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Digestive System SCI Human Biology - 1 Assigned: 10/9 Due: 10/10 Chapter 8 Digestive System

8.1 Overview of Digestion 1. Describe in you words the processes that occur in the digestive system (ingestion, digestion, movement, absorption, elimination) The first step of digestion is placing food in the mouth (ingestion), then through chewing and swallowing the food enzymes begin to act on the particles (digestion). While in the stomach and small intestine, the enzymes hydrolyze the food particles transforming them into molecular nutrients. From there the food moves along the gastrointestinal tract (GI tract), passing form one organ along to another (movement). While in the GI tract nutrients stemming from the digestion cross the wall and enter through blood the cells lining the tract (absorption). Anything left over that cannot be digested is poop (elimination).

8.2 First Part of the Digestive Tract 1. Describe the MECHANICAL and CHEMICAL digestion that occurs in the mouth.
 * 1) The mouth is the starting place for mechanical and chemical digestion processes to begin.
 * 2) Salivary glands in the mouth produce saliva, a mixture of mucus and water also containing bicarbonate and salivary amylase (enzyme) in order to digest starch.
 * 3) Mechanical digestion takes place when teeth chew up food in order to make it easier to swallow.
 * 4) The tongue assists the teeth with mechanical digestion by moving food around in the mouth and molding a bolus, or mass of chewed food that is pushed towards the pharynx.

2. What is heartburn? Caused by acid reflux, heartburn occurs when stomach contents escape into the esophagus.

3. What is a dental cavity? (What causes it?) An eroded tooth which is caused by acid given off by bacteria in the mouth that metabolize sugar.

8.3 Stomach and Small Intestine 1. What are the functions of the stomach and how is the wall of the stomach modified to perform these functions? The stomach is located beneath the diaphragm on the left side of the body and is a thick-walled j-shaped organ. The functions of the stomach are: Within the usual four layers there are a couple "extras," first a smooth muscular layer runs obliquely to the circular and longitudinal layers allows for stretch and food break down (using gastric juice). The mucosa have deep folds called rugae that can fill to an approximate capacity of 1 liter. These folds contain millions of pits that lead into gastric glands which produce gastric juice. Gastric juice contains pepsin an enzyme that digest proteins, hydrochloric acid, and mucus.
 * store food
 * initiate digestion of protein
 * control movement of chyme into small intestine

2. What are the functions of the small intestine and how is the wall of the small intestine modified to perform these functions? The small intestine contain enzymes that digest all types of food. The wall of the small intestine absorbs the molecules, the mucosa is modified for absorption. Mucosa have projections called villi that have microscopic projections called microvilli, causing the villi to have a fuzzy border commonly known as a "brush border."

3. What is lactose intolerance? What causes it and what are the symptoms? Lactose intolerance is a condition characterized by diarrhea, gas, bloating, and adomnial cramps after drinking milk and other dairy products. Lactose is the primary sugar in milk, people without the "brush border" enzyme called lactase cannot digest lactose.

8.4 Three accessory organs. 1. What are the three main accessory organs and how do they assist the digestive process?
 * 1) Pancreas (fish-shaped, spongy, grayish pink - stretches across back of the abdomen behind stomach) - produces pancreatic juice which contain sodium bicarbonate (neutralizes acid chyme from stomach) and digestive enzymes for all types of food.