Download File

Kristine Alemsharyan
Due: April 6, 2014
Carbohydrate Digestion and
Absorption
Step #1:
--> Mouth: Chewing stimulates secretion of saliva from salvary glands.
--> salivary amylase breaks dwon starch into shosrter polysacrharides an malthose.
Step #2:
--> Stomach: Salivary amylase is destroyed by acids.
--> No digestion takes place in the stomach
Step #3:
--> Pancreas:Pancreatic amylase is secreted into small intes
Step #4:
--> Small Intestine: Pancreatic amylase breaks down remaining starch into maltose
--> Specific enzymes in small instestine break down disaccharides into monosaccharides
 all monosaccharides are absorbed by small intestine and enter bloodstream
Step #5:
 Liver: Monosaccharides travel in the bloodstream to the liver via the portal vein, are converted to glucose, and then
transported to cells to provide energy.
 Excess glucose is stored as glycogen in liver.
Step #6
 Large Intestine: Some carbohydrates pass into large intestine undigested.
 Bacteria ferment some undigested carbohydrate.
 Remaining fiber is excreted in feces.
Fat Digestion
Step #1:
Mouth: Salivary glands in the mouth produce an enzyme, lingual lipase, that digests some
triglycerides; however, little lipid digestion occurs here.
Step #2: Stomach: Most fat arrives intact at the stomach, where it is mixed and broken into
droplets.
--> Gastric lipase digests some triglycerides.
Step #3: Gallbladder: Gallbladder contracts due to secretion of CCK and secretin from duodenal
mucosal cells.
--> Gallbladder releases bile into the small intestine.
Step #4: Small intestine: Bile from gallbladder breaks fat into smaller droplets.
--> Lipid-digesting enzymes from the pancrease break triglycerides into monoglycerides and fatty acids.
--> Lipid-digesting enzymes from the pancrease break dietary cholestrol esters and phospholipids into their components.
--> Micelles transport lipid digestion products to the enterocytes of the small intestine for absorption.
Fat
Absorption
--> Majority of
fat absorption
occurs in
mucosal lining
of the small
intestine with
the help of a
micelle.
--> Fats do not mix
with water;
therefore, most fats
cannot be
transported freely in
the bloodstream.
--> Fatty acids are
reformuated back
into triglycerides and
then packaged into
lipoproteins before
being released into
the bloodstream.
--->Once
chylomicrons are
formed, they are
transported from
the intestinal
lining to the
lymphatic ssytem
and then into the
blood.
Protein Digestion & Absorption
Step #1: Mouth: Proteins in food are crushed by chewing and moistened by saliva.
Step #2: Stomach: Proteins are denatured by hydrochloric acid
--> Pepsin is activated to break proteins into single amino acids and smaller polypeptides.
Step #3: Small intestine: Proteases are secreted to digest polypeptides into smaller unites
--> Cells in the wall of the small intestine complete the breakdown of all polypeptides into single amino acids
Step #4: Liver: Amino acids are transported to the liver and sent to the cells as needed.
Most people do not know the importance of the digestive system and how digestion
and absorption actually functions. The digestive system contains a group of organs that
process the food an individual consumes; especially, food that contains nutrients, then
breaks it down into different components. Without this breakdown of the foods
consumed, it would be impossible to digest the food through the intestinal wall and into
one’s bloodstreams because it would be too big of a portion. This process occurs in
numerous steps that happen in different organs depending on the food one intakes.
Furthermore, carbohydrates, fats and proteins all have different pathways until digestion
and absorption is achieved.
When carbohydrates are consumed, digestion and absorption is completed in six steps.
The first step is through the mouth. While chewing one stimulates the secretion of saliva
from the salivary glands. During this step the salivary amylase breaks down start into
shorter polysaccharides and maltose. The second step is when the food reaches the
stomach while acids are destroying the salivary amylase. Although there is no specific
action of digestion in this step, it is still a mandatory step. The third step happens in the
pancreas where the pancreatic amylase is secreted into the small intestine. Directly after
this step the food transports to the small intestine while the pancreatic amylase breaks
down remaining starch into maltose. Enzymes like maltase, sucrose and lactase break
down disaccharides into monosaccharaides in the small intestine. Then the
monosaccharaides are absorbed by the small intestine and finally enter the bloodstream.
The fifth step is when the monosaccharaides travel in the bloodstream to the liver via the
portal vein, which are converted to glucose, then transported to cells to provide energy. If
too much glucose is produced it is later stored as glycogen in the liver. Finally, the last
step occurs in the large intestine. In this step some carbohydrates pass into the large
intestine undigested. The bacteria ferment some undigested carbohydrates and later the
remaining fiber is excreted in feces.
Furthermore, fat also goes through the process of digestion and absorption. The first
step is through the mouth. In this step the salivary glands in the mouth produce an
enzyme, lingual lipase, which digests some triglycerides; however, little lipid digestion
occurs here. The second step goes through the stomach where the fat is mixed and broken
down into droplets. During this step gastric lipase digests some triglycerides. The third
step is through the gallbladder. In this step the gallbladder contracts due to the secretion
of the CCK and secretion from the duodenal mucosal cells while releasing bile into the
small intestine. Finally, the bile from the gallbladder breaks fat into smaller droplets. The
lipid digesting enzymes from the pancreas break triglycerides into monoglycerides and
fatty acids. And lastly, the micelles transport lipid digestion products to the enterocytes of
the small intestine for absorption.
The process of protein digestion and absorption occurs in four steps. The first goes
through the mouth while chewing moistened by saliva crushes the food. The second step
is through the stomach and the proteins are denatured by hydrochloric acid. During this
step, the pepsin is activated to break proteins into single amino acids and smaller
polypeptides. The third step passes through the small intestine while the proteases are
secreted to digest polypeptides into small units. The cells in the wall of the small intestine
complete the breakdown of all polypeptides into single amino acids. Finally, the last step
is through the liver. The amino acids are transported to the liver and sent to the cells as
needed.
In conclusion, the digestion and absorption of the different nutrients is unique in its
own ways. Carbohydrates, fats and proteins have there own individual steps for properly
completing digestion and absorption.