Download Digestion and Nutrition

Human Biology (BIOL 104)
Talk Five:
Digestion and Nutrition
Chapter 11
So, what do we usually eat?
• Carbohydrates: To give us ENERGY! We need energy for heat,
movement, and chemical reactions in our bodies.
• Proteins: Essential amino acid’s. Our body can’t make them; they must
come from foods we eat.
•
Meat, milk, and eggs contain all the essential amino acids we need
• Fats: Energy! We can use it or store it. Fat contains more energy than
carbohydrates. 1 gram of Fat = 2x the energy in 1 gram of Carbs.
•
Used for Cell Membranes and Heat Insulation
Carbohydrates
Protein
Lipids
Copyright ©The McGraw-Hill Companies; used with permission
So, how do we digest food?
• In the human digestive system, the process of digestion has many
stages, the first of which starts in the mouth (oral cavity).
• Digestion involves the breakdown of food into smaller and smaller
components which can be absorbed and assimilated into the body.
• The secretion of saliva helps to produce a bolus which can be
swallowed in the esophagus to pass down into the stomach.
• This initially results in the production of chyme which when fully
broken down in the small intestine is absorbed into the blood.
• Most of the digestion of food takes place in the small intestine.
Water and some minerals are reabsorbed back into the blood,
in the colon of the large intestine.
• The waste products of digestion are defecated from the anus via
the rectum.
• 1: Mechanical processing and
motility
– Teeth, the tongue, and various
muscle layers start the process
and send food on its journey
• 2: Secretion
– Release of enzymes & chemicals
for digestion and absorption
• 3: Digestion
– Chemical breakdown of food –
small molecules absorbed
• 4: Absorption
– Nutrients move into the blood
• 5: Elimination
– Undigested and unabsorbed
residues excreted
Digestion occurs in
5 stages
The first step- Chewing and
swallowing
• Types
– Mechanical (physical)
• Chew
• Tear
• Grind
• Mash
• Mix
– Chemical
• Enzymatic reactions
to improve digestion
of
– Carbohydrates
– Proteins
– Lipids
http://www.daviddarling.info/encyclopedia/T/teeth
The first step- Chewing and swallowing
•
Teeth mechanically break down food
into small pieces.
•
Tongue mixes food with saliva
•
Saliva contains amylase
•
Mucus
•
Buffers
– helps break down starch.
– protects soft lining of digestive system
– lubricates food for easier swallowing
•
neutralizes acid to prevent tooth decay
•
Anti-bacterial chemicals
•
Epiglottis is a flap-like structure at the
back of the throat that closes over the
trachea preventing food from entering
it.
– kill bacteria that enter mouth with food
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From the wikimedia free licensed media file repository
Digestive Glands
• Groups of specialized
secretory cells.
• Found in the lining of the
alimentary canal or
accessory organs.
Taste Buds
• As the food particles dissolve
in the saliva they penetrate
the cells of the taste buds
located on the tongue and
cheeks.
• Humans can differentiate
between
• sweet
• sour
• salty
• bitter
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• Approximately 10” long
• Functions include:
– Secrete mucus
– Moves food from the throat to
the stomach using muscle
movement called peristalsis
The Esophagus
• A good way to describe peristalsis is
an ocean wave moving through the
muscle.
– Has no role in chemical digestion
– all it does is bring food (BOLUS)
to stomach.
• Sphincters – ring of muscle that
encircle tubes.
– Contraction closes tubes
– Keeps acid in stomach – usually!
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The Stomach- Digestion and Storage
• The stomach acts as a
temporary storage site for
food.
• Food usually spends about 4
hours in the stomach.
• It has ridges which allow it
to expand to store about 1.5
litres of food.
• The stomach is also the site
of initial protein digestion.
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The StomachDigestion and Storage
• Millions of cells lining the stomach
secrete various fluids known
collectively as gastric fluids.
• Gastric fluid consists of mucus,
hydrochloric acid, pepsinogens and
other substances.
• Mucus coats and protects the
lining of the stomach.
• Hydrochloric acid kills any harmful
substances that have been
ingested and it also converts
pepsinogen into pepsin.
• Pepsin is a protein digesting
enzyme that breaks large protein
chains into smaller chains.
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The Stomach- Digestion and Storage
• Movement of food into and out of
the stomach is controlled by
circular muscles known as
sphincters.
• One at the top of the stomach
allows food from the esophagus to
enter and prevents food from going
back up into the esophagus.
• Another located at the bottom
slowly releases partially digested
food into the small intestine.
• Alcohol and some water are
absorbed here – food is not.
• The partially digested food is
called chyme.
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The Intestines
• The intestines are named
for their diameter, not
length.
• The small intestine is up
to 7 m in length but only
2.5 cm in diameter.
• The large intestine (also
known as the Colon) is only
1.5 m in length but 7.6 cm
in diameter.
The small intestine
• Where much of the digestion and
absorption of food takes place.
•
It receives bile juice and
pancreatic juice through the
hepato-pancreatic duct,
controlled by a sphincter
• The small intestine is where most
chemical digestion takes place.
• Most of the digestive enzymes
that act in the small intestine are
secreted by the pancreas and
enter the small intestine via the
pancreatic duct
•
Approx 20 feet in length
– First 25 cm – Duodenum
•
A duct brings Bile (from Liver and
Gallbladder)
– emulsifies fat – disperses in water
•
A duct brings Pancreatic Juice from
Pancreas. Contains
– NaCHO3 – neutralizes chyme
– enzymes to complete food digestion.
•
The small intestine contains Villi –
absorb nutrients.
•
Sugars & amino acids enter blood
capillaries
•
Glycerol and fatty acids enter lymph
nodules
•
Almost 90% of our daily fluid intake
is absorbed in the small intestine.
The small intestine
Small Intestine
• Nutrients from the food pass
into the bloodstream through
the small intestine walls.
• Absorbs:
– 80% ingested water
– Vitamins
– Minerals
– Carbohydrates
– Proteins
– Lipids
• Secretes digestive enzymes
Segmentation in the Small Intestine
• Unlike peristalsis, which
predominates in the esophagus,
segmentation contractions
occur in the large intestine and
small intestine, while
predominating in the latter
• When the contractions of the
intestinal wall move chyme in
both directions to allow mixing
with the secretions of the
intestines.
The small intestine - Villi
• Increases surface area of small
intestine
• Each villus contains a capillary
network along with a lacteal.
• The lacteal is a vessel of the
lymphatic system.
• End products of protein and
carbohydrate digestion enter
the capillary network.
• End products of fat digestion
are absorbed into the lacteal.
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The small intestine - Villi
• The Hepatic Portal Vein takes all absorbed nutrients
(except large fat molecules) from villi to the liver for
further processing and storage.
•
4-1/2 feet long
– Absorbs water, salts and some
vitamins
The large Intestine
• Stores indigestible material for
defecation
• Contains the:
– Cecum (blind end of ascending
colon).
– Appendix located here.
• Colon- Ascending, Transverse,
Descending and Sigmoid.
• The sigmoid Colon enters Rectum
(last 20 cm of large intestine, where
it opens at the Anus.
• Feces: ¾ water and ¼ solid
Copyright ©The McGraw-Hill Companies;
used with permission
• Functions
The large Intestine
• Bacterial digestion
• Ferment carbohydrates
• Protein breakdown
•
•
Absorbs more water
Concentrate wastes
• Solid materials pass through the
large intestine.
• These are undigestible solids
(fibers).
• Water is absorbed.
• Vitamins K and B are reabsorbed
with the water.
• Rectum- solid wastes exit the body.
Copyright ©The McGraw-Hill Companies;
used with permission
The large Intestine –
You’ve got company!
• Living in the large
intestine is a community
of helpful bacteria
– Escherichia coli (E. coli)
• produce vitamins
– vitamin K; B vitamins
• generate gases
– by-product of bacterial
metabolism
– methane, hydrogen sulfide
The Accessory Organs
• The Liver:
• 100,000 lobules monitor and
clean blood, produce bile for
gallbladder.
• Detoxify blood, store iron,
vitamins A, D, E and K.
•
Helps regulate blood sugar
(glycogen, glycerol, Amino
acids), destroys old blood
cells.
• Helps regulate cholesterol
(bile salts).
•
Makes urea which is worked
on by kidneys
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Companies; used with permission
The Accessory Organs
• The Gall Bladder:
•
Pouch structure located near the
liver which concentrates and
stores bile
•
Bile duct – a long tube that carries
BILE.
•
The top half of the common bile
duct is associated with the liver.
•
The bottom half of the common
bile duct is associated with the
pancreas, through which it passes
on its way to the intestine.
•
Bile emulsifies lipids (physically
breaks apart FATS)
Copyright ©The McGraw-Hill
Companies; used with permission
The Accessory Organs
• The pancreas:
• An organ which secretes both
digestive enzymes (exocrine)
and hormones (endocrine)
• Pancreatic juice digests all
major nutrient types.
• Exocrine pancreas produces
NaHCO3, amylase (starch),
trypsin (protein) and lipase
(fat).
• Endocrine pancreas produces
insulin and glucagon.
Copyright ©The McGraw-Hill
Companies; used with permission
Human Nutrition
• The provision to obtain the
essential nutrients necessary
to support life and health.
• In general, people can survive
for two to eight weeks without
food, depending on stored
body fat and muscle mass.
• Poor nutrition is a chronic
problem linked to poverty,
poor nutrition understanding
and practices, and deficient
sanitation and food security.
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used with permission
Human Nutrition
• Malnutrition globally provides
many challenges to individuals
and societies.
• Lack of proper nutrition
contributes to worse class
performance, lower test scores,
and eventually less successful
students and a less productive
and competitive economy.
• Malnutrition and its
consequences are immense
contributors to deaths and
disabilities worldwide.
• Promoting good nutrition helps
children grow, promotes human
development and advances
economic growth and eradication
of poverty.
Copyright ©The McGraw-Hill Companies;
used with permission
So, what do we usually eat?
• Carbohydrates: To give us ENERGY! We need energy for heat,
movement, and chemical reactions in our bodies.
• Proteins: Essential amino acid’s. Our body can’t make them; they must
come from foods we eat.
•
Meat, milk, and eggs contain all the essential amino acids we need
• Fats: Energy! We can use it or store it. Fat contains more energy than
carbohydrates. 1 gram of Fat = 2x the energy in 1 gram of Carbs.
•
Used for Cell Membranes and Heat Insulation
Carbohydrates
Protein
Lipids
Copyright ©The McGraw-Hill Companies; used with permission
Eating a balanced diet
• What happens if a human’s diet is missing an
essential nutrient?
– deficiency diseases
•
•
•
•
scurvy — vitamin C (collagen production)
rickets — vitamin D (calcium absorption)
blindness — vitamin A (retinol production)
anemia — vitamin B12 (energy production)
Vegetarian diets
• Need to make sure you get
enough protein
• 20 amino acids to make protein
– 12 amino acids humans can produce
– 8 we have to eat = “essential amino acids”
• Grains (like corn) have 6 amino acids
(orange box)
– missing 2
•
Beans (like soybean & red beans)
have 6 amino acids (green box)
– missing different 2
• mix beans & grains for complete group
of amino acids
–
–
–
–
rice & beans
taco/tortilla & beans
tofu & rice
peanut butter & bread
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used with permission
Vitamins
• Organic compounds needed by the body in small, but
essential amounts
• Cannot be synthesized by the body in sufficient amounts
• Function in a variety of ways in metabolic reactions
• Thirteen known vitamins
• Water-Soluble Vitamins Versus Fat-soluble Vitamins
Water-Soluble Vitamins
C (ascorbic acid)
B1 (thiamin)
B2 (riboflavin)
Niacin
Pantothenic acid
Biotin
B12 (cyanocobalamin)
Folic acid
B6 (pyridoxine)
Fat-soluble Vitamins
Copyright ©The McGraw-Hill Companies;
used with permission
Vitamins
•
•
•
•
•
•
•
•
•
Vit A- Antioxidant: healthy eyes, hair, bones
Vit D – Steroid: bones and teeth
Vit E – Antioxidant: healthy unsaturated fats
Vit K – Clotting blood
Vit C – Antioxidant: Capillaries, bones teeth
Vit B1 – coenzyme for cellular respiration
Vit B6 – coenzyme for hormones and hemoglobin
Vit B12 – coenzyme for synthesis of nucleic acid
Biotin – coenzyme for metabolism of ammino
acids and fatty acids
Minerals
• Essential inorganic elements
• Involved in a variety of
metabolic processes
• Major minerals versus trace
minerals
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Essential dietary minerals
• Chlorine: as chloride ions along with Sodium
•
Magnesium: required for processing ATP and related reactions
– builds bone, causes strong peristalsis, increases flexibility, increases alkalinity.
• Phosphorus: required component of bones; essential for energy
processing Approximately 80% is found in inorganic portion of bones
and teeth. Phosphorus is a component of every cell, as well as
important metabolites, including DNA, RNA, ATP, and phospholipids.
– Also important in pH regulation. Food sources include cheese, egg yolk, milk,
meat, fish, poultry, whole-grain cereals, and many others.
• Potassium: a very common electrolyte (heart and nerve health). With
sodium, potassium is involved in maintaining normal water balance,
osmotic equilibrium, and acid-base balance.
– In addition to calcium, it is important in the regulation of neuromuscular
activity. Food sources include bananas, avocados, vegetables, potatoes,
legumes, and mushrooms.
Trace minerals
• Cobalt required for biosynthesis of vitamin B12 family of coenzymes
• Copper required component of many redox enzymes, including
cytochrome c oxidase
• Chromium required for sugar metabolism
• Iodine required for important organs as breast, stomach, salivary
glands, thymus etc.
• Iron required for many enzymes, and for hemoglobin and some other
proteins
• Manganese required for the processing of oxygen
• Nickel present in urease
• Zinc required for several enzymes such as carboxypeptidase, liver
alcohol dehydrogenase, carbonic anhydrase