How is digestion in the stomach and intestines
In humans, the stomach is located under the diaphragm on the left side of the abdominal cavity. It is a hollow, bag-shaped muscular organ that can stretch when food enters it. The walls of an empty stomach form folds, and it has the size of two fists. A fully stretched stomach of an adult can contain 2-4 liters.food.
What are the functions of the stomach?
In it, food accumulates, mixes and undergoes further chemical processing. The mixing of food contributes to the reduction of the muscle layer, which, in addition to the longitudinal and annular muscles, has oblique muscles. Chemical changes occur with food under the action of gastric juice. The time of food staying in the stomach depends on its composition: the more fat it contains, the longer it stays in the stomach.
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Gastric Juice # 8212;colorless, odorless liquid. It is produced by numerous glands of the gastric mucosa.1 mm2 mucous membrane contains about 100 such glands. Some of them produce enzymes, others # 8212;hydrochloric acid, and others still produce mucus. A person usually produces 2-2.5 liters of gastric juice per day.
The main enzyme in gastric juice is pepsin .It splits protein molecules into simpler molecules consisting of several amino acids. Pepsin is effective only at a temperature of 35-37 ° C and in the presence of hydrochloric acid. Hydrochloric acid destroys pathogens by performing a protective function. The mucus, which is coated with the mucous membrane of the stomach, prevents the action of hydrochloric acid and pepsin on its wall, protecting it from self-poisoning and mechanical damage.
Food lumps swallowed in the stomach turn into a semi-liquid mass # 8212;chyme. From time to time it is pushed out of the stomach into the intestine through a hole surrounded by a sphincter, which prevents the return of chyme to the stomach. Digestion in the small intestine. The division of the small intestine, moving away from the stomach, is called the duodenum, its length is about 25 cm. It opens the ducts of the pancreas and gall bladder. The following sections of the small intestine are # 8212;hollow gut( 1.5-2.5 m) and ileum ( about 3 m).Due to this length of the small intestine, food digestion takes place over a considerable time. When contracted, the smooth muscles of the intestine perform peristaltic and pendulum movements, moving and mixing the hi-mousse.
Digestion in the stomach
Chyme and Bile
While is moving, the chyme turns into compounds that are absorbed by the body. It occurs under the action of pancreatic enzymes and gallbladder secretions, as well as enzymes secreted by the glands of the small intestine. It finally breaks down about 80% of carbohydrates and almost 100% of proteins and fats from food. Proteins are cleaved by the action of two major enzymes: trypsin and , chemotrypsin .carbohydrates # 8212;under the action of amylases, fats break down lipases. These enzymes do not work in an acidic environment. Therefore, to neutralize hydrochloric acid, which enters the chyme in the small intestine, its glands and pancreas secrete alkaline substances.
In bile .which enters the intestine from the gallbladder, no enzymes. Substances of bile "break" water-insoluble fat droplets into smaller droplets. Fats in these droplets become available for the action of lipases and more efficiently split.
Where is digestion happening in the small intestine? In this process, abdominal and parietal digestion are distinguished. The task of abdominal digestion is to crush large organic molecules with enzymes of the glands of the intestine and pancreas, as well as bile. Final splitting occurs during parietal digestion.
A number of folds can be seen on the inner surface of the intestine with the naked eye. Looking at them through a microscope, you will see numerous villi covered with epithelium cells that produce enzymes, mucus, etc. Looking at such a cell, you will see on its membrane a multitude of microvilli. Villi and mucus, enriched with enzymes, is the medium where parietal digestion occurs.
It is to him that small molecules, formed as a result of abdominal digestion, arrive. Between microvilli and in the plasma membrane of epithelial cells contains enzyme molecules. Once in between the microvilli, small molecules break down into even smaller ones # 8212;those that can be transferred through the membranes of epithelial cells. So begins the process of absorption.
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Digestion in the stomach and intestines, absorption
1. What is the structure of the stomach? How is food rhenium in the stomach?
The stomach is an enlarged part of the digestive tube. In its mucosa are glands that produce gastric juice( about 2-2.5 liters per day).The same juice contains hydrochloric acid, so it has an acidic reaction. Hydrochloric acid has a bactericidal effect. The composition of the gastric juice includes enzymes - pepsin, lipase, chymosin. Pepsin breaks down proteins, lipase breaks down milk fats, and chymosin makes milk. Digestion in the stomach occurs only at temperatures from +35 to +37 ° C and in the presence of hydrochloric acid.
For the study of digestion in the stomach, IP Pavlov conducted experiments with imaginary feeding on a dog. He put a fistula on his stomach so that gastric juice could flow out of it. At the same time, the esophagus was cut so that the food did not enter the stomach. Thus, Pavlov showed that the secretion of gastric juice occurs reflexively and is associated with the appearance, smell of food( conditioned reflex), as well as with irritation of the receptors in the mouth cavity( unconditioned reflex).
I.P. Pavlov described the ludo juice produced by the sight, smell and chewing of food, appetizing. Thanks to him, the stomach is prepared in advance for food, and when it is ingested, the splitting of nutrients immediately begins.
2. How does digestion and absorption take place in the intestines?
In the small intestine, food is converted into compounds that are absorbed by the body.
The process of digestion consists of 3 stages: abdominal digestion, parietal( membrane) digestion and absorption. Abdominal digestion occurs in the intestinal cavity under the influence of digestive enzymes secreted in the composition of digestive juices. The parietal wall is made by enzymes located on the cell membrane. Membranes form a large number of villi on which a powerful layer of digestive enzymes is adsorbed. Small arteries penetrate into each villus, in the center there is a lymphatic vessel and nerve fibers. The suction products penetrated through the villus walls enter the blood and lymph vessels. Glucose and amino acids are absorbed directly into the blood, and the products of the breakdown of fats( glycerin and fatty acids), first in the lymph, and from there into the blood. The crown-like movements of the annular and longitudinal muscles contribute to the mixing of the food gruel, the peristal undulating movements of the ring muscles promote the movement of the gruel to the large intestine. Material from the site http://iEssay.ru
Large intestine - the final section of the digestive tract. In the colon, food masses can linger for up to two days. Glands of the colon produce a lot of mucus and a small amount of digestive juices with a small content of enzymes. Colon bacteria destroy and digest cellulose, synthesize vitamin K and vitamins of group B. Up to 10% of food consumed by the body is not absorbed. The remains of food masses are glued together with mucus in the colon, compacted. Stretching the stool walls with fecal masses causes the urge to defecate, which occurs reflexively. The center of defecation is in the sacral spinal cord.
In the large intestine, water and residues of digested food are absorbed, the feces are formed and removed from the body.
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Question 1. What is the role of the pharynx and epiglottis?
The pharynx is the organ that connects the oral cavity to the esophagus and the nasal cavity to the larynx. In the pharynx the digestive tracts intersect with the respiratory.
Question 2. What features of the structure of the trachea allow it, while maintaining its functions, not to interfere with the process of nutrition?
The tracheal cartilage layer is formed by hyaline incomplete cartilages that occupy two thirds of the tracheal tube circumference. Between themselves, the cartilage is connected by ring ligaments. The number of cartilage in humans ranges from 16 to 20. A webbed wall is formed at the back, which is in contact with the esophagus. Thus, the passage of the food bolus does not interfere with the process of nutrition.
QUESTIONS TO THE PARAGRAPH OF
Question 1. What features of the structure of the stomach as a digestive canal do you know?
The stomach is an expansion of the digestive tube with a volume of about 2 liters. The walls of the stomach, as well as the esophagus, consist of the connective tissue sheath, the muscle layer and the inner mucosa.
Millions of small glands that produce gastric juice( about 2 liters per day) are in the gastric mucosa. Some glands produce the digestive enzyme pepsin, which is necessary for the breakdown of proteins, others - hydrochloric acid, which activates pepsin and kills bacteria that enter the gastrointestinal tract with food. Another type of mucosal cells secretes a special mucous substance that protects the walls of the stomach from self-digestion.
Question 2. What are the features of digestion in the stomach?
Depending on the composition and volume of food eaten, its stay in the stomach lasts from 3 to 10 hours. During the mechanical processing of food, the walls of the stomach are slowly reduced( gastric motility), mixing food with gastric juice. For some time, enzymes of saliva that digest sugar continue to act in the food lump, and then the food lump is soaked with gastric juice and protein digestion takes place in it. An important feature and condition for effective digestion in the stomach is the acidic environment.
Question 3. What happens to food in the duodenum?
One of the main functions of the duodenum is to bring the pH of the food pulp from the stomach to alkaline, non-irritating, more distal small intestine and suitable for intestinal digestion. It is in the duodenum and the process of intestinal digestion begins. Another major function of the duodenum is to initiate and regulate the secretion of pancreatic enzymes and bile, depending on the acidity and chemical composition of the food pulp entering it.
Question 4. What is the significance of the relatively large length of the human intestine?
Digestion occurs in the stomach, and in the intestine - the absorption of nutrients. For more efficient suction requires more contact with the surface, and this requires a large intestinal length.
Question 5. What is the role of the liver and secretions secreted by it in digestion?
The liver is the largest gland( weight up to 1.5 kg).The main secret that the liver secretes into the digestive system is bile. Bile emulsifies fats, activates pancreatic fat-splitting enzymes, but does not contain enzymes. In the liver, carbohydrates are converted to glycogen. The liver also performs a barrier function, neutralizing toxic substances that appear in the body during metabolism. Outside the digestive process, bile is collected in the gallbladder.
Expand the mechanism of peristalsis of the alimentary canal.
Intestinal contractions are provided by smooth muscle cells that form the longitudinal and circular layers. Due to the connections of the cells among themselves, the smooth muscles of the intestine are a functional syncytium. Therefore, excitement quickly and over long distances spreads through it. The following types of contractions are observed in the small intestine:
1. Non-propulsive peristalsis. This is a contraction wave of the intestine, due to the contraction of the circular muscles and extending in the caudal direction. It is not preceded by a wave of relaxation. Such peristaltic waves move only a small distance.
2. Propulsive peristalsis. It is also a pervasive local contraction of the smooth muscle circular layer. It is preceded by a wave of relaxation. Such peristaltic waves are stronger and can capture the entire small intestine.
Intestinal motility regulation is performed by myogenic, nervous, and humoral mechanisms. This is the main mechanism of peristalsis.
What is the significance of the change in the acidity of the environment in different parts of the alimentary canal?
This feature of changing acidity plays a big role in the digestion of food. An acidic or alkaline environment is required for the digestion of various components.
Sources: http: //bagazhznaniy.ru/obrazovanie/klass /pasechnik/ 26
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