Digestion

Introduction The digestive system is made up of the gastrointestinal (GI) tract—also called the digestive tract—and the liver, pancreas, and gallbladder. The GI tract is a series of hollow organs joined in a long, twisting tube from the mouth to the anus. The hollow organs that make up the GI tract are the mouth, esophagus, stomach, small intestine, large intestine—which includes the rectum—and anus. Food enters the mouth and passes to the anus through the hollow organs of the GI tract. The liver, pancreas, and gallbladder are the solid organs of the digestive system. The digestive system helps the body digest food.

Digestion in oral cavity and stomach

Chewing 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.

Receptors in the mouth 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 parts of digestion tract – stomach, small intestine, pancreas, in which secreted juices with enzymes

Salivary glands In the mouth cavity open three pair of big salivary glands and a lot of small buccal glands. Submandibular and consist of the cells of serum and mucous types and secrete serous and mucus types of saliva. sublingual glands Parotid glands consist of the serum types cells and secrete serous type of saliva.

Quantity, composition and properties of saliva Quantity of saliva Quantity, composition and properties of saliva By day produce 0,8-1,5 L of saliva. Composition and Properties of saliva water, organic – Enzymes: alpha-amylase, lipase, phosphatase, RNAase, DNAase, mucin, Substances for protective thiocianates, antibodies – and inorganic substances Salts: sodium, potassium, calcium, chlorites, etc.

Formation of saliva A. Conditional مشروط Conditional reactions caused by appearance of food, it smell and other stimulus, which are connect with food. B. Unconditional غير مشروط

B. Unconditional Parasympathetic components beginning from receptors of tongue and oral cavity. From its impulses pass through the fibers of vagus, n. to the center of salivation. Impulses return to saliva glands by n. facialis, n. glossopharyngeus. Sympathetic it begins from upper thoracic segments of spinal cord. Then impulses go to saliva glands through the upper cervix sympathetic ganglion.

Functions of saliva 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.

Influence of autonomic 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.

Watery saliva 1 Mediator of parasympathetic nerve– acetylcholine – stimulate M-cholinoreceptors of base-lateral membrane and activate entrance of Ca2+ and activate calmodulin. These reaction caused production of a big quantity of saliva with low quantity of organic substances.

Organic saliva 1 Mediator of sympathetic nerve system – norepinephrine – stimulate adrenoreceptors of base-lateral membrane, to form cAMP. This reaction caused production of a small quantity of saliva which have a big quantity of organic substances.

Carbohydrates Digestion in Mouth Carbohydrates are the sugars, starches, and fiber found in many foods. Carbohydrates are called simple or complex, depending on their chemical structure. Simple carbohydrates include sugars found naturally in foods such as fruits, vegetables, milk, and milk products, as well as sugars added during food processing. Complex carbohydrates are starches and fiber found in whole-grain breads and cereals, starchy vegetables, and legumes.

Digestion of Carbohydrates Enzyme: Amylase Begins in the mouth with the enzyme Salivary Amylase, which catalyzes the reactions that digest polysaccharides into smaller oligosaccharides. The amylase is denatured in stomach because of acidity