Presentation for teaching human digestion to middle schoolers

1. Digestion In Humans

2. Feeding
• All living organisms, except for plants and other
photosynthetic organisms (e.g. green algae), are
heterotrophs.
• Humans get nutrition through a type of heterotrophic
feeding called holozoic feeding.
• Holozoic feeding is the kind of feeding where an
organism breaks down complex food (e.g. starch) and
then absorbs the simple, broken down form (e.g.
glucose).
AeFA Foundation - Digestion in Humans
Fungus,
e.g. mould
Contains
starch

3. Digestion in Humans
• Digestion is the breakdown of food substances by the body
into smaller, simpler, more soluble forms for easy absorption.
• Digestion is both a physical (or mechanical) and chemical
process.
• The chemical part of digestion is carried out with the help of
biological catalysts known as enzymes.
• Enzymes do not take part in the chemical process to break
food down, but they greatly speed up the process.
AeFA Foundation - Digestion in Humans

4. The Human Digestive System
• The human digestive system is made up of the alimentary
canal and other organs attached to it.
• The alimentary canal is a muscular tube that begins from the
mouth and goes all the way to the anus.
salivary glands
oesophagus (gullet)
stomach
colon
duodenum
ileum
{
small
intestine
gall bladder
liver
mouth
(buccal cavity)
rectum
large
intestine
}
pancreas
anus
appendix
AeFA Foundation - Digestion in Humans

5. Functions of Parts of the Digestive System
Mouth (buccal cavity) and Oesophagus
• Food is ingested
• Food is chewed into smaller pieces
• Saliva moistens and soften food for easy
swallowing.
• Saliva also partially breaks down some
starch into maltose using the enzyme
amylase (or ptyalin). This happens in a
basic medium of saliva
• The tongue rolls the food-saliva mixture
into a small ball for easy swallowing.
• The oesophagus is a muscular tube for
the passage of swallowed food. Food
moves through the oesophagus by a
wavy muscular motion known as
peristalsis.
Salivary glands
AeFA Foundation - Digestion in Humans

6. Functions of Parts of the Digestive System
stomach
• Swallowed food is mixed with gastric
juice secreted by the stomach, and is
churned into one consistent “soup”. This
“soup” is referred to as chyme.
• This is where protein digestion begins
Gastric juice
Hydrochloric acid
• Stops the action of ptyalin
• Provides acidic medium for
the action of proteases.
• Helps kill some germs in food
Digestive enzymes
• Proteases, which break down proteins into peptide
chains, e.g. pepsin and rennin.
AeFA Foundation - Digestion in Humans
Duodenum
• First part of the small intestine
• Where fat and oil digestion
begins
• Chyme from the stomach
passes through here to the
ileum, for final digestion
Liver
• The main function of the liver in digestion
is to produce bile, which helps in fat
digestion in the duodenum
gall bladder
• Stores bile produced in the liver, and
discharges it into the duodenum for fat
digestion
pancreas
• Secretes pancreatic juice, which contains a
variety of digestive enzymes.
• Also provides basic medium to make the
acidic chyme more basic.

7. Functions of Parts of the Digestive System
AeFA Foundation - Digestion in Humans
ileum
• The longest part of the small intestine, i.e. the
small intestine starts with the duodenum and
ends with the ileum.
• Final digestion of all the food types happens
here.
• Carbohydrates become glucose
• Proteins become amino acids
• Fats and oils (lipids) become fatty acids
and glycerol.
• These simple food substances are absorbed
into the body via diffusion into the blood
vessels.
Colon
• Biggest part of the
large intestine
• Absorbs water from undigested food to form faeces, which is
then egested (removed) from the body via the anus.
• Faeces is stored temporarily in the rectum before it is egested.
rectum

8. Digesting Carbohydrates (Sugars)
In humans carbohydrates, such as starch and
sucrose (table sugar), are broken down into
glucose, i.e. the end-product of carbohydrate
digestion.
AeFA Foundation - Digestion in Humans
• Food is chewed
• Saliva softens the food for easy swallowing
• Salivary amylase turns some starch into maltose (a
simpler sugar). This is the beginning of carbohydrate
digestion.
• Tongue rolls food into a bolus for easy swallowing
stomach
• Food is churned and mixed into chyme
• No chemical change to sugars
Pancreatic
juice
• Pancreas secretes pancreatic juice into the duodenum
• Pancreatic juice contains many enzymes for breaking
down carbohydrates, such as maltase (for maltose),
sucrase (for sucrose), lactase (for lactose), fructase (for
fructose), etc. into glucose
• Ileum secretes enzymes for final digestion, and the
glucose is absorbed into the blood via diffusion.ileum

9. Digesting Proteins
In humans proteins are broken down into amino
acids, i.e. the end-product of protein digestion.
Enzymes that break down proteins are known as
proteases.
• Food is chewed and saliva softens it for easy
swallowing. Tongue also rolls food into a bolus for
easy swallowing
• No chemical change to proteins
Pancreatic
juice
mouth
Ileum secretes erepsin for the final
conversion of peptides into amino
acids, which is absorbed into the
blood by diffusion through the
intestinal wall.AeFA Foundation - Digestion in Humans
Gastric juice from stomach contains
pepsin which breaks down proteins
into smaller water-soluble pieces
called peptones.
Pancreatic juice secreted into the duodenum
contains trypsin for converting the peptones
into smaller peptides.

10. Digesting Fats and Oils (Lipids)
In humans fats and oils are broken down into fatty
acids and glycerol, i.e. the end-product of lipid
digestion. Enzymes that break down lipids are known
as lipases.
AeFA Foundation - Digestion in Humans
• Food is chewed and saliva softens it for easy
swallowing. Tongue also rolls food into a bolus for
easy swallowing
• No chemical change to fats or oils
mouth
• Stomach churns and mixes food into chyme.
No chemical change to lipids in the stomach
• Lipid digestion begins in the small intestine
(duodenum).
• Bile stored in the gall bladder (but is
produced by the liver) is released into the
duodenum. Bile emulsifies fats and oils, i.e.
breaks them into small droplets.
• Lipases in the ileum finally break down fats
and oils into fatty acids and glycerol in the
ileum.
bile
lipase

11. Egestion
• Undigested food materials (such as roughage) is removed from
the body through the process of egestion (defecation).
• After digestion is complete in the ileum, undigested food
passes into the colon, where water is absorbed from the
undigested food material.
• After absorption, the undigested food becomes faeces, which
is stored temporarily in the rectum before it is egested through
the anus.
AeFA Foundation - Digestion in Humans