowed, and the gastrointestinal muscles move, turning large pieces of food into small pieces, allowing the digestive juice to fully mix with the food and pushing the food group or the food under the food. Move, from the mouth to the anus, this process of digestion is called mechanical digestion, or mechanical digestion (Mechanical Digestion).

Chemical Digestion refers to the chemical decomposition of food by digestive juice secreted by the digestive gland. The digestive juice secreted by the digestive gland breaks down complex nutrients into simple compounds that can be absorbed by the intestinal wall.

For example, sugars are broken down into monosaccharides, proteins are broken down into amino acids, and lipids are decomposed into glycerol and fatty acids. These decomposed nutrients are then absorbed into the body by the small intestine (mainly the jejunum) into the blood and lymph. This process of digestion is called chemical digestion.

Mechanical digestion and chemical digestion are carried out simultaneously to complete the digestion process.

Food digestion

The digestion of food begins in the mouth. The food is mainly mechanically digested (the food is ground). Because the food stays in the mouth for a short time, the digestion in the mouth is not great.

After the food enters the stomach from the esophagus, it is mechanically digested by the muscles of the stomach wall and chemically digested by the gastric juice.

At this time, the protein in the food is initially decomposed by pepsin in the gastric juice (in the presence of gastric acid), and the contents of the stomach become The porridge-like state of the chyme is pushed to the duodenum several times through the pylorus.

After the chyme enters the duodenum from the stomach, it begins to digest in the small intestine.

The small intestine is the main place for digestion and absorption. The food is chemically digested in the small intestine by the pancreatic juice, bile and intestinal fluid, and the mechanical digestion of the small intestine.

The various nutrients are gradually broken down into simple, absorbable small molecules that are absorbed in the small intestine. Therefore, after the food passes through the small intestine, the digestion process has been basically completed, leaving only the food residue that is difficult to digest, and enters the large intestine from the small intestine.

There is no digestive effect in the large intestine, only a certain absorption function.

Food absorption

The digestion and absorption of food needs to be accomplished through the coordinated cooperation of various organs of the digestive system.

The nutrients in the food we eat every day mainly include sugar, protein, fat, vitamins, inorganic salts and water (six essential substances for human survival), except for vitamins, inorganic salts and water, which can be directly absorbed, protein and fat.

And sugars are complex macromolecular organic substances (Macromolecule), which can not be directly absorbed, must be broken down in the digestive tract (Break Down), decomposed into small molecular substances with simple structure, can enter the blood through the mucous membrane of the digestive tract, send Use it anywhere in the body for tissue cells.

This decomposition process of food in the digestive tract is called “digestion.” After the food has been digested, the process of entering the blood circulation through the visceral mucosal epithelial cells is called “absorption.” Digestion and absorption are two closely related processes.

Digestion includes both mechanical and chemical digestion. Mechanical digestion is the process of digesting the contraction of the muscles of the wall, grinding the food, mixing the food with the digestive juice, and making the digested food components in close contact with the digestive tract wall for absorption, so that the indigestible food residue is The end of the digestive tract is excreted.

Chemical digestion is the process of chemically decomposing food through the digestive juice secreted by the digestive gland to make it a small molecule that can be absorbed. Under normal conditions, mechanical digestion and chemical digestion are carried out simultaneously and with each other.

Change in motor function

The motor function of the elderly in the oral cavity, esophagus, stomach, small intestine and large intestine has changed to varying degrees. Mainly in the partial or total loss of the teeth, the structure and function of the muscles and bones are gradually degraded, resulting in decreased chewing function, poor swallowing function, and food is not easy to chew.

Therefore, the elderly are limited in food selection, and can only enter soft food and fine food. As a result, it is easy to cause indigestion, constipation and even the lack of corresponding nutrients.

In addition, the function of esophagus, gastric peristalsis and food transport is weakened, gastric tension and emptying speed are also weakened, small intestine and large intestine are atrophy, muscle layer is thinned, contraction force is reduced, peristalsis is reduced, rectal pressure on contents Feelings have also subsided.

The above changes in gastrointestinal motility will cause digestive dysfunction and constipation in the elderly.

Absorption function change

The absorption function of the elderly is diminished, mainly in the small intestine, which reduces the absorption of xylose, calcium, iron, vitamin B1, vitamin B12, vitamin A, carotene, folic acid and fat.

Causes of decreased absorption of the elderly, in addition to the reduction of gastric acid and the secretion of various digestive enzymes, poor blood supply to the intestinal wall {the elderly often have intestinal atherosclerosis (similar to atherosclerosis) or heart disease, so that Insufficient blood perfusion} and factors such as mucosal atrophy of the intestinal wall and decreased number of intestinal epithelial cells.

Secretory function changes

The change in the secretion function of the elderly is mainly manifested in the decrease in the secretion of gastric acid and various digestive enzymes, and the decrease in its activity, which leads to the decline of the function of chemical digestion of food in the elderly, which in turn affects the absorption function.

It must be emphasized that although the secretory function of the elderly is worse than that of young people, the digestion of carbohydrates and fats is generally unaffected.

Histological change

The histological changes of the digestive tract in the elderly are mainly manifested in hyperkeratosis of the oral mucosa, the number of taste buds on the tongue is reduced, atrophy, teeth are detached or worn, and the periodontal tissue is degenerated; the glands of the esophagus, stomach and intestine are atrophied.

Smooth muscle atrophy, mucosa, muscle layer are thinner, the stomach and colon are dilated, the internal organs are prone to sagging, and the esophagus, small intestine, and colon are prone to diverticulum. The histological degeneration of the digestive tract in the elderly has led to a decline in digestive and absorptive functions in the elderly.

Physiological characteristics of children

The anatomical and physiological characteristics of the digestive tract in children have the following points:

(1) Oral: Infant oral mucosa is tender, blood supply is abundant, salivary gland is underdeveloped, salivation is less, and amylase content is also insufficient. Salivary gland is fully developed 3 to 4 months after birth, salivary secretion is increased, amylase content is also increase. Because the baby’s mouth is shallow, and does not regulate the excessive saliva in the mouth, it appears as a hooligan phenomenon, the so-called physiological hooliganism.

(2) Esophagus and stomach: The esophagus of newborns and infants lacks glands, and the muscles of the esophageal wall are not well developed. In addition, the baby’s stomach is level, the muscle layer of the stomach is also underdeveloped, and the cardia is wide, and the sphincter is underdeveloped.

The closure effect is not strong enough, so the baby is prone to vomiting and galactorrhea. Infants of different ages have different gastric capacities. The full-term neonatal stomach volume is 30-60 ml; 100 ml at 3 months; about 250 ml at 1 year old. The gastric emptying time of children varies with the type of food.

The water needs 1 to 1.5 hours, the breastfeeding takes 2 to 3 hours, and the milk is 3 to 4 hours. Because the milk emulsion is large, it stays in the stomach for a long time. In addition, since human milk is rich in lipase, the fat of human milk is easier to digest.

(3) Intestine: The intestines of children are longer, and the total length is about 6 times of their length (about 4 times for adults). The intestinal mucosa develops well and is rich in blood vessels and lymph.

All intestinal walls have well-developed villi. Since the intestinal mucosa of infants has incomplete decomposition products, especially the permeability to microorganisms is higher than that of adults and elderly people, it is easy to cause other systemic diseases. Insufficient muscular development in the intestine of children.

There are two forms of movement in the intestine: one is the pendulum movement, which promotes the digestion and absorption of the contents of the intestines; the other is the peristaltic movement, which pushes the food down.

Stimulation of the chyme can enhance bowel movements. The time it takes for food to pass through the intestine varies greatly from 12 to 36 hours, and artificial feeding can be extended to 48 hours.

(4) Pediatric feces: The fetus is discharged from the baby a few hours after birth, which is dark green or dark green, viscous and odorless. After 2 to 3 days, it gradually transitioned to normal baby droppings.

Human milk-fed infants have more frequent bowel movements and 2 to 4 bowel movements per day. They are soft, mushy, even or thin. After 1 year of age, the time can be once a day. The frequency of stools in artificially fed children is less than that of human-fed infants.

About 1 or 2 bowel movements per day, and some even constipation every other day. The reason is that the ratio of bovine and goat milk to the protein contained in human milk is more, the milk mass formed in the stomach is larger and difficult to digest, and the muscular layer of the intestinal wall of the child is incompletely developed, and the amount of intestinal peristalsis is not large enough, resulting in disability.

The residence time in the intestines is lengthened, the water is absorbed, and the stool becomes hard and difficult to discharge. Of course, the number of bowel movements per day varies from person to person and from person to person.

Pediatric defecation is reflexive, as long as the basin is on time, the habit of regular bowel movement can be developed around 2 years old.

Physiological characteristics of pregnant women

During pregnancy, due to the influence of pregnancy, a series of physiological changes occur in each system, and the physiological changes of the digestive tract are as follows:

(1) Oral changes: calcium deficiency due to insufficient intake of calcium in pregnant women or rapid growth of the fetus can cause loosening of teeth in pregnant women; due to the influence of a large amount of estrogen in pregnant women, the gingival hyperemia of the pregnant woman, the softening of the gums and the swelling of the gums.

The vagus nerve of the pregnant woman is in an excited state, resulting in an increase in the amount of saliva secretion in pregnant women. All of the above factors will affect the consumption of pregnant women to varying degrees, such as reduced food intake, soft food or too fine food.

(2) Gastrointestinal changes: nausea, vomiting, food selection, etc. May occur in early pregnancy; due to the relaxation of the sphincter of the cardia, the contents of the stomach are easily returned to the lower end of the esophagus, causing a burning heart; due to the relationship between the progesterone produced by the placenta.

The maternal smoothness of the stomach and intestines is reduced, the activity is weakened, the gastric acid secretion is reduced, and the gastrointestinal motility is weakened. Therefore, pregnant women often have abdominal distension, loss of appetite, constipation and the like.