The Digestive System
Review
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Nutrition: the process by which organisms
obtain food and break it down so it can be
used for metabolism
The 6 Nutrients
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Proteins:
are used for growth, repair and general
maintenance
found in meats, fish, milk etc.
the end products of protein digestion are
amino acids
The 6 Nutrients
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Carbohydrates:
-Include sugars and starches
-provide energy
the end products of starch digestion are
simple sugars (glucose)
The 6 Nutrients
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Lipids include fats and oils
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Used as stored energy
The end products of lipid digestion are fatty
acids and glycerol
The 6 Nutrients
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Vitamins:
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Help to maintain health
Examples: Vitamins C, A, B etc.
The 6 Nutrients
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Minerals
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Chemicals needed for normal functioning
Examples:
calcium
iron
potassium
The 6 Nutrients
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Water
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Needed for most biological functions
Fiber
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Indigestible material , such as cellulose ,
found in the cells walls of plants
Fiber provides roughage which helps to
keep food moving through the digestive
system
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Food is digested chemically ( by enzymes)
or mechanically
Mechanical digestion ( breaking the food
into smaller pieces) increases the surface
area for chemical digestion (ex: chewing)
The Digestive System
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The human digestive system is made of a
long tube called the alimentary canal,
through which the food passes
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There are also accessory organs that
produce substances that help with
digestion (salivary glands, liver, pancreas
and gall bladder)
Food does not pass through these organs
The Mouth
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The mouth is where food is ingested
(taken in)
Chewing (mechanical digestion) breaks
the food into smaller pieces
The salivary glands produce an enzyme
called salivary amylase which begins the
digestion of starches
Pharynx
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From the mouth the food passes to the
pharynx (back of the throat), with help
from the tongue
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Esophagus
From the pharynx, food passes into the
esophagus
The esophagus carries the food to the
stomach
No digestion occurs in the esophagus
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Food is moved through the esophagus by
peristalsis which is the waves of
contractions and relaxation by the walls of
the digestive tract to push the food along
Epiglottis
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The epiglottis is a flap of tissue that helps
prevent food from “going down the wrong
pipe” or to the trachea when swallowing
Stomach
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The stomach is a thick walled muscular
organ
Food is broken down mechanically by the
churning of the muscular walls
Stomach
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Chemical digestion occurs with the help of
gastric juice which is produced in glands
lining the walls of the stomach
Gastric juice contains hydrochloric acid
and the enzyme pepsin
The pH of the stomach is very acidic
Pepsin helps to start the digestion of
proteins
Stomach
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Glands in the stomach also produce mucus
which helps to protect the stomach from
the acidity of the gastric juice
The soupy mixture that is produced is
called chyme
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Small Intestines
The chyme now travels to the small
intestine which is a long coiled tube(about
6.5 meters long and 2.5 cm in diameter)
MOST CHEMICAL DIGESTION TAKES
PLACE IN THE SMALL INTESTINE
Small Intestine
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The pH of the small intestine is more
alkaline
This is due to the secretions from the
pancreas, gall bladder and glands that line
the small intestine
These secretions contains the enzymes
necessary to complete the chemical
digestion of the food
Small Intestine
The small intestine is also the site of
absorption.
The end products of digestion, vitamins,
minerals and other substances move from
the digestive system to the circulatory
system.
n
Small Intestine
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The small intestine have millions of
microscopic fingerlike projections called
villi.
Villi increase the surface area for
absorption
Large Intestine
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Materials that were not digested or
absorbed move to the large intestine
(1.5M long by 6cm in diameter)
Large Intestine
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The main job of the large intestine is the
reabsorption of water
No digestion occurs here
Elimination or the removal of undigested
material (feces) occurs from the large
intestine
Large Intestine
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The feces are stored in the rectum (the
last part of the large intestine)
Accessory Organs
The Pancreas
The pancreas is an accessory organ that
produces pancreatic juice that is secreted
into the small intestine through a duct
Enzymes that are in pancreatic juice include
amylase, protease, and lipase to help break
down starch, proteins and lipids
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Liver
One of the many jobs of the liver is to
produce bile.
Bile helps to emulsify fat (break them into
tiny droplets)
Emulsification is a mechanical process that
helps increase the surface area for
chemical digestion of the fats
Gall Bladder
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The function of the gall bladder is to store
the bile that is produced in the liver
The bile travels from the gall bladder to
the small intestine through the bile duct
Malfunctions
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An ulcer is a painful condition that occurs
when the lining of the stomach is eroded
by the acid in the stomach and can be
caused by bacteria
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Diarrhea occurs when not enough water is
absorbed by the large intestine
Constipation occurs when
too much water is removed
by the large intestine
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Gall stones are hardened cholesterol
deposits that occur in the gall bladder or
bile ducts, causing a lot of pain