Understanding Macro-Nutrients
Karina Sharma
Ms. Post
Human Nutrition
Protein
Proteins are large complex
molecules composed of amino
acids. They contain carbon,
hydrogen, oxygen, nitrogen, and
some amino acids contain sulfur.
Protein digestion begins in the
stomach by the enzyme pepsin
and stomach acid. It is here
where they begin to digest
protein.
Hydrochloric acid is used for
breaking the bonds between
the proteins.
Hydrolysis describes
proteins bonds breaking
down by pepsin.
Following this, more digestion
occur by the enzymes trypsin
and chymotrypsin being
released in the pancreas.
Then the digestion of protein
to amino acids occurs inside
the cells of the small intestine.
Pepsin and trypsin continue
the breakdown of proteins
into amino acids
They enter the bloodstream
through tiny veins.
Amino acids are then absorbed
and transported to the liver.
From there they enter the
blood stream.
Carbs
Carbohydrate digestion begins in the mouth
where chewing stimulates the secretion of
saliva, which contains salivary amylase
No carbohydrate
digestion occurs in the
stomach
Carbohydrates are
composed of carbon,
hydrogen, and oxygen and
are the primary energy
source for the brain and
nervous system.
After swallowing, food transports to the
stomach where salivary amylase is broken down
by the acidic environment and can no longer
function.
Then, the pancreas secretes pancreatic amylase
into the small intestine where it awaits the arrival
of chyme from the stomach.
As the chyme is slowly released into the small
intestine, pancreatic amylase hydrolyzes any starch
into maltose.
Monosaccharides, fructose and galactose are
absorbed by the enterocytes and enter the
bloodstream. They all travel to the liver.
Carbohydrates that are not absorbed pass into the
large intestine.
If they make it to the liver,
fructose and galactose are
converted to glucose
before being transported
to cells where they can be
used for energy
Lipids
Lipids are a diverse class of
molecules that are insoluble in
water. Fats are one type of lipids.
The main cells of the stomach
secrete gastric lipase causing
it to digests some of the
triglycerides
Fat digestion begins in the
mouth, when you begin to
chew. Food containing fat
causes the salivary glands
to produce lingual lipase
that digest triglycerides.
Food arrives in the stomach
where it is mixed and
broken into fat droplets.
Then, the gallbladder
releases bile into the small
intestine, and chyme from
the stomach, which contains
fat molecules, passes
gradually into the small
intestine
Bile from gallbladder break
and micelles transport the free
fatty acids to the mucosal cells
for absorption
The role of bile is not to
digest fat in the sense of
hydrolysis, but rather, to
emulsify it.