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Download Lecture 27. Digestion in oral cavity and stomach
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Digestion in oral cavity and stomach Common characteristic of the mouth cavity digestion In the oral cavity take place such main processes: 1. Primary analyses of substances, which are coming to organism – taste analyzes; 2. Reflector signals from receptor, which are present in these area to the another organs of digestive system, to the central nerve system – medulla oblongata, stomach, small intestine, pancreas; 3. Chemical processing of food; 4. Mechanical processing of food; 5. Absorption of some substances. Chewing of food is important, because fruits and vegetables have cellulose which must be broken before the food can be utilized. In the mouth cavity begin digestion of carbohydrates, which help to the functional activity of pancreas. When our food are in the mouth stimulate the receptors of oral cavity; from which impulses go to the different part of brain and return to different part of digestion tract – stomach, small intestine, pancreas, in which secreted juices with enzymes In the mouth cavity open three pair of big salivary glands and a lot of small buccal glands. Submandibular and sublingual glands consist of the cells of serum and mucous types and secrete serous and mucus types of saliva. Parotid glands consist of the serum types cells and secrete serous type of saliva. Small buccal glands consist of mucous types of cells; produce mucous saliva with a big quantity of water. Saliva necessary for our digestion. In a mouth chewing a food by teeth and lingual. In the mouth cavity begin digestion of carbohydrates by alfa-amilase – ptyalin. To secrete different types of saliva for digestion processes – with a big quantity of water or organic and inorganic substances. Quantity, composition and properties of saliva Quantity, composition and properties of saliva (In the case of dream produce nearly 0,05 mL/minute, in the normal condition – 0,5 mL/minute, in the case of maximal secretion – near 5 mL/minute. By day produce 0,8-1,5 L of saliva. Composition of saliva: water, organic – alfa-amilase, lipase, phosphatase, RNAase, DNAase, mucin, substances for protective – lisocim, thiocianates, antibodies – and unorganic substances – sodium, potassium, calcium, chlorites, etc. Mechanism of saliva forming In acinars' cells produce primary saliva in which synthesis necessary amino acids, glucose, mineral substances (for example, Ca++). In the cells of salivary glands occur passive processes, which provide moving of water and electrolits from blood to the glands’ ductus (strait). In the ductus occur reabsorption of sodium, chlorine, secretion of potassium, HCO3–. This is the secondary saliva. Aldosterone increase reabsorption of sodium and secretion of potassium. Role of saliva in vitality of human 1. Moisten of solid food; 2. Dissolving of substances; 3. Moisten of mouth; 4. Cover food; 5. To help of swallowing; 6. Primary hydrolyzing of carbohydrates; 7. Antibacterial properties; 8. Neutralized the stomach juice. Formation of saliva Conditional reactions caused by appearance of food, it smell and other stimulus, which are connect with food. Unconditional influences have parasympathetic and sympathetic components. Parasympathetic components beginning from receptors of tongue and oral cavity. From its impulses pass through the fibers of n. trigeminus, n. facialis, n. vagus, n. glossopharyngeus, to the center of salivation. Impulses return to saliva glands by n. facialis, n. glossopharyngeus. Sympathetic components of unconditional influences beginning from side cornu of upper thoracic segments of spinal cord – Th2-Th4. Then impulses go to saliva glands through the upper cervix sympathetic ganglion. The cortex of big hemispheres, hypothalamus, lymbic system regulate the salivation through these nerves. Conditional signals, emotions may inhibit salivation. Influence of vegetative nerves on secretor activity of salivary glands Stimulation of the parasympathetic nerve supply causes profuse secretion of watery saliva with a relatively low content of organic material. Stimulation of the sympathetic nerve supply causes profuse secretion of saliva with small quantity of water with a relatively big content of organic material. Mediator of parasympathetic nerve system – acetylcholine – stimulate M-cholinoreceptors of basolateral membrane and activate entrance of Ca2+ and activate kalmodulin. These reaction caused production of a big quantity of saliva with low quantity of organic substances. Mediator of sympathetic nerve system – norepinephrine – stimulate adrenoreceptors of basolateral membrane, activated adenilatcyclase that form cAMP. These reaction caused production of a small quantity of saliva which have a big quantity of organic substances. Swalowing Functions of stomach 1. Digestive (mechanical treatment, absorption, evacuation, secretion, depo); 2. Excretor; 3. Incretor. Secretor activity of stomach Production of stomach juice per day – near 2,5 L of juice. Their main components – enzymes, HCl and mucin. pH of morning saliva is neutral, after eating – sour – 0,8-1,5. Composition of stomach juice and their properties There are 2 types of glands – the oxyntic (or gastric) and the pyloric glands. The oxyntic glands secrete hydrochloric acid, pepsinogen, intrinsic factor, and mucus. The pyloric glands secrete mainly mucus. The main cells (peptic or chief cells) produce non active enzymes (pepsinogens). There are 7 pepsinogens. They hydrolyzed proteins. Optimum pH of its activity is 1,5-2,0. Pepsinogens whose activity the most in the condition of pH 3,23,5 is gastrecsin. In the stomach juice produces lipase and gelatinese. HCl produce in parietal or oxyntic cells. pH of it secrete is near 0,8. These processes need energy of lipids. Mechanism of it production: Cl- activly transported in the canaliculi, Na+ – from the canal into cytoplasm. H2O dissopciated to H+ and OH-. H+ activly go into canaliculi in change of K+. In these processes take plase Na+,K+-ATPase. CO2, which produce in cells act with H+ and syntheses HCO-. This anion go into the cell in change by Cl-. Formation of hydrochloric acid stomach Parietal cell blood metabolism carboanhydrase se Role of the hydrochloric acid in the digestion 1. To promote the swell of protein; 2. To promote the change of pepsinogen in pepsins; 3. To make optimal conditions for actions of pepsins; 4. To fulfill protective role from bacteria; 5. To promote motor and evacuated functions of stomach; 6. To stimulate production of duodinum gormon – secretin. Phases of stomach secretion Cephalic phase is caused by nervous system. It has conditional and unconditional reflexes. Conditional reactions caused by appearance of food, it smell and other stimulus, which are connect with food. Unconditional influences is parasympathetic and beginning from receptors of tongue and other receptors of the oral cavity. From these receptors impulses pass through the fibers of n. trigeminus, n. facialis, n. glossopharyngeus, n. vagus to the medulla oblongata. Impulses return to stomach by n. vagus. Except neuron influences this phase has humoral influences – brunch of n. vagus produce gormon gastrin. These phase is very short. Value of gastric juice secretion In norm gastric juice secretion must be N N Indexes Empty stomach Basal secretion Stimulated secretion 1. pH to 3,5 1,5-2 1,3-1,4 2. Production of common 10-35 HCl, mmol/L 40-60 80-100 3. Production of free HCl, 0-20 mmol/L 20-40 65-85 4. Debit of common HCl, to 1,5 mmol/hour 1,5-5,5 8-14 5. Debit of free HCl, to 1 mmol/hour 1-4 6,5-12 Phases of stomach secretion Stomach phase is depends on the quantity of food, which are present in stomach. It has vago-vagal reflexes (by mean of central nerves system) and local – peripheral reflexes, which are closed in stomach walls. Duration of these phase is longer and quantity of juice is much. It has humoral mechanisms too (production of gastrin and histamin. Intestine phase: presence of food in the upper portion of small intestine can cause the stomach to secrete small amount of gastric juice. This probably results of gastrin are also released by the duodenal mucosa in response to distension or chemical stimuli of the same type as those that stimulate the stomach gastrin mechanism.