Human digestive juices and their actions: note how starch and proteins are broken in several stages catalyzed by different enzymes
Region of
gut
Mouth
Stomach
Small
intestine
(duodenum)
Digestive
juice
Enzymes
Substrate
Other substances
in juice
Function of other
substances
Saliva from
salivary glands

Salivary amylase
Starch
 Maltose
Hydrogencarbonate

Gastric juice
from glands in
wall of
stomach

Pepsin (protease)
Proteins

Amino
acids
Hydrochloric acid

Pancreatic
juice from
pancreas

Pancreatic
amylase
Trypsin (a
protease)
Lipase
Starch
 Maltose
Hydrogencarbonate

Protein
 Amino acids
Neutralises chyme:
alkaline environment
for enzymes
Bile salts

Hydrogencarbonate

Emulsifies fatsconverts globules to
smaller droplets
Neutralises chyme


Emulsified
fats
Bile from liver
(stored in gall
bladder)
Intestinal juice
from cells on
villi
Maltose
Maltase on the
surface
membrane of the
epithelium lining
the small intestine
Alkaline (pH 7.5)
environment for
amylase
Acidic (pH2)
environment for
pepsin; kills bacteria
 Fatty acids &
glycerol
None

Small
intestine
(ileum)
Products

Glucose