February 15, 2021 (Monday) – 3rd Year- 2nd sem. GASTROINTESTINAL SYSTEM It is a pathway 7-7.9 meters (23-26 feet) in length from mouth to the esophagus, stomach, small and large intestines, rectum to the terminal structure which is the anus. Tube that includes: mouth, Pharynx, Esophagus, Stomach, Small intestine, Large intestine Accessory organs: teeth, tongue, salivary glands, liver, gallbladder, and pancreas FUNCTIONS i. Ingestion: the consumption of food (liquid or solid) through the mouth ii. Secretion: secretes enzymes to digest nutrients needed by the body iii. Digestion- is the breakdown of large organic molecule into smaller molecule that can be absorb. Digestion occurs through mechanical and chemical breakdown of foods iv. Absorption: It is the movement of molecules out of the digestive tract and into the blood or lymphatic system. Epithelial cells that line the lumen of small intestine absorb the small molecules of nutrients (amino acids, monosaccharides, vitamins and minerals and water) result from digestive process. v. Defecation/Elimination: the removal of undigested material such as fiber from blood, and feces as waste products from the body. A. Mouth (Oral or Buccal cavity) an oval-shaped cavity inside the skull. The two main functions of the mouth are eating and speaking. Parts of the mouth include the lips, vestibule, mouth cavity, gums, teeth, hard and soft palate, tongue and salivary glands Digestive process begins with the act of chewing Mechanical digestion- through mastication which break down large food particles into smaller ones. Chemical digestion occurs through the action of salivary amylase that breakdowns starches into maltose. Deglutition (swallowing) occurs once the food broken down into small pieces and mixed with saliva (food bolus) Bounded by the lips, cheeks, contains the teeth and tongue. Formed by cheeks, hard & soft palate & tongue Soft palate at back includes a “hangy down” part = uvula During swallowing uvula prevents entry into nasal cavity Lips- are muscular structures formed by orbicularis oris muscle Cheeks- form the lateral wall of the oral cavity. Lips and cheeks are important in the process of mastication or chewing. It moves the food around within the oral cavity and hold the food in place while teeth crush or tears it. B. TONGUE muscular accessory organ that maneuvers food for chewing and occupy most of the oral cavity. It moves food in the mouth in cooperation with the lips ad cheeks. It plays a major role in the process of swallowing. A major sensory organ for taste as well as major organ for speech. Adjusts shape for speech & swallowing Lingual tonsils at base of tongue C. TEETH a. b. 32 teeth in normal adult Permanent teeth/SecondaryTeeth of adults 8 Incisors, 4 Canines, 8 Premolars, 12 Molars (including 4 wisdom teeth) Incisors to cut (central 6-8 months), (lateral- 8-11 months), eight incisor teeth are located in the front part of your mouth. four of them in your upper jaw and four in your lower jaw. use to bite into your food Canine erupt at 16-20months, canines are the next teeth that develop in your mouth. You have four of them and they are your sharpest teeth, used for tearing apart food February 15, 2021 (Monday) – 3rd Year- 2nd sem. c. d. 1. 2. First and Second Pre Molars are used for tearing and crushing food that have a flat biting surface. First (10-16) and Second Molar (2024), Third Molar (wisdom) occur at late teens or late 20/old, Molars are your largest teeth. Their function is similar to that of the premolars, to grind, tear, and crush food. Molars have a large flat biting surface which makes them perfect for this job 20 PRIMARY TEETH/DECIDOUS- baby teeth or milk teeth which are lost during childhood IT HAS THREE REGIONS (PARTS OF TOOTH-PPT) Crown- the visible portion of teeth Neck- the small region between the crown and the root 3. Root- the largest region of the tooth and anchors in the jaw bone 4. PULP CAVITY- located at the center of the tooth filled with blood vessels, nerves and connective tissue 5. 6. DENTIN- surrounds the pulp cavity ENAMEL- extremely hard acellular substance that covered the dentin that protects the tooth against abrasions and acids produced by bacteria in the mouth. D. SALIVARY GLANDS i. 1.5 liters of saliva is secreted daily. Responsible to produce or secretes saliva Parotid Serous glands located inferior & anterior to ii. iii. ears, serous gland that produces saliva to moisten the mouth, helping with chewing, swallowing, phonating, and digestion Mumps- inflammation of parotid glands. Submandibular in floor of mouth, medial & inferior to mandible/below the mandible bilateral salivary glands located in the face. Their mixed serous and mucous salivary secretions are important for the lubrication of food during mastication to enable effective swallowing and aid digestion. produce more serous than mucous, Sublingual secrete saliva into your mouth from under the tongue. The smallest of the three major salivary glands, are almond-shaped and found under the floor of your mouth. Beneath tongue and superior to submandibular Produced more mucous Saliva contains 99.5% water, salivary amylase, mucus and other solutes Dissolves food & starts digestion of starches E. PHARYNX/ THROAT It is tube like structure that connects the nasal and oral cavities to the larynx. It is a passageway for air and food or common opening between the digestive and respiratory system. It connects the mouth with the esophagus 3 PARTS OF PHARYNX a. Nasopharynx Behind the nasal cavities, passageway for air only. b. Oropharynx Located in the middle portion of the pharynx located behind the mouth, and a passageway for both air and food. extends from uvula to epiglottis c. Laryngopharynx Located in the lower portion of the pharynx that opens into the larynx and the esophagus that serves a passageway for both air and food. extends from epiglottis to esophagus NOTE: Oropharynx and laryngopharynx carry food to the esophagus February 15, 2021 (Monday) – 3rd Year- 2nd sem. F. ESOPHAGUS Located in the mediastinum, anterior to the spine and posterior to the trachea and heart It is about 25 cm long It serves as the passage of food bolus from mouth the stomach by peristalsis The upper two thirds of the esophagus has skeletal muscle on its wall while the lower one third has smooth muscle It passes into the diaphragm and ends into the stomach Transport food from the pharynx to the stomach two structures, the UES and the LES/ sphincters located at the upper and lower end of the esophagus. UES and LES prevents gastric reflux, prevent retrograde movement of food by contracting and closing the lumen of the esophagus. During swallowing, these sphincters relax to allow forward passage of food. On swallowing: Bolus of food oropharynxLaryngopharynx esophagus Muscular contractions in pharynx help Upper esophageal sphincter (UES) Skeletal muscle –controls entry to esophagus Lower esophageal sphincter (LES) Smooth muscle- regulates entry to stomach Serves as mixing chamber and holding reservoir, Very elastic & muscular the opening from the esophagus into the stomach is called Gastroesophageal opening. It has the following regions Cardiac region, fundus, body, and antrum or pyloric region. 4 regions Cardia- surrounds upper opening/entrance Fundus- superior part of the stomach Body – largest part of the stomach Pylorus- lower part leading to pyloric sphincter & duodenum Persistaltic contractions in the stomach propels the stomach’s content into the pylorus in order to enter in the small intestines that permits efficient absorption of nutrients. 1. 2. 3. 4. 1. 2. 3. 4. 5. G. STOMACH A hollow muscular organ with a capacity of 1500 ml, Located in the left upper quadrant of the abdomen, under the left lobe of the liver and diaphragm It stores and mixed the food with secretions during eating, secretes digestive fluids and propels partially the digested food into the stomach. It has five epithelial cells: Surface mucous cells located in the inner surface of the stomach which produce MUCUS that protects the stomach lining. Mucous neck cells produce MUCUS Parietal cells produce HYDROCHLORIC ACID and INTRINSIC FACTOR Endocrine cells produce REGULATORY CHEMICALS Chief cells produce PEPSINOGEN-a precursor of the protein digesting enzyme PEPSIN- an important enzyme for protein digestion, the end product of the conversion of pepsinogen from the chief cells. FUNCTIONS a. Mechanical Digestion. Storage, mixing and liquefaction of bolus of food into a semisolid mixture call chyme. The rugae liquefy solid food particles through grinding motion b. Secretion Secretes gastric juices from the gastric glands includes hydrochloric acid, Pepsin, Mucus, and intrinsic factor 1500-3000 ml of gastric juice in the gastric mucosa. The gastric juice is composed of mucus, HCL, pepsinogen and water. February 15, 2021 (Monday) – 3rd Year- 2nd sem. a. b. c. d. HCL- produces a pH of 2.0 in the stomach. The acid kills microorganisms and activates the enzyme, PEPSIN. Pepsin - is converted from its inactive form called Pepsinogen. Pepsin is a digestive enzyme produced by the stomach to digest protein into smaller peptide chains. Mucus- forms a thick layer which lubricates the cells of the stomach wall and protects from the damaging effect of acidic chyme and pepsin. Irritation of the stomach mucosa stimulates the secretion of greater amount of mucus Intrinsic factor- is secreted by the gastric mucosa that binds with vit B 12 and makes it readily absorb in the small intestine. Vit B 12 is important in DNA synthesis and in RBC production. If vitamin B 12 cannot be reabsorbed, Pernicious anemia results. c. Chemical Digestion Digestion of CHON starts in the stomach through the action Pepsin which converts CHON into peptides d. Protection. The acid medium is responsible for the reduce activity from harmful bacteria that may have taken in with food e. Absorption minimal water, alcohol, glucose and some drugs in gastric mucosa CHO- empties within 1-2 hours CHON- within 3-4 hours Fats- within 4-6 hours 1. 2. The longest segment of the GI tract about it folds back and forth on itself approximately 70 m or 230 ft. consists of the duodenum-proximal section, jejunum- middle section, and ileum-distal section. major site of digestion and absorption of food where digestive process is completed in the duodenum The site where the ileum connects to the large intestines is called the Ileocecal junction/valve. This valve or sphincter controls the flow of material from the ileum into the cecal portion of the large intestine and prevents reflux of bacteria into the small intestine. Intestinal Contractions Propels the contents of the small intestines toward the colon Both contractions are stimulated by the presence of Chyme. Emulsify FUNCTIONS A. Mucus secretions Goblet cells and Duodenal glands secretes mucus to protect the mucosa B. Secretion of enzymes. Food ingested as fats, proteins and carbohydrates should be broken down into absorbable particles by the process of digestion. CARBOHYDRATES are broken down into DISACCHARIDES (sucrose, maltose, galactose) and MONOSACCHARIDES (glucose and fructose). Glucose is the major CHO that the tissue cells use as a fuel PROTEINS are source of energy after they are broken down into AMINO ACIDS and PEPTIDES. FATS become MONOGLYCERIDE AND FATTY ACIDS to absorb. H. SMALL INTESTINES TWO TYPES OF CONTRACTION in SMALL INTESTINES Segmentation Contractions Produces mixing waves that move the intestinal content back and forth in a churning/mixing motion. ► a. b. c. d. e. ► a. b. c. In the presence of chyme in the duodenum, the presence of CHO, fats and CHON stimulate the secretion of PANCREOZYMIN. This enzyme stimulate the pancreas to secrete of AMYLASE, LIPASE TRYPSIN). ENZYMES THAT DIGEST CHO PTYALIN (salivary amylase) - produce by salivary glands that converts starch into dextrin, maltose and glucose , AMYLASE- complete the digestion of CHO secreted by the pancreas and intestinal mucosa that converts starch to dextrin, maltose and glucose, MALTASE - produced by intestinal mucosa that converts maltose to glucose SUCRASE - produced by intestinal mucosa that converts sucrose LACTASE- is an enzyme produced by intestinal mucosa converts lactose to glucose ENZYMES THAT DIGEST PROTEIN TRYPSIN-secreted by pancreas that complete the digestion of CHON PEPSIN- produce by gastric mucosa that converts CHON into polypeptides AMINOPEPTIDASE- secreted by intestinal mucosa that converts polypeptides into deptides and amino acids February 15, 2021 (Monday) – 3rd Year- 2nd sem. d. e. ► a. b. c. d. DIPEPTIDASE - is secreted by intestinal mucosa that converts dipeptides into amino acids HYDROCHLORIC ACID - is secreted by gastric mucosa that converts protein into polypeptides to amino acids of waste material particularly the undigested proteins and bile salts ENZYMES THAT DIGEST FATS PHARYNGEAL LIPASE- complete the digestion of fats, from triglycerides into fatty acids, diglycerides to monoglycerides STREPSIN- is secreted by gastric mucosa that converts triglycerides into fatty acids, diglycerides to monoglycerides PANCREATIC LIPASE - is secreted by pancreas that converts triglycerides into fatty acids, diglycerides to monoglycerides BILE - is secreted by liver and gallbladder that emulsify fats C. Hormones Cholecystokinin is produce if there is fat in duodenum, gall bladder is the target tissue in order to release bile into the duodenum secretin inhibit gastric secretions and inhibit stomach contractions GASTRIN it increases secretions of gastric juice rich in HCl d. Absorption. VILLI- small, fingerlike projections that lines the entire intestines and it produce digestive enzymes and to absorb nutrients. Absorption is the major function of the small intestines through the process of active transport and diffusion across the intestinal wall into the circulation. Duodenum and jejunum it absorbs fats, CHO, CHON sodium and chloride, Vit B 12, and bile salts are absorb in the ileum. Mg, phosphate, K are absorb throughout the small intestines. 1. 2. 3. 4. 5. 6. FUNCTIONS Peristalsis that is slow or weak that moves the colonic contents along the tract to allow efficient absorption of water and electrolytes as a major function of the colon Absorb of water, sodium and chloride approximately 800 to 1000ml of water Secretion of mucus that protects the mucosa. Electrolyte solution a bicarbonate solution that acts to neutralize the end products formed by the bacterial action, MUCUS protects the colonic mucosa from the interluminal contents Vitamin synthesis- colonic bacterial flora synthesis vit K, thiamine, riboflavin, vit B 12, folic acid, biotin and nicotinic acid Formation of feces- ¾ water and ¼ solid material. The brown color of feces results from the breakdown of bile by the intestinal bacteria Defecation-the act of expelling feces in the body when the rectum is distended that initiates reflex contractions of the rectal musculature and relaxes the internal anal sphincter. J. RECTUM VILLI IN THE SMALL INTESTINES I. Large intestine Extends from the ileocecal valve to the anus. It is approximately 1.5 meters (5-6 feet long) Consist of cecum, ascending colon, transverse colon, descending colon, sigmoid colon, and rectum and anal canal It absorbs fluids and electrolytes, synthesizes vitamin k. And stores fecal material. Bacteria as a major component of the contents of the large intestine that completes the breakdown the last part of the large intestine and connects the sigmoid colon to the anal canal. The rectum begins at the height of S2-S3 and ends at the perineum. It is important for the water resorption as well as for the resorption of electrolyte from the stool and plays an important role in the defecation process. K. ANUS Last section of the GI tract, outlet of the waste product from the GI system. The anus starts at the bottom of the rectum, the last portion of the colon (large intestine).
