THE DIGESTIVE SYSTEMChapter 2 Section 2

FUNCTIONS OF THE

DIGESTIVE SYSTEM

Digestion is the process that breaks down food into small molecules so

that they can be absorbed and moved into the blood,

then on to the cells.

FOOD IS PROCESSED IN YOUR BODY IN

4 STAGESingestiondigestion

absorptionelimination

MECHANICAL DIGESTIONTakes place when food is

chewed, mixed, and churned. This mainly

occurs in the mouth and stomach.

CHEMICAL DIGESTION

occurs when chemical reactions occur that break down large molecules of food into smaller ones.

ENZYMES IN DIGESTION

Enzymes help you digest carbohydrates, fats and proteins.

Amylase is an enzyme produced in a gland near the mouth.

Amylase helps speed up the breakdown of complex carbs, such as starch, into simpler carbs - sugar.

ENZYMES IN DIGESTION

In your stomach, the enzyme pepsin helps in the breakdown of complex proteins into less complex proteins.

In your small intestine, many other enzymes continue to speed up the breakdown of proteins into amino acids.

ENZYMES IN DIGESTION

The pancreas, an organ on the back outside of the stomach, releases several enzymes through a tube into the small intestine.

They breakdown starches that started to be broken down in the mouth. The starches are broken down into glucose to be used by cells.

Other enzymes from the pancreas are involved in the breakdown of fatty acids and proteins.

ENZYMES

The human digestive system is like a long tube with specialized sections. If it is stretched out, it would be _________ meters long.

6 to 9 meters!!!!!!!Absolutely mind-boggling!

DIGESTIVE SYSTEM HAS 2 PARTS

the digestive tract the accessory organs

mouth

esophagus

stomach

small intestine

large intestine

rectum

anus

tongue

teeth

salivary glands

liver

gallbladder

pancreas

food passes through food does not pass through

MOUTH

•Mechanical and chemical digestion begins in the mouth.

•Mechanical digestion - when you chew with your teeth and mix with your tongue.

•Chemical digestion - watery substances called saliva is added to your mouth. Saliva is produced by 3 sets of glands near your mouth.

•Saliva - mostly water, but also contains mucus and an enzyme that helps in the breakdown of starch into sugar.

MOUTH

•Food mixed with saliva becomes a soft mass and is moved to the back of your mouth by your tongue.

•It is swallowed and passes into your esophagus.

•Ingestion is now complete.

ESOPHAGUS

•Food that passes from the mouth into the esophagus, first passes the epiglottis.

•Epiglottis - structure that automatically covers the opening to the wind pipe to prevent food from entering the lungs and causing you to choke.

•Esophagus - muscular tube about 25 cm long. It takes 4-10 seconds for food to travel through it.

ESOPHAGUS

•No digestion takes place in the esophagus, but there are mucus glands in the wall to keep the food moist.

•The walls are made of smooth muscles, which move the food down to the stomach with a squeezing motion called peristalsis.

STOMACH

•Stomach - muscular bag, that when empty is sausage shaped with folds on the inside.

•As food enters, the stomach expands and the folds smooth out.

•Mechanical and chemical digestion take place here.

•Mechanical - food is mixed by peristalsis

•Chemical - food is mixed with enzymes and strong digestive solutions, like hydrochloric acid.

STOMACH

•Specialized cells in the walls of the stomach release about 2 liters of HCl solution each day.

•WOW!!

•The acidic solution works with the enzyme pepsin to digest protein. It also destroys bacteria that are present in the food.

•The stomach also produces mucus, making the food slippery and protects the stomach from the strong, digestive solutions.

STOMACH

•Food moves out of the stomach after 2-4 hours and is changed into a thin, water liquid called chyme.

•Little by little chyme leaves the stomach and moves to the small intestine.

SMALL INTESTINE

•The small intestine is small in diameter, but is 4-7 meters longs!

•Food from the stomach enters the first section of the small intestine called the duodenum. Most digestion takes place here.

•A greenish fluid, bile, is produced in the liver and stored in the gall bladder.

•The acid from the stomach makes large fat particles float to the top of the bile.

•Bile breaks up the large fat particles, similar to the way detergent breaks up grease.

SMALL INTESTINE

•Chemical digestion of carbohydrates, proteins, and fats occurs when a digestive solution from the pancreas is mixed in.

•The solution contains bicarbonate ions to neutralize the stomach acid and enzymes to continue the breakdown.

•Your pancreas also makes insulin, a hormone that allows glucose to pass from the blood stream into your cells.

SMALL INTESTINE

•Absorption of food’s nutrients takes place in the small intestine.

•The wall of the small intestine has many ridges and folds that are covered with fingerlike projections called villi.

•Villi increase the surface area so that the nutrients in the chyme have more places to be absorbed.

•By how much do villi increase the surface area of the small intestine?

IF YOU WERE TO STRETCH OUT THE VILLI OF THE SMALL INTESTINE THEY WOULD COVER......

...a tennis court!!!!

SMALL INTESTINE

•Peristalsis continues to move and mix the chyme.

•Nutrients move into the blood vessels within the villi.

•The blood transports the nutrients to all cells of your body.

•Peristalsis continues to force the remaining undigested and unabsorbed materials slowly into the large intestine.

LARGE INTESTINE

LARGE INTESTINE

•When the chyme enters the large intestine it is still thin and watery.

•The main job of the large intestine is to absorb water from the undigested mass.

•This keeps large amounts of water in your body and maintains homeostasis.

•Peristalsis slows down in the large intestine.

•The chyme might stay there for as long as 3 days.

LARGE INTESTINE

•After the excess water is absorbed the undigested material become more solid.

•Muscles in the rectum (the last section of the large intestine) and the anus control the release of semisolid wastes from the body in the form of feces.

BACTERIA ARE IMPORTANT

Many types of bacteria are in your body.

They live in many of the organs in your digestive tract, including your mouth and large intestine, where both your body and the bacteria are benefitted.

Bacteria in your large intestine feed on undigested material like cellulose. The bacteria make vitamins you need- vitamin K and 2 vitamin B’s.

BACTERIA ARE IMPORTANT

Vitamin K is needed is needed for blood clotting. The Vitamin B’s are needed for your nervous system for other body functions.

The breakdown of intestinal materials by bacteria produces gas.