Topic 6: Human health & physiology
6.1 Digestion
On your human body
outline, sketch in and name
the organs of the digestive
system.
Large food molecules need to be digested before the
nutrients can be absorbed.
Large molecules are:
• usually insoluble
• too large to diffuse across
membranes and into the blood
Products of digestion are:
• usually soluble
• small enough for absorption into the
bloodstream and assimilation into the
tissues
* Remember! Hydrolysis is the reaction used to break down large organic molecules. Enzymes are
needed in these reactions.
Amylase
Protease
Lipase
Macromolecule
Carbohydrates
Proteins
Lipids/fats
Example
Salivary amylase
Trypsin
Pancreatic lipase
Substrate
Starch
Polypeptides
Triglycerides
Product
Maltose
Amino acids
Fatty acids and glycerol
Source
Mouth (salivary glands)
Duodenum (small
intestine)
Pancreas
Optimal pH
7 – 7.8
8
7.2 – 7.5
Question: Where would an enzyme with an optimum pH of 2 be found?
mouth &
salivary glands
oesophagus
liver
stomach
pancreas
gall bladder
small intestine
duodenum
large
intestine
ileum
rectum
anus
nbThis is NOT to scale
Duodenum (small intestine)
o bile from the liver and gall
bladder neutralises acid and
emulsifies fats.
o pancreatic amylase and lipase
digest carbohydrates and fats.
o trypsin digests polypeptides to
amino acids.
Large intestine
o water is reclaimed and
returned to the blood, leaving
semi-solid faeces which are
stored in the rectum.
Stomach
o muscular contractions
continue mechanical digestion.
o acid kills bacteria.
o pepsin begins digestion of
proteins.
Ileum (small intestine)
o lower half of small intestine.
o absorbs nutrients into the
blood via the villi.
Mouth
o ingestion
ochewing begins mechanical
digestion.
o saliva moistens food to make a
bolus for swallowing.
o salivary amylase begins
chemical digestion of starch.
Egestion
o faeces (containing undigested
food, dead cells and other wastes)
is moved out of the anus.
oThe villi (singular is villus) are finger-like projections in the small
intestine which absorb the products of digestion.
oThe large number of these villi creates a huge surface area for the
absorption of digested food molecules.
o Epithelial (surface) cells have microvilli – tiny finger-like hairs to
increase the surface area even more (only label these on a diagram if
you can see them).
o Each villus has a thin epithelium, only one cell thick, to make
diffusion fast and more efficient.
o A rich blood supply maintains a concentration
gradient down which nutrients can diffuse across
the membranes.
o Lymph vessels (lacteals) close to the surface
allow lipids to be easily absorbed.