Download 4 - Nutrition and Digestive system

Nutrition Digestive system
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Digestion helps homeostasis
A digestive system involves various processes:
Ingestion
Mechanical digestion
Chemical digestion
Absorption
Elimination
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Digestion helps homeostasis
Chemical digestion
involves specific enzymes in
the macromolecule
breakdown.
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Animal strategies
Heterotrophs are divided into four groups on the basis of
their food strategy.
Bulk feeders
eat food in chunks or whole
Filter feeders
collect and eat small
particles from water
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Animal strategies
Fluid feeders
consume fluids as blood
or lymph
Substrate feeders
live on or in the food they eat
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lase,
lase,
which
which
initiates
initiates
the
breakdown
breakdown
of the
of the
polysaccharide
polysaccharide
starch
starch
ate
ebrate
tooth
tooth
shape.
shape.
lase,
which
initiates
thethe
breakdown
of the
polysaccharide
starch
tooth shape.
into
into
the
the
disaccharide
disaccharide
maltose.
maltose.
This
This
digestion
digestion
is usually
is usually
minimal
minimal
he
in digestive
the digestive
process.
process. into
the
disaccharide
maltose.
This
digestion
is usually
minimal
digestive
process.
in humans,
in humans,
however,
however,
because
because
most
most
people
people
don’t
don’t
chew
chew
their
their
food
food
in humans,
however,
because
most
people
don’t
chew
their
food
very
very
long.
long.
very
long.
different
in different
kinds
kinds
of
verof verferent
kinds
of
verStimulation
Stimulation
salivation
of salivation
irds,
e. Birds,
which
which
lack
lack
teeth,
teeth,Stimulation
of of
salivation
ds,
which
lack
teeth,
The
The
secretions
secretions
of the
of
the
salivary
salivary
glands
glands
are
controlled
controlled
by the
by
the
ner-nermachs
stomachs
(figure
(figure
48.5)
secretions
of the
salivary
glands
areare
controlled
by the
nerchs (figure
48.5)
. 48.5)
In. In . InThe
vous
vous
system,
system,
which
which
humans
in humans
maintains
maintains
a constant
a constant
of of
rd,
mall
small
pebbles
pebbles
ingested
ingestedvous
system,
which
in in
humans
maintains
a constant
flowflow
offlow
all
pebbles
ingested
about
about
half
athat
milliliter
a milliliter
per
minute
minute
when
when
the
the
mouth
mouth
is empty
is empty
the
food
food
by
muscular
by muscular
Herbivores:
animals
eat
plants
exclusively;
common
half
a half
milliliter
perper
minute
when
the
mouth
is empty
of of of examples
od
by
muscular
ac-ac- ac-about
food.
food.
This
This
continuous
continuous
secretion
secretion
keeps
keeps
the
the
mouth
mouth
moist.
moist.
and
other
other
hard
hard
plant
plant
ma-ma-food.
This
continuous
secretion
keeps
the
mouth
moist.
ther
hard
plant
mainclude
vertebrates
such
as
cattle,
horses
and
rabbits.
The
The
presence
presence
of food
ofinfood
in the
in the
mouth
mouth
triggers
triggers
an increased
an increased
gested
ed
more
more
easily.
easily.
The
presence
of food
the
mouth
triggers
an increased
more
easily.
rate
of
secretion.
of secretion.
Taste
Taste
buds
buds
as well
asaswell
as olfactory
as olfactory
(smell)
(smell)
neuneurate
ofrate
secretion.
Taste
buds
as
well
olfactory
(smell)
neurons
rons
send
send
impulses
impulses
to
tobrain,
the
brain,
brain,
which
which
responds
responds
by
stimustimudiff
toerent
diff
erent
erent
rons
send
impulses
toeat
thethe
which
responds
by by
stimuCarnivores:
animals
that
other
animals,
such
as
crabs, squid,
iff
lating
lating
the
the
salivary
salivary
glands
glands
(see
(see
chapter
chapter
46).
46).
The
The
most
most
potent
potent
thecats.
salivary glands (see chapter 46). The most potent
many insectslating
and
stimuli
stimuli
are
acidic
acidic
solutions;
solutions;
lemon
lemon
juice,
juice,
for
example,
example,
stimuli
areare
acidic
solutions;
lemon
juice,
for for
example,
cancancan
increase
increase
the
rate
of
salivation
of salivation
eightfold.
eightfold.
The
The
sight,
sight,
sound,
sound,
8.6),
used
used
for
chewing,
for chewing,
thethe
rate
ofrate
salivation
eightfold.
The
sight,
sound,
sed
for
chewing,
or or orincrease
smell
or smell
food
ofthat
food
can
can
stimulate
stimulate
salivation
salivation
markedly
markedly
in many
in other
many
mall
particles
particles
and
and
mix
it itor or
smell
of of
food
can
stimulate
salivation
markedly
in
many
Omnivores:
animals
eat
both
plants
and
animals.
articles
and
mix
itmix
Teeth are adapted to different strategies
Heterotrophs are divided into three groups on the basis of
their food sources.
Humans are omnivores, as are pigs and bears.
n
Herbivore
Herbivore
Herbivore
Carnivore
Carnivore
Carnivore
Omnivore
Omnivore
Omnivore
evolved
ved
d
of
ern of
s
Premolars
olars
Molars
s
Horse
Lion
Horse
Horse
Horse
Human
Lion
LionLion
Human
Human
Human
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Digestive system in mammals
Vertebrate digestive systems include highly specialized
structures molded by diet.
The digestive system consists of a tubular gastrointestinal tract
and accessory digestive organs.
One-way movement through the digestive tract allows different
regions of the digestive system to become specialized for different
functions.
Salamander
Stomach
Intestine
Mouth
Anus
One-way movement
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Digestive system in mammals
Carnivores have a short digestive tract, as they
obtain nutrients from meat more easily.
They also have a relatively small caecum
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Digestive system in mammals
Herbivores have a long digestive tract, as it takes a
long time to digest cellulose from plants, and a large
caecum which houses mutualistic aerobic bacteria
which help animals digest the cellulose
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Digestive system in mammals
Some herbivores called ruminants (cows, sheep) have
specialized stomaches divided into rumen (1), reticulum
(2), omasum (3) and abomasum (4) hosting microbial flora.
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Human digestive system
Our digestive system is adapted to
an omnivorous diet.
The breakdown of the nutrients requires
the coordination of several digestive
enzymes secreted from specialized cells.
The major organs or structures that
coordinate digestion within the human
body include:
• mouth
• esophagus
• stomach
• small and large intestine
• liver
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The mouth
Both first mechanical (biting and chewing) and chemical digestion
occur in the mouth.
Humans have four kinds of 32 teeth: incisors (for biting); canines (for tearing);
premolars and molars (for crushing food).
Three pairs of salivary glands secrete saliva that contains an enzyme called
amylase, which digests starch molecules into smaller disaccharides.
During chewing, the tongue moves food about and manipulates it into a mass
called a bolus. The bolus is pushed down into the pharynx (throat).
Molars (3)
Premolars (2)
Canines (1)
Incisors (2)
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The esophagus
The esophagus is a muscular tube that passes from the pharynx to the
stomach.
During swallowing, the air passage is blocked by soft palate (1) and
epiglottis (2), so the food bolus enters the esophagus (3).
Palate
Epiglottis
Esophagus
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The esophagus
After swallowing, peristaltic movements (a rhythmic
series of muscular contractions) push the food bolus in
the esophagus to the stomach.
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The stomach
The stomach is a saclike organ.
Its inner surface is highly convoluted, enabling it to fold up when
empty and open out like an expanding balloon as it fills with food.
The human stomach has a volume of only about 50
mL when empty, but, it may expand to contain 2 to 4 L
of food when full.
Carnivores that engage in sporadic gorging as an
important survival strategy possess stomachs that are
able to distend even more.
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The stomach
Layers of stomach muscle contract and attack the bolus of food
with gastric juices to form a soupy liquid called chyme.
Where the esophagus joins the stomach, a valvelike muscle, the
cardiac sphincter, relaxes as the bolus passes through and then
quickly closes.
A second sphincter, the pylorus, connects to the beginning of the
intestines.
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The stomach
The stomach
1. stores food
2. prepares food for second chemical digestion.
3. plays a role in protein digestion. Gastric glands secrete an
hormone that is converted to the enzyme pepsin which
digests large proteins into smaller proteins (peptides)
The food is mixed with gastric acid juices
containing pepsin.
To protect the stomach wall from the acid, a
third type of cell secretes mucus that lines
the stomach cavity.
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Gastric acids and the ulcer
The human stomach produces about 2 L of HCl
every day, creating a very acidic solution (pH=2).
The low pH in the stomach helps denature food
proteins, making them easier to digest.
In adult humans, only proteins are partially
digested in the stomach; no significant digestion of
carbohydrates or fats occurs there.
The acidic solution within the stomach also kills
most of the bacteria that are ingested with the food.
Overproduction of gastric acids can occasionally eat a hole through
the wall of the stomach, causing a peptic ulcer.
Different reasons cause peptic ulcers such as the infection of the
bacterium Heliobacter pylori and the consumption of some types of
foods.
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The intestine:
Breakdown, Absorption, and Elimination
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The small intestine
The chyme spurts from the stomach through a sphincter
into the 5 to 9 meters long small intestine. Here absorption
of nutrients takes place.
Small nutrient molecules are absorbed by the villi on the
intestinal wall.
villi
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Accessory organs secrete enzymes
into the small intestine
The main organs that aid digestion are the pancreas, liver, and
gallbladder.
They empty their secretions (pancreatic juice and bile), primarily
composed of enzymes, through ducts directly into the small intestine
Liver
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Pancreas, Liver and Gallbladder
The pancreas, secretes pancreatic fluid into the duodenum through
the pancreatic duct.
This fluid contains a group of enzymes, including trypsin, which digest
proteins; amylase, which digests starch; and lipase, which digests fat.
The liver is the largest internal organ of the body. The main secretion
is bile, a fluid mixture consisting of:
1.The bile pigments: do not participate in digestion; they are waste
products resulting from the liver’s destruction of old red blood cells
and are ultimately eliminated with the feces
2.The bile salts play a very important role in preparing fats for
subsequent enzymatic digestion
After bile is produced in the liver, it is stored and concentrated in the
gallbladder. The arrival of fatty food in the duodenum stimulates the
gallbladder to contract, causing bile to be transported through the
common bile duct and injected into the duodenum
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The chemical digestion
•The enzymes digesting carbohydrate include amylase (for starch), maltase
(for maltose), sucrase (for sucrose) and lactase (for lactose).
•For fats, the principal enzyme is lipase. Before this enzyme can act, the large
globules of fat must be broken into smaller droplets by bile.
•Protein digestion is accomplished by several enzymes, including trypsin.
Peptides are broken into smaller peptides, and peptidase reduces the
peptides to amino acids.
•Nuclease digests nucleic acids into nucleotides.
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The large intestine
The large intestine absorbs water, minerals and vitamins
and prepare waste for elimination. Is divided into cecum,
colon and rectum.
The cecum controls the flux of material
through the intestine and the appendix
protects from infections.
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The large intestine
The colon is the last portion of the digestive tract and extracts the
last water and minerals from waste before final elimination.
Bacteria-aided fermentation occurs.
Transverse
colon
Ascending
colon
Descending
colon
The rectum is the final part of the
large intestine and terminates in
the anus. Here feces are formed
and expelled.
Rectum
Anus
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Nutrition disorders
Obesity is defined as weighing 30% more than ideal body
weight. Obesity is often associated with Type 2 Diabetes
and cardiovascular diseases.
Other common nutrition disorders are anorexia nervosa
(distorted body image that leads to hypo-nutrition) and
bulimia nervosa (binge-eating and purging).
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Liver diseases
Liver malfunctioning has effects on the whole organism.
Liver disorders include:
•
•
•
Hepatitis: inflammation of the liver caused by viruses
Cirrhosis: damage of tissues leading to loss of liver
functions
Liver cancer
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