Digestive System

The digestive system is responsible for the physical and chemical breakdown of food so it can be taken into the bloodstream and used by body cells and tissues.

The Digestive System includes: The Alimentary Canal: Long muscular tube Begins at the mouth and includes the pharynx, esophagus, stomach, small intestines, large intestines, and the anus. The Accessory Organs: The salivary glands, tongue, teeth, liver, gallbladder, and pancreas

Where does digestion start? Mouth, buccal, or oral cavity A. Receives food as it enters the body B. Actions in the mouth 1. Food is tasted 2. Broken down physically by the teeth 3. Lubricated and partially digested by saliva 4. Swallowed

Teeth Special structures in the mouth 2. Break down food physically by chewing and grinding the food, a process called mastication

Tongue Muscular organ 2. Contains special receptors called taste buds that allow person to taste sweet, salt, sour, and bitter sensations 3. Also aids with chewing and swallowing of food

Within the mouth: Hard palate 1. Bony structure that forms the roof of the mouth 2. Separates the mouth from the nasal cavities

Soft palate 1. Located behind the hard palate 2. Separates the mouth from the nasopharynx

Uvula (a) Cone-shaped muscular structure (b) Hangs from the middle of the soft palate (c) Prevents food from entering the nasopharynx during swallowing

Salivary Glands 1. Three pairs of glands Parotid, sublingual, and submandibular  2. Produce a liquid called saliva (a) Lubricates the mouth during speech and chewing (b) Moistens food so it can be swallowed easily (c) Also contains an enzyme called salivary amylase aa. Substance speeding up a chemical reaction bb. Begins the chemical breakdown of carbohydrates or starches into sugars that can be taken into the body  

Pharynx or Throat A. After the food is chewed and mixed with saliva, it is called a bolus and it enters the pharynx or throat B. Tube that carries both air and food C. Carries the air to the trachea or windpipe D. Carries food to the esophagus

In the esophagus: When bolus is swallowed, muscle action causes the epiglottis to close over the larynx 2. Prevents bolus from entering respiratory tract 3. In this way, the bolus enters the esophagus

Normal Swallow Animation - Thick and Easy Dysphagia - YouTube www.youtube.com/watch?v=1YfO11Pry6Y&feature=player_detailpage

Esophagus Muscular tube dorsal to the trachea Receives bolus from the pharynx and carries it to the stomach Relies on a rhythmic, wavelike involuntary movement of its muscles, called peristalsis, to move the food in a forward direction

Stomach Enlarged part of the alimentary canal Receives the food from the esophagus Mucous membrane lining contains folds called rugae, which disappear as the stomach fills with food and expands  

Cardiac Sphincter Circular muscle between the esophagus and stomach Closes after food enters the stomach Prevents food from going back up into the esophagus

Pyloric Sphincter Circular muscle between the stomach and small intestine Keeps food in the stomach until it is ready to enter the small intestine Food usually remains in the stomach for about one to four hours

Gastric Juices Produced by glands in the stomach Converts food into a semi fluid material called chyme

Gastric Juices Juices contain hydrochloric acid Kills bacteria Facilitates the absorption of iron Activates the enzyme pepsin

Gastric Juices Contain enzymes: Lipase, which begins the chemical breakdown of fats Pepsin, which starts protein digestion In an infant, the enzyme rennin is secreted 1) Aids in the digestion of milk 2) Not present in an adult

Small Intestine Coiled section of the alimentary canal about 20 feet long and 1 inch in diameter Receives food, in form of chyme, from stomach

Small Intestines There are three sections: Duodenum—first 9-10 inches Jejunum—next 8 feet Ileum—final 12 feet

Small Intestines--Duodenum The first 9-10 inches Bile from the gallbladder and liver enter this section through ducts or tubes Pancreatic juices from the pancreas also enter this section through ducts or tubes.

Small Intestines--Jejunum Eight feet long Forms the middle section of the small intestine

Small Intestines--Ileum Final 12 feet of the small intestine Connects with the large intestine at the cecum Circular muscle called the ileocecal valve separates the ileum and cecum and prevents food from returning to the ileum.

Functions of the Small Intestines: Completes the process of digestion Absorbs the products of digestion into the bloodstream for use by body cells

Intestinal Juices of the Small Intestines Produced by the small intestine Contain the enzymes maltase, sucrase, and lactase, which break down sugars into simpler forms Contain enzymes known as peptidases, which complete the digestion of proteins Contain the enzyme steapsin, which aids in the digestion of fat

Bile Liquid that enters small intestine from liver and gallbladder 2. Emulsifies or physically breaks down fats

Pancreatic Juice 1.Liquid that enters small intestine from pancreas 2. Contains enzymes that complete the process of digestion A) Pancreatic amylase or amylopsin, which acts on sugars B) Trypsin and chymotrypsin, which act on proteins C) Lipase or steapsin, which acts on fats

Small Intestine--Villi Fingerlike projections that line wall of small intestine Allow food to be absorbed or taken into bloodstream Contain blood capillaries and lacteals

Small Intestine—Blood Capillaries Blood capillaries absorb the digested nutrients and carry them to the liver where they are stored or released into general circulation for use by body cells

Small Intestines--Lacteals Lacteals pick up most of the digested fats and carry them to the thoracic duct in the lymphatic system, which releases them into the circulatory system

Small Intestines When food has completed its passage through the small intestine only wastes, indigestible materials, and excess water remain

Large Intestines Final section of the alimentary canal About 5 feet long and about 2 inches in diameter

Large Intestines--Functions Absorption of water and any remaining nutrients Storage of indigestible materials before they are eliminated from the body Synthesis (formation) and absorption of some B-complex vitamins and vitamin K by bacteria present in intestine Transportation of the waste products out of the alimentary canal

Large Intestines--Sections Cecum: First section Connects with the ileum of the small intestine Contains a small projection called the vermiform appendix

Large Intestines--Sections Ascending colon: continues up on the right side of the body from the cecum to the lower part of the liver

Large Intestine--Sections Transverse colon: extends across the abdomen, below the liver and stomach, but above the small intestine

Large Intestines--Sections Descending colon: extends down the left side of the body

Large Intestines--Sections Sigmoid colon: Connects with descending colon S-shaped section that joins with the rectum

Large Intestines--Sections Rectum: Final 6 to 8inches Storage area for the indigestibles or wastes Has a narrow canal called the anal canal, which opens at a hole called the anus Fecal material or stool, the final waste product of the digestive process

Accessory Organs Liver: Largest gland in the body Accessory organ for the digestive tract Located under the diaphragm in the upper right quadrant of the abdomen  

Functions of the Liver: 1. Secretes bile a. Used to emulsify or physically break up fats b. Also makes fats water soluble, which is necessary for absorption 2. Stores sugar in the form of glycogen a. Glycogen is converted to glucose b. Released into the bloodstream when additional blood sugar is needed 3. Stores iron and certain vitamins 4. Produces heparin, a substance that prevents clotting of the blood 5. Produces blood proteins such as fibrinogen and prothrombin, which aid in the clotting of blood 6. Produces cholesterol 7. Detoxifies (renders less harmful) substances such as alcohol and pesticides, and destroys bacteria that have been taken into the blood from the intestine  

Accessory Organs Gallbladder: 1. Small muscular sac 2. Located under the liver and attached to it by connective tissue  3. Stores and concentrates bile, which it receives from the liver 4. When the bile is needed in the digestive tract to emulsify fats, it contracts and pushes the bile through the common bile duct into the duodenum

Accessory Organs Pancreas: 1. Fish-shaped organ located behind the stomach  2. Produces pancreatic juices a. Juices enter duodenum through pancreatic duct b. Contain enzymes to digest food (1) Pancreatic amylase or amylopsin to break down sugars (2) Trypsin and chymotrypsin to break down proteins (3) Lipase or steapsin to act on fats 3. Produces insulin a. Secreted into the bloodstream b. Regulates the metabolism or burning of carbohydrates to convert glucose (blood sugar) to energy