Transcript File

SBI3U1
The
Digestive
System is
made up of
1) The
Digestive
Tract
2) Accessory
Organs
Mouth
Esophagus
Liver
Gallbladder
Large Intestine
Appendix
Anus
Stomach
Pancreas
Small Intestine
Rectum
Mechanical
digestion:
-Teeth break down
the food into small
pieces ( mouth)
-Stomach muscles
further break
down pieces
( stomach)
Chemical digestion:
- Saliva which
contains amylase
(enzyme) breaks
down the bonds in
carbohydrates
(mouth)
- Digestive enzymes
& stomach acid
break down food
( stomach)



Salivary glands in
the mouth secrete
saliva, which begins
chemical digestion.
Amylase is released
to break down starch
into simple sugars.
Teeth begin the
process of
mechanical
digestion, and the
tongue helps turn the
food into a soft
bolus.

Saliva is secreted from 3 salivary glands:
sublingual, parotid, submandibular

The secretion of saliva is triggered before you have
food in your mouth.
The bolus is swallowed,
entering the esophagus.
 The epiglottis at the top
of the trachea (next to
the esophagus) closes to
ensure the bolus does not
enter the trachea.
 Lined with epithelial
tissue
 Glands in the lining produce
mucus



keeps the tube moist
facilitates movement of food
The esophagus transports the bolus to the
stomach by wave-like muscular contractions
called peristalsis (shown above).
• The bolus enters the stomach
through the esophageal
sphincter.
• The food triggers the secretion
of gastric juice–a mixture of
salts, enzymes, hydrochloric
acid, water, and mucus.
• Mucus protects the stomach
from the acid
• The protein enzyme pepsin is
secreted in a form that remains
inactive until the acid is
present, also protecting the
stomach.
 Stomach
walls are folded and can expand
after a meal
 Three layers of muscle fibres contract and relax to
physically break food particles down.
 The food is reduced to chyme (a thick liquid) before
it leaves the stomach via the pyloric sphincter into
small intestine.
 Most
absorption of
nutrients occurs here
 Made up of 3 parts:
Duodenum, Jejunum,
Ileum
 Intestinal glands
secrete trypsin and
chymotrypsin (further
breaks down proteins
and carbohydrates)
UNIT 4 Chapter 10: The Digestive System
As food passes through the duodenum, the many microvilli
absorb nutrients that have been broken down further by
enzymes from the pancreas and the gall bladder.
U
shaped, first region after the stomach
 Further
breaks down proteins, fats and
carbohydrates
 Folds
are covered in finger-like projetions
called villi. Each villi is covered with microvilli.
 The
folds increase the surface area which
increases absorption of nutrients.
Note* Nutrients diffuse from small intestine into villi, then
diffuses into capillary network
 Approximately
2.5 m long
 Contains
more folds than the
duodenum
 Breaks
down remaining proteins and
carbohydrates to be absorbed
 Approx.
3 m long
 Has
fewer villi than the dueodenum
and jejunum
 Absorbs
nutrients and pushes
undigested material into the large
intestine
 The
large intestine
(a.k.a colon)
reabsorbs fluids and
electrolytes
 Absorbs
90% of
water back into the
blood
 food
is pushed
through by muscle
contractions to the
rectum where feces
are produced

Main component of feces:
• Cellulose: makes up plant cell walls,
cannot be digested by humans
• Living and dead bacteria
• Water
• Toxic wastes are removed
 Feces
is eliminated from your body via
the anus
 Secretes
about 1 L of
pancreatic fluid into the
duodenum each day
 Pancreatic
Fluid contains:
Pancreatic Enzymes - chemically digest
nutrients
Bicarbonates – alters pH of chyme so that
enzymes can be activated. (pH 1 to pH 8)
 Secretes
the enyzme insulin which is used to
regulate blood/glucose levels
 Largest
internal organ in the human body
 Releases
bile (greenish-yellow fluid made up
of bile pigments and salts)

Bile is used to breakdown of fats
Bile is sent to the gallbladder where it is
temporarily stored
Enzymes:
proteins that help speed up chemical
reactions. (ex. hydrolysis)
A.k.a. lock & key model
The substrate and enzyme have complementary
shapes. They must fit perfectly into one another.
Therefore, the enzyme is highly specific to its
substrate.
Temperature:
1)
optimal temperature for
enzyme function
 Most human enzymes have an
optimal activity at 37˚
 If temperature is too high the
chemical bond in the enzyme
breaks thus denaturing the
enzyme

2) pH:
• Optimal pH at which enzymes work
best
• Pepsin, is only active when it is
immersed in a low pH
• Trypsin works best at a pH of 6 to 8.
Read & make notes 10.2
Pg. 419 #1, 3, 4, 6, 7, 13, 15