digestivesystemclass11 Part 1 of digestive system – The Digestion begins when food is taken in through the mouth, mixed with …
Hello friends welcome to scientech biology
In today’s video I am going to show the
mechanism of Digestion.
This is the 2nd part of digestive system video
In the 1st part I have discuss the Anatomy
of digestive system.
If you want to watch part 1 click on the i
button and also the link of the video is given
in description
Let’s start the video……….
The Digestion begins when food is taken in
through the mouth, mixed with saliva and chewed
Structure in the oral cavity work together
to break down foods into a small mass called
During the process of swallowing, the tongue
rises to the roof of the mouth directing the
bolus out of the oral cavity.
. The bolus then passes from the oropharynx
to the pharynx and into the esophagus.
Involuntary muscular contraction called peristaltic
waves, moves the bolus down the esophagus
and into the stomach.
Peristaltic waves continue the Mechanical
breakdown of food in the stomach.
Digested food mixed with digestive enzyme
and acids secreted by stomach is called chyme.
Enzyme in small intestine further do the chemical
A small amount of nutrient absorption occurs
in the stomach but most absorption occurs
as chyme travels through the section of the
small intestine.
The wall of the small intestine are lined
with structure that absorb nutrient from chime
and then pass these nutrient into blood stream.
Some absorption continue in the large intestine.
As indigestible waste moves through the structure of the large intestine it is compacted
The elimination of indigestible waste completes the digestive process.
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There are two kinds of digestion: mechanical
and chemical.
Mechanical digestion involves physically breaking
the food into smaller pieces.
Mechanical digestion begins in the mouth as
the food is chewed.
Digestion begins in the oral cavity where
the salivary glands teeth and the tongue work
to break down food into the small masses that
can be swallowed.
The movement of the jaw enables the teeth
to grind food.
Saliva secreted by salivary glands aids the
mechanical and chemical process of digestion.
The tongue manipulates the chewed food into
a small mass then moves it into the oropharynx.
The next stapes are involuntary: the bolus
passes through the pharynx, the epiglottis
closes off the trachea and peristaltic waves
move the bolus into the stomach.
During swallowing the epiglottis prevent checking
by folding down to close off the larynx and
This prevent the bolus from passing into esophagus
instead of the lower airways.
The autonomic nervous system control contraction
of the alimentary canal, then move swallowed
food down the esophagus churn the stomach
and move chymes through the small intestine
and large intestine.
The alimentary canal is single continues tube
that include the oral cavity, esophagus, stomach
and intestine.
The tissue layer that forms the wall of tube
include layers of smooth muscle.
The contraction and relaxation of these muscle
is called peristalsis.
One peristaltic wave cause enough to move
a bolus down the esophagus and into the stomach.
In the intestine the wave are smaller and
more regular.
As one section of the intestine contracts
the section in front relaxes.
This occurs in the rhythmic wave like patterns
that create the peristalsis that propels substances
Chemical digestion involves the breaking of
covalent chemical bonds in organic molecules
by digestive enzymes.
Carbohydrates are broken down into Glucose,
proteins are broken down into amino acids,
and fats are broken down into fatty acids
and glycerol.
Carbohydrate digestion begins in the oral
cavity with the partial digestion of starches
salivary amylase.
About 30 percent of starch is hydrolyzed here
by salivary amylase into a disaccharide called
A minor amount of digestion occurs in the
stomach through the action of gastric amylase
and gelatinase.
Carbohydrate digestion is continued in the
intestine by pancreatic and intestinal amylase.
A series of disaccharides enzymes that are
released by intestinal epithelium digest disaccharides
into monosaccharides.
Digestion of proteins into single amino acids,
dipeptides, and tripeptides is carried out
by a variety of peptidases enzyme in both
the stomach and the small intestine.
Digestion of proteins begins in the stomach
with pepsin which is secreted by oxyntic glands.
Pancreatic digestive enzymes perform the majority
of protein digestion.
The major proteolytic enzymes include trypsin,
chymotrypsin, elastase, and carboxypeptidase.
These enzymes digest proteins to short chains
of a few amino acids.
The final stage of protein digestion occurs
on the brush border of the small intestine
Here, membrane-bound peptidases complete digestion
of oligopeptides to either single amino acids
or dipeptides and tripeptides.
The major dietary lipids include triglycerides,
phospholipids, cholesterol, steroids, and
fat-soluble vitamins.
The first step in lipid digestion is emulsification,
which is the transformation of large lipid
droplets into much smaller droplets.
Emulsification is accomplished by bile salts
secreted by the liver and stored in the gallbladder.
The primary location for lipid digestion is
the small intestine where strong emulsifiers
synthesized by the liver are present together
with strong lipid-digesting enzymes synthesized
by the pancreas.
Pancreatic Lipase digests triglycerides into
components fatty acids and 2-monoglycerides
Pancreatic Cholesterol Esterase digests cholesterol
esters into component cholesterol and fatty
Pancreatic Phospholipase digests phospholipids
into their component head groups and fatty
Mechanical and chemical digestion in the stomach
results in chymes.
periliastic wave propel chymes through the
pyloric sphincter into the duodenum of the
small intestine.
Finger like projection called villi line the
interior wall of the small intestine.
Most absorption of nutrient from ingested
food occurs through these.
In the small intestine nutrient in the chymes
are further broken down by secretion from
Inside each villus there are lacteals of the
lymphatic system that fatty acid pass into,
and capillary beds of the circulatory system
into which other nutrient pass.
Water and other substance from chymes that
are not absorbed move into the large intestine
for further absorption, digestion or elimination.

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