Lesson 2: The HumanAlimentary Canal
The Human Alimentary Canal
… includes theentire tube fromthe mouth allthe way to theanus
Human Alimentary Canal
Mouth
Pharynx
Esophagus
Stomach
Small intestine
Large intestine
Rectum
Anus
Accessory Organs
Salivary glands
Secrete saliva
Liver
Secretes bile
Gallbladder
Stores and concentrates bile
Pancreas
Secretes digestive enzymes
…Organs that are involved
in digestion but that food
does not pass directly
through
Types of Digestion
Physical Digestion:
Food is physically broken down
Example – Teeth chew food
Chemical Digestion:
Food is broken down by acids, bases orenzymes in the human alimentarycanal
Example – HCl in stomach
Mouth (Oral Cavity)
Site of Ingestion
Salivary Amylasebreakscarbohydrates intosimpler sugars
???
What type of digestion takes
place in the mouth?
Physical?
Chemical?
Saliva
Produced by salivary glands at backof mouth and under tongue
Saliva includes
Salivary amylase (enzyme)
Bicarbonate (buffer)
Mucins (bind food into bolus)
Water
Salivary Glands
Accessory Organfound at back ofmouth and undertongue
Releases salivaryamylase into themouth
Swallowing
Tongue forces food into pharynx
Epiglottis closes off the trachea to preventchoking (breathing temporarily stops)
Bolus moves into oesophagus
Once chewed, food is
called a bolus
Pharynx (The throat)
No physical orchemical digestionoccurs here
Links in with therespiratory system
Esophagus
Function: to transportfood from mouth to thestomach
Food considered a BOLUSat this stage
wet ball of chewed food
How does the bolus
get from the mouth
to the stomach?
Peristalsis
Peristalsis:
waves of muscularcontraction that movefood along the humanalimentary canal
Stomach
Muscular sac-like organ
Lined with a thickprotective mucus
The stomach liningsecretes Gastric Juicesthat contain:
Hydrochloric Acid
Pepsinogen (inactive form ofpepsin)
Mucus
Discuss the types of
digestion occurring in the
stomach…
Chemical Digestion in the Stomach
Pepsinogen is activated by the acidHCl in the stomach and becomespepsin
Pepsin chemically digests proteininto amino acids
Physical Digestion
Food is mixed andmoved by waves ofstomach contractions(peristalsis)
Becomes Chyme –thick liquid made ofpartially digested foodand stomach juices
Small Intestine
Over 6.5 meters long
Duodenum
First 10 cm of small intestine
What happens in the small intestine?
1.Pancreatic juicesneutralise acidic chyme
2.Digestion is completed induodenum
Liver secretes bile, viagallbladder, whichemulsifies fats
Pancreas secretes variousenzymes which completethe breakdown of protein,carbs and fats
3.Absorption takes place ofdigested products intobloodstream
LIVER
produces bile whichbreaks up the largerfats (emulsification)
GALLBLADDER
stores the bile untilneeded
Large Intestine
Function: to absorb water into blood
Also the site of vitamin K production
End section: rectum & anus
Stages of Digestion
1.Ingestion – the process by which foodis taken into the body
2.Digestion - the process of breaking upcomplex substances into simplersubstances.
3.Absorption – the process by whichdigested food diffuses into blood
4.Assimilation - the conversion orincorporation of absorbed simple foodinto the complex substances that areuseful in our bodies
5.Egestion - the elimination of undigestedfood (faeces) from the body
YOU DECIDE!
Look at your diagram of the DigestiveSystem.
Where does each stage of digestion takeplace?
Hint: Some stages take place at multiplelocations…
Warning:Do not confuseEgestion with Excretion
Egestion – removal of undigested food(faeces) via the anus
Excretion – removal of waste products ofmetabolism (like urine, carbon dioxide,sweat)
