Download Chapter 7 - Heritage Christian School

Chapter 7. Digestive System
Aside:
The Systemic Hierarchy
• Cells, similar in type and function are organized into tissues
• Several tissue types are organized into organs
• Several organs (types) are organized into systems such as
nervous, circulatory, respiratory, digestive, lymphatic et al.
7.1 Food Utilization
The digestive system is responsible for the breakdown of food items
into their component parts to make them available to the body for
utilization. Nutrients cannot be used until they are transformed into
useable ‘pieces’ to provide your body with the necessary raw material
to
• build new cells and tissues
• repair damaged cells and tissues
• provide energy for movement, etc.
The Mouth
Function:
• break down large chunks of food into smaller, swallow-able
pieces and to increase surface area of food; WHY?
• pre-mix with a lubricant for easy swallowing and initial
digestion.
• positioning of food for swallowing
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How accomplished:
• Teeth – to tear, cut, crush and grind food into smaller particles.
(a.k.a. - physical digestion)
• Tongue – to taste (avoid baddies); to move food into favourable
position for swallowing; to mix food with saliva.
• Salivary glands – to produce saliva (which moistens food for
easy passage to stomach and to add digestive enzymes to
begin breaking down process, especially of complex
carbohydrates which are broken down into glucose) (a.k.a. –
chemical digestion)
The Esophagus
Function:
• Transfer of food to stomach through tube (esophagus)
• Protect respiratory system from foreign particles food
How accomplished:
• Peristalstis (-ic contractions) – this is a wave of relaxation and
contraction of the muscles that form rings around the
esophagus. This causes food to move, even f you are hanging
upside down.
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• Epiglottis – a flap which covers the trachea during swallowing.
The epiglottis is marked by the number 2.
Notice how it is in the closed position to keep
Food from going into the lungs.
Demo: Peristalsis
Review 7.1(?)
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7.2 The Stomach
Function:
• physically digestion - mix and churn chime(food) with digestive
enzymes.
• chemical digestion – produce chemicals which will further break
down chime.
• storage – provide storage while chime is broken down into
proper consistency for next phase consistency
How accomplished:
• Contraction and relaxation of stomach walls
• Production of:
Pepsin – breaks down proteins
Hydrochloric acid – assists in protein breakdown (pepsin
works better in presence of acid)
Mucus – protects stomach lining from pepsin + HCl.
• Pyloric sphincter – muscle on the exit end of stomach, only
opens when chime reaches a certain acidity.
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Aside: Heartburn, acid reflux and the cardiac sphincter
In the above diagram, the stomach acid has seeped
back through the opening at the top of the stomach
(called the cardiac sphincter). It has eaten away at
esophagus and has caused scarring. This causes a
burning sensation, but is actually quite dangerous
because it can lead to cancer.
Review 7.2 (?)
7.3 The Intestines and related organs
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The above diagram shows how all of the digestive glands and the
tubes carrying the chemicals they produce are located right under the
stomach. As a matter of fact, once the food leaves the stomach all
these additional chemicals are added to the mix within the first 25 cm
of the small intestine. This gives time for each chemical to do its job
in further breaking down the food into useable molecules as the food
travels down the tube.
What chemical are used?
Organ
Chemical
What it does
Hydrochloric acid
Kills most bacteria
Increases activity of pepsin
Pepsin
Breaks down protein
Mucus
Protects stomach walls from being
attacked by acid and pepsin and it
Lubricates the food.
Mucus
Lubricates food
Protection from the hydrochloric acid
Enzymes
Break down food
Enzymes
Break down food
Pancreas
Neutralizer
To neutralize hydrochloric acid so it
won't warm the intestine.
Bile
Breaks down fats
Liver
(but it is stored in the gall
bladder)
Stomach
Small
intestine
The last 3.75 to 5.75 meters of the small intestine is dedicated to
absorbing these molecules.
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How nutrients are absorbed from the intestine:
The inner walls of the intestines are covered with small finger-like
projections called villi. These villi greatly increase the surface area of
the intestine so much more contact can be made with the broken
down food (and hence, increase how fast absorption takes place).
Below is a diagram of a single villus.
See class room overhead diagrams.
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