Transcript Digestion

Digestion
Section 1
The Digestive System: An
Overview
True or false?
• “You are what you eat.”
• “If it’s true that you are what you eat, part of
what is now my body used to be sitting in a
box in the cereal aisle at Safeway.”-C. Phipps
All living things are made of similar
molecules
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Carbohydrates
Lipids
Proteins
Nucleic acids
Also:
Vitamins & Inorganic minerals
All are digested and absorbed differently
Metabolism- all the chemical reactions
utilized by a living thing to power its activities
Catabolism- breaking down
food for energy
Anabolism- building up
molecules for structure
How plants eat
• Plants make their own
food…
• Using energy from the
sun,
• Electrons from water,
• And CO2 from the
atmosphere
• Their food sources
surround them
How fungi eat
• Fungi secrete digestive
enzymes into their
surroundings
• They must absorb
nutrients that they
digest externally
Animals can take it with them
• Having a digestive
system that is internal
allows animals to be
mobile
• Generalized term is gut
The simplest animals have an
incomplete gut
• Sponges (porifera) are
filter feeders, and
cnidarians (anemones
and jellyfish) have an
incomplete gut
• Food enters, and waste
is expelled, through
same opening
Your digestive system is on the
“outside” of your body
The digestive system absorbs nutrients
from food
• The digestive system
(gastrointestinal tract
or GI tract) is a 6-9
meter long tube
• Food processing takes
place to bring nutrients
into the body
• Food is transported through
the lumen of the tube from
the mouth to the anus
The digestive tube has four layers
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Mucosa- epithelial
layer
Submucosaconnective tissue
(blood vessels, etc.)
Muscularis externa
(2 smooth muscle
layers, longitudinal
and circular)
Serosa- (protective
connective tissue)
Lumen- inner space
Functions of the human digestive
system
• Mechanical breakdown and processing of food
• Secretion- adding enzymes and surfactants to
food to aid digestion
• Digestion- chemical breakdown of food into
absorbable particles
• Absorption- uptake of food
• Elimination- removing waste
• Also: attenuation/interaction with gut flora
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Overview of the gastrointestinal
(GI) tract
Mouth
Pharynx
Esophagus
Stomach
Small intestine
Gall bladder
Liver
Large intestine
Overview of the gastrointestinal
(GI) tract
The mouth
• Containment and
mechanical processing
are primary functions
• Also, salivary amylase is
secreted by salivary
glands
• Chewed food, mixed
with saliva, is called a
bolus
Mouth flora influence rate of cavity
formation of teeth
• Streptococcus mutans
is associated with
greater rates of
cavities
• Food sugars are
converted into acids
• Is genetically modified
yogurt the answer?
Enzymes are a special kind of protein
Enzymes are protein catalysts
• Catalysts- things which
speed up chemical reactions
• Catalysts are not consumed
in a reaction
• -ase: The enzyme suffix
Catalase
How enzymes work
 Structure aids
function
 An active site
naturally fits
substrate
 Enzyme specificity
depends on shape
 Shape changes to
fit substrateinduced fit
Enzymes increase the rates of
reactions by 108 or more
Enzyme available
with empty active
site
Enzymes
are not
consumed
by the
reactions
they
catalyze
Active site
Substrate
(sucrose)
Substrate binds
to enzyme with
induced fit
Glucose
Enzyme
(sucrase)
Fructose
H2 O
Products are
released
Substrate is
converted to
products
Salivary amylase breaks down
starch
The Pharynx is the last point of
voluntary control for digestion
• Epiglottis covers
breathing
pathway to
prevent choking
• Once
swallowing
begins, it
cannot be
stopped
The esophagus uses peristalsis to
move food to stomach
• Circular and
longitudinal muscle
layers cooperate to
move bolus of food
from pharynx to
stomach
Peristalsis
• 2 layers of muscles
work in coordination to
move food
• Circular muscles on
outside layer
• Long muscles on inside
layer
The stomach’s acidity kills most
invaders
• Hydrochloric acid
pH=~2
• Peristaltic waves in
the stomach also
• Acid hydrolysis can
digest
carbohydrates,
proteins
• Food, now mixed
with gastric juices,
is now chyme
Secretions of the stomach
-Digestive enzymes:
Pepsinogen pepsin, a
proteinase
-Cells of the stomach
lining also secrete intrinsic
factor, required for
absorption of vitamin B12
Pyloric sphincter is
controlled by
hormones of
duodenum
Pepsinogen is a proenzyme
• Stomach’s acid cleaves
pepsinogen subunit,
exposing active site of
enzyme
• Pepsin is a protease
Helicobacter pylori is associated
with stomach ulcers
• Stress is also a cause, albeit
much more frequent
• Survives in stomach
• Discovery earned Nobel
prize for medicine, 2005
• Natural flora for some
people
• H. pylori not always so
bad?
The digestion of which class of foods
begins in the mouth?
1.
2.
3.
4.
5.
a. carbohydrates
b. proteins
c. lipids
d. amino acids
e. nucleic acids
MAJOR ARTICLE: Helicobacter pylori
Colonization Is Inversely Associated with
Childhood Asthma
• Yu Chen1,2,3 and Martin J. Blaser3,4,5
• Background.Asthma, a serious health problem worldwide, is becoming
more common. Colonization with Helicobacter pylori, a major human
indigenous (commensal) microbe, during early life may be relevant to the
risk of childhood asthma.
• Methods. We conducted cross‐sectional analyses, using data from 7412
participants in the National Health and Nutrition Examination Survey
(NHANES) 1999–2000, to assess the association between H. pylori and
childhood asthma.
• Results.H. pylori seropositivity was inversely associated with onset of
asthma before 5 years of age and current asthma in children aged 3–13
years. Among participants 3–19 years of age, the presence of H. pylori was
inversely related to ever having had asthma (odds ratio [OR], 0.69; 95%
confidence interval [CI], 0.45–1.06), and the inverse association with etc.
Stomach chyme is sent through the
pyloric sphincter to the duodenum
• Chyme: food mixed with
digestive juices
• The small intestine has
three regions:
– Duodenum
– Jejunum
– Allium
• Duodenum has digestive
functions, as well as
absorptive
Gastric bypass surgery bypasses most of
the stomach and duodenum
• Patients feel much
fuller, much more
quickly
• Regulation and nutrient
uptake of duodenum
bypassed
• ~80% reduction in Type
II diabetes
• ~2% surgery-related
mortality
Alternatives to gastric bypass
• Adjustable sleeves are
less invasive than a
bypass
• Still really invasive
• 30-day mortality of
0.11%, and 90-day
mortality of 0.3%
The pancreas contains two kinds of
glands
• Contains endocrine glands
and exocrine glands
• Exocrine glands: secrete
proteolytic digestive
enzymes into duodenum
• Endocrine glands: secrete
hormones (insulin,
glucagon, etc.) into
bloodstream to regulate
blood sugar levels
The liver has many functions
• Bile is made in the
liver-~1.5 liters/ day
• Bile contains bile salts,
which emulsify fats
• Bile salts are made
from cholesterol
• Bile salts are stored in
gall bladder
Bile salts emulsify fats for
absorption
• Emulsifying- surrounding
hydrophobic lipids with
amphipathic molecule
Other functions of the liver
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Also synthesizes & releases cholesterol
Synthesizes glucose & releases it
Stores glycogen
Process toxins (lead, mercury, pesticides, etc.)
~500 functions total
Hepatitis, caused by one of many
viruses, causes jaundice
• Jaundice is caused by
accumulation of
bilirubin, a metabolic
waste product from
broken down heme
Bile is stored in the gall bladder
• When fats arrive in the
duodenum, bile is
released
• When bile salts are
insufficient to emulsify
cholesterol, gallstones
can form
The small intestine is designed to
maximize surface area for absorption
• Mucosal layer is folded
• Folds have millions of
villi
• Villi themselves are
made of absorptive
cells with a brush
border of microvilli
submucosa
serosa
(thin
connective
tissue
layer)
thin layer
of longitudinal
muscle
thick layer
of circular
muscle
mucosa
Extensive circular folds
of mucosa
Fig. 7.7a, p. 125
Villi (many
fingerlike,
epitheliumcovered
projections
from the
mucosa)
epithelium
blood
capillaries
lymph
vessel
connective
tissue
vesicles
artery
vein
lymph
vessel
Villi on one of the folds,
longitudinal section
One villus
Fig. 7.7cd, p. 125
microvilli at
free surface
of absorptive
cells
ctyoplasm
absorption
mucus secretion
(goblet cell)
hormone secretion
phagocytosis
lysozyme secretion
Fig. 7.7e, p. 125
The jejunum and illeum complete
digestion in the small intestine
• Chymosin and trypsin
hydrolize proteins into
amino acids
• Lipases break down
triglycerides into fatty
acids and glycerol
bile salts
bile salts
+
+
Micelles
Fat Globules
(triglycerides)
Emulsification
fatty acids,
monoglycerides
triglycerides + proteins
© 2007 Thomson Higher Education
Fig. 7.10, p. 129
The large intestine reclaims water
and prepares feces for elimination
• Active transport of salts
leads to osmosis of
water
• This concentrates feces
• Appendix is not used;
can rupture, causing
appendicitis
• Feces is then passed to
rectum for elimination
Flora of large intestine secrete
important vitamins
• Vitamins B1,
“K”vitamins
(phylloquinones for
blood coagulation)
secreted
• 10:1 ratio of human:
bacterial cells in human
body
The breaking up of large units of fat into
smaller ones is called
1.
2.
3.
4.
5.
a. digestion.
b. saponification.
c. neutralization.
d. emulsification.
e. denaturation.
Many nutrients are interconvertible
Catabolism- breaking down
food for energy
Anabolism- building up
molecules for structure
Other nutrients cannot be replaced
• Essential nutrients cannot be manufactured by the
body
• 8/20 Essential amino acids: Val, Thr, Phe, and Leu,
Ile, Lys, Trp, and Met
• Animal sources have complete protein
• Vegetarian sources are often deficient in some
amino acids but can be complemented
• Beans have Ile and Lys but not Trp and Met. Corn
has Trp, Met but not Ile and Lys.