Transcript Digestion

Digestion
• Explain why digestion of large food molecules is
essential
• Explain the need for enzymes in digestion
• State the source, substrate, products and optimum
pH conditions for one amylase, one protease, and
one lipase
• Draw and label a diagram of the digestive system
• Outline the function of the stomach, small intestine
and large intestine
• Distinguish between absorption and assimilation
• Explain how the structure of the villus is related to
its role in absorption and transport of the products
of digestion
Why do we digest food?
To start with, this is a breakdown of basic processes:
1. Ingestion – you eat the food
2. Digestion – series of chemical reactions that
convert food into smaller and smaller
molecular forms
3. Absorption – food molecules absorbed by cells
and passed to blood vessels
4. Transport – you circulatory system moves food
molecules throughout your body
• Many of the foods that we eat are composed of
very large molecules and these molecules may
be too big to cross the cell membranes and
enter your bloodstream
Molecule Type
Protein
Lipids
Ingested Form
Protein
Triglycerides
After Digestion
Amino acids
Glycerol/fatty
acids
monosaccharides
Carbohydrates Poly, di,
monosaccharides
Nucleic acids
DNA, RNA
nucleotides
Proteins to amino acids via
hydrolysis reactions
Triglycerides
into glycerol
and fatty
acids via
hydrolysis
reactions
Polysaccharides
into
Monosaccharides
via hydrolysis
reactions
• Using enzymes specific for certain tasks,
your body is able to breakdown the foods
you eat via hydrolysis reactions (your body
can then reassemble the monomers into
polymers as needed)
• Remember, enzymes are protein
molecules which act as catalysts for
reactions; they don’t cause the reactions,
they just lower the activation energy (heat)
required to allow the reaction to take place
(temperature, pH, substrate levels help
determine enzyme effectiveness)
Salivary
Amylase
Source
Salivary
glands
Pepsin
(Protease)
Pancreatic
Lipase
Stomach cells Pancreas
cells
Substrate Carbohydrates Proteins
Lipids
Products maltose and
glucose
Glycerol and
fatty acids
Amino acids
Optimum Neutral (pH 7) Acidic (pH 3)
pH
Neutral
(pH 7)
Parts of the Digestive System
• Much of the
digestive system is
a tube called the
alimentary canal
which consists of:
Mouth
Esophagus
Stomach
Small Intestine
Large Intestine
Rectum
The Stomach
• Food is forced down the esophagus to the
stomach via muscle contractions called peristalsis
• Food is held in the stomach in order for it to mix
with secretions known as gastric juice
• Gastric juice is:
- pepsin – a protease enzyme most active in
acidic pH
- hydrochloric acid – makes the pH necessary for
pepsin to activate and helps break down foods
- mucus – lines the stomach wall to prevent
stomach damage from hydrochloric acid
The Small Intestine
• 2-6 hours after a meal, the valve at the bottom of
the stomach will start slowly releasing the
food/enzyme/acid mixture into the small intestine
• The beginning of the small intestine (named the
duodenum) is where accessory organs begin
secreting juices into the small intestine for the
purposes of continuing digestion
• What is added includes:
- bile from liver and gall bladder
- trypsin (a protease), lipase, amylase and
biocarbonate from the pancreas
• Duodenum is ~25 cm of 6 m of small intestine
(most digestion compete by the end of duodenum)
Absorption in Small Intestine
• In the small intestine food molecules are small enough
to be absorbed into the bloodstream/lymphatic system
• This can happen b/c inner wall of small intestine is
made up of thousands of finger-like extensions called
villi and each villi contains a capillary bed and lacteal
(this increases surface area for maximum absorption
of monomers)
• Most molecules go into bloodstream via capillaries but
fatty acids are absorbed into lacteal (remember
diffusion/active transport from earlier this year)
because they are too large to pass through the
membranes of capillaries
Assimilation of Molecules
• After molecules are absorbed into bloodstream via
capillaries or into lymphatic system via lacteals it is
transported around the body by the circulatory system
• Once a molecule has reached a body cell where it is
needed, it will leave the bloodstream the same way it
entered (diffusion or active transport across
membranes) into the cell
• The molecule may be used for energy (e.g. glucose)
or it may be used to build a polymer inside the cell
(e.g. amino acids used to make proteins)
• The process of bringing a molecule to a body cell and
then using it to make larger molecules (polymers) is
called assimilation
The Large Intestine
• Most useful nutrients are absorbed in the small
intestine but the H2O we drink/eat is still present
• The primary function is water absorption (this makes
sense b/c having our undigested foods in an aqueous
environment for as long as possible aids in movement)
• contains many bacteria including E. coli (these are
mutualistic organisms – we provide food/H2O,warm
enviro and they help us synthsize vitamin K and
maintain healthy intestines)
• Any undigested food by us or the bacteria (e.g.
cellulose) is eliminated as solid waste