Transcript dnt 200 nutrition for health sciences

DNT 200
NUTRITION FOR HEALTH
SCIENCES
DIGESTION AND ABSORPTION
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DIGESTION AND ABSORPTION
“I have finally cum to the konklusion that a
good reliable set ov bowels iz worth more
to a man than enny quantity of brains.”
Josh Billings, 19th century American writer
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DIGESTION AND ABSORPTION
• Digestion is the process
by which food is broken
down into absorbable
units
• The digestive system
includes all the organs
and glands associated
with the ingestion and
digestion of food; it is a
flexible muscular tube
about 26 feet long from
the mouth to the anus
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DIGESTION AND ABSORPTION
The Digestive Organs
The Mouth
– Fiber is crushed and
torn
– Food is moistened with
saliva for swallowing
– Amylase in saliva
begins the digestion of
starch to smaller
polysaccharides and
maltose
– Some hard fats begin
to melt as they reach
body temperature
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DIGESTION AND ABSORPTION
The Digestive Organs
The Epiglottis
– Cartilage in the throat
that guards the entrance
to the trachea and
prevents fluid or food
from entering it when a
person swallows
The Esophagus
– The food pipe; the
conduit from the mouth
to the stomach
– Digestion of starch
continues as swallowed
food moves down the
esophagus
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DIGESTION AND ABSORPTION
The Digestive Organs
Cardiac Sphincter
– The sphincter muscle
at the junction between
the esophagus and the
stomach
– Closes behind the
bolus so that it cannot
slip back up the
esophagus
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DIGESTION AND ABSORPTION
The Digestive Organs
The Stomach
– A muscular elastic portion
of the digestive tract that
grinds and churns
swallowed food mixing it
with acid and enzymes to
form chyme
– Starch digestion stops in
stomach as stomach acid
and enzymes digest the
salivary enzymes
– Sucrose and maltose begin
to be hydrolyzed by
stomach acid
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DIGESTION AND ABSORPTION
The Digestive Organs
The Stomach (continued)
– Triglycerides are split into
diglycerides and fatty acids
(a slight action for most fats
except milk)
– Protein, through the action
of pepsin and stomach acid
is split into smaller
polypeptides
– Intrinsic factor attaches to
Vitamin B-12 (Intrinsic
factor is a substance made
in the stomach and aids in
the absorption of Vitamin
B-12)
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DIGESTION AND ABSORPTION
The Digestive Organs
The Stomach (continued)
– Stomach acid acts on iron to
make it more absorbable
– A watery fluid is secreted
turning a moist chewed
mass of solid food into
chyme (a semi-liquid mass
of partially digested food),
which is then expelled into
the duodenum
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DIGESTION AND ABSORPTION
The Digestive Organs
Pyloric Sphincter
– The sphincter muscle
separating the stomach
from the small intestine
– Is the “gate keeper”
keeping chyme from
going back into the
stomach
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DIGESTION AND ABSORPTION
The Digestive Organs
The Small Intestine
– Composed of three
segments
• Duodenum
(upper-most
portion)
• Jejunum (middlemost portion)
• Ileum (last-most
portion)
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DIGESTION AND ABSORPTION
The Digestive Organs
The Small Intestine
(con’t)
– Pancreas produces
carbohydrases and
releases them into the
small intestine
• Polysaccharides are
broken down into
maltose (glucose +
glucose) by pancreatic
amylase
• Maltose is broken down
by maltase to glucose
• Sucrose is broken down
by sucrase to glucose 12
and fructose
DIGESTION AND ABSORPTION
The Digestive Organs
The Small Intestine (con’t)
– Bile flows in from the
liver and emulsifies fat
– Pancreatic lipase flows in
from the pancreas and
breaks the emulsified fat
into monoglycerides,
glycerol and fatty acids,
which are absorbed
– Pancreatic and small
intestine enzymes split
polypeptides into
dipeptides, tripeptides
and amino acids, which
are absorbed
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DIGESTION AND ABSORPTION
The Digestive Organs
The Small Intestine (con’t)
– Bile emulsifies fat
soluble vitamins and aids
in their absorption with
other fats
– Water soluble vitamins
are absorbed
– Many minerals are
absorbed
– Water is secreted from
the small intestine,
pancreas, and liver
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DIGESTION AND ABSORPTION
The Digestive Organs
Ileocecal Valve
– The sphincter
muscle separating
the small and large
intestine
– Keeps chyme from
going back to the
small intestine
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DIGESTION AND ABSORPTION
The Digestive Organs
The Large Intestine
– Most fiber has passed so
far intact -- bacterial
enzymes break down
some fiber into glucose,
which is absorbed
– Some fat and cholesterol,
trapped in the fiber, is
excreted
– Bacteria produce Vitamin
K, which is absorbed
– More minerals and most
of the water are absorbed
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DIGESTION AND ABSORPTION
The Digestive Organs
Rectum
– The muscular terminal
part of the intestine to
the anus
Anus
– The terminal sphincter
muscle of the GI tract
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DIGESTION AND ABSORPTION
Involuntary Muscles and Glands
• Except for swallowing and defecating, the muscles
and glands of the digestive tract work with no
conscious effort
• Salivary glands secrete just enough saliva to
moisten each mouthful of food
• Muscles of the GI tract help liquefy the bolus into
chyme (i.e. chewing, in addition to saliva and the
action of the tongue, reduces food into a coarse
mash suitable for swallowing)
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DIGESTION AND ABSORPTION
Involuntary Muscles and Glands
• Stomach muscles work to force the chyme downward
toward the pyloric sphincter
• Peristalsis begins when the bolus enters the
esophagus
– Entire GI tract is ringed with muscles that can squeeze
tightly
– During peristalsis, successive waves of involuntary
muscle contraction passes along the walls of the
intestine
• Intestines segment their contents
– Segmentation -- a periodic squeezing or partitioning of
the intestine by its circular muscles
– Allows the digestive juices and absorbing cells of the
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intestinal wall to make better contact
DIGESTION AND ABSORPTION
The Process of Digestion
• Body renders food into the basic units that make
up carbohydrate, protein and fat, absorbs these
units, and builds its tissues from them
• Five different organs secrete digestive juices
–
–
–
–
–
Salivary glands
Stomach
Small intestine
Liver
Pancreas
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DIGESTION AND ABSORPTION
The Process of Digestion
Digestion in the Mouth
• Digestion of carbohydrate begins in the mouth
– Saliva (water, salts, and enzymes -- including salivary
amylase) break the bonds in the chains of starch
• Enzymes in the mouth have no effect on
–
–
–
–
–
Fats
Proteins
Vitamins
Minerals
Fiber
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DIGESTION AND ABSORPTION
The Process of Digestion
Digestion in the Stomach
• Major event -- initial breakdown of protein
• Gastric juice is composed of water, enzymes, and
hydrochloric acid
– Acidity prevents bacteria growth
– Acidity kills bacteria that enter the body with food
• Acid helps uncoil proteins tangled strands so that the
stomach enzymes can attack the bonds
• Minor stomach events
– Digestion of some fat by gastric lipase
– Digestion of sucrose (to a small extent) by stomach acid
– Attachment of a protein carrier to vitamin B-12
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DIGESTION AND ABSORPTION
The Process of Digestion
Digestion in the Small and Large Intestine
• Pancreas and liver contribute digestive juices through ducts
leading into the duodenum
• Pancreatic juice
– Contains enzymes which act on fats, proteins, and
carbohydrates (glands in the intestinal wall also secrete
digestive enzymes)
– Also contains sodium bicarbonate (a base) which neutralizes
the acid chyme as it enters the small intestine
• Bile
– Secreted by the liver continuously
– Stored in the gall bladder
– Emulsifies fats and brings them into suspension with water
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enabling enzymes to work on them and subsequent absorption
DIGESTION AND ABSORPTION
The Process of Digestion
Digestion in the Small and Large Intestine (continued)
• All three energy-yielding nutrients are digested in the small
intestine
• Rate of digestion depends on the contents of the meal
– High in simple sugars -- digestion proceeds rapidly
– High in fat -- digestion is slower (fat increases a meal’s satiety
value)
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DIGESTION AND ABSORPTION
The Process of Digestion
Digestion in the Small and Large Intestine (continued)
• Bacteria in the intestine produce a variety of vitamins
(bacterial alone cannot meet the need for these vitamins)
– Biotin
– Vitamin K
• GI bacteria protect from infection
– If normal intestinal flora is thriving, infections have a hard
time getting established
– Several types of defending cells are present and confer
specific immunity against intestinal diseases
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DIGESTION AND ABSORPTION
The Absorptive System
The Small Intestine
– Provides a surface
whose extent is
comparable to a quarter
of a football field in
area
– Nutrient molecules
make contact with this
surface and are
absorbed
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DIGESTION AND ABSORPTION
The Absorptive System
The Small Intestine (con’t)
– A rush of blood
circulation
continuously bathes the
underside of this
surface
• Removes these
molecules rapidly
• Makes room for more to
be absorbed
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DIGESTION AND ABSORPTION
The Absorptive System
The Small Intestine (con’t)
– Is a tube about 20 feet long and an
inch across
– Inner surface, through a
microscope, is wrinkled into
hundreds of folds
– Each fold is covered with with
thousands of finger-like projections
(villi) which are in constant motion
– Any nutrient molecule small
enough to be absorbed is trapped in
the microvilli (projections from the
cells of the villi), drawn in and
absorbed
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DIGESTION AND ABSORPTION
The Absorptive System
Release of Absorbed Nutrients
• Once inside the intestinal cells, the products of digestion
must be released for transport to the rest of the body
• Water soluble nutrients are released directly into the
bloodstream via the capillaries
• Larger fats and fat soluble vitamins
– Are insoluble in blood (water)
– Fats are assembled into triglycerides
– These triglycerides, with fat soluble vitamins and other lipids
(phospholipids, cholesterol) form with proteins into
lipoproteins called chylomicrons
– They are then released into the lymphatic system
– Then go from the lymphatic system to the blood stream near
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the heart
DIGESTION AND ABSORPTION
Transport of Nutrients
The Vascular System
• Also known as the blood
circulatory system
• Is a closed system of
vessels through which
blood flows continuously
in a figure eight
• Heart is the pump at the
crossover point
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DIGESTION AND ABSORPTION
Transport of Nutrients
The Vascular System (con’t)
• Except for the digestive system,
blood goes from the heart to arteries
to capillaries to veins back to the
heart
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DIGESTION AND ABSORPTION
Transport of Nutrients
The Vascular System (con’t)
• Digestive system
– Blood gets to the digestive system
(intestines) by way of arteries to capillaries
– When leaving the digestive system the
blood goes not back to the heart but by
vein to the liver
• Liver has the first chance at nutrients absorbed
form the GI tract
• Liver is the body’s major metabolic organ
– Must prepare nutrients for use by the body
– Performs many other jobs in this process
– There capillaries give the liver access to
the blood
– From the liver the blood goes via vein back
to the heart
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DIGESTION AND ABSORPTION
Transport of Nutrients
The Lymphatic System
• Is a one-way route for fluid
from the tissue spaces to
enter the blood
• Has no pump
– Like water in a sponge, lymph
is squeezed from one portion
of the body to another as
muscles contract and create
pressure here and there
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DIGESTION AND ABSORPTION
Transport of Nutrients
The Lymphatic System
(continued)
– Ultimately collects in a large
duct behind the heart
– Duct terminates in a vein that
conducts the lymph into the
heart and thereby into the
bloodstream
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DIGESTION AND ABSORPTION
Review
Secretion
ORGAN OR GLAND
TARGET
ACTION
?
Salivary Glands
Amylase
Mouth
Starch
?
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DIGESTION AND ABSORPTION
Review
Secretion
ORGAN OR GLAND
TARGET ACTION
Saliva
Salivary Glands
Amylase
Mouth
Starch
?
Pepsin, HCl
?
Smaller Polypeptides
Gastric Juice
Gastric Glands
Maltose
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DIGESTION AND ABSORPTION
Review
Secretion
ORGAN OR GLAND
TARGET
ACTION
Saliva
Salivary Glands
Amylase
Mouth
Starch
Stomach
Pepsin, HCl
Protein
Smaller Polypeptides
Gastric Juice
Gastric Glands
Maltose
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DIGESTION AND ABSORPTION
Review
Secretion
ORGAN OR GLAND
TARGET
Saliva
Salivary Glands
Mouth
Amylase
Starch
Maltose
Stomach
Pepsin, HCl
Protein
Smaller Polypeptides
Gastric Juice
Gastric Glands
ACTION
Intestinal Juice
?
Intestinal Glands
Small Intestine Carbohydrate Monosaccharides
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DIGESTION AND ABSORPTION
Review
Secretion
ORGAN OR GLAND TARGET
Saliva
Salivary Glands
Mouth
ACTION
Amylase
Starch
Maltose
Gastric Juice
Gastric Glands
Stomach
Pepsin, HCl
Protein
Smaller Polypeptides
Intestinal Juice
Intestinal Glands
Small Intestine
Carbohydrase
Carbohydrate
Monosaccharides
? Juice
Pancreas
Small Intestine
Protease
Protein
dipeptides, tripeptides
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DIGESTION AND ABSORPTION
Review
Secretion
ORGAN OR GLAND
TARGET
Saliva
Salivary Glands
Mouth
Gastric Juice
Gastric Glands
Stomach
Intestinal Juice
Intestinal Glands
Small Intestine
ACTION
Amylase
Starch
Maltose
Pepsin, HCl
Protein
Smaller Polypeptides
Carbohydrase
Carbohydrate
Monosaccharides
Pancreatic Juice
Pancreas
Bile
Liver
Protease
Small Intestine
Protein
Small Intestine
Bile
Fats
Bile
?
dipeptides, tripeptides
and amino acids
?
(Emulsified fat)
monoglycerides, ?, & fatty 40
acids
DIGESTION AND ABSORPTION
Review
Secretion
ORGAN OR GLAND
TARGET
Saliva
Salivary Glands
Mouth
ACTION
Amylase
Starch
Maltose
Gastric Juice
Gastric Glands
Pepsin, HCl
Protein
Smaller Polypeptides
Stomach
Intestinal Juice
Intestinal Glands
Small Intestine
Carbohydrase
Carbohydrate
Monosaccharides
Pancreatic Juice
Pancreas
Bile
Liver
Protease
Small Intestine
Protein
Small Intestine
Bile
Lipase
Fats
(Emulsified fat)
monoglycerides, glycerol, & fatty41acids
Bile
Gall
Bladder
*****
dipeptides, tripeptides
and amino acids
DIGESTION AND ABSORPTION
Review
DIGESTION IN THE MOUTH
Amylase
Starch
Maltose
Carbohydrate
Fat, Protein, Vitamins
Minerals, Fiber
No chemical action
Water
Added
****
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DIGESTION AND ABSORPTION
Review
DIGESTION IN THE STOMACH
Protein
Pepsin-Acid
Smaller Polypeptides
Carbohydrate, Fat, Vitamins
Minor action
Minerals, Fiber
No chemical action
Water
Added
***
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DIGESTION AND ABSORPTION
Review
DIGESTION IN THE SMALL INTESTINE
Carbohydrases
Carbohydrate
All Carbohydrates
Monosaccharides
Bile
Fat
All Fats
Emulsified fats
Lipases
Emulsified fats
Monoglycerides or
Glycerol and
Fatty Acids
Proteases
Protein
All Proteins Dipeptides, Tripeptides
and Amino Acids
Vitamins, Minerals, No Chemical Action
& Fiber
Water
Added
**
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DIGESTION AND ABSORPTION
Review
TRANSPORT OF NUTRIENTS INTO BLOOD
The following are transported directly into the blood
– Water Soluble Nutrients
• Carbohydrates
– Monosaccharides
• Lipids
– Glycerol
– Short Chain Fatty Acids
– Medium Chain Fatty Acids
• Proteins
– Amino Acids
• Vitamins
– B Vitamins and Vitamin C
• Minerals
*
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DIGESTION AND ABSORPTION
Review
TRANSPORT OF NUTRIENTS INTO BLOOD (Con’t)
The following are made into triglycerides
– Lipids
• Long Chain Fatty Acids
• Monoglycerides
These, along with
• Cholesterol
• Phospholipids
Are assembled into lipoproteins and transported through
the lymphatic system to the blood
Vitamins A, D, E, and K are transported through the
lymphatic system to the blood
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