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The Digestive System
VIDEO
Food Processing
• Ingestion – eating or drinking
• Digestion – break down molecules to absorb
– Hydrolysis: the process of breaking bonds in food
molecules by adding water to them in the presence of
specific enzymes
• Absorption – small intestine
• Elimination – removal of wastes
What is digestion?
•
Chemical and mechanical breakdown of
organic molecules into units small enough
for the body to absorb
•
These molecules provide:
1. Energy resources
2. Raw materials to build materials for the cell
THE MOUTH
• Physical digestion –
chewing and teeth break
food into smaller pieces
Canines 1- Used
for tearing
• Saliva moistens food
(produced by salivary
glands)
Molars 2– Used for
crushing
•Chemical digestion of
starch by enzyme
amylase, which is
dissolved in saliva
Pre-molars –
3
Used for grinding
Incisors4– Used for
cutting
THE TONGUE
• Has taste buds that are
groups of cells located
on the tongue that
enable one to
recognize different
tastes
• Assists with moving
food around mouth
while chewing
Check this Out!
• http://www.youtube.com/watch?v=2Fhc0t_QN
hs
ESOPHAGUS
What is this called?
Food going down the
esophagus has a new
name, bolus.
Peristalsis - contraction and
relaxation of the smooth muscle
down the esophagus moves
bolus down to the stomach
The cardiac sphincter opens to
allow the bolus of food to enter the
stomach
Peristalsis
VIDEO
THE STOMACH
• Along with HCl
(hydrochloric) acid,
enzymes, and muscle
contractions, the bolus
is churned and broken
down further into a
solution called chyme
• Chemical digestion of
protein occurs here by
the enzyme pepsin
The pyloric sphincter, regulates the
movement of chyme to the small
intestine.
VIDEO
How does it work?
• The pH of your stomach
is about 1-2 (facilitates
breakdown of protein)
• Stomach cells secrete
hydrochloric acid (gastric
juices) which helps to
break down the food and
kills pathogens
• A layer of mucous
secreted by cells lining
the stomach protects the
stomach from damage
SMALL INTESTINE
• 3 sections: duodenum,
jejunum, ileum
• Digestion is completed
here
• Undigested food (waste)
passes on to the large
intestine
SMALL INTESTINE
• 1st section - duodenum majority of digestion (fats)
• 2nd section - jejunum absorption of nutrients such as
carbohydrates and proteins
occur here
• 3rd section – ileum - longest
section; fats and bile salts are
absorbed here
SMALL INTESTINE
• Contains little finger-like
projections called villi which
increase the surface area
• Why is this advantageous?
Regions of the Small Intestine
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
Figure 24.16a
The Intestinal Wall
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
Figure 24.17b, c
THE COLON
(LARGE INTESTINE)
• Undigested food is not
needed by the body
• Waste is stored and
eliminated
•Absorption of water, vitamins,
minerals, and inorganic salts
• Most of the water from food is
reabsorbed here
• Bacteria that reside in the
colon produce vitamin B12
THE RECTUM
• “Warehouse for feces”
• Waste (feces) is stored
here until it is ready to be
excreted
THE ANUS
• Opening at the far end of
the digestive tract through
where stool leaves the
body
• A muscular ring (anal
sphincter) keeps the anus
closed until a person has a
bowel movement.
The Pancreas
• HCl enters the duodenum triggers the
production of digestive enzymes
• Produces chemicals (bicarbonate) that
neutralize stomach acids that pass from
the stomach into the small intestine
The Liver
• The liver produces bile
salts which are stored in
the Gallbladder
Gallbladder
• Bile salts aid in the
physical breakdown,
emulsification, and
absorption of fats
•Bile is secreted into the
small intestine
(duodenum)
Gallbladder
• The bile salts
produced by the liver,
are stored in the
gallbladder
Small Intestine
• A hormone, CCK,
triggers their release
into the small intestine
Figure 24.21 The Gallbladder
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
Figure 24.21a, b
Food moves down
the esophagus
using muscle
contractions, called
peristalsis.
Review
The liver produces
bile salts that break
down fats. Bile salts
are stored in the gall
bladder.
The mouth contains
different teeth, used
for different purposes.
The stomach breaks
down the food, and
passes it on to the
small intestine
The pancreas
produces enzymes
to digest the food
The gall bladder, stores
the bile salts, and
releases them when
CCK is present.
The colon absorbs the remaining moisture
The small intestine
has three parts. The
majority of digestion,
and some absorption
happens here.
Common Disorders
Ulcer
• Stomach lining is broken down and
irritated by gastric acid
• Peptic Ulcers: Sores found in stomach
lining, esophagus or upper small intestine
Inflammatory Bowel Disorder
• IBD
• Intestines become irritated and inflamed
• Develop many ulcers causing abdominal
pain and diarrhea
• Crohn’s and colitis
Constipation
• Two reasons:
– Peristalsis moves feces along too slowly
– colon absorbs too much water so feces
becomes too compacted
• Temporary condition – eat fibre, exercise
and drink lots of H2O
• Sometimes results from surgery,
pregnancy, medication, air travel
Diarrhea
• Lining of colon irritated (bacterial or viral
infection)
• Less effective in reclaiming water
• Can cause dehydration
Nausea and Vomiting
• Nausea: feeling associated with urge to
vomit
• Vomiting: expulsion of stomach contents
through esophagus and mouth
• Safety mechanism for eliminating toxic or
foreign contents
• Causes: inner ear, drugs, infections, brain,
injury, diseases
Please Complete
1. What happens during hydrolysis?
2. Compare and contrast the terms “mechanical digestion”
and “chemical digestion”
a)
In the mouth
b) in the stomach
3. What is bile? What is its role in digestion?
4. As the end result of digestion:
Carbohydrates are broken down to form ____, which provide your cells
with _______.
Proteins are broken down to form ____, which provide your cells with
_______.
Fats are broken down to form ____, which provide your cells with
_______.
5. What is the major function of the large intestine?