Digestion is the process by which nutrients are broken down into molecules that can be absorbed into the bloodstream. There are two types of digestion: physical and chemical. Physical digestion involves no new substances being formed through processes like chewing and churning. Chemical digestion involves enzymes forming new substances, such as starch being broken down into sugar by the enzyme salivary amylase and proteins broken down into amino acids. The digestive system, made up of the mouth, esophagus, stomach, small intestine, and large intestine, uses physical and chemical digestion to break down food and absorb nutrients into the bloodstream to be used by cells.

1. Digestion
© PDST Home Economics

2. Physical and Chemical Digestion
• Digestion is: the process by which nutrients are broken down into
simple molecules that can be absorbed into the bloodstream.
• There are two types of digestion Physical and chemical
• Physical digestion :
• No new substance is formed
• Chewing, melting, mixing churning
• Chemical digestion:
• New substances are formed
• Enzymes (biological catalysts) are needed to control the reactions.
• Example starch is change into sugar in the mouth with the help of the
enzyme salivary amylase.
• Proteins are changed into amino acids
• Fats are changed into fatty acids and glycerol
• Carbohydrates are changed into simple sugars like glucose

3. Digestive system/ alimentary
canal
• MOUTH
• food chewed and melted
• mixed with saliva
• starch changed to maltose
by amylase in saliva.
• OESOPHAGUS
• Tube (25cm) from mouth to
stomach
• Muscle contract and relax
to push food down
(peristalsis)

4. Digestive system
• STOMACH
• pouched shape bag with walls
made of muscle
• top left of abdomen under
diaphragm
• lining makes gastric juice which
contains HCl and enzymes
pepsin & rennin
• Food is churned into chyme
• fat melts
• HCl kills bacteria
• Enzymes change protein into
peptides

5. • SMALL INTESTINE
• joins stomach to large intestine
• 6m long, coiled up in centre of
abdomen.
• Food moves by peristalsis.
• Bile made in liver and stored in gall
bladder flows into intestine and
emulsifies fat.
• Pancreatic juice made in pancreas
flows into the intestine contains
enzymes that change peptides into
amino acids, and starch into sugar.
• Intestinal juice is made by the
intestine wall. It contains enzymes
that finish of the digestion of protein,
fat and carbohydrate.
Digestive
system

6. Absorption • Absorption is the passing of
digested food into the
bloodstream.
• Happens mainly in the small
intestine.
• The inside of the small
intestine is covered with tiny
hairlike projections called
villi.
• The villi give a large surface
area through which food can
be absorbed.
• The blood carries the digested
food to every body cell where
it is used for energy & growth

7. The Large
Intestine
• 2m long , also called the bowel or
colon.
• Joins the small intestine to the
anus.
• It passes up the right side of the
abdomen, across under the stomach
and down the left side.
• The start is called the caecum and
the last few cms. are called the
rectum
• Functions: 1. completes absorption,
2. absorbs water, 3. makes Vits B &
K, 4. eliminates waste.
• This solid waste is called faeces
• A high fibre diet is important for
the health of the large intestine