PHYSIOLOGY Digestive System PDF

‫ا‪.‬د‪ /‬محمد الغـــزالي‬  PHYSIOLOGY: It is the branch of biology deals with the functions and activities of living organisms and their parts.  Physiology OF Digestive System The digestive system consists of: 1-The GIT (gastrointestinal tract): Mouth, Pharynx, Esophagus, Stomach, Small inte...

‫ا‪.‬د‪ /‬محمد الغـــزالي‬  PHYSIOLOGY: It is the branch of biology deals with the functions and activities of living organisms and their parts.  Physiology OF Digestive System The digestive system consists of: 1-The GIT (gastrointestinal tract): Mouth, Pharynx, Esophagus, Stomach, Small intestine, Large intestine and anus. 2-The accessory digestive organs:  Supply secretions contributing to the breakdown of food.  Teeth, tongue, Salivary glands, Gallbladder, Liver and Pancreas.  Pathways of the Digestive Process 1) Ingestion:Taking in food through the mouth. 2) Mechanical digestion: Chewing in mouth, Churning in stomach, mixing by segmentation. 3) Propulsion: (movement of food), Swallowing, Peristalsis propulsion by alternate contraction & relaxation. 4) Chemical digestion: Complex food molecules (carbohydrates, proteins and lipids) broken down into chemical building blocks (simple sugars, amino acids, and fatty acids and glycerol). It is carried out by enzymes secreted by digestive glands into lumen of alimentary canal 5) Absorption: Transport of digested products into the blood and lymph in wall of intestine. 6) Defecation: Elimination of indigestible substances (wastes) from body as feces. 1- Mouth  1- Mouth  Mechanical digestion: teeth breaking up food  Chemical digestion:Tongue mixes food with saliva which includes: 1- Salivary amylase: digests starch into maltose. 2- Mucin protein (mucus): protects soft lining of digestive system and lubricates food for easier swallow. 3- Buffers: neutralizes the acidity in mouth to prevent tooth decay. 4- Anti-bacterial chemicals kill bacteria: kill bacteria that enter mouth with food. Epiglottis: is a flap-like structure at the back of the throat that closes over the trachea preventing food from entering it.  2-Pharynx  Located at the back of the throat, it is approximately 1.5 cm long  Function: passage of food and air.  Larynx: passage for air, closed when we swallow.  3-Esophagus  Approximately 10 cm” long  Functions include: 1. Secrete mucus. 2. Moves food from the throat to the stomach using muscle movement called peristalsis. 3. If acid moved from the stomach to esophagus will cause heartburn.  4- Stomach  Food is temporarily stored in the stomach.  Gastric juices are secreted.  Have layers of muscle that line the inside.  Mechanically and chemically breaks down food.  The mucus secreted by stomach cells protects the stomach lining (protect against gastric ulcers). Functions of stomach: I. Food storage. II. Disinfect food by HCl = pH 2-2.5= acidic. III. Kills bacteria. IV. Chemical digestion: pepsin enzyme breaks down proteins into aminoacids. V. Food is further broken down into a thin liquid called chyme.  5- Gall bladder  Pouch structure located near the liver which concentrates and stores bile.  Bile duct: a long tube that carries bile. The top half of the common bile duct is associated with the liver, while the bottom half of the common bile duct is associated with the pancreas, through which it passes on its way to the intestine.  Bile is a bitter, greenish-yellow alkaline fluid, stored in the gallbladder between meals and upon eating is discharged into the duodenum where it aids the process of digestion of fats. The Functions of Bile: i. Interacts only at surface of lipid droplet. ii. Bile salts break droplets apart (emulsification) iii. Increases surface area exposed to enzymatic attack. iv. Creates tiny emulsion droplets coated with bile salts.  6- Pancreas  An organ which secretes both digestive enzymes (exocrine) and hormones (endocrine).  Pancreatic juice digests all major nutrient types.  Pancreatic Enzymes: 1. Pancreatic alpha-amylase: A carbohydrase, breaks down starch into maltose, similar to salivary amylase. 2. Pancreatic lipase: Breaks down complex lipids, into fatty acids, gycerol that are easily absorbed. 3. Nucleases: Break down nucleic acids. 4. Proteolytic enzymes: 70% of all pancreatic enzyme production, Secreted as inactive proenzymes, become activated after reaching small intestine. 5. Proteases: break large protein complexes into small polypeptide chains. 6. Peptidases: break small peptides into amino acids.  7- Liver  Functions of the liver: 1. Production of bile, which helps carry away waste and breakdown fats in the small intestine during digestion. 2. Production of certain plasma protein. 3. Production of cholesterol and special proteins to help carry fats through the body. 4. Store and release glucose as needed. 5. Processing of hemoglobin for use of its iron content (the liver stores iron). 6. Conversion of harmful ammonia to urea (urea is one of the end products of protein metabolism that is excreted in the urine). 7. Clearing the blood from drugs and other harmful substances. 8. Regulating blood clotting. 9. Resisting infections by producing immune factors and removing bacteria from the bloodstream. 10. Clearance of bilirubin (if there is a buildup of bilirubin, the skin and eyes turn yellow).  8- Small Intestine  Structure:  The small intestine is about 4.75–6 metres long and an average of 2.5 centimetres in diameter.  It is looped and coiled and fills up much of the abdominal cavity (the space in the abdomen that contains the intestines and other organs). The small intestine has 3 parts: 1) Duodenum:  about 25 centimetres long.  considered the mixing bowl and is where most digestive enzymes enter the small intestine. 2) Jejunum:  about 2.4 metres long.  most of the chemical digestion and absorption takes place here. 3) ileum : about 3.6 m.  9- Large intestine (caecum + colon + rectum)  The large intestine is responsible for removing water from the contents of the intestine and making it ready for removal from the body.  Function of Large Intestine: 1. Absorb Water: Within 24 hours after eating, undigested food moves from the small intestine into the large one for absorbing water and prepare the waste as a solid stool that will be expelled from the body. 2. Absorb Vitamins:  There are a number of beneficial bacteria that normally live in the large intestine and play an important role in breaking down undigested sugars and fibers into fatty acids.  These commensal bacteria also create the gases that is composed of methane, hydrogen sulfide, carbon dioxide and other gases as a result of the breakdown of the sugars by the bacteria.  The beneficial bacteria produce many vitamins, of which is Vitamin K and Biotin that are absorbed back into the body. 3. Reduce Acidity and Protect from Infections:  The fatty acids that are produced by the bacteria in the large intestine cause an acidic environment in the gut. The large intestine produces alkaline solutions that help to reduce the acidity and balance the pH in the large intestine.  The mucous lining of the large intestine acts as a protective layer that prevents harmful bacteria from being reabsorbed into the body. ` 4. Produce Antibodies:  the large intestine produces antibodies that help to boost immunity.  It is believed that the appendix may have been a major producer of antibodies at some point in the evolutionary process.