Stomach
• From the stomach, the food passes into the small
intestine.
• The small intestine is called
“small” because it is the thinnest of the tubes, but it is about 20 feet long!
• It is coiled up so that it can fit into the abdomen.
Large
Intestine
Small intestine

• The small intestine has two roles:
1. It performs the final digestions of the food.
2. It absorbs the broken-down nutrients.

• The small intestine is the mixing-bowl for three different digestive chemicals:
1. Bile- from liver and gallbladder (will explain)
2. Pancreatic Juice- from pancreas
3. Intestinal Juice- from small intestine

• Bile is produced in the liver and stored in the gallbladder. It breaks up fat globules into tiny droplets.
• Pancreatic Juice is produced and stored in the pancreas. It contains amylase (breaks polysaccharides into disaccharides) and trypsin
(breaks large polypeptides into small polypeptides) and lipase (breaks tiny fat droplets into fatty acids and glycerol).
• Intestinal Juice is produced and stored in the small intestine. It breaks disaccharides into monosaccharides (glucose) and small polypeptides into amino acids.

Name of Chemical Where is it from Function
Bile
Pancreatic Juice
Liver (produced)
/gallbladder
(stored)
Pancreas
Breaks fat globules into tiny droplets.
Intestinal Juice Small Intestine
Breaks large polypeptides into small polypeptides and polysaccharides into disaccharides and tiny fat droplets into fatty acids and glycerol.
Breaks small polypeptides into amino acids and disaccharides into monosaccharides
(glucose).

Nutrient Step 1 Step 2 Final form
Fat
Protein
Carbohydrate
Fat globules -> tiny droplets (bile)
Large polypeptides
-> Small polypeptides
(pancreatic juice)
Tiny droplets -> glycerol and fatty acid (pancreatic juice)
Small polypeptides
-> amino acids
(intestinal juice)
Glycerol and fatty acids
Amino acids
Polysaccharides -> disaccharides
(pancreatic juice)
Disaccharides -> monosaccharides
(intestinal juice)
Monosaccharides

• What are the three digestive juices in the small intestine?
• Where do each of them come from?
• What does bile do?
• What does pancreatic juice do?
• What does intestinal juice do?
• What is the final, most broken-down form of fat, carbohydrates and proteins?

• At this point, the food is completely broken down into its monomer (smallest) form.
• Key to remember: Until now, the food has been isolated in the digestive tube. Now the body begins to absorb from the digestive tube to the blood stream and from there to feed the rest of the body.
• Absorption begins in the small intestine, as well.

• The small intestine is not a smooth tube on the inside.
It has many ridges and indentations. Inside these indentations are tiny little fingerlike structures called
villi (plural of villus).
• This gives the small intestine enormous surface area to come into contact with the food it contains.

• The villi contain tiny blood vessels called capillaries.
The food in the small intestine is very rich in amino acids, fatty acids and monosaccharides.
• These diffuse from the small intestine (high concentration) through the villi and into the capillaries
(low concentration)
• The nutrients travel from the capillaries to arteries to the rest of the body.

• It is called “large” because it is much wider than the small intestine. It is actually shorter, only 5 feet long.

• The large intestine does not do any digestion at all. Its role is purely absorption.
1. Water absorption
2. Bacteria / Vitamin K production

• The large intestine reabsorbs water from the food mass (very liquidy) into the blood supply through villi that line the intestine.
• If not enough water is reabsorbed, the result is that the food mass is too liquid when it is expelled (diarrhea).
• If too much water is reabsorbed, the result is that the food mass is too solid when it is expelled
(constipation).

• The second function of the large intestine is that it contains bacteria that live off the undigested food particles.
• The body allows these bacteria to live there because they are beneficial to the body. They produce Vitamin K (necessary for blood clotting).
• This Vitamin K is then absorbed along with the water into the capillaries in the villi of the large intestine.

• At this point, the important nutrients, vitamins and water have all been absorbed from the food mass into the body.
• All that remains in the food mass is indigestible plant fiber, bacteria (that fall off the large intestine wall), bile, worn out cells from the digestive tract and other waste products.
• The body must now remove these waste products.

• When the food mass travels through the large intestine and the last useful nutrients are removed, it is called
feces, or stool.
• Feces is stored in the last part of the large intestine, the rectum.
• It is periodically removed, or defecated, through the anus.

• What are villi?
Tiny, finger-like structures that line the inside of the intestines.
• How do villi help the small and large intestine absorb nutrients from the food?
The villi increase the surface area of the intestine so that it can come into direct contact with the food mass.
• What three types of nutrients does the small intestine absorb? 1) Monosaccharides 2) Glycerol/Fatty
Acids 3) Amino Acids
• How do those nutrients enter the blood stream?
They diffuse into the villi and then into the capillaries (small blood vessels) and then into the arteries.

• How does the large intestine help digest the food?
Trick Question! The large intestine does not play a role in the digestion of food.
• What nutrients does the large intestine absorb?
Water and vitamin K
• What is in feces? Indigestible plant fiber, bacteria, bile, worn out cells, other waste products
• What is the difference between the rectum and the anus?
The rectum is the name of the last piece of the large intestine. The anus is the opening of the rectum through which feces is expelled.