Mouth• Mouth starts mechanical
digestion– Teeth grind and cut food
• Saliva starts chemical digestion– Salivary amylase breaks
down amylose into disaccharides
• After chewing, tongue forms a ball from the food, called a bolus
Stomach
• Muscular and J-shaped• Mechanical digestion
(contractions of muscle to churn food)
• Chemical digestion (enzymes such as pepsin)
Stomach
• Stomach contains gastric pits, which have different cells specializing in different secretions
Gastric secretionsCell Secretion Purpose/Function
Mucus Cells Mucus, Bicarbonate
Protect the stomach lining from acidEnsure proper activity of some enzymes
G Cells Gastrin Hormone that stimulates the release of HCl from parietal cells
Parietal Cells HCl HCl lowers pH of stomach, which denatures protein and activates pepsinogen into pepsin
Chief Cells Pepsinogen Pepsinogen is activated by low pH into pepsin
Digestion in Stomach
Salivary Amylase inactivated by low pH of stomach
HCl denatures proteins (denaturing is the unfolding/breakdown of the 3D structure of proteins)
Pepsin digests long polypeptides into shorter polypeptides
Small Intestine Anatomy
• Divided into three components:– Duodenum– Jejunum– Ileum
• 6-8 meters long• 1.5” in diameter
Small Intestine• Liquid leaving the stomach is called chyme • Chyme has a low pH, and must be neutralized
to ensure it doesn’t damage the small intestine
• Secretin, a hormone from the stomach, has stimulated the release of bicarbonate from the pancreas
• Bicarbonate released by the pancreas into the small intestine, neutralizes the chyme (weakly basic pH8)
Bile (made in liver)
Bile (stored in gall
bladder)
Bile is made in the liver, stored
in the gall bladder
Bile is released when fat is
digested
Bile emulsifies fats.
Pancreatic Secretions:Pancreatic amylase – digests starchPancreatic lipase – digests lipidsTrypsinogen (trypsin) – digests small polypeptides into small peptidesChymotrypsin – digests small polypeptides into small peptidesPeptidases – digest small peptides into smaller peptides/amino acids
Small Intestine Secretions:
Carbohydrases-Sucrase-Lactase-Maltase
Peptidases – digest small peptides into smaller peptides and amino acids
All of these enzymes
work best at pH 8
Absorption• Once all macromolecule
polymers have been broken down into their monomer subunits, the subunits are small enough to be absorbed into the blood
Monosaccharides Amino acids Fatty acids/glycerol
Transported to liver to be converted to glucose
Some are converted into glucose for energy
Used to provide energy to cells
Extra glucose is converted to glycogen
Some are transported throughout the body to be used to make body proteins/enzymes
2.• Match the enzyme/secretion with the description
Enzyme/Secretion Description
A – Pancreatic lipase I – emulsifies fats
B – Salivary amylase II – stimulates release of bicarbonate in pancreas
C – Pepsin III – digest small polypeptides into amino acids
D – Peptidases IV– digests polypeptides into smaller polypeptides
E – bile V – product is glucose and fructose
F – sucrase VI – protects stomach from HCl
G – Pancreatic amylase VII – stops working in the stomach
H - Secretin VIII – digests fats in small intestine
I - Mucus IX – digests starch in small intestine
6.
• Which of the following are secreted by the pancreas?
a) Bileb) Amylasec) Lipased) Bicarbonatee) Secretin
f) Pepsing) Trypsinh) Mucusj) Sucrasek) Fructase