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EXOCRINE PART OF THE PANCREAS EMBRYONIC DEVELOPMENT AND PHYSIOLOGY OF THE PANCREAS
Embryogenesis. The pancreas appears on the 5th week of pre-natal development from two rudiments of a duodenum, ventral and dorsal. By 7th week they merge with each other to the left of a duodenum, and from a ventral rudiment forms back and lower speak rapidly heads with the main pancreatic channel, and from a dorsal rudiment — a body and a tail of gland with an additional (santoriniyevy) channel. There is a set of options of merge of these channels. Virzungov Canal (the main exocrine pancreat duct) is usually reported with the general bilious channel and opens in a big nipple of a duodenum. Santoriniyev Canal usually merges with the main pancreatic channel, but at 10% of people has a separate exit in a duodenum. Perhaps also division of a virzungov and general bilious channel.
Exocrine and endocrine cells form in places of a branching of small channels, gradually filling mesenchymal spaces between them. Exocrine cells form the ferruterous segments having small channels which through a network of wider channels open to the main pancreatic canal. Endocrine cells are located nests in interlobular spaces. The zymogen granules containing pancreatic enzymes are found in exocrine cells on the 4th month of pregnancy, but forming of segments completely comes to the end only on the second year of life. Therefore, at chest age production of enzymes is rather low, though is sufficient for adequate digestion in intestines, even at premature children.
Physiology. Acinar cells cosecrete various enzymes which split macromolecular components of food on simpler. The last are digested and soaked up in intestines. a-Amilaza destroys long oligosakharidny chains of starch and other polysaccharides, splitting and - 1,4-glucosidic bonds therefore are formed a maltose, isomaltose and low-molecular branched dextrins with and-1,6 communication. Proteolytic hydrolases (trypsin, chymotrypsin and elastase) affect internal bonds in a protein molecule owing to what it breaks up to peptides which are in turn split by aminopeptidases of an intestinal epithelium. Ekzopeptidaza (carboxypeptidase A and B) cut off trailer amino acids of some - peptides. All proteolytic enzymes cosecrete in an inactive form (proferments) as their function is blocked by trailer segments. Trypsin proferment — trypsinogen — is activated by enterokinase (an endopeptidase of a brush border), and trypsin activates proferments of other proteases. Thus, proteolytic activity of pancreatic juice is shown only in an intestines cavity, and in channels and fabric of gland it is absent that protects them from an autolysis. The phospholipase which could also digest gland fabric cosecretes in the form of proferment and is activated by trypsin. The lipase hydrolyzing triglycerides to monoglycerides and fatty acids cosecretes in an active form.
The pancreas also excretes liquid and electrolytes. The daily volume of pancreatic juice at adults is equal to about 1,5 l. Concentration of sodium and potassium in juice same, as in a blood plasma. Bicarbonates are produced by the cells covering small pancreatic channels; in a pancreatic secret concentration is several times higher than them, than in plasma.
Secretory function of gland is under hormonal and nervous control. In an epithelium of upper part of a small bowel 2 hormones are produced: the cholecystokinin stimulating secretion of enzymes, and the secretin influencing release of liquid and bicarbonates. Cholecystokinin also strengthens release of enterokinase from a brush border of an epithelium in an intestines gleam, promoting thereby contact of this activating enzyme with tripsinogeiy. Secretion of hormones depends on character of food and acidity of contents of a duodenum, and, therefore, is defined by requirements of process of digestion. Besides, pancreatic secretion is regulated by visceral efferent fibers of a vagus nerve which work similar to cholecystokinin.
Zoppi and soavt. studied secretion of pancreatic juice in response to stimulation by cholecystokinin and secretin at the premature and been born in time children. In both groups secretion of trypsin and a lipase was approximately identical at the birth, but secretion of amylase at been born in time — is 5 times higher. At children of advanced age of trypsin and a lipase it is allocated in 10 times more, than at the newborns who were born in time. Level of enzymes normal gradually increases during feeding by breast milk, however Zoppi showed that the maximum secretion can be induced within 1 month if to give to the child the food enriched with protein. At children of chest age amylase is produced in a small amount, but in the next years its products increase by 300 — 500 times; content of this enzyme slowly changes under the influence of the food saturated with starch. Nevertheless the intolerance of starch caused by its insufficient digestion is observed extremely seldom. Therefore, production of amylase, apparently, corresponds to needs of the child.
Secretory function of a pancreas is estimated, measuring the content in juice of enzymes, liquid and bicarbonates after stimulation by hormones (exogenous reaction) or food, fats and amino acids (endogenous reaction). For this purpose under roentgenoscopic control enter a probe for collecting pancreatic juice into a duodenum. Exogenous and endogenous reactions can be inadequate, especially when the mucous membrane of intestines is injured and its cells are incapable to produce endogenous cholecystokinin and secretin. More exact quantitative data on total secretory activity of gland can be obtained if to perfuse the liquid containing not absorbed marker through a duodenum and at the same time to stimulate secretory activity of gland with the hormones entered intravenously. At the same time other probe pump out gastric contents to prevent its mixing with pancreatic juice.
Indirectly it is possible to estimate function of a pancreas by means of microscopic examination a calla regarding detection of droplets of not hydrolyzed neutral fat and muscle fibers testimonial of deficit of digestive enzymes. Definition in Calais of proteases, usually trypsin and chymotrypsin, gives useful information if material is collected during 3 — 5 days as activity of these enzymes in Calais quite low at insufficiency of a pancreas. Deficit of enterokinase, the rare, but important reason of insufficiency of food and diarrhea at early children's age, can be found software decline in the ability of duodenal juice to activate trypsinogen.
ANOMALIES OF DEVELOPMENT OF THE PANCREAS
This rare anomaly arises when on the 6th week of embryonic development the ventral rudiment of gland remains behind a duodenum, and other part of body turns kzad and merges with it. Thus there is a closed pancreatic ring around a duodenum.
The symptomatology depends on on what extent the gut is squeezed. This disease is observed at the children who were born from pregnancy abounding in water; it can be shown by full or partial duodenal obstruction during the period
neonatality, impassability during other age periods; possibly and asymptomatic current. If the general bilious channel is squeezed, then incidentally there are bilious gripes or attacks of pancreatitis. On roentgenograms narrowing of the descending part of a duodenum is visible. Treatment consists in creation of a bypass anastomosis; a pancreas it is impossible neither to make cuts, nor to divide.
The ring-shaped pancreas is often combined with other anomalies, including a Down syndrome, an atresia of intestines, commissure of an abdominal cavity, the wrong turn of an intestinal tube, a nonperforated anus.
Inborn cysts of a pancreas usually happen multiple. They are bessimptomna, are often combined with a polycystosis of other bodies.
The malrelated tissue of a pancreas is found in a stomach or a small bowel. The ectopic centers, asymptomatic in most cases, can sometimes become the reason of bleedings, ulcerations and impassability; cases when malrelated gland caused intestines invagination are known. Insufficiency of a pancreas — a mucoviscidosis see in appropriate section.
OTHER TYPES OF INSUFFICIENCY OF THE PANCREAS
The insufficiency of a pancreas which is combined with a neutropenia, low growth and anomaly of bones (Shvakhman's syndrome). This state meets 100 times less often than a mucoviscidosis, but nevertheless is the reason of pancreatic insufficiency, the second for frequency, at children. Its etiology is unknown. Disturbance of migration of peripheral polymorphonuclear leukocytes in response to hemotaksichesky incentives is noted. It is possible to speak about an autosomal and recessive mode of inheritance if in a family there are more than one sick sibs; quite often also sporadic cases meet.
Segments of a pancreas are usually substituted with fatty tissue without development of fibrosis, but islands and channels are damaged slightly. However the functioning ferruterous fabric, apparently, is lost to a lesser extent, than shows studying of bioptat as some patients quite well acquire fats, especially becoming is more adult. After stimulation by cholecystokinin and secretin production of enzymes steadily remains low, but unlike a mucoviscidosis secretion of liquid and bicarbonates is not changed. The neutropenia can be heavy or easy, constant, incidental or cyclic. Thrombocytopenia and hypoplastic anemia are observed often, but are, as a rule, expressed slightly. Process of maturing of granulocytes in marrow is broken, the quantity of granulotsitarny stem cells can be reduced, but these phenomena are observed not always. Approximately at 50% of patients on roentgenograms of bones symptoms of a dyschondroplasia of metaphyses are visible; the first the femur head usually is surprised, but changes of metaphyses and other bones are possible. At some patients with a bright symptom short edges with the free front ends are. At a number of patients the thorax at the birth is so narrow that complicates breath. If there is no expressed insufficiency of food, then growth of the child is not broken though at 80% of patients growth is less than 3rd percentile. Development of bones corresponds to growth.
The diagnosis is usually made at chest age when patients suffer from heavy recurrent infections and disturbances of absorption. Shvakhman's syndrome differs from a mucoviscidosis in the normal content of chlorides in a secret of sweat glands. Other reasons of malabsorption can be excluded quite easily, having found insufficiency of a pancreas in combination with a neutropenia. Sometimes at patients with heavy insufficiency of food secondary pancreatic insufficiency and a leukopenia develop. In such cases Shvakhman's syndrome can be excluded, having only proved that function of gland is recovered in process of food improvement. Migration of leukocytes is broken both at insufficiency of food, and at Shvakhman's syndrome.
There is no specific treatment. At chest age it is necessary to enter in addition pancreatic enzymes, but further they are not required if there is no malabsorption. Most of children endure early age, and further the illness proceeds surprisingly easily.
Inborn insufficiency of enterokinase (see section 12.45).
Deficit of separate enzymes of a pancreas. In literature there are single messages on deficit of separate enzymes of a pancreas, apparently, of hereditary character, but these cases are documented insufficiently fully. The children who had according to the description, selective insufficiency of a lipase, perhaps, had a pancreas hypoplasia (Shvakhman's syndrome), and the described cases of insufficiency of trypsinogen can be actually caused by insufficiency of enterokinase.
Secondary insufficiency of a pancreas as it was noted above, arises at insufficiency of food, and also against a heavy enteropathy. Production of pancreatic enzymes can be reduced at insufficiency of food owing to protein synthesis disturbance, and their secretion is broken because of shortage of the stimulating hormones. (At an enteropathy the cells producing secretin and cholecystokinin collapse.) Normal reaction of a pancreas to exogenous hormones and lack of reaction to introduction to a duodenum of acid or digestive enzymes are characteristic of a gluten illness.
Pancreas at system diseases
Some system diseases are followed by acute or chronic changes in a pancreas, but gland defeat symptoms at the same time are absent. At leukoses, Hodzhkin's illness and other lymphogranulomatoses gland infiltration is often observed. The expressed fibrosis of gland is possible at heavy inborn syphilis. Fibrosis in combination with a widespread atrophy of acinar fabric can be a consequence of long stagnation of blood in iron at chronic heart failure. Miliary abscesses accompany a septicaemia, and tuberculomas — to miliary tuberculosis. Pancreas new growths occur at children seldom.