Food must be broken down into nutrients that can be absorbed
into the blood and carried to our body The collection of organs
that carry out digestion is the digestive system
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1. Ingestion the taking in of nutrients 2. Digestion the
physical and chemical breakdown of complex food molecules into
smaller molecules 3. Absorption the transfer of digested nutrients
from the digestive system to the bloodstream 4. Egestion the
removal of waste food materials from the body
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Human digestive system is complete Two openings Specialized
regions GI tract is approximately 9 meters long.
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Digestion begins! Physical digestion by teeth Teeth related to
diet! Ex. Carnivores, need canine teeth to grab and kill prey
Presence, sight, smell of food triggers salivary glands to secrete
saliva
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Contains enzymes Dissolves food particles, letting you taste
your food Contains mucus Lubricant and aids in swallowing Contains
water Which moistens the food into a ball, or bolus
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Long, muscular tube that undergoes rhythmic, wavelike
contractions of smooth muscles Peristalsis Ensures the movement of
food down the esophagus into the stomach in approximately 8 seconds
Its not actually all about gravity
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J-shaped, muscular organ Can store up to 2L of food Proteins
are partly digested Lipids and carbohydrates are NOT digested at
all Movement into and out of stomach is controlled by circular
muscles called sphincters Gastroesophageal Pyloric
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Gastroesophageal sphincter does not close completely Acid from
stomach can enter the esophagus causing a burning sensation in the
lower throat Common causes: Overfilled stomach Smoking
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Stomach acid is usually strong enough to kill most bacteria
Helicobacter pylori is able to survive Prevent mucus producing
cells from producing enough mucus to protect the stomach lining
Lining becomes exposed to acid, causes an open sore, called an
ulcer.
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Long tube that is only about 2.5cm in diameter and can be up to
7 meters long Most digestion and absorption of nutrients takes
place in the small intestine Lipids and carbohydrates, as well as
any remaining proteins are digested in the small intestine
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Duodenum: first 25 cm, where most enzymes are added and
digestion begins Jejunum: digestion continues and some nutrients
are absorbed Ileum: Majority of nutrients are absorbed
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Inner surface of the small intestines is adapted to provide the
maximum surface area for efficient nutrient absorption Villi: the
ridges and small finger-like projections that increase the surface
area tenfold Microvilli: Even smaller microscopic projections from
the cell membrane of villi epithelial cells
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Long flat nestled between the stomach and the duodenum. Dual
role Secretes enzymes for digestion and secretes hormones that
regulate the absorption and storage of glucose
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Liver is the largest internal organ In terms of digestion it is
considered a gland because it produces and secretes bile Bile: a
substance that helps break down fats This increases the surface
area for the lipases to act on.
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Liver is also involved with the removal and breakdown of
toxins, such as alcohol.
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Once proteins, carbohydrates, and lipids are digested they can
be absorbed in the jejunum and ileum; along with vitamins, minerals
and water Structure of the small intestine is very important for
absorption of nutrients
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Most absorption has been completed before the large intestine
Cellulose, which cannot be broken down by humans Approximately 20L
of fluids pass through the large intestine Most of this is absorbed
back into the body Vitamins B and K, sodium and chloride are also
absorbed
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More than 500 species of bacteria normally inhabit the large
intestine Most common is E Coli. Mutually beneficial relationship
They get food, we get essential substances such as Vitamin K and
some B vitamins
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Removal of waste food materials Absorption of water in the
large intestine Changes liquid material to soft solid called feces
Defecation reflex caused by the nerves in the wall of the
intestines The anus is surrounded by two sphincter muscles: the
internal smooth and external skeletal sphincter.