Transcript The Digestive System

The Digestive System
The Digestive System
4 steps for processing nutrients from food
1.
2.
3.
4.
Ingestion
Digestion
Absorption
Elimination
Ingestion & Digestion
Ingestion: Eating or drinking
Digestion: the breaking down of food into molecules that are
small enough to be absorbed by the body
Mechanical digestion: Chewing and grinding food into
smaller pieces, increasing the surface area
Chemical digestion: Breaking chemical bonds of
macromolecules (carbs, proteins and lipids) into monomers
(sugars, amino acids, glycerol & fatty acids)
• Hydrolysis reactions that are carried out by enzymes
Absorption & Elimination
Absorption:
• Cells absorb small molecules (monomers)
allowing them to enter into the circulatory
system for immediate use or be transported
to storage organs for later use
Elimination:
• Removing undigested waste (feces)
Digestive System
Digestive Tract
– A.k.a. an alimentary canal (2
openings)
– The mouth, pharynx, esophagus,
stomach, small intestine, and large
intestine
Accessory Glands & Organs
– Aid in digestion, but not a part of
the digestive tract
– Salivary glands, pancreas, liver,
gallbladder.
– Secrete digestive juices and
enzymes into the digestive tract
What’s Your Size?
Predicted Length
(m)
Mouth
Pharynx
Esophagus
Stomach
Duodenum
Jejunum
Ileum
Large Intestine
Total
Actual Length
(m)
0.15
0.05
0.25
0.25
0.2
2.8
4.2
1.5
~9
Mouth
• Plays a role in ingestion and
digestion
• Teeth, tongue, hard palate aid in
mechanical digestion
• Tongue moves food down to the
esophagus
• Salivary glands aid in chemical
digestion
– Release saliva (~1L/day), a watery liquid
containing digestive enzymes
– Salivary amylase begins to break down
starch into smaller carbohydrates
– Lubrication
Chewed up food is now
called a bolus
Esophagus
• Located behind the trachea
• As you swallow, the epiglottis
closes over the trachea and
the food bolus passes through
pharynx into the esophagus
• The bolus is pushed through
the esophagus by a series of
muscle contractions called
peristalsis
Heart
Burn
• After food passes into the stomach, the cardiac
sphincter closes the esophagus
• If the sphincter opens at an inappropriate time,
stomach acid can flow back into the esophagus
• Esophagus does not have the same protective
lining as the stomach
Stomach
I ate too
much…I’m
STUFFED!
• Elastic, muscular sac with
a protective lining that
contains millions of gastric
glands
• Can ~ 2 L
• Mechanical and chemical
digestion
Stomach
Chemical Digestion:
• The hormone, gastrin, stimulates gastric glands to
release gastric juice
– Hydrochloric acid breaks apart cells and kills bacteria
– Enzymes e.g. pepsin
– Mucus lubrication and protection
Mechanical Digestion:
• Stomach muscles churn
• Bolus becomes an acidic,
nutrient-rich liquid called
chyme
Small Intestine
• Chyme passes through the pyloric sphincter
and enters the small intestine (peristalsis)
• Long, narrow tube where digestion is
completed and absorption begins
• 3 parts:
– Duodenum
– Jejunum
– Ileum
Duodenum
• Bile from the liver and gallbladder are
secreted into the duodenum to help with lipid
digestion
• Pancreas secretes pancreatic juice into the
duodenum
– Neutralizes acidic chyme
– Pancreatic amylase
– Trypsin & chymotrypsin (protein digestion)
– Pancreatic lipase
• Small intestine releases enzymes too
Jejunum & Ileum
Jejunum
• Contains more villi, therefore
more absorption
• Breakdown of remaining
polypeptides and
carbohydrates
Ileum
• Absorption
• Push remaining undigested
material into the large
intestine
Large Intestine
• Undigested material passes through the sphincter
between the ileum and the cecum
• Absorption of water and dissolved minerals
• Intestinal bacteria produce vitamins
• Indigestible material (feces) passes through the
rectum to the anus
– Anal sphincters help control timing of elimination
Increased Surface Area
• The small and large
intestine are folded to 
surface area and therefore
 absorption
• Within the folds, there are
finger-like projections
called villi
– Lacteal absorbs fats and fatsoluble vitamins
– Capillaries absorb glucose,
amino acids, minerals and
water-soluble vitamins
Regulation of Digestive
Processes
• http://www.neok12.com/php/watch.php?
v=zX680f4e7e6e7c420f746402&t=Dige
stive-System
• http://www.neok12.com/quiz/DIGSYS04
• http://www.neok12.com/quiz/DIGSYS01
• http://www.neok12.com/diagram/Digesti
ve-System-01.htm