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Digestion
Bio 391
2.9 – 2.11
Answer: QUESTION #1
INGESTION
DIGESTION
PERISTALSIS
ABSORPTION
DEFECATION
DIGESTION  breakdown of large food
molecules into smaller ones
Why is it necessary?
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MECHANICAL
Physical change
Breaking food into smaller
parts by ripping, churning
Increases surface area
TEETH  tear & crush
STOMACH  churns
BILE  separates
Gizzard  grinds
CHEMICAL
• Chemical change
• Enzymes break bonds of food
molecules
• Enzymes are made and used
by organs
– Not always the same
• Each enzyme is specific to a
type of macromolecule
– Carb, fat or protein
Where does digestion occur?
EXTRACELLULAR
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Alimentary canal / GI tract
Most animals, us too
More complex = 1 way
Carnivore vs. herbivores
– Venus fly trap
– Bread mold
INTRACELLULAR
• Inside the cells
• Plants – make own food,
process within same cell
• Single-celled organisms and
simple animals
– Hydra
Why specialized?
1. Mouth
• Physical digestion
• Chemical digestion
– Saliva, salivary glands
– Starts carbohydrate digestion
– Amylase
• Starch  complex smaller sugars (maltose)
• Saliva’s pH at 6.0-7.4
– Short time in mouth  lots left undigested
2. Esophagus & Epiglottis
• Esophagus connects
mouth to stomach
– Peristalsis – wavelike
contrxns force food down
– Mucus secreted
• Epiglottis
– “trap door” prevents food
“going down the wrong
way”
3. Stomach
• Physical digestion
• Chemical digestion
– Presence of food triggers gastrin release
• Hormone, controls juice prodxn
– Gastric juice
• HCl + mucus + pepsinogen
• pH 1.0 – 3.5
• Pepsinogen  pepsin once in acid
(inactive)
(active)
– Protein digestion begins
– Proteins  polypeptides
• Chyme
• Mucus lining
• Sphincters
4. Small Intestine
• All digestion completed, nutrients absorbed
• S.I. secretions
– Secretin – presence of acid stimulates SI cells to release hormone
to pancreas via blood stream
• Stimulates pancreas to release NaHCO3
– Carbohydrases (ex: maltase)
• Carbo digestion completed
• Maltose  glucose
• Left over starch  glucose
• Liver & Gallbladder
– Adds bile to the mix
• Emulsifies fats
S. I. Digestion via pancreatic secretions
• Pancreas adds pancreatic juice
– Shifts pH from acidic to basic – WHY?
– Protein digestion completed
• Trypsinogen  trypsin
(inactive)
(active)
– Polypeptides  amino acids
– Fat digestion completed
• Lipases
– Lipids  fatty acid + glycerol
– Pancreatic amylase
• Carbo’s (maltose)  glucose
S.I. Absorption
• Large surface area
– Villi & Microvilli
– Capillaries enter each
5. Large Intestine
• Waste condensation
– Water absorption
– Feces
• Bacterial symbionts
– Synthesize vitamins
– Vitamins absorbed
• Also has villi
• Diarrhea &
constipation
• Undigested food leaves
through anus
– Cellulose, fiber, etc.
DISORDERS
• Heartburn  stomach acid enters esophagus
because of weak cardiac sphincter
• Peptic Ulcer  Hole in stomach wall caused
by Helicobacter pylori. The pain is caused by
the acid.
• Diarrhea  Not enough water is absorbed
• Constipation  Too much water is absorbed
• Diabetes  Glucose cannot enter cells of
body very well, therefore glucose cannot get
turned into energy!!
Diabetes
• 6th killer in America (and rising)
• Pancreas cannot produce insulin or the body
does not use it properly
• Insulin is a hormone that decreases the
amount of sugar in the blood by helping it
enter the cells of the body.
– Glucose does not enter cells easily, insulin must
“act like a butler” and bind to a cell membrane
protein to help it in.
Where does Digestion occur?
What Nutrient is Digested?
ORGAN
TYPE OF DIGESTION
Mechanical
Mouth
Chemical
Mechanical
Stomach
Chemical
Small Intestine
Chemical
NUTRIENT DIGESTED
ENZYMES OF DIGESTION
ENZYME
Amylase
Pepsin
Lipase
Amylase
Trypsin
Peptidase
Maltase
Sucrase
Lactase
SITE OF ACTION
SITE of PRODUCTION
NUTRIENT DIGESTED
OTHER SUBSTANCES INVOVLED IN DIGESTION
SUBSTANCE
SITE OF ACTION
Saliva
ACTION
Moistens Food
Esophagus, Stomach
Mucus
Gastrin (H) 
Hydrochloric Acid (HCl)
Secretin (H) 
Sodium bicarbonate
Bile
Bacteria
Sm. & Lg. Intestines
Helps breakdown food
Kills bacteria