the body convert large, chemically complex foods to a size that can be
passed through a cell membrane (yet still large enough to contain
useable chemical energy)?
organic carbon molecules + O2
-> CO2 + H2O + useable
But first, let us
consider other organisms:
Where do they get organic carbon for energy metabolism?
Are CO2, light, and water alone sufficient for maintenance
sponges get away without
a digestive system?
Why are herbivore digestive systems
"dis-ASSEMBLY LINE" (21 to 30 ft. in
What regulates the direction and speed of this dis-assembly line?
The cause of ulcers has been
re-examined in recent years, and now the bacterium Helicobacter pylori has been
Infection by H. pyloris is linked to stomach
. The prevalence of infection is lowest in developed
and the incidence of ulcers and stomach cancers have been on the
decline. However, the incidence of acid reflux disease and
adenocarcinoma of the esophagus is on the rise, suggesting
that H. pyloris protects the
(coevolution between host and parasite has given H. pyloris
the ability to regulate
Bile emulsifies fats. How does this aid digestion?
food molecules into the circulatory system:
Why is the lining of the small
intestine so folded?
What do the presence of capillaries indicate?
Glucose, vitamins, and amino acids
require active transport into epithelial cells and diffuse into
blood. Fructose and fatty acids cross by diffusion. Fatty
acids and glycerol recombine and are coated with protein
cholesterol to become chylomicrons
which are water soluble and are moved to the lymphatic system.
of food molecules upon entering the circulatory system:
you have to eat a diet perfectly balanced according to the metabolic
needs of cells for the types of molecules discussed above?
Why do the veins leaving the villi of
the small intestine collect into the hepatic portal vein and pass
through the liver before joining the main branch of the circulatory
system? What would happen after your breakfast of coke and a
candy bar if not?
aids in the conversion of molecules from on class to another.
Can the body manufacture all the
types of molecules required by the body?
For example, after meal, high sugar in blood results in release of
insulin from the pancreas resulting in:
Opposite occurs when blood sugar is low; several hormones involved,
glucagon (from the pancreas):
- liver and
other cells convert glucose to amino acids, fats, glycogen
- stimulate cells to use glucose as energy source by facilitating
its entry into cells.
- breakdown of glycogen
- release of glucose to
can also become scarce in
Much starvation is
one of poor quality
(e.g. iron deficiency) not quantity, resulting in a weakening of the
immune system and
nation be 'over-nourished'?
Does a nation have to be wealthy?
What is the evolutionary explanation for this?
The movement of peoples from areas in which they
evolved is also
important in explaining susceptibility to disorders associated with
Sunlight is required for production of vitamin D, though UV light
destroys folic acid (or folate,
one of the B vitamins). Skin pigment
blocks UV light so how would migration of peoples differing in skin
color to different latitudes affect their health?
Not all ingested material enters the circulatory system and instead is
passed to the large intestine
- storage and
concentration of feces
- re-absorption of water
that produce vitamin K, folic acid,
several B vitamins, and biotin (and methane). When the appendix
ruptures, intestinal bacteria enter the abdominal cavity (Is the inside of the digestive system
really 'internal', and why do we have an appendix
in the first place?)