Post on 23-Feb-2016
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Topic 6.1: Digestion
Assessment Statements 6.1.1: Explain why digestion of large food molecules is
essential 6.1.2: Explain the need for enzymes in digestion 6.1.3: State the source, substrate, products and
optimum pH conditions for one amylase, one protease, and one lipase
6.1.4: Draw and label a diagram of the digestive system
6.1.5: Outline the function of the stomach, small intestine and large intestine
6.1.6: Distinguish between absorption and assimilation 6.1.7: 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?When you eat a snack or a meal,
you begin a set of events that leads to your body cells being provided with needed nutrients◦Ingestion◦Digestion◦Absorption◦Transport
DigestionDigestion solves a problem of
molecular size◦Food is too large to pass through cell
membranes◦Food must be chemically digested to
a suitable sizeMolecule type
Molecular form ingested Molecular form after digestion
Protein Protein Amino acidsLipids Triglycerides Glycerol and fatty
acidsCarbohydrate Polysaccarides, disaccharides,
and monosaccharidesMonosaccharides
Nucleic acids DNA, RNA Nucelotides
DigestionDigestion allows you to turn
molecules into ‘your own’◦All the food that you eat is composed
of plant or animal cells, thus containing molecules characteristics of a living organisms that is not a human being Each type of living organism has its own
set of proteins, nucleic acids, and carboydrates
DigestionWhen we digest food molecules,
we break them down (hydrolyze them) into smallest components. ◦The components can be reassembled
into larger molecules that are useful to you!!
DigestionAs food moves through your
alimentary canal, many digestive enzymes are added along the way◦Each digestive enzyme is specific for
a specific food type◦Examples:
Lipase: is an enzyme is specific for lipid molecules
Amylase: is specific for amylose (starch)
DigestionThe real function of enzyme is to
lower the activation energy of reactions that they catalyze◦Digestive enzymes all help to
catalyze hydrolysis reactions
Examples of digestion enzymes
Salivary Amylase
Pepsin (a Protease)
Pancreatic Lipase
Source Salivary glands Stomach cells Pancreas cellsSubstrate Amylose (starch) Proteins
(polypeptides)Lipids
Products Maltose and glucose
Amino acids Glycerol and fatty acids
Optimum Neutral (pH 7) Acidic (pH 3) Neutral (pH 7)
Human Digestive SystemMuch of the human digestive
system is a tube called the alimentary canal
Alimentary canal consists of:◦ Mouth◦ Esophagus◦ Stomach◦ Small Intestine◦ Large Intestine (colon)◦ Rectum
Any foods that you ingest must either be digested and absorbed for use by the body or remain undigested and be eliminated as solid waste
StomachFood is brought to
your stomach by a muscular tube called the esophagus◦When you swallow,
the food is forced down to your stomach by a sequential series of smooth muscle contractions called peristalsis
StomachOnce in the stomach, the food is
held for a period of time in order to mix it with a variety of secretions collectively known as gastric juice
StomachGastric juice is a mixture of three
secretions form the cells of the stomach inner lining:◦Pepsin- a protease enzyme most active
in acidic pH◦Hydrochloric acid- helps degrade and
break down foods and creates the acidic pH necessary for pepsin to be active
◦Mucus- lines the inside the stomach wall to prevent stomach damage from the hydrochloric acids
StomachThe muscular wall of the stomach
creates a churning motion in order to mix food with the gastric juice◦After a period of time, a valve at the
lower end of the stomach opens and the food enters the small intestine
Small IntestineThe first portion of the
small intestine is called the duodenum◦Three different accessory
organs secrete juices into the small intestine in order to continue the digestive process
◦These secretions include: Bile from the liver and gall
bladder Trypsin (a protease), lipase,
amylase, and bicarbonate from the pancreas
Small IntestineAs the digestive process
continues in the small intestine, molecules are produced that are small enough to be absorbed◦The inner wall of the small intestine
is made up of thousand of finger-like extensions called villi
Small IntestineEach villus contains a capillary bed and a lacteal
◦Lacteal is a small vessel of your lymphatic system
If the inner lining of your small intestine were smooth, you would have a fairly limited membrane surface area for absorption◦The function of the villi is to greatly increase
the surface area for absorption of molecules such as glucose, amino acids, and fatty acids
Small IntestineMost molecules absorbed are
taken into the capillary bed within each villus ◦Except fatty acids which are more
efficiently absorbed into the lactealAll absorbed molecules are taken
to a wide variety of body cells by the circulatory system
Large IntestineThe vast majority of useful
nutrients are absorbed while food is still inside the small intestine◦Much of the water that we drink or
that is naturally contained in many food is also present
Large IntestineThe primary
function of the large intestine is water absorption◦Leaving water in
the alimentary canal as long as possible is beneficial because it keeps the moving food in a fluid environment
Large IntestineThe large intestine is also home
to a very large number of naturally occurring bacteria including Escherichia coli.
Large IntestineThese bacteria are examples of
mutualistic organisms within us.◦We provide nutrients, water, and a
warm environment for them while they synthesize vitamin K and maintain a healthy overall environment for us in our large intestine
Any food undigested by us or the bacteria is eliminated from the body as solid waste or feces