HOMEOSTASIS AND THE DIGESTIVE SYSTEM Essential Questions: How do living organisms maintain a relatively constant internal environment when outside conditions are always changing? How does food breakdown into usable molecules like glucose, fatty acids, and peptides?

Lesson Overview Lesson Overview Organization of the Human Body The organ systems, along with their structures and main functions, are shown below.

WHAT IS HOMEOSTASIS? Homeostasis describes the relatively constant internal physical and chemical conditions that organisms maintain despite changes in internal and external environments.

Feedback Inhibition  Process where a stimulus produces a response that opposes what ever is happening. (negative feedback)  You sweat when you get hot  You shiver when you get cold.  When you are starving, your body sets your metabolism at a lower rate so your body can operate with less energy.

Lesson Overview Lesson Overview Organization of the Human Body THINK ABOUT IT The only system in the body that food actually enters is the digestive system. So how does food get to the rest of the body after the process of digestion?

Lesson Overview Lesson Overview Organization of the Human Body Functions of the Digestive System What are the functions of the digestive system? The digestive system converts food into small molecules that can be used by the cells of the body. Food is processed by the digestive system in four phases—ingestion, digestion, absorption, and elimination.

Steps in Digestion  Ingestion: Putting food in mouth  Digestion: mechanical and chemical breakdown of food  Absorption: In the small intestine, molecules enter the circulatory system (bloodstream)  Elimination: molecules and indigestible food like cellulose move to large intestine to be eliminated

Lesson Overview Lesson Overview Organization of the Human Body The Process of Digestion The human digestive system is built around an alimentary canal—a one-way tube that passes through the body.

Lesson Overview Lesson Overview Organization of the Human Body Mouth Teeth The teeth cut into, tear, and grind and crush food into a fine paste that can be swallowed. Tongue moves food around so that it comes in contact with your teeth. The salivary glands secrete saliva, which helps to moisten the food and make it easier to chew. The release of saliva is under the control of the nervous system and can be triggered by the scent of food.

Lesson Overview Lesson Overview Organization of the Human Body Saliva Saliva also begins the process of chemical digestion. Saliva contains enzymes Amylase: begins to break the chemical bonds in starches, forming sugars. Lysozyme: fights infection by digesting the cell walls of many bacteria that enter the mouth with food. Salivary Lipase: breaks down triglycerides (lipids) into 1 glycerol molecule and 3 fatty acids

Lesson Overview Lesson Overview Organization of the Human Body The Mouth Once food is chewed, the combined actions of the tongue and throat muscles push the clump of food, called a bolus, down the throat.

Lesson Overview Lesson Overview Organization of the Human Body Chemical Digestion in the Stomach The stomach is a large muscular sac that continues chemical and mechanical digestion of food. The lining of the stomach contains millions of microscopic gastric glands that release hydrochloric acid and an enzyme called pepsin that functions best in acidic conditions. Pepsin (peptidase) is an enzyme that breaks proteins down into small peptides (short chains of amino acids)

Lesson Overview Lesson Overview Organization of the Human Body Mechanical Digestion in the Stomach Peristalsis: Alternating contractions of the stomach’s three smooth muscle layers thoroughly churn and mix the swallowed food, breaking it down and allowing enzymes greater access to the food. chyme : mixture with an oatmeal-like consistency is produced. After an hour or two, the pyloric valve—located between the stomach and small intestine—opens, and chyme begins to spurt into the small intestine.

Lesson Overview Lesson Overview Organization of the Human Body Digestion in the Small Intestine As chyme enters the duodenum from the stomach, it mixes with enzymes and digestive fluids from the pancreas, the liver, and the lining of the duodenum. *** Most of the food of the nutrients from the food is absorbed through the walls of the small intestine.****

Lesson Overview Lesson Overview Organization of the Human Body Just behind the stomach is the pancreas, a gland that serves three important functions. 1.One function is to produce hormones that regulate blood sugar levels. 2. It also produces enzymes that break down carbohydrates, proteins, lipids, and nucleic acids. 3. The pancreas also produces sodium bicarbonate, a base that quickly neutralizes stomach acid as chyme enters the duodenum. Pancreas (Intestinal Gland)

Lesson Overview Lesson Overview Organization of the Human Body Effects of Digestive Enzymes (page 878) Digestive enzymes hasten the breakdown of foods and make nutrients available to the body.

Lesson Overview Lesson Overview Organization of the Human Body The Liver and Gallbladder Liver: Organ that helps pancreas to digest fat Produces bile, a fluid loaded with lipids and salts. Bile is stored in a small, pouchlike organ called the gallbladder. The cholesterol contained in bile will occasionally accrete into lumps in the gall bladder, forming gallstones.cholesterolgallstones

Lesson Overview Lesson Overview Organization of the Human Body Absorption and Elimination How are nutrients absorbed and wastes eliminated? small intestine: Most nutrients from food are absorbed here large intestine: absorbs water and several vitamins and prepares waste for elimination from the body. Produces compact feces that contain indigestible material.

Lesson Overview Lesson Overview Organization of the Human Body Elimination If not enough water is absorbed by the large intestine, a condition known as diarrhea occurs. If too much water is absorbed from the undigested materials, a condition known as constipation occurs.