Digestive System PDF

Digestive System Dr/ Ahmed Nabeeh Sallam  What is the digestive system? The energy required for all the processes and activities that take place in our bodies is derived from the foods we ingest. The digestive system allows us to utilize food from such diverse sources as m...

Digestive System Dr/ Ahmed Nabeeh Sallam  What is the digestive system? The energy required for all the processes and activities that take place in our bodies is derived from the foods we ingest. The digestive system allows us to utilize food from such diverse sources as meat from an animal and the roots of a plant, and utilize them as an energy source. Whether it is the ability to coordinate the chewing of the food without injuring our tongue and lips or the propulsion of the food from the stomach into the duodenum while releasing the appropriate enzymes, Our digestive system allows us to manage the process without much thought and often while performing other tasks.  The process of digestion is a fascinating and complex one that takes the food we place in our mouth and turns it into energy and waste products. This process takes place in the gastrointestinal tract, a long, connected, tubular structure that starts with the mouth and ends with the anus. The food is propelled forward within the system, altered by enzymes and hormones into usable particles and absorbed along the way. Other organs that support the digestive process are the liver, gallbladder, and pancreas. The time it takes for food to travel from entering the mouth to be excreted as waste is around 30 to 40 hours.  Characteristics of digestive system 1-The digestive system in the mouth, larynx and pharynx responsible upon speakining and sound production via the tongue, lips, the pharynx and vocal cords. 2-Ingestion, sheewing, grinding and crumping of the food particles. 3-Secreation of the digestive and protective juices. 4-Absorption of the digested end products of proteins, fats and carbohydrates, and non- digested water, minerals, vitamins and drugs ingested and taken in the food. 5-Regulation of the of the water intake and content via the salivary glands and sensation of thirst. 6-Regulation of the blood sugars mainly glucose via the digestion and absorption. 7-Regulation of the blood PH through the secretion of HCL from the stomach and sodium bicarbonate from the pancreas.  8-Excreation of some waste products via the bile juice, saliva and faces such as drugs, heavy metals and others. 9-Regulation of the erythropoiesis process via the stomach secretion of the intrinsic factor essential for the absorption of the vit.B12 (the extrinsic factor) promotes the formation and maturation of the red blood cells. 10-Movements of the digestive system parts help in: a) Production of the voice and speaking. b) Grinding and crumping of the food large and solid particles c) Mixing of the food particles with the digestive juices. d) Transporting of the food particles through the different parts and segments. e) Help in the blood and lymph return to the circulatory system from the wall of the digestive system.  Digestive System Ingestion ‫ –أﻛل‬the oral cavity allows food to enter the digestive tract and have mastication (chewing) occurs , and the resulting food bolus is swallowed. The act or process of taking in something for or as if for digestion  Digestive System Digestion is the breakdown of large insoluble food molecules into small water-soluble food molecules so that they can be absorbed into the watery blood plasma. Digestion is a form of catabolism that is often divided into two processes based on how food is broken down: mechanical and chemical digestion.  Digestive System Mechanical digestion – muscular movement of the digestive tract (mainly in the oral cavity and stomach) physically break down food into smaller particles. Chemical digestion – hydrolysis reactions aided by enzymes (mainly in the stomach and small intestine (chemically break down food particles into nutrient molecules , small enough to be absorbed.  Digestive System Secretion – enzymes and digestive fluids secreted by the digestive tract and its accessory organs facilitate chemical digestion. Absorption – passage of the end – products (nutrients) of chemical digestion from the digestive tract into blood or lymph for distribution to tissue cells. Elimination – undigested material will be released through the rectum and anus by defecation.  Organization of the Digestive System Organs of the digestive system are divided into 2 main group: the gastrointestinal tract (GI tract) and accessory structures. GI tract is a continuous tube extending through the ventral cavity from the mouth to the anus – it consists of the mouth, oral cavity, oropharynx, esophagus, stomach, small intestine, large intestine, rectum, and anus. Accessory structures include the teeth, tongue (in oral cavity) , salivary glands , liver , gallbladder , and pancreas. Muscular movement of the GI tract Peristalsis – wavelike movement that occurs from the oropharynx to the rectum , allowing GI tract to push food particles toward the anus. Mixing—mixing motion in the oral cavity and stomach that allows the GI tract to repeatedly break down food into smaller particles , using mechanical digestion. Segmentation – regions of the small intestine contracting and relaxing independently , allowing the small intestine to digestive and absorb more efficiently. Peristalsis and Segmentation  The Main Parts of the Digestive System The mouth The pharynx and esophagus The stomach and small intestine (The small intestine has three segments. Duodenum, jejunum and ileum) After the small intestine, the leftover waste leaves the upper gastrointestinal tract (the large intestine) include The colon, rectum, and anus  The Main Parts of the Digestive System The large intestine (colon) has four parts: ascending colon, transverse colon, descending colon and sigmoid colon.  The Main Parts of the Digestive System Three accessory digestive organs (pancreas, liver, gallbladder) Digestive System Dr/ Ahmed Nabeeh Sallam  Gastrointestinal tract The GI tract is a series of hollow organs joined in a long, twisting tube from the mouth to the anus. Gastrointestinal tract, also called digestive tract or alimentary canal, Gastrointestinal tract include mouth, pharynx, esophagus, stomach, small intestine and large intestine. Plus The accessory organs which include salivary gland, liver, gallbladder and pancreas). The GI tract contains all the major organs of the digestive system.  Gastrointestinal tract The tract is divided into upper and lower tracts. The upper gastrointestinal tract consists of: the mouth, pharynx, esophagus, stomach, and duodenum. The lower gastrointestinal tract includes: most of the small intestine and all of the large intestine. In human anatomy, the intestine (bowel, or gut) is the segment of the gastrointestinal tract extending from the pyloric sphincter of the stomach to the anus and as in other mammals, - Consists of two segments: the small intestine and the large intestine. In humans, the small intestine is further subdivided into the duodenum, jejunum, and ileum while the large intestine is subdivided into the cecum, ascending, transverse, descending and sigmoid colon, rectum, and anal canal.  Regulation of GI Tract Activities Autonomic nervous system - Parasympathetic nerves stimulate GI tract activities. - Sympathetic nerves inhibit GI tract activities. Hormonal control - Hormones from endocrine gland and from GI tract itself help regulate GI tract activities. Reflex mechanism - Regions of the GI tract (especially the stomach and small intestine) use reflexes to stimulate or inhibit one another. Histology of the Alimentary Canal  Mouth & Oral Cavity Mouth, also called oral cavity or buccal cavity, Food enters the GI tract by ingestion. Food is broken down by mechanical digestion , using mastication One chemical digestive process occur where amylase enzyme in saliva breaks down polysaccharide into disaccharides. The tongue , made of skeletal muscle, manipulates the food during mastication. it also contains taste buds to detect taste sensations(intrinsic). Food particles are mixed with saliva during mastication ، resulting in a moist lump called bolus for easier passage into or pharynx.  Teeth Tooth, plural teeth, any of the hard, resistant structures occurring on the jaws and in or around the mouth and pharynx areas of vertebrates. Teeth are used for catching and masticating food, for defense, and for other specialized purposes.  Teeth Adapted for mechanical digestion (mastication) in the oral cavity. 20 deciduous ‫ ﻣﺗﺳﺎﻗطﺔ‬or primary teeth before the age of 6. By age 7, 32 permanent or secondary teeth are developed & are divided into 4 types: incisors (for cutting (Canines (for tearing ، (Premolars (for crushing ،(and Molars (for grinding.(these teeth follow the human dental formula of 2-1-2-3.  Salivary Glands 3 pairs of salivary glands called parotid , submandibular ،and sublingual gland secrete most of the saliva in the oral cavity , using salivary ducts. Saliva helps moisten the food during mastication , dissolve the food in forming the bolus , and help cleanse the teeth. Saliva consists of 99.5% water , the remaining 0.5% is dissolved substances including amylase enzyme (for chemically digesting carbohydrate ), bicarbonate ion )HCO3 ‫؛‬-maintains pH of saliva at 6.5-7.5) , and many electrolytes.  Stomach A pouch-like organ primarily designed for food storage (for 2-4 hours) , some mechanical and chemical digestion also occur. Contains two sphincters at both ends to regulate food movement cardiac sphincter near the esophagus ,and pyloric sphincter near the small intestine. Divided into 4 regions : cardiac stomach (or cardiac), fundic stomach (or funded) , body of stomach , and pyloric stomach or (Pylorus). Contain thick folds called rugae at its layer , for providing larger surface area for expansion , secretion , digestion , and some absorption. Stomach  Gastric Secretory Cells Gastric Secretory Cells Chief cells: secrete pepsinogen (an inactive enzyme). Parietal cells: secrete hydrochloric and (HCl) and "intrinsic factor" (which helps absorption of vitamin B12 in the intestines). Mucous cells: secrete mucus and alkaline substances to help neutralize HCl in the gastric juice. G cells: secrete a hormone called gastrin, which stimulates the parietal cells and overall gastric secretion. Gastric Cells  Chemical digestion & absorption in the stomach Carbohydrate digestion is continued with gastric amylase ، esulting in disaccharides. Protein digestion begins with pepsin (activation of pepsinogen by (HCl) , resulting in peptides (small chains of protein). Lipid digestion begins with gastric lipases which can only break down certain lipids such as butterfat , resulting in fatty acids. Absorption in the stomach is limited, where only small and fat- soluble substances can be absorbed—water , alcohol, aspirin ، and certain drugs. The result of all these mixing , chemical digestion , secretion ، and absorption is a yellowish paste called chyme , which will be passed on to the small intestine.  Pancreas Pancreas: most pancreatic enzymes are produced as inactivate molecules , or zymogens , so that the risk of self – digestion within the pancreas is minimized. More than 98% of the pancreas mass is devoted to its exocrine function: the secretion of pancreatic juice by the pancreatic acini and their ductile cells. Ductile cells produce Sodium bicarbonate which helps neutralize the acidic gastric contents. Acinar cells of the exocrine pancreas produce a variety of digestive enzymes to break down food substances into smaller absorbable molecules. Only 2% of pancreas mass is devoted to the islets of langerham, which produce insulin and glucagon, hormones that regulate blood sugar and carbohydrate metabolism (they have opposite effects). Pancreas  Major pancreatic Enzymes Pancreatic amylase: digest polysaccharides into disaccharides. pancreatic lipases digest triglycerides into fatty acids. pancreatic nucleases digest nucleic acids into nucleotides. Pancreatic proteinases (all secreted in their inactive forms) digest peptides into amino acids: Trypsinogen is activated by enterokinase (secreted by duodenum) into trypsin , which in turn activates the other 3 enzymes – chymotrypsinogen becomes chymotrypsin, proaminopeptidase becomes aminopeptidase, and procarboxypeptidase becomes carboxypeptidase.  Pancreatic Secretion 1.The parasympathetic nervous system increases pancreatic secretion 2. Two duodenual hormones also influence pancreatic secretion: Secretin and Cholecystokinin. 3. Food entering the small intestine stimulates the secretion of both hormones. 4. Secretin stimulates the secretion of pancreatic electrolyte – rich fluid , while CCK enhances the enzymatic secretions of the pancreas.  Regulation of pancreatic Juice Regulation of pancreatic Juice 1. Acidic chyme enters duodenum. 2. Secretin is released into blood stream from intestinal mucosa. 3. Secretin stimulates pancreas. 4. Pancreas secretes pancreatic juice. 5. Pancreatic juice , high in bicarbonate ions , neutralizes acidic chyme.  Functions of The Liver Important in carbohydrate metabolism where hepatic cells conduct glycogenesis (converting glucose into glycogen) , and glycogenolysis (breaking glycogen down to glucose). Also is critical in lipid metabolism where hepatic cells produce bile (for fat emulsification), oxidize fatty acids , synthesize various forms of lipids ,and convert glucose to fatty acids (lipogenesis). Other functions of the liver include : Storage of glycogen, iron , and vitamins A,D,B12. Contains phagocytes to destroy damaged erythrocytes and foreign substances, using phagocytosis. Detoxifies harmful substances in the blood. Serves as a blood reservoir (contains 7% of blood volume). Liver  Gall Bladder A small sac located on the inferior , visceral surface of the liver. Stores and concentrates bile secreted by the liver. Regulation of Bile Release: 1. Chyme with fat enters small intestine. 2. Cells of intestinal mucosa secrete the hormone Cholecystokinin (CCK) into the blood stream. 3. CCK stimulates muscular layer of gallbladder wall to contract. 4. Bile passes down the cystic duct and common bile duct to duodenum. 5. Hepatopancreatic sphincter relaxes and bile enters duodenum.  Small Intestine A long tube, with a small diameter (about 1 inch), extending from pyloric sphincter to the ileocecal valve. Divided into Duodenum, Jejunum, and ileum. 1. Secretions of small intestine: a. Intestinal glands secrete a watery fluid that lack digestive enzymes but provides a vehicle for moving chyme to villi.  Small Intestine Intestinal enzymes include : Maltase digests maltose into glucose. Sucrase digests sucrose into glucose and fructose. Lactase digests sucrose into glucose and glucose. peptidases digest peptides into amino acids. Lipases digest triglycerides into fatty acids and glycerol. Nucleases digest nucleotides into nitrogenous bases. Enterokinase converts trypsinogen into trypsin.  Small Intestine B. Each villus contains blood capillaries to absorb water , glucose , amino acids , vitamins , minerals , and short-chain fatty acids , and also contains lymphatic capillaries called lacteals to absorb long – chain fatty acids in the forms of micelles. C. Water is absorbed by osmosis , fatty acids are absorbed by diffusion (since they are fat-soluble), and most other nutrients (glucose, amino acids, & minerals) are absorbed by active transport.  Large intestine The last segment of the GI tract , with a large diameter (2-3 inches) , extending from the ileocecal valve to the anus. Divided into cecum , ascending colon , transverse colon , descending colon , sigmoid colon , rectum , anal canal , and anus. Large intestine  Large intestine The large intestine has little or no digestive function , although it secretes mucus. Its mucosa has no villa or microvillus , but contains numerous goblet cells for secreting mucus to aid in the formation of feces and maintain an alkaline condition. mechanical stimulation and parasympathetic impulses control the rate of mucus secretion. The large intestine only absorbs water, electrolytes and some vitamins. Many bacteria inhabit the large intestine , where they break down certain indigestible substances and synthesize certain vitamins. Feces are formed and stored in the large intestine. Defecation involves a reflex mechanism aided by voluntary contraction of the diaphragm , abdominal muscles ,and the external anal sphincter.  Major Hormones of The Digestive Tract 1. Gastrin : (Gastric & intestinal) : released by Gastric cells , in response to the presence of food. Causes Gastric glands to increase their secretory activity. 2. Somatostatin : (Gastric inhibitory peptides - GIP): Inhibits secretion of acid by parietal cells. 3. Cholecystokinin : released by intestinal wall cells , in response to the presence of proteins and fats in the small intestine. It causes gastric glands to decrease their secretory activity and inhibits gastric motility ; stimulation of pancreas to secrete digestive enzyme; stimulates gall – bladder to contract and release bile. 4. Secretin: released by cells in the duodenal wall, in response to acidic chyme entering the small intestine.  Major Digestive Enzyme Salivary enzyme: Begins carbohydrates digestion by breaking down starch and glycogen to disaccharides Gastric enzymes: Pepsin , from Gastric glands – Begins protein digestion. Lipase, from Gastric glands – Begins fat digestion. Pancreatic enzymes: Amylase , from pancreas – breaks down starch and glycogen into disaccharides. Lipase, from pancreas – breaks down fats into fatty acids and glycerol. Proteolytic enzymes : Trypsin, Chymotrypsin, and Carboxypeptidase from pancreas breaks down peptides into amino acids. Nucleases, from pancreasbreaks down nucleic acids into nucleotides. Intestinal Enzymes: Peptidase, from mucosal cells, breaks down peptides into amino acids. Sucrase, maltase, and lactase , from mucosal cells, breaks down disaccharides into monosaccharides. Lipase, from mucosal cells, breaks down fats into fatty acid and glycerol. Enterokinase , from mucosal cells, (breaks down) converts trypsinogen into trypsin.  Clinical Terms Achalasia‫ ﺗﻌذر اﻻرﺗﺧﺎء‬: failure of the smooth muscle to relax at some junction in the digestive tube. Cholecystitis ‫اﻟﺗﮭﺎب اﻟﻣرارة‬: Inflammation of the gallbladder. Chloelithiasis : stones in the gallbladder. Cholestasis ‫رﻛود ﺻﻔراوي‬: Blockage in bile flow from the gallbladder. Cirrhosis : liver cells degenerate and the surrounding connective tissue thicken. Diverticulitis : Inflammation of small pouches that sometimes form in the lining and wall of the colon. Dysentery : Intestinal infection. Dyspepsia: Indigestion Dysphasia: Difficulty in swallowing Enteritis: Inflammation of the intestine.