Life Science Chapter 3<br />The Digestive and Urinary Systems<br />
Life Science 3.1<br />The Digestive System<br />
Objective:<br />Compare mechanical digestion with chemical digestion.<br />Describe the parts and functions of the digestive system.<br />
Digestive System at a Glance<br />Digestive system<br />Group of organs that break down food so that it can be used by the body.<br />Food passes through the digestive tract. <br />The digestive tract includes <br />your mouth, pharynx, esophagus, stomach, small intestine, large intestine, rectum, and anus.<br />The liver, gallbladder, pancreas, and salivary glands are also part of the digestive system.<br />
Breaking Down Food<br />Mechanical digestion <br />Breaking, crushing, and mashing of food.<br />Chemical digestion<br />Large molecules are broken down into nutrients with the aid of enzymes.<br />
Digestion Begins in the Mouth<br />Teeth <br />With the help of strong jaw muscles, teeth break and grind food.<br />Saliva<br />Contains an enzyme that begins the chemical digestion of carbohydrates.<br />
Leaving the Mouth<br />Once the food has been reduced to a soft mush, the tongue pushes it into the throat, which leads to a long, straight tube called the esophagus.<br />
Stomach<br />Muscular, saclike, digestive organ attached to the lower end of the esophagus.<br />Tiny glands in the stomach <br />Produce enzymes and acid to break food down into nutrients.<br />After a few hours of combined mechanical and chemical digestion, <br />Food leaves your stomach as a soupy mixture called chyme.<br />The Harsh Environment of the Stomach<br />
The Pancreas and Small Intestine<br />Pancreas <br />Organ located between the stomach and small intestine. <br />Makes fluids that protect the small intestine from the acid in chyme.<br />Small Intestine <br />Muscular tube that is about 2.5 cm in diameter and about 6 m long. <br />Nutrients are absorbed into the bloodstream through fingerlike projections called villi.<br />
The Liver and the Gallbladder<br />Liver<br />Large, reddish brown organ that helps with digestion by making bileto break up fat.<br />Stores excess nutrients until the body is ready to absorb them into the bloodstream.<br />Breaks down toxins.<br />Gallbladder <br />Saclike organ that stores bile<br />Squeezes the bile into the small intestine.<br />Breaks large fat droplets into smaller ones.<br />
The End of the Line<br />Large intestine <br />Wider and shorter portion of the intestine that removes water from mostly digested food and that turns the waste into semisolid feces, or stool.<br />Feces are stored in the rectum until they can be expelled.<br />About 1.5 m long, 7.5 cm diameter<br />
Feces pass to the outside of the body through an opening called the anus.<br />It has taken each of your meals about 24 hours to make this journey through your digestive system.<br />Digestive system visual concept<br />
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