Gastrointestinal System PDF

Digestive System Dr Asmaa Seddek Lecturer Of Physiology FOM-SCU  INTRODUCTION Digestion is defined as the process by which food is broken down into simple chemical substances that can be absorbed and used as nutrients by the body  Organization 1. Primary Digestive...

Digestive System Dr Asmaa Seddek Lecturer Of Physiology FOM-SCU  INTRODUCTION Digestion is defined as the process by which food is broken down into simple chemical substances that can be absorbed and used as nutrients by the body  Organization 1. Primary Digestive Accessory Organs 1. Mouth 1. Teeth 2. Pharynx 2. Tounge 3. Esophagus 3. Salivary glands 4. Stomach 4. pancreas 5. Small intestine 5. Liver 6. Large intestine. 6. Gallbladder.  Primary Functions Motility: This refers to the movement of food through the digestive tract. Secretion: This includes both exocrine and endocrine secretions Digestion : the breakdown of food molecules into their smaller subunits, which can be absorbed. Absorption: the passage of digested end products into the blood or lymph.  Four Major Process In GIT: -Digestion -Absorption -Secretion -Motility  WALL OF GASTROINTESTINAL TRACT In general, wall of the GI tract is formed by four layers which are from inside out: 1. Mucus layer (mucosa) 2. Submucus layer(submucosa) 3. Muscular layer(muscularis) 4. Serous or fibrous layer.(serosa)  Nervous Supply Of The GI tract GI tract has two types of nerve supply: I. Intrinsic nerve supply a. Submucousal plexus(Meissner) b. Myenteric (Auerbach) plexus II. Extrinsic nerve supply. a. Sympathetic system(T5 to L2). b. Parasympathetic system(cranial nerves 8,9,10 and sacral nerves 2,3,4) Functions Of The Nervous Supply Submucousal plexus: regulate the secretory functions of GI tract. Myenteric plexus: regulate the movements of GI tract. Sympathetic nerve fibers: inhibit the movements and decrease the secretions of GI tract Parasympathetic nerve fibers: accelerate the movements and increase the secretions of GI tract. Hormones of GIT hormone stimulus Source of secretion Action Gastrin Proteins in antrum of stomach Stimulates gastric secretion and stomach motility Secretin Acids in small intestine Stimulates secretion of watery and duodenum alkaline pancreatic secretion Cholecystokinin Fat in small intestine Contracts gallbladder duodenum Stimulates pancreatic secretion with enzymes Gastric Glucose in small intestine Stimulates insulin secretion inhibitory duodenum peptide (GIP) MOUTH The first step in the digestive process is chewing or mastication occur in the mouth Three pairs of salivary glands secrete saliva into the oral cavity: 1. Parotid Glands: Located between the angle of the jaw and the ear. 2. Sublingual Glands: Located below the tongue. 3. Submandibular Glands: Located below the jaw. FUNCTIONS OF SALIVA 1. PREPARATION OF FOOD FOR SWALLOWING When food is taken into the mouth, it is moistened and dissolved by saliva. 2. APPRECIATION OF TASTE Taste is a chemical sensation. By its solvent action, saliva dissolves the solid food substances, so that the dissolved substances can stimulate the taste buds. The stimulated taste buds recognize the taste. „ 3. DIGESTIVE FUNCTION Saliva has three digestive enzymes, namely salivary amylase, maltase and lingual lipase 4. CLEANSING AND PROTECTIVE FUNCTIONS antimicrobial property, saliva prevents bacterial Growth 5. REGULATION OF WATER BALANCE When the body water content decreases, salivary secretion also decreases. This causes dryness of the mouth and induces thirst.  FUNCTIONS OF MOUTH Primary function of mouth is eating and it has few other important functions also. Functions of mouth include: 1. Ingestion of food materials 2. Chewing the food and mixing it with saliva 3. Appreciation of taste of the food 4. Transfer of food (bolus) to the esophagus by swallowing 5. Role in speech 6. Social functions such as smiling and other expressions. Oesophagus The oesophagus is the portion of the GI tract that connects the pharynx to the stomach. It is a muscular tube approximately 25 cm long Swallowed food is pushed from pharynx to the oesophagus by a wavelike muscular contraction called peristalsis The oesophagus is sealed off by two sphincters, one at either end of the tube: the upper oesophageal sphincter and the lower oesophageal sphincter. Each of these sphincters is normally closed except during the process of swallowing Lower oesophageal sphincter : prevents the reflux of the corrosive gastric contents into the oesophagus  Stomach PARTS OF STOMACH In humans, stomach has four parts: 1. Cardiac region (cardiac sphincter) 2. Fundus 3. Body or corpus 4. Pyloric region.  FUNCTIONS OF STOMACH 1. MECHANICAL FUNCTION i. Storage Function Food is stored in the stomach for a long period, i.e. for 3 to 4 hours and emptied into the intestine slowly. The maximum capacity of stomach is up to 1.5 L. Slow emptying of stomach provides enough time for proper digestion and absorption of food substances in the small intestine. ii. Formation of Chyme Peristaltic movements of stomach mix the bolus with gastric juice and convert it into the semisolid material known as chyme 2. PROTECTIVE FUNCTION Refer functions of gastric juice. FUNCTIONS OF STOMACH 3. Digestive function Gastric juice is a mixture of secretions from different gastric glands Gastric juice is highly acidic with a pH of 0.9 to 1.2. Acidity of gastric juice is due to the presence of hydrochloric acid. It acts mainly on proteins. 4. Hematopoietic function Intrinsic factor secretion which is necessary for the absorption of vitamin B12 from ileum into the blood. Vitamin B12 is an important maturation factor during erythropoiesis. Absence of intrinsic factor in gastric juice causes deficiency of vitamin B12, leading to pernicious anemia 5. EXCRETORY FUNCTION Many substances like toxins, alkaloids and metals are excreted through gastric juice Small Intestine Most absorption and digestion occur in the small intestine The small intestine is divided into three segments: An initial short segment, the duodenum, is followed by the jejunum and then by the longest segment, the ileum. Normally, most of the chyme entering from the stomach is fully digested and absorbed in the first quarter of the small intestine ( in the duodenum and part of the jejunum).  Small Intestine Hydrolytic enzymes in the small intestine break down molecules of intact or partially digested carbohydrates, fats, proteins, and nucleic acids into monosaccharides, fatty acids, amino acids, and nucleotides. Some of these enzymes are on the apical membranes of the intestinal lining cells, whereas others are secreted by the pancreas and enter the intestinal lumen. The products of digestion are absorbed across the epithelial cells and enter the blood and/or lymph. Vitamins, minerals, and water, which do not require enzymatic digestion, are also absorbed in the small intestine.  PANCREAS Pancreas is a dual organ having two functions, namely endocrine function and exocrine function. Endocrine function is concerned with the production of hormones Exocrine function is concerned with the secretion of digestive juice called pancreatic juice. Exocrine Function Of The Pancreas FUNCTIONS OF PANCREATIC JUICE Pancreatic juice has digestive functions and neutralizing action. High bicarbonate content makes the pancreatic juice highly alkaline, so that it protects the intestinal mucosa from acid chyme by neutralizing it. Pancreatic juice plays an important role in the digestion of proteins and lipids. It also has mild digestive action on carbohydrates  LIVER It is the largest gland in the body, weighing about 1.5 kg in man. Liver receives maximum blood supply of about 1,500 mL/minute. It receives blood from two sources, namely the hepatic artery and portal vein 1. Hepatic artery arises directly from aorta and supplies oxygenated blood to liver 2. Portal vein brings deoxygenated blood from stomach, intestine, spleen and pancreas. Portal blood is rich in monosaccharides and amino acids. It also contains bile salts, bilirubin, urobilinogen and GI hormones. Functions Of Liver 1- METABOLIC FUNCTION Liver is the organ where maximum metabolic reactions such as metabolism of carbohydrates, proteins, fats, vitamins and many hormones are carried out. 2. STORAGE FUNCTION Many substances like glycogen, amino acids, iron, folic acid and vitamins A, B12 and D are stored in liver 3. SYNTHETIC FUNCTION Liver produces glucose by gluconeogenesis. It synthesizes all the plasma proteins 4. SECRETION OF BILE 5. EXCRETORY FUNCTION Liver excretes cholesterol, bile pigments, heavy metals (like lead, arsenic and bismuth), toxins, bacteria and virus (like that of yellow fever) through bile. 6. Heat production Enormous amount of heat is produced in the liver because of metabolic reactions. Liver is the organ where maximum heat is produced. 7. hemopoietic function In fetus (hepatic stage), liver produces the blood cells 8. Hemolytic function The senile rbcs after a lifespan of 120 days are destroyed by reticuloendothelial cells (kupffer cells) of liver. 9. Inactivation of hormones and drugs 10. DEFENSIVE AND detoxification FUNCTIONS BILE The liver produces and secretes 250 to 1,500 ml of bile per day. The major constituents of bile are bile pigment (bilirubin), bile salts, phospholipids (mainly lecithin), cholesterol, and inorganic ions. The components of bile are secreted by two different cell types. The bile salts, cholesterol, lecithin, and bile pigments are secreted by hepatocytes, whereas most of the HCO3 -rich solution is secreted by the epithelial cells lining the bile ducts. Function of bile salts Emulsification of Fats Emulsification is the process by which the fat globules are broken down into minute droplets by the action of bile salts. Lipolytic enzymes of GI tract cannot digest the fats directly because the fats are insoluble in water. Bile salts emulsify the fats due to their detergent action.  Gallbladder Between meals, secreted bile is stored in the gallbladder, a small sac underneath the liver that branches from the common hepatic duct. The gallbladder concentrates the organic molecules in bile by absorbing some ions and water. During a meal, the smooth muscles in the gallbladder wall are stimulated to contract, causing a concentrated bile solution to be injected into the duodenum via the common bile duct  Large Intestine The large intestine temporarily stores the undigested material (some of which is metabolized by bacteria) and concentrates it by absorbing ions and water. Contractions of the rectum, the final segment of the large intestine, and relaxation of associated sphincter muscles expel the feces in a process called defecation. Thanks for your attention