Download Functions of alimentary canal, ingestion, digestion, absorption

Lesson 2: The Human
Alimentary Canal
The Human Alimentary Canal
… includes the
entire tube from
the mouth all
the way to the
anus
Human Alimentary Canal
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Mouth
Pharynx
Esophagus
Stomach
Small intestine
Large intestine
Rectum
Anus
Accessory Organs
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Salivary glands
…Organs that are involved
in digestion but that food
 Secrete saliva
does not pass directly
Liver
through
 Secretes bile
Gallbladder
 Stores and concentrates bile
Pancreas
 Secretes digestive enzymes
Types of Digestion
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Physical Digestion:
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Food is physically broken down
Example – Teeth chew food
Chemical Digestion:
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Food is broken down by acids, bases or
enzymes in the human alimentary
canal
Example – HCl in stomach
Mouth (Oral Cavity)
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Site of Ingestion
Salivary Amylase
breaks
carbohydrates into
simpler sugars
???
What type of digestion takes
place in the mouth?
Physical?
Chemical?
Saliva
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Produced by salivary glands at back
of mouth and under tongue
Saliva includes
 Salivary amylase (enzyme)
 Bicarbonate (buffer)
 Mucins (bind food into bolus)
 Water
Salivary Glands
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Accessory Organ
found at back of
mouth and under
tongue
Releases salivary
amylase into the
mouth
Swallowing
Once chewed, food is
called a bolus
Tongue forces food into pharynx
Epiglottis closes off the trachea to prevent
choking (breathing temporarily stops)
Bolus moves into oesophagus
Pharynx (The throat)
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No physical or
chemical digestion
occurs here
Links in with the
respiratory system
Esophagus
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Function: to transport
food from mouth to the
stomach
Food considered a BOLUS
at this stage

wet ball of chewed food
How does the bolus
get from the mouth
to the stomach?
Peristalsis
Peristalsis:
waves of muscular
contraction that move
food along the human
alimentary canal
Discuss the types of
digestion occurring in the
stomach…
Stomach
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Muscular sac-like organ
Lined with a thick
protective mucus
The stomach lining
secretes Gastric Juices
that contain:
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Hydrochloric Acid
Pepsinogen (inactive form of
pepsin)
Mucus
Chemical Digestion in the Stomach
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Pepsinogen is activated by the acid
HCl in the stomach and becomes
pepsin
Pepsin chemically digests protein
into amino acids
Physical Digestion

Food is mixed and
moved by waves of
stomach contractions
(peristalsis)
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Becomes Chyme –
thick liquid made of
partially digested food
and stomach juices
Small Intestine
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Over 6.5 meters long
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Duodenum
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First 10 cm of small intestine
What happens in the small intestine?
1.
2.
Pancreatic juices
neutralise acidic chyme
Digestion is completed in
duodenum
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3.
Liver secretes bile, via
gallbladder, which
emulsifies fats
Pancreas secretes various
enzymes which complete
the breakdown of protein,
carbs and fats
Absorption takes place of
digested products into
bloodstream
LIVER

produces bile which
breaks up the larger
fats (emulsification)
GALLBLADDER

stores the bile until
needed
Large Intestine
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Function: to absorb water into blood
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Also the site of vitamin K production
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End section: rectum & anus
Stages of Digestion
1.
2.
3.
4.
5.
Ingestion – the process by which food
YOU
DECIDE!
is taken into the
body
Look at your diagram of the Digestive
Digestion - the process
System. of breaking up
complex substances into simpler
Where does each stage of digestion take
substances.
place?
Absorption – the process by which
digested
foodstages
diffuses
Hint: Some
takeinto
placeblood
at multiple
Assimilation - locations…
the conversion or
incorporation of absorbed simple food
into the complex substances that are
useful in our bodies
Egestion - the elimination of undigested
food (faeces) from the body
Warning:
Do not confuse
Egestion with Excretion
Egestion – removal of undigested food
(faeces) via the anus
Excretion – removal of waste products of
metabolism (like urine, carbon dioxide,
sweat)