Life Science Chapter 3

The Digestive and Urinary Systems

Life Science 3.1

The Digestive System

1. Compare mechanical digestion with chemical digestion.

2. Describe the parts and functions of the digestive system.

Objective:

Digestive system Group of organs that break down food so that it

can be used by the body.Food passes through the digestive tract. The digestive tract includes

your mouth, pharynx, esophagus, stomach, small intestine, large intestine, rectum, and anus.

The liver, gallbladder, pancreas, and salivary glands are also part of the digestive system.

Digestive System at a Glance

Mechanical digestion Breaking, crushing,

and mashing of food.

Chemical digestionLarge molecules

are broken down into nutrients with the aid of enzymes.

Breaking Down Food

Teeth With the help of

strong jaw muscles, teeth break and grind food.

SalivaContains an

enzyme that begins the chemical digestion of carbohydrates.

Digestion Begins in the Mouth

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.

Leaving the Mouth

Stomach Muscular, saclike, digestive organ attached to the lower

end of the esophagus.Tiny glands in the stomach

Produce enzymes and acid to break food down into nutrients.

After a few hours of combined mechanical and chemical digestion, Food leaves your stomach as a soupy mixture called chyme.

The Harsh Environment of the Stomach

Pancreas Organ located between the stomach and small

intestine. Makes fluids that protect the small intestine from

the acid in chyme.Small Intestine

Muscular tube that is about 2.5 cm in diameter and about 6 m long.

Nutrients are absorbed into the bloodstream through fingerlike projections called villi.

The Pancreas and Small Intestine

Liver Large, reddish brown organ that

helps with digestion by making bile to break up fat.

Stores excess nutrients until the body is ready to absorb them into the bloodstream.

Breaks down toxins.

Gallbladder Saclike organ that stores bileSqueezes the bile into the small

intestine.Breaks large fat droplets into

smaller ones.

The Liver and the Gallbladder

Large intestine Wider and shorter portion of the intestine that

removes water from mostly digested food and that turns the waste into semisolid feces, or stool.

Feces are stored in the rectum until they can be expelled.

About 1.5 m long, 7.5 cm diameter

The End of the Line

Feces pass to the outside of the body through an opening called the anus.

It has taken each of your meals about 24 hours to make this journey through your digestive system. Digestive syst

em visual concept