The Digestive System

The Digestive System 4 steps for processing nutrients from food Ingestion Digestion Absorption Elimination

Ingestion & Digestion Ingestion: Eating or drinking Digestion: the breaking down of food into molecules that are small enough to be absorbed by the body Mechanical digestion: Chewing and grinding food into smaller pieces, increasing the surface area Chemical digestion: Breaking chemical bonds of macromolecules (carbs, proteins and lipids) into monomers (sugars, amino acids, glycerol & fatty acids) Hydrolysis reactions that are carried out by enzymes

Absorption & Elimination Cells absorb small molecules (monomers) allowing them to enter into the circulatory system for immediate use or be transported to storage organs for later use Elimination: Removing undigested waste (feces)

Digestive System Digestive Tract Accessory Glands & Organs A.k.a. an alimentary canal (2 openings) The mouth, pharynx, esophagus, stomach, small intestine, and large intestine Accessory Glands & Organs Aid in digestion, but not a part of the digestive tract Salivary glands, pancreas, liver, gallbladder. Secrete digestive juices and enzymes into the digestive tract

What’s Your Size? Predicted Length (m) Actual Length (m) Mouth 0.15 Pharynx 0.05 Esophagus 0.25 Stomach Duodenum 0.2 Jejunum 2.8 Ileum 4.2 Large Intestine 1.5 Total ~9

Chewed up food is now called a bolus Mouth Plays a role in ingestion and digestion Teeth, tongue, hard palate aid in mechanical digestion Tongue moves food down to the esophagus Salivary glands aid in chemical digestion Release saliva (~1L/day), a watery liquid containing digestive enzymes Salivary amylase begins to break down starch into smaller carbohydrates Lubrication Chewed up food is now called a bolus

Esophagus Located behind the trachea As you swallow, the epiglottis closes over the trachea and the food bolus passes through pharynx into the esophagus The bolus is pushed through the esophagus by a series of muscle contractions called peristalsis

Heart Burn After food passes into the stomach, the cardiac sphincter closes the esophagus If the sphincter opens at an inappropriate time, stomach acid can flow back into the esophagus Esophagus does not have the same protective lining as the stomach

I ate too much…I’m STUFFED! Stomach Elastic, muscular sac with a protective lining that contains millions of gastric glands Can ~ 2 L Mechanical and chemical digestion I ate too much…I’m STUFFED!

Stomach Chemical Digestion: The hormone, gastrin, stimulates gastric glands to release gastric juice Hydrochloric acid breaks apart cells and kills bacteria Enzymes e.g. pepsin Mucus lubrication and protection Mechanical Digestion: Stomach muscles churn Bolus becomes an acidic, nutrient-rich liquid called chyme

Small Intestine Chyme passes through the pyloric sphincter and enters the small intestine (peristalsis) Long, narrow tube where digestion is completed and absorption begins 3 parts: Duodenum Jejunum Ileum

Duodenum Bile from the liver and gallbladder are secreted into the duodenum to help with lipid digestion Pancreas secretes pancreatic juice into the duodenum Neutralizes acidic chyme Pancreatic amylase Trypsin & chymotrypsin (protein digestion) Pancreatic lipase Small intestine releases enzymes too

Jejunum & Ileum Jejunum Contains more villi, therefore more absorption Breakdown of remaining polypeptides and carbohydrates Ileum Absorption Push remaining undigested material into the large intestine

Large Intestine Undigested material passes through the sphincter between the ileum and the cecum Absorption of water and dissolved minerals Intestinal bacteria produce vitamins Indigestible material (feces) passes through the rectum to the anus Anal sphincters help control timing of elimination

Increased Surface Area The small and large intestine are folded to  surface area and therefore  absorption Within the folds, there are finger-like projections called villi Lacteal absorbs fats and fat-soluble vitamins Capillaries absorb glucose, amino acids, minerals and water-soluble vitamins

Regulation of Digestive Processes

http://www. neok12. com/php/watch. php http://www.neok12.com/php/watch.php?v=zX680f4e7e6e7c420f746402&t=Digestive-System http://www.neok12.com/quiz/DIGSYS04 http://www.neok12.com/quiz/DIGSYS01 http://www.neok12.com/diagram/Digestive-System-01.htm