Digestive System PDF

Digestive System The digestive system or the digestive tract. This like tube some nine meter in total through the middle of the body. Its start at the mouth where the food an drink enter the body and finished at the anus where the food and waste leave the body.  THE MAIN PART OF THE DIG...

Digestive System The digestive system or the digestive tract. This like tube some nine meter in total through the middle of the body. Its start at the mouth where the food an drink enter the body and finished at the anus where the food and waste leave the body.  THE MAIN PART OF THE DIGETIVE SYSTEM The mouth (buccal cavity) Esophagus Stomach Small intestine (duodenum-jejunum- ileum Large intestine(caecum-colon-rectum)- Auns.  Accessory Gland Salivary gland Liver Pancreas.  Buccal cavity (mouth) The buccal cavity or oral cavity is entrance to the digestive tube , it contain: The tongue, the teeth and the two lips. In the mouth cavity the major and minor salivary gland open by difference duct. Teeth bite off and chew food into a soft pulp that is easy to swallow, chewing mixes the food with watery saliva from salivary gland, to make it moist. The basic secretary units of salivary gland are water, mucus and enzymes which flow out through collecting ducts to the mouth. Three major Salivary gland are Parotid gland (which found in front of both ears) which secreted water at the buccal cavity. Submandibular glands (which found inner to the mandible) these glands produce mucus secretion. Sublingual glands (which found under the tongue) these glands secreted saliva.  The Important Function of Saliva:- Lubricates and moistens the buccal mucosa and lips. It washes the mouth cavity from the food debris. It transforms the food into a semi-solid mass in order to be swallowed and to be tasted easily. Saliva helps digestion of certain food because it contains glycoprotein and maltase enzymes, thus saliva initiates starches and polysaccharides digestion  Esophagus Is the long muscular tube, its lining membrane of compound epithelium is very much folded and at the opening-leading pharynx. Food passes through the esophagus using the process PERISTALSIS( the mechanism of movement of food inside the esophagus) which extends through the chest and diaphragm to reach stomach.  STOMACH The stomach is an expanded section of the digestive tube between the esophagus and small intestine. It has an ovoid shape and lies inside the abdominal cavity. The esophagus enters the stomach at its wider portion, the cardiac portion. The most distal and narrow section of the stomach is termed pylorus as food is liquefied in the stomach it passes through the pyloric canal into the small intestine.  The function of oxyntic cells is secrete HCL acid. The function of peptic cells is produce enzyme such as (pepsin). The function of columnar cells is Absorption of liquids. The main function of stomach are:- Digestion of food. Store of food. Kill the pathogens by HCL. Absorption of liquids such as water and alcohol and medicine  Small intestine Following the stomach comes the longest section of the digestive tube which consist (duodenum, jejunum, and ileum). Duodenum:- A short section that takes the form u-or C shaped. Duodenum receives secretions from the pancreatic duct into the distal limb and the bile duct opening beginning of the duodenum. Following the duodenum the rest of small intestine (jejunum 8 feet and ileum 12 feet) The small intestine which is the longest part of the alimentary canal and forms of loop and coils. The main function of small intestine is ABSORPTION OF DIGESTED FOOD. ❖Function of Crypts of lieberkuhn is secretion water mainly and secrete alkaline fluids to neutralize the acidity of the chyme. ❖Function of the goblet cells is secretion mucus which prevent auto-digestion. ❖The function of columnar cells is Absorption of digested food. ❖ Function of the lymphatic vessel (lacteal) is absorption of fatty acids  Large intestine This formed of Caecum, colon and rectum. Caecum: Is recognized by its large size, most of its thin walled end by a thick walled much narrower and finger- like, vermiform appendix.  Colon Is Sacculated (to delay passage of food ) and lead into the narrower rectum. Any useful substances in the leftovers, such as water and body minerals, are absorbed through the walls of the large intestine, back into the blood. Therefore the main function of large intestine is Reabsorption of water. The remains substance are formed into brown, semi-solid (feces) ready to be removed from the body.  Rectum and Anus The end of the large intestine , the rectum, its function is to store the feces. These are finally squeezed through a ring muscle, (the anus) and out of the body.  Digestion Digestion is the breakdown of large substances into small parts, these changes are brought out by organic catalysts known as enzymes. This process takes place in the digestive system. Digestion is usually divided into mechanical and chemical action, and the digestion separated into five separated processes:-  Ingestion: placing food into mouth. Mechanical digestion: Mastication; the use of teeth to tear and crush food and movement of food by the muscles of the stomach. Chemical digestion: Addition of the chemical (acid,bile,enzymes and water) to breakdown complex molecules into simple molecules.  Absorption: movement of nutrients from the digestive system to circulatory and capillaries through Osmosis and active transport, and diffusion. Elimination: removal of undigested material from the digestive system through defecation. Digestion consists of a process of hydrolysis during which the molecular size of the substances progressively reduced until a true solution is possible. These changes are brought out by organic catalysts knows as enzymes.. Each particular enzyme act only upon particular substance or group of substances called substrate, and the end of the reaction it self remain unchanged. Enzyme can be rendered in active or killed by heat and others they act best at particular temperature called optimum temperature and require that the medium in which they work shall have a certain alkalinily or acidity( pH value). The enzyme are classified according to the types of substances upon which they act: ❖Amylolytic enzymes digest carbohydrates. ❖Proteolytic work on proteins. ❖Lipolytic enzymes act on fats. Digestion begins in the buccal cavity, where chemical and mechanical digestion occurs. The food is chewed with teeth, the process stimulate salivary gland produced saliva. Saliva begins to break down food, moistening it and make it easier to swallow, saliva which usually contains enzymes (amylolytic enzyme) this act on certain polysaccharides or starches turning them into compound sugars such as dextrin and maltose. Movement of tongue push the food to the back of the throat to be swallowed. Once food is swallowed, its enters the esophagus , muscular wavelike contractions known as peristalsis push the food down through the esophagus to the stomach. A muscular ring ( called the cardiac sphincter) at the end of the esophagus allow food to enter the stomach then it squeezes shut to prevent food and fluid from going back up esophagus. In the stomach the food is subjected to the action of the gastric juice, the flow of which is included by the hormone gastric secreted by gastric gland. The secretion of gastric juice also promoted by appetite. These responses are mediated by the nerves system. The chemical nature of the food also act directory on the gastric mucosa as also does presence of any food in the stomach by stimulating it mechanical by contraction and relaxation of the muscles(L.M.L,C.M.L). In this juice which contains 90% water, two enzymes are usually present, pepsin and rennin. Pepsin is the proteolytic enzyme acting upon protein and reducing them to peptones {polypeptide}. Rennin are is a proteolytic enzyme its rule in digestion is to coagulate milk in the stomach longer periods in the stomach for initial digestion of it’s proteins. For the efficient action of these enzymes it’s necessary for the medium to be acid and this is produced by the hydrochloric acid secreted by oxyntic cell of gastric gland, further action of the HCL acid helps to sterilize the food, thus giving the protection against pathogenic bacteria. In the duodenum the food meets further conditions in the form of the bile from the liver, the pancreatic juice from pancreas and brush border from the wall of the intestine. Bile is greenish alkaline watery fluid contains no digestive enzymes secreted by hepatocytes The bile containes two salts: 1- bicarbonate, which reduces the acidity of intestinal contents, 2- glycocholate active the pancreatic lipase and lower the surface tension of the fat so that they become emulsified. The pancreatic juice is watery, alkaline fluid very rich in enzymes it contains: Trypsin act on undigested protein and convert them into amino acid. Amylase converts polysaccharide starches into maltose. Lipase splits certain fats into glycerol and fatty acid. Intestinal enzymes: the inner wall of the small intestine is cover by millions of tiny finger like projection called villi. The villi covered with even tinier projection called microvilli. It secreted alkaline watery fluid containing must important enzymes, but also containing mucus. This enzymes complete the various digestive processes of all kind of food substances.  Absorption very little absorption of digested food takes place either in the buccal cavity or stomach certain drugs and alcohol may be absorbed in the stomach , the greater part of the absorption take place in the jejunum and ileum where digestion completed the food will pass through the walls into the capillary blood vessels by absorption. the digested carbohydrates (glucose) and proteins (amino acid ) are absorbed by the blood vessels while the fats (fatty acid) is absorbed by lymphatic vessels (lacteal).. The liver besides acting as a regulator also acts a store house for carbohydrates. The amino acid which form the basis for elaborating the body proteins, are liberated in suitable quantities into blood stream, but any excess is subjected in the liver to the process of deamination to form harmless substance, urea into other product, which can inter the glycolytic cycle.