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Anatomy of a digestive tract of the child
Laying of digestive organs occurs at an early stage of an embryogenesis. Already to 7 — to the 8th day from an entoderm the organization in the form of a tube of primary gut begins, and for the 12th day primary gut is divided into two parts: intra germinal — future digestive tract and not germinal — a vitellicle.
In the beginning primary gut terminates blindly in connection with existence of oropharyngeal and kloakalny membranes. On the 3rd week of pre-natal development there is a fusion oropharyngeal, and on the 3rd month — kloakalny membranes. Disturbance of this process causes development of anomalies of a digestive tract. Formation of various departments of a digestive tract begins with the 4th week of embryonal life: from a front gut the throat, a gullet, a stomach and part of a duodenum with rudiments of a pancreas and liver develops, from an average gut the part of duodenal, lean and ileal guts forms, from back all departments of a large intestine develop.
In the beginning (on the 4th week) the gullet has an appearance of a tube which gleam owing to proliferation of cellular weight is filled. On 3 — the 4th month laying of glands which begin to cosecrete actively that promotes formation of a gleam in a gullet is observed. Disturbance of process of a rekanalization is the reason of inborn narrowings and strictures of a gullet. By the birth the gullet is generally created. Length of a gullet increases with age. The mucous membrane of a gullet near an entrance to a stomach has glands similar to glands of initial part of a stomach. At children time of renewal of cells of a mucous membrane of a gullet is not defined. In a gullet the upper and lower sphincter is allocated. The esophageal phase of swallowing includes peristaltic waves. Length of a peristaltic wave is equal in a gullet to 2 — 4 cm, and distribution speed — 2 — 4 cm / page.
The stomach as local spindle-shaped expansion of a front gut appears on the 3rd week of a gestation. Its growth happens very intensively. Gastric poles I arise! and areas of small curvature on the 7th week. Further the quantity of gastric poles increases. On the 10th week there is laying of future glands in the form of accumulation of cells. Large oxyphilic cells probably are obkladochny. The main cells are differentiated on 17 — the 18th week from additional.
The peloric sphincter begins to form with the 12th week, and cardial — on the 16th.
In the post-natal period there is a further development of a stomach. Newborns have about 200 thousand gastric poles in which openings of gastric glands open. In 15 years the number of gastric poles reaches 4 million. About 150 — 200 thousand glands are the share of 1 kg of body weight at newborns that is 2,5 times less, than at the adult. From the beginning of an enteroalimentation the amount of gastric glands begins to increase quickly. In 15 years about 18 million gastric glands are defined.
The stomach of newborn (fig. 1.1) differs in a special originality.
The stomach at the newborn vertical, is located to the left of a midline, the gatekeeper — in the average and longitudinal plane or a little to the right of it. Depending on a degree of admission the stomach of the newborn can have 3 various forms.
The first form is a form at the time of delivery. At this time the stomach is filled and has the bag form with very small bottom making 1/5 part of its total length. The body of a stomach leans on a colon which is filled. The slanting axis of a stomach passing caudally and kpered, forms with intestines a corner 45 — 50 °. The pyloric part long, a cylindrical form is also located ahead of portal fissures, under a share having a tail. The stomach dorsalno and kranialno adjoins to a pancreas, and caudally — to a cross colon. It has 3 surfaces and 2 curvatures.
Gradually, in process of gastric emptying, its form and situation in relation to surrounding bodies change.
The second form (after release of meconium) — the empty stomach is flattened, has square shape and located slantwise.
Fig. 1.1. A stomach of the newborn 1 — the cardia, 2 — a bottom, 3 — a body, 4 — antral department, 5 — peloric department
The mass of a stomach — 6,5 g. A mucosal surface — 40 — 50 cm2. Anatomic volume — 30 — 35 cm3. Physiological volume — 7 cm3. Stomach length — 5 cm (the adult — 27 cm) a stomach Axis — 5,5 cm (adult — 34 cm). Distance between big and small curvature when emptying — 1,4 cm, when filling — 2,3 — 3,3 cm. The greater cul-de-sac makes 1/4 lengths (the adult — 1/3.) Channel of the gatekeeper: length — 0,6 — 1 cm, width — 0,4 — 1,2 cm
The pyloric part of a stomach forms almost right angle opened to the right with small curvature. The gatekeeper still closed by a liver as well as other part of a stomach, comes for the average line, being located to the right of a rachis.
In several days after release of meconium the third shape of a stomach appears (transitional to a shape of a stomach of the baby) — the stomach is located cross, big curvature caudally. At the age of 2 — 3 the stomach starts holding vertical position over again and only after 8 flyings acquires the constant provision, as from the adult.
The stomach plays a reservoir role. Here food masses mixes up with a gastric juice and then in the small portions comes to a duodenum for further processing and absorption.
The movements of a stomach are closely connected with its filling, and also with hashing and movement of food. Its characteristic is that even at receipt of a large number of food pressure in a gleam changes slightly that is partially connected with plasticity of unstriated muscles, and also with change of a structure of a wall of a stomach when filling.
Hashing of food masses with a gastric juice is carried out thanks to peristaltic reductions. Usually they begin from the site located in a stomach upper body in the field of big curvature ("pacemaker"). From here circular peristaltic reductions extend to peloric department with a speed of 10 — 40 cm / with, the interval between reductions makes about 20 pages. The food masses mixed with a gastric juice is called a chyme.
Receipt of separate portions of a chyme in a bulb of a duodenum happens during strong reductions of antral area. During their this area almost completely separates from a stomach body, and then the peloric channel is shortened in the longitudinal direction ("a systole of antral department"). After reception of the mixed food gastric emptying happens almost exponential — at first quickly, and then more and more slowly. Speed of emptying depends on a number of factors, for example, of quantity and structure of food and the sizes of its particles. Badly chewed food is late in a stomach longer, than liquid or kashitseobrazny. Greasy food is evacuated from a stomach later 4 h after reception or longer. Squirrels leave from a stomach quicker, and carbohydrates — even quicker.
In an empty stomach sometimes there are reductions with the period characteristic of a gastric vermicular movement — 20 pages. Such reductions call "hungry", however, their connection with feeling of hunger is not established. Perhaps, hormone motilin participates in generation of "hungry" reductions.
Intestines in the antenatal period develop quickly enough. On the 3rd month of pre-natal development there is a process of movement of a small and large intestine which carries the name of turn of intestines. At this moment different types of disturbances are possible (hernia of an umbilical cord, impassability of a duodenum, etc.).
At a human embryo about 24 mm in size the gleam of an intestinal tube is for the first time planned. At the child of the first year of life the small bowel has length of 1,2 — 2,8 m that is almost twice less, than at the adult.
Nevertheless, at recalculation 1 m is the share of 1 kg of body weight at the newborn, and the adult has 10 cm of length of a small intestine. Possibly, it is expression of evolutionarily developed adaptation to laktotrofny food at which the main link of digestion is pristenochny which, according to A. M. Ugolev, is enough for hydrolysis and assimilation of milk by the fermental systems deployed on a membrane of a brush border. The surface area of a small intestine in the form of the simple cylinder at children on the 1st week of life makes 85 cm3 (40 — 144 cm3), adults have 3,3 x 103 cm3. Intestinal folds increase this surface by 3 times, and fibers — by 10 times in comparison with the cylinder. Microvillis increase a surface of a small intestine by 20 times in comparison with the surface area measured with fibers.
The small intestine is divided into 3 parts in the proksimalnodistalny direction — a duodenal, lean and ileal gut. The sphincteric device of a duodenum is provided by 3 functional sphincters. The relief of a mucous membrane differs from that in a stomach. Circular (kerkringova) folds have the cross direction.
It is considered to be that the jejunum occupies 2/5 lengths of intestines between a duodenum and the ileocecal valve (a bauginiyeva the gate), and ileal — the others 3/5. Cells of an epithelium of a mucous membrane of a small intestine are quickly updated. Time necessary in order that the cell from the center of reproduction in a crypt reached a fiber surface, is called transition time which is approximately equal in an ileal gut to 80 h.
Small intestine richly vaskulyarizirovan. Blood volume in a mezenterialny bed makes 10 — 30% of all volume of blood.
In a small intestine the acid chyme mixes up with alkaline secrets of a pancreas, liver and intestinal glands. Digestion of food is carried out mainly at the expense of enzymes of pancreatic and intestinal juice with bile participation. Absorption of products of digestion happens almost only in a small intestine.
The movements of a small intestine first of all provide full hashing of a chyme with pancreas juice, bile and secrets of intestinal glands. Such hashing is possible thanks to not propulsive peristaltics, rhythmic segmentation, the pendulum movements and reductions of fibers. All these movements promote continuous contact of a mucous membrane with various sites of a chyme. Mainly the intermuscular texture is responsible for motor control of a small intestine. As the irritant starting and supporting the movements of intestines serves stretching of its wall. Peristaltic waves always extend on a small intestine in the oral and proctal direction (Kennon's law). The movements of fibers are regulated submucosal by neuroplex. After receipt of an acid chyme in a duodenum in a mucous membrane of intestines there is a substance which received the name villikinin, starting and supporting reductions of fibers which does not influence other muscular layers.
Its length is equal in any age to body length. It has all departments, as at the adult, but in various extent of development. Unlike the adult the newborn has no adnexal epiploons, ledges of a large intestine (gaustra). The structure as at the adult is established after 3 — 4.
The large intestine possesses characteristic feature of a structure: its outside longitudinal muscular layer is located on a surface in the form of strips. Thanks to their tone, and also reductions of separate sites of a circular muscular layer the large intestine forms folds and swellings (gaustra). Waves of haustration represent a slow not propulsive peristaltics. At the same time in a large intestine also rhythmic segmentation meets. The propulsive peristaltics in this department of a digestive tract is shown by "peristaltic throws" — the powerful waves of reduction beginning from a caecum and extending on all colonic and sigmoid gut. During such waves arising 2 — 3 times a day, contents of a colon are expelled in sigmoid and a rectum. Time of stay of fecal masses in a large intestine usually makes at least 12 h.
Rhythmic segmentation and propulsive peristaltics of a large intestine are regulated intermuscular and submucosal by neuroplexes.
From a small intestine via the ileocecal gate about 200 — 500 ml of a chyme daily come to a caecum. In a large intestine there is its concoction by a water reabsorption. Electrolytes and water-soluble vitamins reabsorbirutsya at the same time. Absorption of all these substances in a large intestine is insignificant.
Bookmark it occurs at an embryo on the 3rd week. By 26th week exocrine cells of an acinus already vysokoorganizovana. Except a ferruterous parenchyma pancreatic islands (Langergans) are formed. By the birth the pancreas is finally not created. At the birth the mass of gland makes from 3 to 7 g. Most intensively it grows in the first 3 years and in the pubertal period.
Liver and bilious ways.
Liver with system of channels and a gall bladder develop on the 4th week of pre-natal development. By the birth the liver is one of the largest bodies. Its weight makes 4,38% of the body weight of the newborn. The left hepatic lobe by the birth of a massivn that is explained by an originality of its blood supply. The liver continues to grow in the post-natal period, however the speed of increase in its weight lags behind body weight. The main morfo-functional unit of a liver is the segment which has the hexagonal form. Believe that the liver contains about 500 thousand segments. The normal liver consists of 300 billion hepatocytes. The general surface of all cellular and subcellular membranes makes 33 sq.m. On this huge membrane surface and in it numerous biological responses proceed. Carry to cellular elements of a liver — hepatocytes, an epithelium of the bilious courses, endothelial cells of sinusoid, kupferovsky cells, lipopita (cells, etc.) and PIT-cells.