Human digestion

Human digestion. Process by which food is converted into essential nutrients, that is: proteins , carbohydrates , fats , vitamins and minerals, which in turn are broken down into simpler compounds: amino acids , monosaccharides , glycerol . This occurs by the action of mechanical and chemical phenomena in the digestive tract.

Digestion begins in the mouth and culminates with the absorption of the resulting substances at the level of the intestines. It forms the basis of all physiological processes. Hence the great importance of healthy digestion along with a proper diet.


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  • 1 Anatomical process
  • 2 Digestive System
    • 1 Mouth
    • 2 Pharynx and Esophagus
    • 3 Stomach
    • 4 Small intestine
    • 5 Large intestine
  • 3 glands attached to the digestive system
    • 1 Salivary glands
    • 2 liver
      • 2.1 Gallbladder
    • 3 Pancreas
  • 4 Other glands
    • 1 Gastric glands
    • 2 intestinal glands
    • 3 Mucus-secreting glands
  • 5 Care to achieve proper digestion
  • 6 External links
  • 7 Sources

Anatomical process

Complete scheme of the digestive system

Ingested food is transformed into a chemical that can be absorbed by the blood and transported by it to all body tissues, including: muscle tissue that uses glycogen immediately or stores it as a reserve. Adipose tissue , for fat storage as an energy reserve. Liver , for conversion into other more complex elements.

Digestion is the act of breaking, shaking, diluting, and dissolving food into simple chemical compounds. Carbohydrates are broken down to monosaccharides (simple sugars); the protein in amino acids and fats are degraded to (glycerin) fatty acids and glycerol.

This process takes place in the digestive tract also called the alimentary canal or digestive system . The salivary glands , the liver, the gallbladder and the pancreas are located outside the alimentary canal but are accessory organs of digestion since their secretions provide the essential enzymes for it.

Digestion can be classified differently:

  • Saliva: Change from starchto maltose due to saliva .
  • Intestinal: Digestion due to the action of intestinal juice.
  • Pancreatic: Digestion due to the action of pancreatic juice.
  • Primary: Digestion that occurs in the gastrointestinal tract.

Digestive system

Organs involved in the digestion process.

System or group of organs whose specific function is the ingestion, digestion and absorption of food or nutritional elements. These organs are: the mouth where we find the tongue and teeth as well as the salivary glands, the pharynx, the esophagus, the stomach and the intestines.

The accessory organs of digestion, which contribute important secretions to it, include the salivary glands, the pancreas, the liver, and the gallbladder.

There are also mucus-secreting glands throughout the gastrointestinal tract, glands that produce the components of gastric juice, located in the gastric mucosa, and glands that secrete the components of intestinal juice, located in the intestinal mucosa.


Oral cavity.

The entrance to the alimentary canal is the mouth where the teeth , tongue and jaws begin the process of digestion by chewing. The Saliva is secreted in the mouth of three separate pairs of salivary glands located under the tongue , inside of the jaw and cheeks.

The saliva softens and lubricates the food, dissolves part of it and begins the conversion of starches into sugar by the action of ptialin , the enzyme in saliva, and it also moistens the inside of the mouth, tongue and teeth, which it cleans later that the food has left for the next stage of its journey.

Behind the jaws four routes meet: oral, nasal, larynx   and esophagus . During swallowing, the nasal and laryngeal inlets are momentarily closed by the soft palate and epiglottis , so that food can pass into the esophagus without diverting to the respiratory tract .

Pharynx and Esophagus

Through them the food bolus passes until it reaches the stomach , driven by Peristalsis .


Driven by rhythmic muscle contractions called peristalsis , food moves rapidly through the esophagus, passes into the cardia (orifice surrounded by circular muscle at the base of the esophagus), and enters the stomach.

Here, peristaltic movements are stronger and more frequent, occurring at a rate of 3 per minute, beating, liquefying and mixing food with gastric juice, where the enzymes pepsin and lipase are found, in infants, renin; a secretion called mucin, which covers and protects the gastric lining, from hydrochloric acid.

Pepsin and hydrochloric acid together begin the breakdown of proteins in food. Lipase in the stomach is weak degradadora over something, which acts on fats that have been emulsified as cream milk and yolk egg . In the intestine, where most of the fats are digested, there is a more powerful lipase.

The adult stomach has a capacity of 1.25 L. It reaches maximum digestive activity almost 2 hours after a meal and can empty in 3 to 4 and a half hours. A hearty meal can take up to 6 hours to pass into the small intestine.

Small intestine

Small intestine structures.

Place where true digestion takes place. Divided into three segments, duodenum , jejunum, and ileum . The food leaves the stomach in the form of chyme, a thick mixture, that passes through the pylorus, a muscular sphincter that opens from the lower part of the stomach to the duodenum. This sphincter is closed most of the time and opens whenever a peristaltic sling passes through it. The stomach is much wider than the rest of the canal and has a J-shaped curve at the bottom so that the passage of food through the pylorus slows down until the food is of the right consistency to pass through the narrow hole toward small intestine.

The small intestine is approximately 6 m. It is covered by deep folds and structures called intestinal villi that give it an area of ​​approximately 900 square meters, through which absorption occurs. The duodenum is curved in a C shape with a length of approximately 25 cm, it is the first and widest part of the small intestine. In the pancreatic juice is poured, with enzymes that break down starch, protein and fat. Choledochus flows so well into the duodenum. Bile emulsifies fats into small particles, facilitating the action of enzymes that break them down.

Below the duodenum is the jejunum, the longest portion of the small intestine, and then the ileum, the last and narrowest portion of the small intestine. Throughout its entire journey, carbohydrates, proteins and fats are divided into sugars, amino acids, fatty acids and glycerin respectively. The lining of the small intestine absorbs these nutrient compounds as quickly as they are produced. Unusable compounds in the diet pass into the large intestine.

Large intestine

At the junction of the small intestine with the large intestine is the ileocecal valve, so called because it is at the end of the ileum and at the beginning of the cecum. A small blind tube called the vermiform appendix is attached to this structure.

The longest portion of the large intestine is called the colon and is divided into the ascending, transverse, and descending colon, and the sigmoid colon, curved S-shaped at its distal end. The sigmoid colon empties into the rectum and the rectum ends in the anal sphincter.

The large intestine measures approximately 1.65m. The waste fluid is gradually reabsorbed through the intestinal walls. Thus, the waste forms fairly solid stool that is carried down into the rectum for final disposal. This takes ten to 20 hours. The fecal content consists of bacteria, cells released from the intestines, mucus and indigestible substances such as cellulose. The normal dark brown color of the stool is produced by the bile pigments.

Glands attached to the digestive system

Salivary glands

Salivary system

The main ones are three pairs of glands known as, parotid, submaxillary and sublingual. There are other smaller ones inside the cheeks and on the tongue.
Saliva is produced in the salivary glands in an approximate daily quantity of between 1 and 1.5 liters. Saliva can be serous, mucous, or mixed. The secretion from the parotid glands is serous. That of the submaxillae is mixed and the sublinguals mainly produce saliva with a mucous component.


Liver – Body energy store

Large, dark red gland located in the upper right portion of the abdomen , below the diaphragm. Its functions are multiple: storage and filtration of the blood, conversion of sugars into glycogen, synthesis and degradation of fats, temporary storage of fatty acids, synthesis of serum proteins, and essential factors for coagulation. Its function for the digestive system consists in the secretion of bile.


Anatomical location

Organ in the shape of a pear or sac, located under the liver where bile is stored, which in turn is produced by the liver and intervenes in the digestion of fats.


Large, elongated gland that is located transversely and behind the stomach, between the vessel and the duodenum. It has a mixed function. Endocrine consists of the production of insulin and glucagon, hormones that intervene in the metabolic regulation of carbohydrates. Exocrine is given by the production of pancreatic juice, a container of enzymes that, when poured into the duodenum, act in the chemical digestion of proteins, lipids and carbohydrates. Its function for the digestive system is in the production and secretion of pancreatic juice.

Other glands

Gastric glands

Gastric glands are simple or compound tubular type and are named according to their location in the stomach. So we have:

Own glands , located in the body and fornix or gastric dome. They are the most numerous, approximately 100 for each square mm, formed by several cells that secrete the main elements of gastric juice:

  • Mucous cells that secrete mucus protective mucus and pepsinogen II
  • Parietal cells, secrete hydrochloric acid and intrinsic factor.
  • Main or zymogenic cells producing enzymes, pepsinogen I
  • Endocrine cells that produce hormonal substances: gastrin, gastric glucagon, somatostatin, prostaglandins.

Pepsinogen is converted to pepsin upon contact with hydrochloric acid.

Castle’s intrinsic factor is involved in the absorption of cobalamin also known as vitamin B12.

Cardiac glands , located in the cardia, secreting mucus.

Pyloric glands , found in or near the pylorus, secrete mucus and hormonal substances such as gastrin.

The secretions of the gastric glands make up the gastric juice on which chemical digestion in the stomach depends.

Intestinal glands

Located throughout the small intestine (Lieberkuhn glands), they secrete intestinal juice that complements digestion, facilitating absorption. They are of the simple tubular type and are found in the mucosa without reaching the submucosa.

There are also duodenal glands located in the submucosa, similar in structure to the pyloric glands. A large number of Lieberkuhn crypts can also be seen in the large intestine; but they contain almost no enzymes.

Mucus-secreting glands

They are located along the entire length of the digestive tract or tube. They produce and secrete mucus in a somewhat different consistency depending on the place but with the same functions: lubricant and protector.

Care to achieve proper digestion

  • Sitting correctly at the table avoiding torsion of the trunk facilitates the passage of food through the esophagus.
  • Maintaining a healthy denture ensures that food is properly crushed before going to the stomach.
  • Free yourself from worries before sitting at the table. The viscera are very sensitive to the vagal action produced by nervous tension.
  • Chew and salivate food properly. Determine that the rest of the digestive process is optimal.
  • Drinking only the necessary water avoids imbalance of the gastric pH, which favors a more effective assimilation of the nutrients.
  • Keeping the abdominal region free of pressure favors free peristaltic movement.
  • Physical or mental exertion should be avoided after meals.
  • Very large meals overload the digestive and cardiovascular systems, slow down metabolism and thus digestion.
  • Eating in a pleasant and harmonious environment predisposes to good digestion.
  • Proper hygiene and food handling are important to avoid digestive disorders.
  • Well presented meals are usually better digested.
  • Avoid drinking milk before during or after sitcoms. Milk basifies gastric pH, hindering digestion.
  • Eating dietary fiber considerably improves digestive function, due to its properties, it increases salivation, delays gastric emptying, improves the function of intestinal villi, accelerates transit in the large intestine, among others.


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