DIGESTIVE SYSTEM - SoF.pdf

DIGESTIVE SYSTEM Objectives: Define the digestive system Main steps and Layers of GI The pathway of food : Mouth Pharynx Esophagus Stomach Accessory organs: Pancreases, Liver and Gallbladder Small intestine Large intestine  What is the digestive system? It is a system of th...

DIGESTIVE SYSTEM Objectives: Define the digestive system Main steps and Layers of GI The pathway of food : Mouth Pharynx Esophagus Stomach Accessory organs: Pancreases, Liver and Gallbladder Small intestine Large intestine  What is the digestive system? It is a system of the human body that is responsible for breaking down food into nutrients. These nutrients are passed to the circulatory system where the cells of the body will utilize them for energy, growth, or cell repair. This system is divided into two main parts: - Digestive tract (gastrointestinal tract): a long tube where the food passes. - The accessory organs: these are important for the digestion process, but the food does not pass through them. Organs of the digestive system Gastrointestinal tract: this tract can be divided into two main parts; - The upper digestive tract: Oral cavity, pharynx, epiglottis, esophagus, and stomach. - Lower digestive tract: The small intestine, large intestine, and the anus. - The accessory organs that help in these processes: Pancreas, salivary glands, liver, gall bladder, teeth, tongue What are the main steps in the digestive process? Ingestion – intake of food via the mouth Digestion – mechanically or chemically breaking down food into their subunits Movement – food must be moved along the GI tract to fulfill all functions Absorption – movement of nutrients across the GI tract wall to be delivered to cell via the blood Elimination – removal of indigestible molecules What are the 4 major layers that make up the wall of the GI tract? ❑Mucosa – innermost layer that produces mucus that protect the lining and produce digestive enzymes ❑Submucosa – 2nd layer of loose connective tissue that contains blood vessels, lymphatic vessels and nerves ❑Muscularis – 3rd layer made of 2 layers of smooth muscle that move food along the GI tract ❑Serosa – outer lining that is part of the peritoneum The pathway of the food: Mouth Pharynx Esophagus Stomach Small intestine Large intestine Rectum Anus The Mouth (Oral cavity) ❑Salivary Glands: 3 pairs glands are located between the ear and mouth, under the tongue. - They produce and secrete a watery liquid known as saliva, is made of three main contents: 1) Water: most of the saliva, this helps to liquify and dissolve food. 2) Mucus: makes the food slippery and easy to move down the tract. 3) Amylase: an enzyme that starts to break down starch in the mouth. 4) Lysozyme: an enzyme that gets rid of harmful bacteria. ❑Tonsils: at the back of the mouth and other lymphatic tissues are important in fighting disease ❑Tongue: This is an organ that contains many bumps known as taste buds, these allow us to taste food. - Food has five basic flavors: sweet, sour, salty, bitter, and umami. ❑ Teeth: 32 in adults used for mechanical breakdown of food. Each tooth is made of a crown and a root A hard covering called enamel and dentin covers the crown with an inner pulp area with nerves and blood vessels Cavity: occur when bacteria metabolize sugars and produce acids, so limiting sugar intake and brushing teeth to avoid cavities. ❑Each type of tooth has a specific shape and function; 1) Incisor: a total of 8 flat teeth that are found at the front of the mouth. These are used for biting and cutting the food. 2) Canines: a total of 4 teeth that are found beside the incisors. They are sharp and have the function of tearing food. 3) Premolars: a total of 8 teeth found beside the canines, they are used for chewing and grinding food. 4) Molars: a total of 12 teeth that are located at the very back of the mouth. They are also used to grind food. Anatomy of the mouth  After the food is chewed and covered with saliva, it must swallowed be and transferred to the stomach. The food will travel to the pharynx, esophagus then to the stomach. o Pharynx: is a cavity between the mouth and esophagus that serves as a passageway for food (and air) The Epiglottis covers the voice box (Larynx) to make sure food is routed into the esophagus o Esophagus: a long muscular tube that leads to the stomach. Food moves down the esophagus through peristalsis (rhythmic contraction) The stomach There are 3 layers of muscle in the muscularis layer of the stomach wall helping in mechanical digestion and allowing it to stretch The mucosa layer has deep folds called rugae and gastric pits that lead into gastric glands that secretes Gastric juice Gastric juice contains Pepsin, an enzyme that breaks down proteins, and HCl HCl gives the stomach a pH of 2 which activates pepsin and helps kill bacteria found in food Alkaline mucus: this covers the walls to protect them from the strong acid At The end of the stomach there is another muscle flap known as the pyloric sphincter, this will relax and allow the food to enter the small intestine (in small amounts not all at once). The three accessory organs: Pancreas Liver Gallbladder The Pancreas: Functions of the pancreas: 1. Secretes enzymes into the small intestine - Trypsin: digests proteins - Lipase: digests fats - Pancreatic amylase: digests carbohydrates 2. Secretes Bicarbonate into the small intestine to neutralize stomach acids 3. Secretes insulin into the blood to keep blood sugar levels under control The Liver and Gallbladder: Liver takes poisons(e.g. alcohol and drug) out of the food Removes iron, vitamins A, D, E, K and B12 from the blood and stores them Breaks down hemoglobin Stores glucose as glycogen and breaks it down to help retain blood glucose levels Liver makes bile that is then stored in the Gallbladder to be secreted into the Duodenum to emulsify fats (emulsification of fat to be digested and absorbed easily) Liver disorders: ❑Hepatitis: Inflammation of the liver Caused by Hepatitis viruses: A, B and C ❑Cirrhosis: The liver becomes fatty and eventually this tissue is replaced by fibrous tissue Seen in alcoholics and obese people The Small Intestine: Averages 6m in length Digestion completed by pancreatic enzymes and enzymes of the small intestine (secreted by Normal flora) Digested food is absorbed through large surface area created by numerous villi (finger-like projections) and microvilli. Therefore, most of nutrient absorption occur in small intestine Amino acids and sugars enter the capillaries while fatty acids and glycerol enter lymph vessels The Large Intestine: Includes the Colon, Rectum and Anus Larger in diameter but shorter than the small intestine The Appendix that may play a role in fighting infections Functions to:  Absorb water, sodium, potassium  Absorbs vitamins (B complex and K) produced by intestinal flora  Elimination of indigestible food (feces) through the anus Disorders of the colon and rectum: Diarrhea and Constipation Hemorrhoids – enlarged and inflamed blood vessels of the anus due to chronic constipation, pregnancy. Irritable bowel syndrome (IBS) –problem that causes abdominal pain, cramping, and changes in your bowel movements. Symptoms: bloating, gas, diarrhea, abdominal pain, or constipation. Inflammatory bowel disease/colitis (IBD) – a group of inflammatory disorders such as ulcerative colitis or Crohn’s disease.