Digestion

Mouth to Small Intestine

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

Swallowing Reflex

• Epiglottis is a flap of tissue meant to prevent food from entering the trachea

Peristalsis

• Rhythmic contracts of smooth muscle around esophagus pushes food toward the stomach

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

Villi to Microvilli

What benefit does having villi and microvilli give to the organism?

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)

Stomach

PancreasDuodenum

Gall Bladder

Liver (Not shown)Liver ducts

Common Bile Duct

Pancreatic Duct

Secretin

bicarbonate

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

Formative Quiz

• Answer the questions on the following slides as best as you can.

B

FE

C

A

D

G

1.

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

3.• List three ways in which the body contributes

to mechanical digestion.

4.

• Where is bile created?

5.

• Summarize the digestion of proteins.

6.

• Which of the following are secreted by the pancreas?

a) Bileb) Amylasec) Lipased) Bicarbonatee) Secretin

f) Pepsing) Trypsinh) Mucusj) Sucrasek) Fructase

7.

• How does the small intestine increase its surface area?