Transcript Digestion Absorption and Alcohol

Digestion Absorption
and Alcohol, Protein &
Vegetarianism
Basic Human Nutrition
Lecture 2
Introduction
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All cells require nutrients to provide energy.
Hormones and enzymes work with the
digestive tract to break complex nutrients
from food into smaller ones that can be
absorbed through the lining of the intestines
into the blood and lymph.
These nutrients are then distributed (via
blood and lymph) to all cells in the body.
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Digestion
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Process of breaking down foods into
nutrients to prepare for absorption.
The GI tract is the flexible muscular
tube from mouth to anus.
Consists of the esophagus, gallbladder,
liver, stomach, pancreas, small
intestine, large intestine, rectum and
anus.
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Digestion is both mechanical &
chemical
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Mouth.
Teeth and jaws - mastication.
Mastication (mashing the food)
increases the surface area
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Secretions
of Digestion
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Saliva
 Salivary glands
 Water, salts,
mucus,
enzymes
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Esophagus
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Tube that leads the bolus to the
stomach.
The esophageal sphincter is at the
upper end.
The cardiac sphincter is at the lower
end.
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Stomach
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The stomach contains gastric glands.
The parietal cells of the gastric glands
secrete hydrochloric acid
Mucosal neck cells secret mucous to
protect the mucosal lining.
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Secretions
of Digestion
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Stomach
 Gastric juice
 Gastric glands
 Water, enzymes,
hydrochloric acid
(HCl)
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Stomach continued
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The stomach contents are churned into
an acidic liquid called chyme.
It can take 2 to 3 hours to empty the
stomach depending on the mixture of
nutrients (CHO, protein and fat).
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Small intestine
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The small intestine consists of
duodenum (first 0.3m), jejunum (next
1-2 m, where most of digestion occurs)
and ileum (last 1.5 m).
Approximately 90% of digestion takes
place in the first 2 sections of the long
small intestine.
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Small intestine continued
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Chyme release to small intestine through the
pyloric valve at the end of the stomach.
Rhythmic contractions of the small intestine
move the intestinal contents along its length.
By the time it reaches the large intestine or
colon, digestion and absorption are nearly
complete.
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Large intestine
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Consists of the ascending and descending
colon, transverse colon, sigmoid colon,
rectum and anal canal.
In the colon, the digested food remnants are
further acted upon by bacteria that ferment
the remaining undigested food residues.
The bacteria synthesize small amounts of
vitamin K and the B vitamin biotin that
become absorbed.
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Large intestine continued
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Bacterial fermentation also produces about
500 ml of gas (flatus) each day.
The gas is a mixture of hydrogen, nitrogen,
methane, hydrogen sulfide and carbon
dioxide.
The colon absorbs water and compacts the
residue into a paste, feces which it moves
along to the rectum.
The rectum stores feces until eliminated
through the anus.
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Chemical digestion
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Chemical digestion occurs through digestive
enzymes that are secreted by gland cells
along the alimentary tract.
Enzymes are biological catalysts which speed
up chemical reactions.
These enzymes are specific in their action
and to specific nutrients.
Enzymes are manufactured in the salivary
glands, the gastric glands, the intestinal
glands and the pancreas.
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Digestive Juices
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Salivary glands:
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secrete saliva to moisten and lubricate
food.
Amylase - starts the breakdown of starch
Amylase is inactivated in the stomach by
the acid medium.
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Digestive Juices
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The gastric glands produce gastric juice
which includes hydrochloric acid.
The pancreas secretes sodium bicarbonate
to neutralize the acids from the stomach.
Pancreatic juice contains intestinal enzymes
(carbohydrase, lipase and protease).
Bile is produced by the liver, stored in the gall
bladder and acts as an emulsifier to suspend
fat.
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Disaccharides are digested
by..
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Enzymes secreted by the gland cells in
the small intestine.
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Maltase splits maltose into 2 glucose units
Sucrase splits sucrose into glucose and
fructose
Lactase splits lactose into glucose and
galactose.
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Protein digestion begins in the
stomach
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Proteins are amino acids in long chains
called polypeptides.
Gastric glands secrete the enzyme
pepsin in its inactive form pepsinogen.
Pepsin is activated by gastric acid. It
splits the bonds between proteins
(amino acids) into polypeptides of
different lengths.
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Protein digestion continued
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Pepsin works best at a pH of less than 2. This
is carefully maintained by the gastric glands
to facilitate protein digestion.
Protein and polypeptides are further broken
down in the intestine at a neutral pH by the
pancreatic enzyme called trypsin.
Enzymes from the intestinal glands and the
pancreas called peptidases complete the
process.
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Fat digestion occurs mainly in the
intestine
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Tongue produces traces of a fatdigesting enzyme that helps to break
down milk fats. Very important to
nursing infants.
Fat broken down by pancreatic lipase
to fatty acids and glycerol.
Fats form large globules in the intestinal
juices.
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Fat globules are broken up by
Bile salts
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Liver secretes bile (salts), the gallbladder
stores it and releases it into the small
intestine.
Bile salts are not enzymes but emulsifiers
which help to break up the fat into smaller fat
droplets.
The lipase then has a greater surface area to
work on.
If bile salts are not secreted by the liver, the
fat passes undigested into the feces.
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Absorption of nutrients
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For absorption a large area of contact
between the digested food molecules
and the intestinal lining is necessary.
Small intestine provides a large
absorptive area:
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Very long (7 metres in the adult)
It has circular folds
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Absorption continued
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Villi.
Microvilli.
Folding of the intestinal surfaces greatly
increases absorptive capacity.
Large supply of blood vessels in small
intestine transport the nutrients from
the gut to the cells in the body.
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The liver – dispatch centre for the
refinery
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Nutrients pass through the epithelial cells
lining the small intestine and into the
capillaries below them.
They are then carried away in veins which
eventually join one large vein, the hepatic
portal vein.
This vein carries all blood from the blood
vessels of the intestine to the liver.
The liver can store the nutrients or change
them and release them through general
circulation.
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Maintaining glucose levels
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Liver, along with insulin from the
pancreas, maintains fairly constant
levels of blood glucose.
Large quantities of glucose reach the
liver from the alimentary canal via the
hepatic portal vein.
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Maintaining glucose continued
The liver can:
 1) break the glucose down as an energy
source for liver cells.
 2) convert it to glycogen and store it in
liver cells.
 3) convert it into fats which are then
sent to fat depots in the body.
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Liver and proteins & fats
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Amino acids cannot be stored in the body.
The liver breaks them down (deamination)
and converts them to ammonia and urea.
Urea enters the general circulation and is
removed by the kidneys.
Excess CHO, protein and fats are converted
to fat in the liver and sent to fat depots.
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Liver – the cleansing organ
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The liver also makes bile salts.
Stores some vitamins and minerals
particularly iron.
Removes worn out red blood cells from
circulation and destroys them.
Inactivates hormones.
Detoxifies or inactivates many toxic chemicals
and drugs, which can then be eliminated by
the kidneys.
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Digestive Problems
Vomiting
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The waves of peristalsis reverse direction.
If severe, the contents of the duodenum with
its green bile can come up.
Solution: drink small amounts liquid as
tolerated until nausea subsides.
Dehydration can occur.
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Diarrhea
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Frequent, loose, watery stools.
Diarrhea is a symptom of a variety of
medical conditions and treatments.
It can be the result of disorders of the
GI tract – IBS or colitis.
Treatment depends on its cause and its
severity.
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Constipation
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Is a symptom, not a disease.
Often a person’s lifestyle may be the
cause.
Treatment often involves increasing the
fibre content of the diet as well as
increasing fluids.
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Diverticulosis
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Condition in which the intestinal walls
develop bulges in weakened areas
(most common in the colon).
These diverticula can worsen
constipation, entrap feces, and become
painfully infected and inflamed
(diverticulitis).
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Heartburn and Acid Indigestion
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Occurs soon after eating a meal and
can be very painful.
The esophageal sphincter allows the
stomach contents to reflux into the
esophagus.
Treatment: eat less at a meal, chew
food more thoroughly and eat slow.
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Ulcers
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Ulcer is an erosion of the top layer of
cells.
The erosion leaves the underlying layers
of cells unprotected and exposed to
gastric juices.
Gastric and duodenal ulcers are a
common digestive problem.
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Ulcers
There are 3 major causes of ulcers:
 Bacterial infection with Helicobacter
pylori
 The use of certain anti-inflammatory
drugs (aspirin, ibuprofen, naproxen).
 Disorders that cause excessive gastric
acid secretion.
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Alcohol
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Alcohol is a drug
Provides energy (7 kcal/ml), but is not a
nutrient.
Small molecule, easily diffuses in and
out of cells, therefore rapidly absorbed.
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Alcohol and Nutrition
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Absorption of Alcohol
continued
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Alcohol dehydrogenase (enzyme in
Liver) breaks down small to moderate
amounts of alcohol to acetaldehyde.
This can reduce the amount of alcohol
entering the blood by about 20%.
Alcohol is rapidly absorbed in the small
intestine. It gets absorbed and
metabolized before most nutrients.
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Absorption of Alcohol
continued
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The liver possesses an enzyme system that
metabolizes alcohol and several types of
drugs. This is called the Microsomal ethanoloxidizing system (MEOS).
Chronic alcohol abusers use this pathway
more frequently and may develop an
increased tolerance to alcohol.
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Alcohol absorption continued
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Liver can process only a certain amount
of alcohol per hour (1/2 oz ethanol/hr).
When amount of alcohol exceeds
capacity, spills over into all bodily fluids
including the cerebrospinal, brain, (in
pregnancy, placenta and fetus).
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Alcohol absorption continued
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10% of circulating alcohol is lost through
urine, breath and skin.
Excess alcohol deprives brain of oxygen, brain
shuts down functions that regulate breathing
and heart rate. Lose consciousness.
Alcohol poisoning due to rapid ingestion of
large amounts of alcohol; body shuts down,
but processing of alcohol continues causing
death.
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Absorption of Alcohol
continued
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Acetaldehyde in GI tract not completely
converted to acetate. Damages gut
lining.
Alcohol digestion takes priority over
fats, protein and carbohydrates.
Liver cells detoxify alcohol and uses
products to make fatty acids which are
further made into fats.
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Hangover
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Ethanol competes with methanol for
absorption and processing in the liver.
Methanol metabolite formaldehyde
builds up.
Dehydration occurs, leading to
headache and dry mouth.
Alcohol irritates stomach and intestinal
lining causing diarrhea and vomiting.
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Hangover
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Vomiting/diarrhea causes further loss of
electrolytes and dehydration.
Processing of alcohol diverts liver from
glucose production which leads to
hypoglycemia.
Effects can last up to one day.
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Treatment of hangover
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Only time is an effective treatment combined
with fluids and some carbohydrates to replace
losses and reverse hypoglycemia.
Caffeine compounds dehydration.
More alcohol continues process.
Type of alcohol and mixes not responsible for
hangover. Total amount of alcohol
responsible.
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Not all individuals handle
alcohol the same.
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Women – produce 40% less of ADH in
stomach than men
Smaller body size equals smaller liver,
less enzymes.
Less water more body fat than men, get
drunk quicker and stay drunk longer
than men on same amount of alcohol.
Seniors – less body water.
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University and alcohol
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Accepted means of stress relief among
students.
Binge drinking common more negative
effects; property destruction, drunk
driving, accidents, missed classes, etc.
Greater risk of rape for women.
Acceptable alcohol intake is 1 drink per
day for women and 2 per day for men.
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Low-Risk Drinking Guidelines
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Zero
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Two
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Being alcohol free
provides the lowest
risk of alcoholrelated problems.
Have no more than
2 standard drinks on
any one-day.
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Low-Risk Drinking Guidelines…
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Nine
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Fourteen
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Women may have
up to 9 standard
drinks a week.
Men may have up to
14 standard drinks a
week.
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Low-risk drinking guidelines
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One standard drink = 13.6 grams of alcohol
One standard drink = 5 oz/142 ml of
wine (12% alcohol)
One standard drink = 1.5 oz/43 ml of
spirits (40% alcohol)
One standard drink = 12 oz/341 ml of
regular strength beer (5% alcohol)
Higher alcohol beers and coolers have more
alcohol than one standard drink!
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Alcohol and Malnutrition
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In moderate drinkers alcohol may stimulate
appetite.
Alcohol can contribute to body fat and weight
gain.
Heavy drinkers usually consume alcohol as
substituted energy.
Chronic alcohol abuse displaces nutrients
from the diet and interferes with the body’s
metabolism of nutrients.
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Proteins
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Proteins have a unique structure that consists
of carbons, oxygen, hydrogen and nitrogen.
Amino acids are the building blocks of
protein. They are linked together by peptide
bonds in strands that may consist of up to
1000 amino acids.
About 20 amino acids are required by the
body.
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Amino Acids
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Essential amino acids
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The body can make up about half of the
20 amino acids
Essential amino acids must be obtained
from food.
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Recycling amino acids
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The body can reuse its amino acids.
Both food proteins after digestion and body
proteins after use are dismantled to release
their amino acids.
Cells can use the amino acids as energy and
discard the nitrogen as waste.
By reusing amino acids to build proteins, the
body recycles and conserves a valuable
nutrient while easing its burden of disposing
nitrogen.
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The variety of proteins…
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The unique shapes of proteins perform
different tasks:
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Globular shape—blood proteins, are water soluble;
hollow balls can carry and store materials in their
interiors.
Some form rope fibers that lend support and
elasticity to body parts.
Enzymes are proteins which act on other
substances to change them chemically.
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DNA & protein
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Heredity and DNA.
Any mistake in the sequence leads to
disease. Example sickle cell anemia.
Each person is different because of
differences in body proteins that is
determined by their genetic code or
DNA.
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Protein digestion
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Denaturation of proteins begins in the
stomach acid.
Enzymes in the intestine break down the
protein strands into single amino acids,
dipeptides, tripeptides polypeptides.
Intestinal cells further break down the smaller
strands into amino acids and absorb them
into the bloodstream.
A few dipetides and tripeptides cross into the
bloodstream without further digestion.
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Absorption of amino acids
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Different sites in small intestine absorb
different types of amino acids.
Amino acids of the same type compete for
absorption.
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A large intake of a single amino acid may limit
absorption of other amino acid of its general type.
In the bloodstream, amino acids can be used
by any cell in the body.
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Functions of proteins
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Growth & maintenance of body tissues.
Enzymes facilitate needed chemical
reactions
Hormones – regulate body processes. Some
hormones are proteins and some are made
from amino acids.
Antibodies – proteins form the immune
system molecules that fight disease.
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Function of proteins continued
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Fluid & electrolyte balance.
Acid-base balance.
Energy.
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Function of proteins continued
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Transportation.
Blood clotting.
Structural components.
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Protein Quality
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High quality proteins contain all the essential
amino acids. These are obtained from meat,
fish poultry, milk, cheese, eggs, milk and
many soybean products.
Plant proteins are diverse in amino acid
content and offer less protein.
Combining plant foods that together contain
all the essential amino acids is considered
complementary.
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Complementary proteins
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Need not be eaten together as long as
they are eaten in the same day and the
diet supplies adequate energy and a
total protein from other sources.
Vegetarians need to eat a variety of
grains, legumes, seeds, nuts, and
vegetables.
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Recommended
Intakes
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RDA
 0.8 g/kg/day
 10% - 35% of energy intake
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Vegetarianism
Main Types:
Vegan: Includes foods only from plant
sources, vegetables, grains, legumes,
fruits,nuts.
Lacto-ovo: includes plant foods, dairy
foods and eggs. No flesh or fish.
Lacto-vegetarian includes plant foods and
dairy foods. No eggs, flesh or fish.
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Vegetarian diet in general
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Less fat and protein
More complex carbohydrate from whole
grains, fruits and vegetables
More fibre
Vegetarians need to select calcium-rich foods.
Vitamin D supplements may be required.
Vegans must rely on vitamin B12frotified
sources.
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Benefits of vegetarian diet in
general
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Less obesity from fewer calories.
Lower blood pressure.
Less heart disease – less saturated fat, high
intake of phytochemicals and antioxidants
from fruits & vegetables.
Less constipation and diverticular disease –
due to high fibre.
Less cancer – (reasons similar to heart
disease).
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Vegetarian diets throughout the
lifespan
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Diet planning during pregnancy, lactation,
infancy, childhood and adolescence must
provide for the increases in energy and
nutrients needed.
Fortified foods or supplements for Vitamin D,
Calcium and Vitamin B12 may be required.
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