Digestion: Accessory Organs
• Gall Bladder
• The process of PHYSICALLY
(mechanically) and CHEMICALLY…
Changing the composition of food
into simpler substances that your
cells can use for growth, repair
• As food is digested, it passes through
a muscular tube leading from the
mouth to the (GASTROINTESTINAL
TRACT/ GI TRACT).
• The GI tract is about 25 to 30 feet
in length and each part plays very
• Grinding and mixing by teeth
(MASTICATION) in the mouth and
muscular actions of the stomach and
small intestine and…
• Liquefying by the addition of water
and digestive juices in the mouth,
stomach and small intestine
Digestion: Chemical Changes
• In Chemical Digestion, food is mixed
with powerful acids and enzymes!
• Complex nutrients are broken down
into particles usable by cells:
- Polysaccharides and disaccharides to
monosaccharides (carb chains)
- Proteins to amino acids
- Fats to fatty acids to glycerol
Chemical Environment of the GI
Neutral in mouth
- (pH approx 7)
Acid in stomach
- (pH approx 2)
Neutral in small
- (pH approx 7)
•Big food molecules can’t pass
through cell walls.
•ENZYMES are types of proteins used
to break up big molecules into small
ones (they act like chemical scissors).
•These small molecules can pass
through the wall of the small
intestine into the blood. They then
pass into cells and are used.
Big food molecules
can’t pass through cell
ENZYMES are used
to break up big
molecules into small
ones (they act like
These small scissors).
pass through the
wall of the small
intestine into the
• Physical Changes:
- First step in
- Teeth grind food
-Salivary glands add
• Chemical Changes:
• Transport tube (10
• Muscular (muscular
contractions move the
food - peristalsis)
• Enables swallowing to
move bolus (food) from
the mouth to the
• No enzymes added
• Other tube in the
Digestion: Stomach (3 hrs)
• pH Shift
• Inflow of gastric juice containing HCL
(hydrochloric acid)…almost as strong as
• pH rapidly decreases
• Mucus (thick fluid) helps soften and
lubricate food and protect it from the
• Protein digestion begins in the stomach as
the major gastric enzyme that begins to
break down protein is PEPSIN.
• The mixture of food and juices is called
chyme…and it moves to the SI next!!
Digestion: Small Intestine(SI) –
• About 95% of digestion takes place in SI
• Coiled and folded
• Made of 3 sections: duodenum (12 inches),
jejunum (4ft) and ilium (5ft)….can stretch
to over 20 feet!!
• Peristalsis moves food through the SI
• Another pH shift…what happens?
• Site of NUTRIENT ABSORPTION!!!
• Walls of intestine pleated with folds
covered with villi. (increase surface area)
Digestion: Large Intestine
(aka: colon) – up to 3 days
• The small intestine is
connected to the large
intestine (3-5 feet
long in the body…5-6
• Chyme is very liquid
when enters the LI, so
main function is to
• Solid wastes called
feces leave through
the rectum and then
finally out the anus
lining of LI and water)
• Pancreas – gland behind stomach –
secretes bicarbonate to neutralize
environment of SI, produces 3 digestive
enzymes to break down carbs, pro, fat.
• Liver – large gland above stomach.
Produces digestive juice called bile.
(Helps to digest fat)
• Gall Bladder – muscular sac that stores
Match the organ to its function!!
Mouth 1. This is where water is absorbed.
2. Makes bile which breaks up fats and it is alkaline to
give the right pH for the enzymes in the S. intestine.
Stomach 3. Makes all 3 enzymes.
4. Mixes the food with enzymes that digest proteins
AND contains acid to kill bacteria.
5. Produces more enzymes AND this is where the food
is absorbed through the gut wall into the blood.
Small 6. Chew and mix the food with saliva (contains
7. Links the mouth to the stomach.
8. Here food that can’t be digested is stored as
faeces and then leaves through the anus.