The Digestive System PDF

THE DIGESTIVE SYSTEM Lesson 3 Function The primary function of the digestive system is to change the foods you eat into chemical forms your body can use. Anything your body can’t use must be properly eliminated. Steps in Digestion 1. Ingestion: the taking in of food 2. Digestion: the prep...

THE DIGESTIVE SYSTEM Lesson 3 Function The primary function of the digestive system is to change the foods you eat into chemical forms your body can use. Anything your body can’t use must be properly eliminated. Steps in Digestion 1. Ingestion: the taking in of food 2. Digestion: the preparation of food for breakdown Mechanical Digestion: occurs in the mouth and stomach – solid food masses are shredded, torn, ground and shaken into smaller pieces = increased surface area Chemical Digestion: food is mixed with various juices from the digestive glands where enzymes act upon the food particles 3. Absorption: nutrients and water are taken in through the small and large intestine 4. Egestion/Elimination: the removal of waste food material from the body Digestion and the Alimentary Canal The digestive tract in most animals is a long open tube called the alimentary canal. It starts at the mouth and ends at the anus. Food is broken down and distributed as it moves along.  In humans, six main organs make up the alimentary canal: the mouth, pharynx, esophagus, stomach, small intestine, and large intestine. Accessory glands and organs include the salivary glands, pancreas, liver, and gallbladder, which secrete digestive juices into the alimentary canal. The Length of the Digestive Tract Herbivores and omnivores usually have longer digestive tracts, relative to body size, than carnivores. Why? The Digestive System A Closer Look  Mouth In mammals, the mouth is equipped with a number of teeth arranged along the lower and upper jaw. Teeth vary in number and structure depending on species Incisors – flat for biting & cutting food into smaller pieces Canines/Bicuspids – shred and tear Molars – grind and crush  Mouth The uvula prevents food from entering the pharynx (upper portion of the throat that connects the digestive and respiratory systems) while we swallow. Saliva, secreted from salivary glands, contains enzymes (amylase) for chemical digestion, and it lubricates food. Bolus = a well-lubricated, ball-like mass of food ready to be swallowed  Esophagus A tube the runs from the mouth to the stomach. The epiglottis covers the opening to the trachea to ensure that food does not go into the lungs. The muscular contractions (peristalsis) of the esophagus move the bolus of food from the mouth to the stomach.  Stomach A muscular, J-shaped, sac-like organ. Food enters the stomach from the esophagus through the cardiac/esophageal sphincter. Lined with gastric glands that secrete gastric juices – contain hydrochloric acid and enzymes (pepsin), as well as mucus to protect the stomach lining.  Stomach Muscles in the stomach mix food with gastric juices to create a thick liquid called chyme. The pyloric sphincter controls the flow of chyme leaving the stomach.  Small Intestine After leaving the stomach, the food enters the small intestine – approximately 6m long, 2.5 cm wide. It is divided up into 3 main parts:  Small Intestine Duodenum the shortest of the three (25-30 cm) the pancreatic and bile ducts open up into this part of the intestine making it an important site for chemical digestion Jejunum about 2.5 meters long breaks down remaining proteins, fats, and carbohydrates for absorption Ileum about 3 metres long also absorbs nutrients pushes remaining undigested material on to the large intestine  A Closer Look at the Small Intestine It has many folds (plica) which increase the surface area of the intestine to better absorb nutrients. To further increase the surface area, the plica have small, finger-like projections called villi. Further, the villa have on them microvilli. Approximately 80% of absorption occurs in the small intestine. Villi contain networks of capillaries that allows for easy diffusion of nutrients into the blood stream. A Closer Look at the Small Intestine  Large Intestine Consists of several consecutive sections cecum  colon (4 parts)  rectum  anus It is about 1.5m long and 5cm wide.  Large Intestine Cecum: receives chyme from small intestine appendix is found off of this part – function is debateable – possibly immune function Colon: divided into the ascending, transverse, descending and sigmoid colon main function is to absorb water also the site for vitamin K production by micro-organisms living in this part of the intestine Rectum: end of the digestive tract  Large Intestine Anus: site of feces elimination which is controlled by 2 sphincters Fecal Composition 75% water 25% solid matter  Accessory Organs in Digestion Salivary Glands Secrete a watery fluid that contains salivary amylase which is responsible for the breakdown of starches Also secrete mucus to aid in the swallowing of food.  Accessory Organs in Digestion Liver Largest internal organ of the human body! Filters blood leaving the digestive tract in order to cleanse it of any toxins. Stores large amount of glycogen Synthesizes bile for the digestion of foods.  Accessory Organs in Digestion Gall Bladder Found under the right lobe of the liver. Stores and concentrates bile. When large amounts of fats are detected in the duodenum, the gall bladder is signalled to release bile. Bile is NOT an enzyme! It works as an emulsifying agent for fats in the small intestine and aids in the absorption of lipids.  Accessory Organs in Digestion Pancreas Lies in behind the stomach. Neutralizes acidic chyme. Also releases enzymes to break down carbohydrates, proteins and lipids. The pancreas helps to regulate blood sugar levels by secreting 2 antagonistic hormones at appropriate times: Insulin decreases blood sugar levels Glucagon increases blood sugar levels Digestion Timeline Enzymes in the Digestive System Practice/Homework Digestive System Diagram Textbook Page 419 # 3-7, 9, 11 Digestive System Concept Map