Download Digestion

Digestion
What we’ll cover
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What are the digestive system structures
and their functions?
Where does carbohydrate, protein and fat
digestion and absorption occur?
What are the 3 accessory organs of
digestion?
Diseases of digestive system
Main stages of digestion
Mouth
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Cheese protein
(a polymer of amino acids
in a specific sequence)
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Amino acid
monomer
Ingestion – intake of food
Digestion – breaking
Food
down food into subunits
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Breakdown of protein
by human digestive
system
Absorption – nutrients
cross the GI tract
Amino acids
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Absorption of amino acids by cells lining the small
intestine; transport via bloodstream to other cells
Elimination – removal of
undigested food
Human protein
Figure 22.2-3
Digestion: A Closer Look
Mechanical digestion
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Chemical digestion
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Involves physical processes like chewing
the breakdown of food by digestive
enzymes.
Small
intestine
Large
intestine
Cells use amino acids from the cheese and
other foods to produce new human proteins
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Stomach
Anus
A Tour of the Human
Digestive System
The Digestive Tract
(or alimentary canal)
Accessory organs
ACCESSORY ORGANS
ALIMENTARY CANAL
Salivary glands
Mouth
Tongue
The Oral Cavity
Pharynx
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Mouth
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Esophagus
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Liver
Gallbladder
Pancreas
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Stomach
Salivary glands
Teeth
Tongue
Functions:
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Small intestine
Colon of large intestine
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Appendix
Rectum
Anus
Eating and chewing
Digestion of
carbohydrates and
lipids begins here
Figure 22.5
Salivary Glands
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Produce saliva
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Lubrication
Contains salivary
amylase
Enzyme that breaks down
starch.
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Teeth
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Contains lysozyme
Enzyme that prevents
bacterial infection
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.
Heath Focus
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Gingivitis
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Inflammation of the gums, often caused by
bacterial infection
Can cause erosion of gums, root damage,
and tooth loss
Tooth decay
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Dental caries (cavities) occur when bacteria
metabolize sugars and produce acids
limiting sugar intake and brushing teeth
reduces these
Used for mechanical
breakdown of food
Each tooth is made of
a crown and a root
A hard covering called
enamel covers the
crown
Inner pulp with nerves
and blood vessels
Tongue
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A muscle that shifts food
around to the teeth
Forms food into bolus
Contains taste buds
Secrets lingual lipase
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a digestive enzyme that
begins to break down
triglycerides
Pharynx and Esophagus
Pharynx – between
the mouth and
esophagus
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Oral cavity
Pharynx
passageway for food
Esophagus – long,
muscular tube that
carries food to the
stomach
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Swallowing
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Why doesn’t food go down the wind pipe?
During swallowing,
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Esophagus
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Liver
a reflex tips the epiglottis
Closes the entrance to the windpipe
Stomach
Esophagus
NOT SWALLOWING
SWALLOWING STARTED
SWALLOWING FINISHED
Tongue
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Ball of
food
Epiglottis
up
Pharynx
Trachea
(windpipe)
open
Esophageal
sphincter
(contracted)
Adam’s
apple
Esophagus
closed
Trachea
closed
Esophagus
open
The esophagus:
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Epiglottis
down
Epiglottis
up
Trachea
open
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Esophageal
sphincter
(contracted)
a muscular tube
Connects the mouth
to the stomach
Moves food down
by peristalsis,
alternating waves of
muscular contraction
and relaxation
Esophageal sphincter
(contracted)
Food ball
Relaxed muscles
Contracted muscles
Relaxed muscles
Stomach
Figure 22.7-3
What is a sphincter muscle?
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A circular muscle
that closes off one
end of an organ.
The lower
esophageal
sphincter allows the
bolus to drop into
the upper part of the
stomach
Functions of the Stomach
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Churns food into a
thick soup called
chyme
Secretes acid & starts
protein digestion
Stores food
Controls movement of
food into the small
intestine
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The stomach has
Figure
deep21.9
folds2called
rugae and gastric
pits that lead into
gastric glands that
secrete gastric juice
Digestion in the stomach
Lamina propria
Mucous epithelial cells
Gastric pit
Neck
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Cells of Gastric Glands
Parietal cells
(secrete intrinsic factor)
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G cells
(produce a variety
of hormones)
Gastric glands
Secretes gastric juice (2-3
quarts per day)
Contains HCl
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Chief cells
(secrete pepsinogen)
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Enzymes
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Why doesn’t the stomach
digest itself?
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Gives the stomach a pH of 2
Converts pepsinogen to pepsin
Helps kill bacteria found in food.
Pepsin: digests protein, active
only at pH 2
Gastric lipase: breaks down fats
What causes gastric ulcers?
It secretes mucus
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Protects
Lubricates
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The bacteria
Helicobacter pylori
H. pylori is especially
well-adapted for living in
the stomach.
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It lives in the mucus
It produces an enzyme
that shields the
bacterium from the
acidity of the stomach
Copyright 2009, John Wiley &
Sons, Inc.
What causes Heartburn?
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The backflow of chyme
into the esophagus
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Stomach
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Pyloric Sphincter :
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Acid reflux
HCl from the stomach
contents irritates the
esophageal wall
Tips for decreasing
heartburn:
Avoid high fat meals
Don’t overeat
Gastric Pits
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separates the stomach
from the small intestine.
the strongest muscle in
the GI tract.
Controls how much
chyme enters the
small intestine
Small intestine
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Anatomy of the small intestine
The longest part of the
digestive tract (~20 ft)
Function: digestion
and absorption of
nutrients
3 regions –
duodenum, jejunum,
and ileum
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The duodenum
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Surface area is increased by folding
Small intestine
The first part of the
small intestine
Receives chyme
from stomach and
digestive secretions
from liver and
pancreas
Neutralizes acidic
chyme
Digestion is completed in the
small intestine
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Jejunum
 Majority of digestion
and nutrient
absorption occurs
here.
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Ileum
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Final segment of small
intestine
Foods are digested by hydrolysis
Protein
Carbohydrate
pancreatic amylase
+
peptidase
pH = basic
pH = basic
blood capillary
a. Carbohydrate digestion
blood capillary
b. Protein digestion
H2 O
Sugar
OH
monoglycerides
and free
fatty acids
amino acids
pH = basic
Carbohydrate
lipase
glucose
lymphatic
capillary
H
Enzyme
(pepsin)
emulsification
droplets
peptides
cell of
intestinal
villus
Amino acid
OH
bile salts
trypsin
maltase
H2 O
Fat globules
Protein
chylomicron
H
Enzyme
(amylase)
Fat
H2 O
Fatty acid
Glycerol
H2 O
H
H O
OH
H
OH
H
H2 O
c. Fat digestion
Enzyme (lipase)
Figure 22.3
Nutrients are absorbed in the
small intestine
Nutrients are absorbed in the
small intestine
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Simple sugars
Amino acids
Fatty acids
Most nutrients
(~90%) are
absorbed in the
small intestine
The rest?
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Stomach & large
intestine
Copyright 2009, John Wiley &
Sons, Inc.
Blood goes from the intestine
to the liver
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The three accessory organs
Blood rich in amino
acids and glucose
travels from the
digestive tract to the
liver
The liver
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Stores the glucose as
glycogen
Synthesizes proteins
Salivary Glands
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Produce saliva
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Prevents bacterial infection
Lubrication
Secretes salivary amylase
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Salivary glands
Pancreas
Liver
The pancreas
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Secretes pancreatic juice into
duodenum
Secretes:
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Enzyme that breaks down
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starch.
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Digestive enzymes
Trypsin digests proteins
Lipase digests fats
Pancreatic amylase digests
carbohydrates
Bicarbonate to neutralize
stomach acids
Hormones Insulin and glucagon –
regulate blood sugar levels
Fat digestion is completed in
the small intestine
Liver – role in fat digestion
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Makes bile
Secretes bile into the
duodenum after a meal
Bile breaks down large
fat globules to smaller
ones = emulsification
Bile is stored in the
gallbladder
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Bile salts emulsify
fats – break down
large fat globules to
smaller ones
Then pancreatic
lipase digests fats
into fatty acids
Which are absorbed
Fat globules
+
bile salts
emulsification
droplets
lipase
monoglycerides
and free
fatty acids
pH = basic
chylomicron
lymphatic
capillary
c. Fat digestion
The Large Intestine
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The colon
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Large intestine
the main part of the Colon
large intestine
Absorbs water
Produces feces, the
waste product of
food
The rectum stores
feces
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Small
intestine
Rectum
Anus
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Figure
22.14a
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Involves chronic
inflammation of all or
part of your GI tract.
Cause not known
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Virus or bacterium might
trigger an autoimmune
reaction
Genetic makeup may play a
role
Treatment
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Anti-inflammatory drugs
Immune system
suppressors
Antibiotics
Expandable for
temporary feces
storage
Fecal material within
rectum triggers
defecation urge
Defecation
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Health Focus:
Inflammatory Bowel Disease
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Rectum
Conscious control over
external anal sphincter
Diverticulitis
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Outpocketing of the bowel that becomes
inflammed
Diarrhea
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Can quickly lead to
dehydration
Affects absorption of
food, vitamins,
Rids body of toxins
Some antidiarrheals
can prolong fever and
delay clearance of
causative pathogens
Overview of Digestion
Mouth
Ingestion
Food into mouth
Digestion
Mechanical digestion
Chewing in mouth
Churning in stomach
Why is digestion important?
Food
Chemical digestion
Saliva in mouth
Acid and pepsin in
stomach
Enzymes in small
intestine
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Stomach
Digestion breaks down food to create:
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Small
intestine
Absorption
Nutrients and water
in small intestine
Water in large
intestine
Large
intestine
Elimination
Feces formed in
large intestine
Anus
Elimination from anus
Figure 22.15-4
Food as Fuel
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Cells
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Break down food
molecules in cellular
respiration.
Generate many
molecules of ATP.
Molecules small enough for cells to absorb
Monomers that can be recombined into
new molecules