Abstract: Gastrointestinal tract. Lesson plan: "The structure of the digestive system" Plan a story about the digestive
The digestive system is designed to provide the body with nutrients, which are an energy substrate, for all cells of the body.
Digestive system structure plan
Alimentary canal (alimentary tube)
Liver
Pancreas
Salivary glands.
Digestion is the process of gradual, gradual mechanical and chemical breakdown of food components, followed by their absorption, which occurs in various parts of the gastrointestinal tract.
There are 3 sections in the digestive system:
Initial department
Middle department
Caudal department
The initial section of the gastrointestinal tract includes:
Organs of the oral cavity
Salivary glands
Throat
Esophagus
Carried out: mechanical processing of food and its conduction in the middle section of the gastrointestinal tract.
The middle section of the gastrointestinal tract includes:
Stomach
Small intestine
Colon
Liver
Pancreas
Carried out: chemical (enzymatic) processing of food, followed by absorption of digested products, the formation of feces.
The posterior (caudal) section of the gastrointestinal tract includes:
Lower third (3-4 cm) of the rectum
Carried out: excretion of non-processed body products.
The wall of the alimentary canal has a layered structure and consists of 4 membranes:
Mucous
Submucosa
Muscular
External (adventitial and serous)
The mucous membrane (tunic mucosa) is constantly moistened with the secretion of the mucous glands. It is covered with epithelial tissue, which, depending on the type of epithelium, is divided into 2 types:
The mucous membrane of the cutaneous type is covered with stratified squamous and non-keratinized epithelium.
The intestinal-type mucous membrane is covered with a single-layer, columnar epithelium.
The mucous membrane has a different relief (surface irregularities).
The mucous membrane of the gums and palate is almost smooth, and the intestines are uneven and may contain:
Gastric dimples
Intestinal crypts
Outgrowths (folds or intestinal villi). increase the functioning surface of the mucous membrane.
Submucosa (tunic submucosa) (located outside of the mucous membrane) Consists of connective tissue, which contains blood and lymphatic vessels, nerves, nerve endings and nerve plexus (Mesner's plexus) as well as various glands: 1) own glands in the esophagus
Duodenal glands in the duodenum.
Some organs of the gastrointestinal tract are devoid of a mucous membrane, such as the back of the tongue, the mucous membrane, tightly grows together with the deeper muscular membrane and loses its mobility.
Submucous function:
Trophic function (nutrition)
Participation in the formation of the relief of the mucous membrane
Providing mobility of the mucous membrane.
The muscular membrane (tunic muscularis) (located to the outside of the submucosa)
Consists of 2 layers of muscle el-in:
Internal circular
Outer longitudinal
The third layer appears in the stomach in the organ of the middle section, is the innermost in the arrangement of the fibers, oblique.
Muscle tissue in different parts of the gastrointestinal tract has different structure and the origin, for example, in the cadulum and initial section, it is formed mainly by striated, skeletal, arbitrary (we can control its work), but in the organs of the middle section, it is formed only by smooth muscle tissue.
Functions of the muscular membrane: 1) participates in the formation of pendulum-like and peristaltic movements of the wall of the digestive canal, which leads to the advancement of the food lump from the initial to the posterior part.
Outer sheath:
In the organs of the initial section - adventitia, represented by loose tissue containing vessels, nerves and nerve plexuses
In the organs of the middle section, it is serous. in addition to the connective tissue component, it contains 1 layer of flat cells called mesothelium
Mesothelium produces serous fluid and helps to relieve friction between adjacent organs in the middle gastrointestinal tract.
Oral cavity (kavitas oris):
Vestibule of the mouth
Oral cavity.
Vestibule of the mouth limited from external environment, from the front with the lips, from the sides with the cheeks, and from the inside with the teeth and gums. The vestibule of the mouth, through the lips forming the mouth opening, communicates with the external environment, and through the gaps between the teeth communicates with the oral cavity itself. The structure of the lips is based on orbicular muscle of the mouth (Musculus orbicularis oris).
It is customary to distinguish several parts of the lips:
Skin (outer part) covered with skin
The inside (mucous part) is covered with a mucous membrane
The intermediate part of the lips is lined with stratified squamous keratinizing epithelium, does not contain hair follicles and mucous glands. The red color becomes due to the capillaries, which are located superficially.
Oral cavity. The boundaries of the oral cavity: in front of the teeth and gums, on the sides of the cheeks, on top of the hard and soft palate, on the back of the pharynx, below the diaphragm of the bottom.
Hard palate - forms the upper wall of the oral cavity. Formed by bone tissue. Covered with a mucous membrane. Consists of horizontal plates of the paired palatine bones and palatine processes of the maxillary bones.
The soft palate (adjacent to the back of the hard palate) is distinguished by:
Uvula (Uvulya)
Palatine curtain.
The palatine curtain is a double fold, which is divided into two parts: 1) Front (palatine curtain) or arch
The back (palatopharyngeal curtain) or arch.
Between the two arches is the paired organ of the immune system, the palatine tonsil. The palatine curtain and uvula form the pharynx, which is the border between the mouth and the mouth of the pharynx.
The oral cavity is formed by the diaphragm of the mouth. The diaphragm of the mouth is formed by a paired jaw-hyoid muscle that has grown along the midline, covered from the surface with a mucous membrane rich in numerous blood vessels.
Language (lingua) (located on the diaphragm of the mouth) is divided into sections:
The root of the tongue
The top of the tongue
Body of the tongue (between apex and root)
The language is also distinguished:
Two side surfaces,
The back of the tongue (top),
Ventral surface (bottom)
The tongue belongs to the organs of the layered type of structure. The basis of the tongue is transversely striated muscle tissue (muscular membrane), up from which (in the back area) is the mucous membrane, and to the bottom of the muscular membrane is the submucosa and to the outside of it the mucous membrane.
The muscular basis of the tongue is formed by two muscle groups:
Outdoor
Own muscles of the tongue
The mucous membrane of the tongue includes a stratified squamous non-keratinizing epithelium and the loose connective tissue located under it ... Teeth (Dents) are very important organs of the initial part of the gastrointestinal tract that provide ...Dental formula concept. Dental formula is graphic image the number of different types of teeth on the upper and lower jaw, the dental form of the milk bite is as follows. 2 incisors, 1 canine, no small short teeth, 2 large short teeth tooth.numerator (upper jaw) denominator (lower jaw) on both sides.
Permanent bite: 2 incisors, 1 canine, 2 small. tooth cortex and 3 large cortex teeth
Salivary glands. Ducts of 3 pairs of large salivary glands and numerous ducts of small salivary glands open into the human oral cavity, small glands- these are lingual palatine buccal, pharyngeal - located in the thickness of the mucous membrane, in the submucosa, as well as in the muscular membrane of the oral cavity organs. cName depending on where they are located. Large salivary glands: parotid, submandibular and sublingual. All of them are paired, located behind the perches of the alimentary canal.
Parotid salivary gland (glossdula parotis) -20-30 grams, covered with a connective tissue capsule and is located on the lateral surface of the face in front and slightly below the auricle, behind it goes into the back of the jaw fossa, and in front partially covers the chewing muscle, the gland produces exclusively protein secretion , which, along the common duct of the gland (varton duct), is allocated in the vestibule of the mouth on its lateral wall against the second upper large molar, under the lower jaw gland (glossdula submanidibularis) -13-16 grams, covered with a dense capsule and located posterior to the body of the lower jaw in the submandibular triangle. It is located superficially and is covered with skin and a connective tissue capsule, has a common duct (varton duct), which removes a mixed secretion (protein-mucous) with a predominance of the protein component to the apex of the sublingual month on the side of the frenum of the tongue. The sublingual salivary gland (glossudula sublingualis) has a mass of about 5 grams, is covered with a ton of connective tissue capsule and is located on the diaphragm of the mouth, has 1 main sublingual duct and several additional ducts, the main sublingual duct (revinus) opens together with the Warton duct, at the apex of the sublingual month , on the side of the frenum of the tongue. It secretes a mixed mucous-protein secret with a predominance of the mucous component, it moisturizes the mucous membrane and helps to form articulate speech, has a bactericidal effect and chemically breaks down food.
The pharynx is a funnel-shaped tubular organ with a length of 11-12 cm (up to 15 cm). The upper part of the pharynx is expanded and attached to the base of the skull, the lower part of the pharynx is narrowed and at the level of the 6th cervical vertebra passes into the esophagus.
Pharynx
1.Nasopharynx - communicates with the nasal cavity through the juan,
Oropharynx - through the pharynx communicates with the oral cavity
Larynx - communicates with the larynx through an opening called the entrance to the larynx.
The mucous membrane of the nasopharynx is lined with ciliated epithelium. The mouth and laryngopharynx are non-irritating epithelium.
On the side walls of the nasal part of the pharynx there are paired openings of the auditory or Eustachian tubes, which communicate the nasal part of the pharynx with the ear cavity (with the tympanic cavity) and help to equalize the pressure. On the side of each of the openings of the estachian tubes is an accumulation of lymphoid tissue, called the tubal tonsil, on the border of the upper and posterior walls of the pharynx is the pharyngeal unpaired tonsil. The pharyngeal tonsil, tubal tonsils, palatine tonsils, lingual mendalin form the Pirogov-Valdeer's lymphoepithelial ring, located in the area of the airway and digestive tract intersection.
The pharyngeal wall has a layered structure and includes the mucous membrane, an analogue of the submucosa, the pharyngeal-basilar fascia, which is involved in the attachment of the pharynx to the bones of the base of the skull, and the muscular membrane, consisting of the muscles of the constrictors (narrowing) of the pharynx; there are 3 upper middle and lower constrictors. In their posterior part, the contractors exchange fibers to form a longitudinal suture of the pharynx. The muscles that lift the pharynx - with the act of swallowing, the longitudinal muscles lift the pharynx to the top and the circular ones - contribute to the movement of food.
The esophagus (Aesaphagus) is a tube 30 centimeters long, between 6-7 cervical vertebrae to 11-12 thoracic vertebrae, where the esophagus passes into the stomach, the section of the digestive tract that connects the pharynx to the stomach. Takes part in swallowing food, the peristaltic contractions of P.'s muscles ensure the movement of food into the stomach.
P.'s length of an adult is 23-30 cm, wall thickness is 4-6 mm. In the esophagus, the cervical, chest and abdominal parts are distinguished. The cervical part 5-6 cm long begins at the level of the VII cervical vertebra behind the cricoid cartilage of the larynx, located between the trachea and the spine; to the right and left of it are the lobes of the thyroid gland. The thoracic part, 17-19 cm long, runs along the posterior mediastinum, first between the trachea and the spine, then between the heart and the thoracic part of the aorta. The abdominal part of P., located between the diaphragm and the cardiac part of the stomach (at the level of the XI-XII thoracic vertebrae), has a length of 2-4 cm. There are three narrowings in the esophagus. The upper narrowing (the most pronounced) corresponds to the area of transition of the pharynx into the esophagus, the middle one is in the zone of contact of P. to the back surface of the left bronchus, the lower one - at the place of P.'s passage through the diaphragm. In the course of P. on close range from it, in addition to the trachea, heart and aorta, are the bronchi, the common carotid artery, the thoracic duct, the sympathetic borderline trunk, the lungs and pleura, the diaphragm, the superior and inferior vena cava.
The wall of the esophagus consists of the mucous membrane, submucosa, muscle and connective tissue (adventitia, in the abdominal part of the serous) membranes (Fig. 2). The mucous membrane is covered with stratified squamous epithelium and is separated from the submucosa by a layer of muscle tissue - the muscle plate of the mucous membrane. P.'s glands, which produce mucus, are scattered in the mucous membrane. In the submucosa, among the loose connective tissue, there are small glands, lymph nodes, blood vessels and nerves. The muscularis membrane consists of two layers; circular (internal) and longitudinal (external), between which there is a layer of loose connective tissue. In the area of P.'s transition to the stomach, muscle fibers form a sphincter.
Blood supply to the cervical part of P. is carried out mainly due to the lower thyroid arteries, the thoracic - due to the branches of the thoracic part of the aorta; abdominal - left gastric and left lower phrenic arteries.
The outflow of venous blood from P.'s capillary bed occurs into the submucosal venous plexus, which connects to the superficial and deep veins of P. From the cervical part of P., venous blood enters the lower thyroid vein, from the chest - into the unpaired and semi-unpaired veins, from the abdominal part of P. the outflow blood is carried into the left gastric vein. The presence of portocaval anastomoses leads to the expansion of P.'s veins with portal hypertension.
The outflow of lymph occurs in the regional lymph nodes: from the cervical part of P. into the deep lymph nodes located along the internal jugular vein and trachea, from the chest - the prevertebral and posterior mediastinal lymph nodes, from the abdominal part of P. into the left gastric lymph nodes.
The vagus nerves and branches of the sympathetic trunks innervate P., together forming the thoracic aortic plexus.
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Lesson on the topic: The importance of digestion. Digestive system: digestive tract, digestive glands.
The purpose of the lesson: To give an idea of the importance of nutrition and digestion. Ensure the assimilation of knowledge about the structure and functions of the digestive tract and digestive glands.
Tasks:
Educational:
Development of knowledge about the structure and functions of the digestive system;
Development of skills to analyze, establish relationships between structure and function; improve the ability to highlight the main thing;
Carry out hygienic education of students.
Developing:
To teach how to apply the knowledge gained about the digestion process in everyday life;
-development of logical thinking;
- continue to develop skills to compare objects, work with drawings and diagrams;
To teach to analyze and systematize information, to creatively process it.
Educational:
-development of interest in knowledge, motivation and culture of mental work;
-development of a culture of communication and reflexive personality traits,
- creating conditions for emotionally pleasant intellectual activity of students, with high cognitive activity of students
-show the importance of biological knowledge;
- to carry out hygienic education of students.
Lesson type: study of new material, repetition and consolidation of the passed.
Forms of organizing educational activities : oasking at the blackboard, frontal survey, conversation, working with slides computer presentation, watching a video, differentiated homework.
Lesson plan:
Organizational moment 2 min
Homework survey. 12 minutes
Problematic task. 3 min.
Learning new material. 18 minutes
Securing the material. 3 min.
Summarizing. Homework... 2 minutes.
Lesson summary.
I... Hello guys! Let's smile, clap our hands, be positive about the lesson.
II... In the last lesson, we started to study a large section. Today we will continue to study it.
Homework survey.
Several students work with cards. (Annex 1).
Those who wish to answer the following questions at the board:
How important are nutrients to the body?
What substances should be in our food?
What organic compounds does the body receive from food?
What are the functions of proteins, and what organic compounds do they break down into?
What are the functions of fats, and what organic compounds do they break down into?
What are the functions of carbohydrates, and what organic compounds do they break down into?
What is the role of water in the body?
III. We looked at the importance of nutrients to find out which topic is today
Let's turn to the historical background ...
… Even in ancient India, the "rice test" was used. At the trial, to decide the question of guilt or innocence, the defendant was offered to eat dry rice. If he eats it, then he is not guilty, if not, then he is guilty.
What do you think this test was based on? Knowing about what organ systems helped to find out the truth?
Pupils: Oh, the digestive organs.
That's right, today in the lesson we will learn aboutthe beginning of digestion. digestive system: digestive tract, digestive glands ". We will return to the problem of rice a little later.
Pupils write down the topic of the lesson.
Who can tell what is the purpose of our lesson?
Assumption of students.
Generalization of the answers, the formulation of the goal.
The purpose of our lesson: to learn about the importance of digestion, about the structure and functions of the digestive tract and digestive glands.
Have you all had breakfast today? Why do we eat? what digestive organs do you know?
Students' answers.
We will now look at how food is converted into energy and building materials.
IV... Digestion- a process that ensures the process of splitting complex organic matter and their entry into the blood and lymph.
The role of the digestive system is to make nutrients assimilable for the cells of our body.
Pupils sketch diagrams in a notebook.
Digestive system functions
Mechanical Chemical Ingestion, food chopping Suction Food digestion
under the influence of enzymes
The composition of the digestive system
Alimentary canal Digestive glands
Oral cavity Salivary glands
Pharynx Liver
Esophagus Pancreas
Stomach Intestinal glands
Small intestine
Colon
The composition of the walls of the alimentary canal
Outdoor Medium Indoor
(connective tissue) (muscle tissue) (epithelial tissue)
Alimentary canal. Watching a video.
The oral cavity is closed outwardly by the muscles of the cheeks and lips. Inside are the jaws, gums, teeth, pharynx, palate, uvula. The space between the cheeks, lips and mouth is called the vestibule. At the bottom is the tongue - it mixes food and pushes it down the throat. The ducts of the salivary glands open into the oral cavity. (Slide number 7).
Pharynx - formed by striated muscle tissue, located in front of the cervical vertebrae. It is divided into 2 sections, one connected to the larynx, the other by the esophagus. (Slide number 9).
The esophagus is a hollow muscular organ with a length of 25 cm. The mucous membrane is formed by stratified epithelium. (Slide number 10).
The stomach is a hollow muscular organ located in the upper abdomen, just below the diaphragm. At the junction with the esophagus and duodenum, there are annular muscles (sphincters). The place of transition to the duodenum 12 is the gatekeeper (Slide number 11).
Small intestine - length about 5 m. Divided into: duodenum (25-30 cm), jejunum, ileum. The walls consist of 2 muscle layers - longitudinal and transverse, their rhythmic contraction is called intestinal peristalsis. This is where the process of digesting food ends. The numerous villi absorb nutrients. (Slide number 12).
The large intestine is 1.3 m long. It absorbs water, breaks down fiber.
Consists:
1. The cecum, from it a process departs - the appendix.
2. Colon (ascending, transverse, descending, sigmoid).
Liver(1.5 kg., Bile, ducts flow into the duodenum, barrier role, storage of glucose, activates digestive enzymes). Slide number 19.
Pancreasiron (pancreatic juice, ducts flow into the duodenum, insulin) Slide number 16
Intestinalglands (enzymes capable of breaking down food substances, secrete mucus). Slide number 18.
Mucosal glandsstomach (transparent viscous odorless secret, pepsin proteins, NSIbactericidal action). Slide number 16.
V... Today in the lesson we got acquainted with the structure of the digestive tract and the digestive glands.
Oral questioning of students.
What are the organs of the digestive tract?
What are the digestive glands?
Briefly describe the properties of enzymes?
What are the main groups of enzymes you know.
VI... Lesson summary: So, our lesson comes to an end. What did you know before the lesson? What did you learn in today's lesson?
Students' answers.
Homework §41 §43 §44. Fill in the table with. 196 - 197.
You've worked hard today, let's clap our hands for it. Goodbye!
Plan
Introduction
1. The structure of the digestive system
Oral cavity
Small intestine
2. Functions of the gastrointestinal tract
Digestion in the mouth, chewing
Saliva functions
Swallowing
Digestion in the stomach
Principles of regulation of digestion processes
Transfer of chyme from the stomach to the intestine.
Digestion in the small intestine
Digestion in the colon
Bibliography
Introduction
In the process of vital activity of the body, nutrients are continuously consumed, which perform a plastic and energetic function.
The body has a constant need for nutrients, which include: amino acids, monosugar, glycine and fatty acids. The source of nutrients is a variety of foods, consisting of complex proteins, fats and carbohydrates, which are converted into simpler substances that can be absorbed during digestion. The process of breaking down complex nutrients by enzymes into simple chemical compounds that are absorbed, transported to and used by cells is called digestion. The sequential chain of processes leading to the breakdown of food substances into monomers that can be absorbed is called the digestive conveyor. The digestive conveyor is a complex chemical conveyor with a pronounced continuity of food processing processes in all departments. Digestion is the main component of a functional nutritional system.
1. The structure of the digestive system
The digestive system includes organs that carry out mechanical and chemical processing food products, absorption of nutrients and water into the blood or lymph, formation and removal of undigested food debris. The digestive system consists of the alimentary canal and digestive glands, details of which are shown in Figure 1.
Digestive system
Let's consider schematically the passage of food through the digestive tract. Food first enters the oral cavity, which is limited by the jaws: upper (motionless) and lower (mobile).
Oral cavity
The jaws contain teeth - organs that serve to bite off and grind (chew) food. An adult has 28-32 teeth.
An adult's tooth consists of a soft part - a pulp, penetrated by blood vessels and nerve endings. The pulp is surrounded by dentin, a bone-like substance. Dentin forms the basis of the tooth - it consists of most of the crown (the part of the tooth protruding above the gum), the neck (the part of the tooth located at the border of the gum) and the root (the part of the tooth located in the depth of the jaw). The crown of the tooth is covered with tooth enamel, the most solid matter human body, which serves to protect the tooth from external influences (increased wear, pathogenic microbes, excessively cold or hot food, etc. factors).
The teeth are divided according to their purpose: incisors, canines and molars. The first two types of teeth serve for biting off food and have a sharp surface, and the last one for chewing it and for this has a wide chewing surface. An adult has 4 canines and an incisor, and the rest of the teeth are molars.
In the oral cavity, in the process of chewing food, it is not only crushed, but also mixed with saliva, turns into a food lump. This mixing in the mouth is done with the tongue and cheek muscles.
The mucous membrane of the oral cavity contains sensitive nerve endings - receptors, with the help of which it perceives the taste, temperature, texture and other qualities of food. Excitation from receptors is transmitted to the centers of the medulla oblongata. As a result, according to the laws of the reflex, the salivary, gastric and pancreas begin to be included in the work sequentially, then the above-described act of chewing and swallowing occurs. Swallowing is the act of pushing food down the throat with the tongue and then, as a result of contraction of the muscles in the larynx, into the esophagus.
Pharynx
The pharynx is a funnel-shaped canal lined with mucous membrane. The upper wall of the pharynx is fused with the base of the skull, at the border between the VI and VII cervical vertebrae of the pharynx, narrowing, passes into the esophagus. Food enters the esophagus from the oral cavity through the pharynx; in addition, air passes through it, coming from the nasal cavity and from the mouth to the larynx. (There is an intersection of the digestive and respiratory tract in the pharynx).
Esophagus
The esophagus is a cylindrical muscular tube located between the pharynx and the stomach 22-30 cm long. The esophagus is lined with a mucous membrane, in its submucosa there are numerous own glands, the secret of which moisturizes food during its passage through the esophagus into the stomach. The movement of the food lump along the esophagus occurs due to the wave-like contractions of its wall - the contraction of individual areas alternates with their relaxation.
Stomach
From the esophagus, food enters the stomach. Stomach - resembling outward appearance retort, an expandable organ that is part of the digestive tract and is located between the esophagus and the duodenum. It connects with the esophagus through the cardiac opening, and with the duodenum - through the opening of the pylorus. The inside of the stomach is covered with a mucous membrane, which contains glands that produce mucus, enzymes and hydrochloric acid. The stomach is a reservoir for absorbed food, which is mixed in it and partially digested under the influence of gastric juice. Produced by the gastric glands located in the gastric mucosa, gastric juice contains hydrochloric acid and the enzyme pepsin; these substances take part in chemical processing food entering the stomach during digestion. Here, under the influence of gastric juice, proteins are broken down. This - along with the mixing action exerted on food by the muscular layers of the stomach - turns it into a partially digested semi-liquid mass (chyme), which then enters the duodenum. Mixing chyme with gastric juice and its subsequent expulsion into the small intestine is carried out by contraction of the muscles of the walls of the stomach.
Small intestine
The small intestine occupies most of the abdominal cavity and is located there, in the form of loops. Its length reaches 4.5 m. The small intestine, in turn, is divided into the duodenum, the jejunum and the ileum. It is here that most of the processes of food digestion and absorption of its contents take place. The area of the inner surface of the small intestine is increased by the presence of a large number of finger-like outgrowths called villi. The duodenum 12 is located next to the stomach, which is secreted in the small intestine, since the cystic duct of the gallbladder and the pancreatic duct flow into it.
The duodenum is the first of the three sections of the small intestine. It starts from the pylorus of the stomach and reaches the jejunum. The duodenum receives bile from the gallbladder (through the common bile duct) and pancreatic juice from the pancreas. In the walls of the duodenum there are a large number of glands that secrete an alkaline secretion rich in mucus that protects the duodenum from the effects of acidic chyme entering it from the stomach.
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The lean intestine is part of the small intestine. The jejunum makes up about two-fifths of the entire small intestine. It connects the duodenum and ileum.
The small intestine contains many glands that secrete intestinal juice. This is where the main food digestion and absorption of nutrients into the lymph and blood take place. The movement of the chyme in the small intestine occurs due to the longitudinal and transverse contractions of the muscles of its wall.
From the small intestine, food enters the large intestine with a length of 1.5 m, which begins with a saccular protrusion - the cecum, from which a 15 cm process (appendix) departs. It is believed to have some protective function. The colon is the main part of the large intestine, which consists of four sections: the ascending, transverse, descending, and sigmoid colon.
The large intestine mainly absorbs water, electrolytes and fiber, and ends with the rectum, which collects undigested food. The rectum is the end of the large intestine (about 12 cm long) that starts from the sigmoid colon and ends with the anus. During the act of defecation, feces pass through the rectum. Further, this undigested food is excreted from the body through the anus (anus).
2. Functions of the gastrointestinal tract
The motor or motor function is carried out due to the muscles of the digestive apparatus and includes the processes of chewing in the mouth, swallowing, moving food through the digestive tract and removing undigested residues from the body.
The secretory function is the production of digestive juices by glandular cells: saliva, gastric juice, pancreatic juice, intestinal juice, bile. These juices contain enzymes that break down proteins, fats and carbohydrates into simple chemical compounds. Mineral salts, vitamins, water enter the blood unchanged.
Endocrine function is associated with the formation of certain hormones in the digestive tract that affect the digestion process. These hormones include: gastrin, secretin, cholecystokinin-pancreozymin, motilin and many other hormones that affect the motor and secretory functions of the gastrointestinal tract.
The excretory function of the digestive tract is expressed in the fact that the digestive glands secrete metabolic products into the cavity of the gastrointestinal tract, for example, ammonia, urea, heavy metal salts, medicinal substances, which are then removed from the body.
Suction function. Absorption is the penetration of various substances through the wall of the gastrointestinal tract into the blood and lymph. Absorption are mainly products of hydrolytic breakdown of food - monosaccharides fatty acids and glycerin, amino acids, etc. Depending on the localization of the digestion process, it is divided into intracellular and extracellular.
Intracellular digestion is the hydrolysis of nutrients that enter the cell as a result of phagocytosis (a protective function of the body, which is expressed in the capture and digestion of foreign particles by special cells - phagocytes) or pinocytosis (absorption of water and substances dissolved in it by cells). In the human body, intracellular digestion takes place in leukocytes.
Extracellular digestion is divided into distant (cavity) and contact (parietal, membrane).
Distant (abdominal) digestion is characterized by the fact that enzymes in the digestive secretions hydrolyze nutrients in the cavities of the gastrointestinal tract. It is called distant because the process of digestion itself is carried out at a considerable distance from the place of formation of enzymes.
Contact (parietal, membrane) digestion is carried out by enzymes fixed on the cell membrane. The structures on which the enzymes are fixed are represented in the small intestine by the glycocalyx - a network-like formation from the processes of the membrane - microvilli. Initially, the hydrolysis of nutrients begins in the lumen of the small intestine under the influence of pancreatic enzymes. Then the formed oligomers are hydrolyzed by pancreatic enzymes. Directly at the membrane, the hydrolysis of the formed dimers produce intestinal enzymes fixed on it. These enzymes are synthesized in enterocytes and transferred to the membranes of their microvilli.
The presence of folds, villi, microvilli in the mucous membrane of the small intestine increases the inner surface of the intestine by 300-500 times, which ensures hydrolysis and absorption on the huge surface of the small intestine.
Digestion in the mouth, chewing
Digestion in the oral cavity is the first link in a complex chain of enzymatic breakdown of food substances into monomers. The digestive functions of the oral cavity include testing food for edibility, mechanical processing of food and its partial chemical processing.
Motor function in the oral cavity begins with the act of chewing. Chewing is a physiological act that provides crushing of food substances, wetting them with saliva and the formation of a food lump. Chewing ensures the quality of the mechanical processing of food in the mouth. It affects the digestion process in other parts of the digestive tract, changing their secretory and motor functions.
One of the methods for studying the functional state of the masticatory apparatus is masticiography - recording of the movements of the lower jaw when chewing. On the record, which is called a masticiogram, a chewing period can be distinguished, consisting of 5 phases:
Phase 1 - resting phase;
Phase 2 - the introduction of food into the oral cavity;
Phase 3 - tentative chewing or initial chewing function, it corresponds to the approbation process mechanical properties food and its initial crushing;
Phase 4 - the main or true phase of chewing, it is characterized by the correct alternation of chewing waves, the amplitude and duration of which is determined by the size of the portion of food and its consistency;
Phase 5 - the formation of a food lump looks like a wavy curve with a gradual decrease in the amplitude of the waves.
Chewing is a self-regulatory process based on a functional chewing system. A useful adaptive result of this functional system is a food bolus formed during chewing and prepared for swallowing. A functional chewing system is formed for each chewing period.
When food enters the oral cavity, irritation of the receptors of the mucous membrane occurs.
Excitation from these receptors along the sensory fibers of the lingual (branch of the trigeminal nerve), glossopharyngeal, tympanic cord (branch of the facial nerve) and superior laryngeal nerve (branch of the vagus nerve) enters the sensory nuclei of these nerves of the medulla oblongata (the nucleus of the salitaric tract and the nucleus of the trigeminal nerve). Further, the excitation along a specific path reaches the specific nuclei of the visual hillocks, where the excitation is switched, after which it enters the cortical section of the oral analyzer. Here, on the basis of the analysis and synthesis of the incoming excitations, a decision is made about the edibility of the substances entered into the oral cavity.
Inedible food is rejected (spit out), which is one of the important protective functions of the oral cavity. Edible food remains in the mouth and chewing continues. In this case, excitation from the mechanoreceptors of the periodontium, the supporting apparatus of the tooth, is added to the flow of information from the receptors.
The voluntary contraction of the masticatory muscles is provided by the participation of the cerebral cortex. Saliva takes part in the act of chewing and the formation of a food lump. Saliva is a mixture of secretions from three pairs of large salivary glands and many small glands located in the oral mucosa. Epithelial cells, food particles, mucus, salivary bodies (leukocytes, lymphocytes), microorganisms are mixed with the secret secreted from the excretory ducts of the salivary glands. This saliva, mixed with various impurities, is called oral fluid. The composition of the oral fluid changes depending on the nature of the food, the state of the body, as well as under the influence of environmental factors.
The secret of the salivary glands contains about 99% water and 1% dry residue, which includes anions of chlorides, phosphates, sulfates, bicarbonates, iodites, bromides, fluorides. Saliva contains cations of sodium, potassium, calcium, magnesium, as well as trace elements (iron, copper, nickel, etc.).
Organic matter is represented mainly by proteins. Saliva contains proteins of various origins, including mucin, a mucous protein. Saliva contains nitrogen-containing components: urea, ammonia, etc.
Saliva functions
The digestive function of saliva is expressed in the fact that it moistens the food lump and prepares it for digestion and swallowing, and saliva mucin glues a portion of food into an independent lump. More than 50 enzymes have been found in saliva.
Despite the fact that food is in the oral cavity for a short time - about 15 s, digestion in the oral cavity is of great importance for the implementation of further processes of food breakdown, since saliva, dissolving food substances, contributes to the formation of taste and affects appetite.
In the oral cavity, under the influence of saliva enzymes, the chemical processing of food begins. The saliva enzyme amylase breaks down polysaccharides (starch, glycogen) to maltose, and the second enzyme, maltase, breaks down maltose to glucose.
The protective function of saliva is expressed in the following:
saliva protects the oral mucosa from drying out, which is especially important in a person who uses speech as a means of communication;
the protein substance of saliva, mucin, is able to neutralize acids and alkalis;
saliva contains an enzyme-like protein substance lysozyme, which has a bacteriostatic effect and takes part in the processes of regeneration of the epithelium of the oral mucosa;
nuclease enzymes contained in saliva are involved in the degradation of viral nucleic acids and thus protect the body from viral infection;
blood coagulation enzymes were found in saliva, on the activity of which the processes of inflammation and regeneration of the oral mucosa depend;
substances that prevent blood clotting (antithrombinoplastins and antithrombins) were found in saliva;
saliva contains a large amount of immunoglobulins, which protects the body from the ingress of pathogens.
Trophic function of saliva. Saliva is biological environment, which is in contact with the enamel of the tooth and is for it the main source of calcium, phosphorus, zinc and other trace elements, which is an important factor for the development and preservation of teeth. The excretory function of saliva. Metabolic products - urea, uric acid, some medicinal substances, as well as salts of lead, mercury, etc., which are excreted from the body after spitting out, due to which the body is freed from harmful waste products, can be released into the composition of saliva.
Salivation is carried out by a reflex mechanism. Distinguish between conditioned reflex and unconditional reflex salivation.
Conditioned salivation is caused by the sight, smell of food, sound stimuli associated with cooking, as well as talking and remembering food. In this case, visual, auditory, olfactory receptors are excited. Nerve impulses from them go to the cortical section of the corresponding brain analyzer, and then to the cortical representation of the salivation center. From it, excitement goes to the department of the center of salivation, the commands of which go to the salivary glands.
Certainly reflex salivation occurs when food enters the oral cavity. Food irritates the receptors in the mucous membrane. Nerve impulses are transmitted to the center of salivation, which is located in the reticular formation of the medulla oblongata and consists of the upper and lower salivary nuclei.
Exciting impulses for the process of salivation pass through the fibers of the parasympathetic and sympathetic parts of the autonomic nervous system.
Irritation of the parasympathetic fibers that excite the salivary glands leads to the separation of a large amount of liquid saliva, which contains many salts and little organic matter.
Irritation of the sympathetic fibers causes the separation of a small amount of thick, viscous saliva, which contains little salt and a lot of organic matter.
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Of great importance in the regulation of salivation are humoral factors, which include hormones of the pituitary gland, adrenal glands, thyroid and pancreas, as well as metabolic products.
The separation of saliva takes place in strict accordance with the quality and quantity of nutrients taken. For example, when drinking water, saliva is almost not separated. And vice versa: with dry food, saliva is released more abundantly, its consistency is more liquid. When harmful substances enter the oral cavity (for example: ingestion of too bitter or acidic food), a large amount of liquid saliva is separated, which washes the oral cavity from these harmful substances, etc. Such an adaptive nature of salivation is provided by the central mechanisms for regulating the activity of the salivary glands , and these mechanisms are triggered by information coming from receptors in the oral cavity.
Salivation is a continuous process. In an adult, about one liter of saliva is released per day.
Swallowing
After the food lump has formed, swallowing occurs. This is a reflex process in which there are three phases:
oral (voluntary and involuntary);
pharyngeal (fast involuntary);
esophageal (slow involuntary).
The swallowing cycle lasts about 1 s. By coordinated contractions of the muscles of the tongue and cheeks, the food bolt moves to the root of the tongue, which leads to irritation of the receptors of the soft palate, the root of the tongue and the back of the pharynx. Excitation from these receptors along the glossopharyngeal nerves enters the swallowing center, located in the medulla oblongata, from which impulses go to the muscles of the oral cavity, larynx, pharynx and esophagus as part of the trigeminal, hypoglossal, glossopharyngeal and vagus nerves. The contraction of the muscles that lift the soft palate ensures that the entrance to the nasal cavity is closed, and the raising of the larynx closes the entrance to the airway. During the act of swallowing, contractions of the esophagus occur, which have the character of a wave that occurs in the upper part and propagates towards the stomach. Esophageal motility is regulated mainly by the fibers of the vagus and sympathetic nerves and by the nerve formations of the esophagus.
The swallowing center is located next to the medulla oblongata breathing center and interacts with it (when swallowing, breathing is delayed). From the pharynx, a lump of food enters the esophagus, and then into the stomach.
Digestion in the stomach
The digestive functions of the stomach are:
deposition of chyme (preservation for processing of stomach contents);
mechanical and chemical processing of incoming food;
evacuation of chyme into the intestine.
The excretory function of the stomach is to excrete metabolic products, medicinal substances, and heavy metal salts.
Motor function of the stomach. The motor function of the stomach is carried out by contraction of smooth muscles located in the wall of the stomach. The motor function of the stomach ensures the deposition of the food taken in the stomach, mixing it with gastric juice, moving the contents of the stomach to the exit into the intestine, and finally, portionwise evacuation of the gastric contents into the duodenum.
There are two main types of movement in the stomach - peristaltic and tonic.
Peristaltic movements are carried out by contraction of the circular muscles of the stomach. These movements begin at the greater curvature in the area adjacent to the esophagus, where the cardiac pacemaker is located. A peristaltic wave traveling through the body of the stomach transfers a small amount of chyme to the pyloric part, which is adjacent to the mucous membrane and is most exposed to the digestive action of gastric juice. Most of the peristaltic waves are extinguished in the pyloric region of the stomach. Some of them spread along the pyloric section with increasing amplitude (suggest the presence of a second pacemaker localized in the pyloric section of the stomach), which leads to pronounced peristaltic contractions of this section, increased pressure, and part of the contents of the stomach passes into the duodenum.
The second type of stomach contraction is tonic contractions. They arise due to changes in muscle tone, which leads to a decrease in the volume of the stomach and an increase in pressure in it. Tonic contractions help to mix the contents of the stomach and saturate it with gastric juice, which greatly facilitates the enzymatic digestion of food gruel.
The intestinal phase of gastric secretion begins from the moment the chyme enters the duodenum. Chyme irritates the receptors of the intestinal mucosa and reflexively changes the intensity of gastric secretion. In addition, local hormones (secretin, cholecystokinin-pancreosimin), the production of which is stimulated by the acidic gastric chyme entering the duodenum, exert an influence on gastric secretion in this phase.
Principles of regulation of digestion processes
The activity of the digestive system is regulated by nervous and humoral mechanisms.
The secretion of juice of the digestive glands is conditioned-reflexive and unconditionally reflexive. Such influences are especially pronounced in the upper part of the digestive tract. With distance from it, the participation of reflexes in the regulation of digestive functions decreases and the importance of humoral mechanisms increases. In the small and large parts of the intestine, the role of local regulatory mechanisms is especially great - local mechanical and chemical irritation increases the activity of the intestine at the site of the stimulus. Consequently, there is an unequal distribution of nervous, humoral and local regulatory mechanisms in the digestive tract. Local mechanical and chemical stimuli are influenced by peripheral reflexes and through the hormones of the digestive tract. Chemical stimulants of nerve endings in the gastrointestinal tract are: acids, alkalis, products of hydrolysis of food substances. Entering the blood, these substances are carried by its current to the digestive glands and excite them.
Especially great is the role in the humoral regulation of the activity of the digestive organs of hormones formed in the endocrine cells of the mucous membrane of the stomach, duodenum, jejunum, in the pancreas.
The main hormones and the effects to which their action leads: Gastrin - increased secretion of the stomach and pancreas, hypertrophy of the gastric mucosa, increased motility of the stomach, small intestine and gallbladder.
Secretin - an increase in the secretion of bicarbonates by the pancreas, inhibition of the secretion of hydrochloric acid in the stomach.
CCK-PZ (cholecystokinin-pancreosimin) - increased contraction of the gallbladder and bile secretion, the secretion of enzymes by the pancreas, inhibition of the secretion of hydrochloric acid in the stomach, increased secretion of pepsin in it, increased motility of the small intestine.
MOTILIN - increased motility of the stomach and small intestine, increased secretion of pepsin in the stomach.
Willikinin - increased motility of the villi of the small intestine, etc.
Hence, it can be concluded that the role of hormones in the gastrointestinal tract is important. They affect the functions of the entire gastrointestinal tract, namely: on motility, on the secretion of water, electrolytes and enzymes, on the absorption of water, electrolytes and nutrients, on the functional activity of the endocrine cells of the gastrointestinal tract. In addition, they affect the metabolism, the endocrine and cardiovascular systems, and the central nervous system. Several hormones are found in various structures of the brain.
Stimulates gastric secretion: the hormone gastrin is formed in the gastric mucosa; histamine - is found in nutrients and is formed in the gastric mucosa; protein digestion products; extractive substances of meat and vegetables; secretin - is formed in the intestinal mucosa (inhibits the secretion of hydrochloric acid, but enhances the secretion of pepsinogens) cholecystokinin-pancreosimin enhances the secretion of pepsins (inhibits the secretion of hydrochloric acid) and other substances.
They inhibit gastric secretion: products of fat hydrolysis and other substances.
Transfer of chyme from the stomach to the intestine.
The rate of evacuation of stomach contents into the intestine is influenced by many factors:
Food consistency - The contents of the stomach pass into the intestine when its consistency becomes liquid or semi-liquid. Fluids begin to pass into the intestine as soon as they enter the stomach.
The nature of the food - carbohydrate food is evacuated faster than protein, fatty food is retained in the stomach for 8-10 hours.
The degree of filling of the stomach and duodenum.
Motor function of the stomach and duodenum.
Hormones: secretin, cholecystokinin-pancreozymin - inhibit gastric motility and the rate of evacuation of its contents.
Enterogastric reflex - is expressed in inhibition of motor activity of the stomach when chyme enters the duodenum.
Digestion in the small intestine
Contractions of the small intestine are carried out as a result of coordinated movements of the longitudinal (outer) and transverse (inner) layers of smooth muscle cells. Functionally, abbreviations are divided into two groups:
1) local - provide grinding and mixing of the contents of the small intestine;
There are several types of abbreviations:
pendulum,
rhythmic segmentation,
peristaltic,
tonic.
Pendulum contractions are caused by the successive contraction of the annular and longitudinal muscles of the intestine. Consecutive changes in the length and diameter of the intestine lead to the movement of food gruel in one direction or the other (like a pendulum). Pendulum contractions promote mixing of chyme with digestive juices.
Rhythmic segmentation is provided by the contraction of the annular muscles, as a result of which the resulting transverse interceptions divide the intestine into small segments. Rhythmic segmentation promotes grinding chyme and mixing it with digestive juices. Peristaltic contractions are caused by the simultaneous contraction of the longitudinal and annular muscle layers. In this case, the annular muscles of the upper segment of the intestine contract and the chyme is pushed into the simultaneously expanded, due to the contraction of the longitudinal muscles, the lower part of the intestine. Thus, peristaltic contractions ensure the movement of the chyme along the intestine.
Tonic contractions have a low speed and may even not spread at all, but only narrow the intestinal lumen over a small extent.
The small intestine and, first of all, its initial section - the duodenum, is the main digestive section of the entire gastrointestinal tract. It is in the small intestine that food substances are converted into those compounds that can be absorbed from the intestine into the blood and lymph. Digestion in the small intestine occurs in its cavity - cavity digestion, and then continues in the zone of the intestinal epithelium with the help of enzymes fixed on its microvilli and folds - parietal digestion. The folds, villi and microvilli of the small intestine increase the inner surface of the intestine by 300-500 times.
In the hydrolysis of nutrients in the duodenum, the role of the pancreas is especially great. Pancreatic juice is rich in enzymes that break down proteins, fats and carbohydrates.
Amylase in pancreatic juice converts carbohydrates into monosugar. Pancreatic lipase is very active due to the emulsifying effect of bile on fats. Ribonuclease of pancreatic juice cleaves ribonucleic acid to nucleotides.
Intestinal juice is secreted by the glands of the entire mucous membrane of the small intestine. More than 20 different enzymes have been found in intestinal juice, the main of which are: enterokinase, peptidases, alkaline phosphatase, nuclease, lipase, phospholipase, amylase, lactase, sucrase. Under natural conditions, these enzymes carry out parietal digestion.
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The motor activity of the small intestine is regulated by nervous and humoral mechanisms. The act of eating briefly inhibits and then enhances the motility of the small intestine. The motor activity of the small intestine largely depends on physical and chemical properties chyme: rough food and fats increase its activity.
Humoral substances affect directly the muscle cells of the intestine, and through the receptors - on the neurons of the nervous system. Strengthen the motility of the small intestine: histamine, gastrin, motilin, alkalis, acids, salts, etc.
The initial secretion of the pancreas is caused by conditioned reflex signals (sight, smell of food, etc.). Inhibition of pancreatic secretion is observed during sleep, during painful reactions, during intense physical and mental work.
The leading role in the humoral regulation of pancreatic secretion belongs to hormones. The hormone secretin causes the secretion of a large amount of pancreatic juice, rich in bicarbonates, but poor in enzymes. The hormone cholecystokinin-pancreosimin also enhances the secretion of the pancreas, and the secreted juice is rich in enzymes. Increase the secretion of the pancreas: gastrin, serotonin, insulin. The department of pancreatic juice is inhibited: glucagon, calcitonin, ZhIP, PP.
The secretion of the intestinal glands increases during food intake, with local mechanical and chemical irritation of the intestine and under the influence of certain intestinal hormones.
Chemical stimulants of the secretion of the small intestine are the products of the digestion of proteins, fats, etc.
Digestion in the colon
The motor activity of the large intestine ensures the accumulation of intestinal contents, the absorption of a number of substances from it, mainly water, the formation of feces and their removal from the intestines. There are the following types of colon contractions:
tonic,
pendulum,
rhythmic segmentation,
peristaltic contractions,
antiperistaltic contractions (promotes the absorption of water and the formation of feces),
The regulation of the motor activity of the large intestine is carried out by the autonomic nervous system, moreover, sympathetic nerve fibers inhibit motility, and parasympathetic ones enhance it. Colon motility is inhibited by serotonin, adrenaline, glucagon, as well as irritation of rectal mechanoreceptors. Local mechanical and chemical irritations are of great importance in stimulating the motility of the colon.
The secretory activity of the large intestine is poorly expressed. The glands of the mucous membrane of the colon secrete a small amount of juice, rich in mucous substances, but poor in enzymes. The following enzymes are found in small quantities in the juice of the large intestine:
cathepsin,
peptidases,
amylase and nucleases.
The microflora of the large intestine is of great importance in the life of the organism and the functions of the digestive tract. The normal microflora of the gastrointestinal tract is necessary condition vital functions of the organism. The stomach contains little microflora, much more of it in the small intestine and especially a lot in the large intestine.
The importance of the intestinal microflora lies in the fact that it is involved in the final decomposition of undigested food residues. Microflora is involved in the decomposition of enzymes and other biologically active substances. Normal microflora suppresses pathogenic microorganisms and prevents the infection of the organism. Bacterial enzymes break down fiber that is undigested in the small intestine. The intestinal flora synthesizes vitamin K and B vitamins, as well as other substances necessary for the body. With the participation of the intestinal microflora in the body, the exchange of proteins, bile and fatty acids and cholesterol occurs.
Juice secretion in the large intestine is due to local mechanisms, with its mechanical stimulation, secretion increases by 8-10 times. Absorption is understood as a set of processes that ensure the transfer of various substances into the blood and lymph from the digestive tract.
Distinguish between the transport of macro- and micromolecules. The transport of macromolecules and their aggregates is carried out by phagocytosis and pinocytosis. A certain amount of substances can be transported through the intercellular spaces. Due to these mechanisms from the intestinal cavity to internal environment penetrates a small amount of proteins (antibodies, enzymes, etc.), some bacteria.
From the gastrointestinal tract, mainly micromolecules are transported: monomers of nutrients and ions. This transport is divided into:
active transport;
passive transport;
facilitated diffusion.
Active transport of substances is the transfer of substances through membranes with the expenditure of energy and with the participation of special transport systems: mobile carriers and membrane transport channels.
Passive transport is carried out without energy consumption and includes: diffusion, filtration. Driving force diffusion of solute particles is the presence of a change in their concentration.
Filtration is understood as the process of transporting a solution through a porous membrane under the action of hydrostatic pressure.
Facilitated diffusion, like simple diffusion, is carried out without the expenditure of energy by changing the concentration of the solute. However, facilitated diffusion is a faster process and is carried out with the participation of a carrier.
Absorption of vital substances in various parts of the digestive tract.
Absorption occurs throughout the digestive tract, but its intensity is different in different parts. In the oral cavity, absorption is practically absent due to the short-term stay of substances in it and the absence of monomeric (simple) hydrolysis products. However, the oral mucosa is permeable to sodium, potassium, some amino acids, alcohol, and some medicinal substances.
In the stomach, the intensity of absorption is also low. Here water and mineral salts dissolved in it are absorbed, in addition, weak solutions of alcohol, glucose and small amounts of amino acids are absorbed in the stomach.
In the duodenum, the intensity of absorption is greater than in the stomach, but even here it is relatively low. The main absorption process takes place in the small intestine. The motility of the small intestine is of great importance in the processes of absorption, since it not only promotes the hydrolysis of substances (due to the change in the parietal layer of the chyme), but also the absorption of its products. In the process of absorption in the small intestine, the contractions of the villi are of particular importance. The stimulants of villous contraction are the products of hydrolysis of nutrients (peptides, amino acids, glucose, food extractives), as well as some components of the secretions of the digestive glands, for example, bile acids. Humoral factors also increase the movement of the villi, for example, the hormone villikinin, which is produced in the mucous membrane of the duodenum and in the jejunum.
Absorption in the colon under normal conditions is negligible. It is mainly the absorption of water and the formation of feces occurs here. In small quantities, glucose, amino acids, and also other easily absorbed substances can be absorbed in the large intestine. On this basis, nutritional enemas are used, i.e., the introduction of easily digestible nutrients into the rectum.
After hydrolysis to amino acids, proteins are absorbed in the intestine. The absorption of different amino acids in different parts of the small intestine occurs at different rates. The absorption of amino acids from the intestinal cavity is carried out actively with the participation of the carrier and with the expenditure of energy. Then amino acids are transported into the intercellular fluid by the mechanism of facilitated diffusion. The amino acids absorbed into the bloodstream enter the liver through the portal vein system, where they undergo various transformations. A significant proportion of amino acids are used for protein synthesis. Amino acids dispersed by the bloodstream throughout the body serve as the starting material for the construction of various tissue proteins, hormones, enzymes, hemoglobin and other substances of a protein nature. Some of the amino acids are used as a source of energy.
The intensity of absorption of amino acids depends on age (it is more intense at a young age), on the level of protein metabolism in the body, on the content of free amino acids in the blood, on nervous and humoral influences.
Carbohydrates are absorbed mainly in the small intestine as monosaccharides. Hexoses (glucose, galactose, etc.) are absorbed with the highest rate, pentoses are absorbed more slowly. The absorption of glucose and galactose is the result of their active transport across the membranes of the intestinal walls. The transport of glucose and other monosaccharides is activated by the transport of sodium ions across membranes.
The absorption of different monosaccharides in different parts of the small intestine occurs at different rates and depends on the hydrolysis of sugars, the concentration of the formed monomers, and on the characteristics of the transport systems of intestinal epithelial cells.
Various factors, especially the endocrine glands, are involved in the regulation of carbohydrate absorption in the small intestine. The absorption of glucose is enhanced by hormones of the adrenal glands, pituitary gland, thyroid and pancreas. Absorbed in the intestine, monosaccharides enter the liver. Here, a significant part of them is retained and converted into glycogen. Some of the glucose enters the general bloodstream and is carried throughout the body and used as a source of energy. Some of the glucose is converted into triglycerides and is deposited in fat depots (fat storage organs - liver, subcutaneous fat layer, etc.). Under the action of pancreatic lipase in the cavity of the small intestine, diglycerides are formed from complex fats, and then monoglycerides and fatty acids. Intestinal lipase completes lipid hydrolysis. Monoglycerides and fatty acids with the participation of bile salts are transferred to intestinal epithelial cells through membranes using active transport. In the intestinal epithelial cells, the breakdown of complex fats occurs. From triglycerides, cholesterol, phospholipids and globulins, chylomicrons are formed - the smallest fat particles enclosed in a lipoprotein membrane. Chylomicrons leave the epithelial cells through the membranes, pass into the connective tissue spaces of the villi, from there, with the help of villus contractions, they pass into its central lymphatic vessel, thus, the main amount of fat is absorbed into the lymph. Under normal conditions, a small amount of fat enters the bloodstream.
Parasympathetic influences enhance, and sympathetic ones - slow down the absorption of fats. The hormones of the adrenal cortex, thyroid gland and pituitary gland, as well as the hormones of the duodenum - secretin and cholecystokinin - pancreosimin, increase the absorption of fats.
Fats absorbed into the lymph and blood enter the general bloodstream. The main amount of lipids is deposited in fat stores, of which fats are used for energy purposes.
The gastrointestinal tract takes an active part in the body's water-salt metabolism. Water enters the gastrointestinal tract as part of food and liquids, secretions of the digestive glands. The main amount of water is absorbed into the blood, a small amount into the lymph. The absorption of water in the stomach begins, but it occurs most intensively in the small intestine. Actively absorbed solutes by epithelial cells "pull" water along. Sodium and chlorine ions play a decisive role in the transfer of water. Therefore, all the factors affecting the transport of these ions also affect the absorption of water. Absorption of water is associated with the transport of sugars and amino acids. The exclusion of bile from digestion slows down the absorption of water from the small intestine. Inhibition of the central nervous system (for example, during sleep) slows down the absorption of water.
Sodium is intensively absorbed in the small intestine. Sodium ions are transferred from the cavity of the small intestine into the blood through intestinal epithelial cells and through the intercellular channels. The entry of sodium ions into the epithelial cell occurs passively (without energy consumption) due to the difference in concentration. Sodium ions are actively transported from epithelial cells through membranes to the intercellular fluid, blood and lymph.
In the small intestine, the transfer of sodium and chlorine ions proceeds simultaneously and according to the same principles, in the large intestine there is an exchange of absorbed sodium ions for potassium ions.With a decrease in the sodium content in the body, its absorption in the intestine increases sharply. The absorption of sodium ions is enhanced by hormones of the pituitary gland and adrenal glands, and they inhibit gastrin, secretin and cholecystokinin-pancreosimin.
The absorption of potassium ions occurs mainly in the small intestine. Chlorine ions are absorbed in the stomach, and most actively in the ileum.
Of the divalent cations absorbed in the intestine, the most important are the ions of calcium, magnesium, zinc, copper and iron. Calcium is absorbed along the entire length of the gastrointestinal tract, but its most intense absorption occurs in the duodenum and the initial part of the small intestine. In the same part of the intestine, ions of magnesium, zinc and iron are absorbed. Copper absorption occurs primarily in the stomach. Bile has a stimulating effect on the absorption of calcium.
Water-soluble vitamins can be absorbed by diffusion (vitamin C, riboflavin). Vitamin B2 is absorbed in the ileum. The absorption of fat-soluble vitamins (A, D, E, K) is closely related to the absorption of fats.
Bibliography
Great Medical Encyclopedia Vasilenko V. Kh., Galperin E. I. et al., Moscow, "Soviet Encyclopedia", 1974.
Disease of the digestive system Daikhovsky Ya. I., Moscow, "Medgiz", 1961.
Diseases of the liver and biliary tract Tareev EM, Moscow, "Medgiz", 1961.
Treatment of diseases of the digestive system Gazhev B. N., Vinogradova T. A., St. Petersburg, "MiM-Express", 1996.
Medical assistant's handbook Bazhanov N. N., Volkov B. P. et al., Moscow, "Medicine", 1993.
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