The digestive system functions to ingest, digest, absorb, and eliminate food. It is made up of the gastrointestinal tract and accessory organs. The GI tract includes the mouth, esophagus, stomach, small intestine, large intestine, rectum, and anus. Accessory organs include teeth, tongue, salivary glands, liver, gallbladder, and pancreas. Food is ingested, mechanically and chemically digested, absorbed in the small intestine, and eliminated as waste. The liver, gallbladder, and pancreas secrete enzymes and bile to further break down food for absorption.
The digestive system functions to ingest, digest, absorb, and eliminate food. It is made up of the gastrointestinal tract and accessory organs. The GI tract includes the mouth, esophagus, stomach, small intestine, large intestine, rectum, and anus. Accessory organs include teeth, tongue, salivary glands, liver, gallbladder, and pancreas. Food is ingested, mechanically and chemically digested, absorbed in the small intestine, and eliminated as waste. The liver, gallbladder, and pancreas secrete enzymes and bile to further break down food for absorption.
The digestive system functions to ingest, digest, absorb, and eliminate food. It is made up of the gastrointestinal tract and accessory organs. The GI tract includes the mouth, esophagus, stomach, small intestine, large intestine, rectum, and anus. Accessory organs include teeth, tongue, salivary glands, liver, gallbladder, and pancreas. Food is ingested, mechanically and chemically digested, absorbed in the small intestine, and eliminated as waste. The liver, gallbladder, and pancreas secrete enzymes and bile to further break down food for absorption.
The digestive system functions to ingest, digest, absorb, and eliminate food. It is made up of the gastrointestinal tract and accessory organs. The GI tract includes the mouth, esophagus, stomach, small intestine, large intestine, rectum, and anus. Accessory organs include teeth, tongue, salivary glands, liver, gallbladder, and pancreas. Food is ingested, mechanically and chemically digested, absorbed in the small intestine, and eliminated as waste. The liver, gallbladder, and pancreas secrete enzymes and bile to further break down food for absorption.
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The key takeaways are the overall functions and organization of the digestive system.
The main organs of the digestive system are the mouth, esophagus, stomach, small intestine, large intestine, liver, pancreas and gallbladder.
The main functions of the liver are to produce bile, metabolize carbohydrates and lipids, store vitamins and minerals, and detoxify harmful substances.
The Digestive System
Functions of the Digestive System
Ingestion – the oral cavity allows food to enter the digestive tract and have mastication (chewing) occurs , and the resulting food bolus is swallowed . Digestion: o Mechanical digestion – muscular movement of the digestive tract (mainly in the oral cavity and stomach) physically break down food into smaller particles. o 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 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 . o GI tract is a continuous tube extending through the ventral cavity from the mouth to the anus ¡V it consists of the mouth, oral cavity, oropharynx , esophagus , stomach , small intestine , large intestine , rectum , and anus . o 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 THE HUMAN DIGESTIVE TRACT Mouth & Oral 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 Adapted for mechanical digestion (mastication) in the oral cavity . 20 deciduous or 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. 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 . Chemical digestion & absorption in the stomach - Carbohydrate digestion is continued with gastric amylase , resulting 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 fatsoluble 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) . 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 chymotrypisn , proaminopeptidase becomes aminopeptidase, and procarboxypeptidase becomes carboxypeptidase. Functions of The Liver Important in carbohydrate metabolism where hepatic cells conductglycogenesis (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). 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. Intestinal enzymes include : maltase digests maltose into glucose. sucrose 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. b. Digestive enzymes embedded in the surfaces of microvilli split molecules of sugars, proteins and fats . c. Regulation of small intestine secretions: secretion is stimulated by gastric juice , chyme , and reflex stimulated by distension of the small intestinal wall . d. 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 . e. 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. 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 . Clinical Terms Achalasia : failure of the smooth muscle to relax at some junction in the digestive tube. Cholecystitis : Inflammation of the gallbladder. Chloelithiasis : stones in the gallbladder. Cholestasis : Blockage in bile flow from the gallbladder. Cirrhosis : liver cells degenerate and the surrounding connective tissue thicken.