Human Digestive

System

1. Describe the functions of the stomach, duodenum, pancreas, gall bladder, liver, ileum, jejunum in relation to physical digestion, chemical digestion, absorption of nutrients and water.

2. State the function of proteases pepsin and rennin on proteins and list the end products of protein digestion in the stomach.

3. List the digestive enzymes produced by the intestinal glands and pancreas.

4. Describe the function of bile in the emulsification of fats.

Objectives

Stomach Peristalsis in the stomach wall churns and break up the food

Peristalsis also mix food with the gastric juice

Gastric gland secrete gastric juices into the stomach

Hydrochloric acid

Proteases •Pepsin •Rennin

Hydrochloric acid

•Kills most bacteria taken in with food

•Provides an acidic medium suitable for the action of gastric enzymes.

Stomach

Hydrochloric acid

Pepsinogen Pepsin (active enzyme)

Prorennin Rennin (active enzyme)

Why is pepsinogen produced instead of pepsin?

To prevent pepsin from digesting the

stomach walls

Protein Digestion

Proteins Polypeptides

Pepsin

Soluble Insoluble milk proteins milk proteins

Rennin

Insoluble Polypeptides milk proteins

Pepsin

Why is there no digestion of starch in the stomach?

The acidic environment in the stomach due to the presence of hydrochloric acid. Salivary amylase works best in alkaline pH. Thus no starch is digested in the stomach.

Question Time!

Stomach After mixing and enzyme digestion, food becomesa nutrient-rich broth : Chyme

Small IntestineDigestion of carbohydrates, proteinsand fats and absorption of digestedfood products, water and mineral salts

Liver

Pancreas

Gall bladder

Duodenumof Small intestine

DuodenumChyme from the

stomach is mix with digestive juices

produced from the intestinal gland, liver and

pancreas

Liver

Pancreas

Gall bladder

Duodenumof Small intestine

Pancreatic juice, bile and intestinal juice are

alkaline.• Neutralize the acidic

chyme• Provide a suitable

medium for the action of pancreatic and intestinal enzymes.

Secrete Intestinal juice

Maltase Sucrase

Lactase ErepsinIntestinal

lipase

Intestinal Gland

Secrete Pancreatic Juice:

• Pancreatic amylase,• Pancreatic lipase • Trypsinogen

trypsin (active enzyme)

Pancreas

enterokinase

Region of Digestion

Source Enzyme Action

MOUTH Salivary glands Salivary amylase Starch Maltose

STOMACH Gastric glandsPepsin

Rennin

Protein Polypeptide Soluble Insoluble milk proteins milk proteins

SMALL INTESTINE

Pancreas

Intestinal glands

Pancreatic Amylase

Trypsinogen trypsin

Pancreatic Lipase

Maltase

Erepsin

Lipase

Starch Maltose

Protein Polypeptides

Fats Fatty acids+ glycerol

Maltose Glucose

Polypeptides Amino acids

Fats Fatty acids+ glycerol

Liver produces bile which is an enzyme that breaks down fats

The bile salts which emulsify fats into tiny fat droplets is stored in the liver

Four friends werediscussing about the

role of the gall bladder,

liver and the function of

bile. Who do you agree

with the most? Explain why

others are not correct.

Bile which emulsify fats is produced from the liver and stored in the gall bladder

Gall bladder produces bile which breaks down fats

John

Daniel

Mary Bella

Liver cells secrete bile containing bile salts and bile pigmentBile = bile salts + bile pigment

Bile is temporarily stored in the gall bladder

Bile flows into the duodenum via the bile duct

Bile salts emulsify the fats by reducing the attractive forces between the fat molecules

Physically breaks-up the fat molecules

Bile Salts

Tiny fat droplets

Increase surface area to volume ratio – speed up digestion by lipase.

Bile salts

1. Describe the functions of the stomach, duodenum, pancreas, gall bladder, liver, ileum, jejunum in relation to physical digestion, chemical digestion, absorption of nutrients and water.

2. State the function of proteases pepsin and rennin on proteins and list the end products of protein digestion in the stomach.

3. List the digestive enzymes produced by the intestinal glands and pancreas.

4. Describe the function of bile in the emulsification of fats.

Let’s Review

Due to cancer of the stomach, the entire stomach of Patient A have being surgically removed.

As the doctor of Patient A, you are to provide information on the effect on the lifestyle and digestive function upon removing the stomach.

• Stomach is the site of initial protein digestion. Removal of stomach will cause protein digestion to be greatly affected;

• Patient A can rely only on the small intestine for protein digestion, rate of protein digestion will be lowered.

• No HCl, prone to food infection by bacteria.• Need to reduce protein intake to avoid congesting

the small intestine.