Six Processes of Digestion and Structure of Digestive System Organs

Biology
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1.1 Six Processes of Digestion
Large molecules like starch cannot pass through cell membrane. Hence, it needs to be broken
down into smaller particles. Breakdown of starch molecule in the smaller molecules occur in
the first step of digestion which is called as ingestion. Starch digestion starts in the mouth
which is called as ingestion. Teeth, saliva and tongue play important role in mastication of
the ingestion process. Saliva secreted by salivary glands in the mouth is useful in moistening
the consumed starch. After moistening starch is chewed. During this process, salivary glands
secret enzyme like salivary amylase. This enzyme is useful in breaking down starch in
simpler carbohydrates like maltose and glucose. Breaking down and moistening with saliva
results in soft mass of starch. It is easy to swallow and travel this soft mass through entire
length of oesophagus. This process is known as propulsion. Tongue and pharyngeal muscles
propel soft mass of starch into the oesophagus. This is last voluntary process in the digestive
process until defecation. In this process, there is movement of starch throughout entire
digestive tract. This movement include both voluntary swallowing and involuntary peristalsis.
In peristalsis, there is sequential and discontinuous waves of contraction and relaxation of
gastrointestinal tract wall smooth muscle. It leads to propel food along the gastrointestinal
tract. Peristalsis moves starch back and forth and segmentation is helpful in mixing starch
with digestive juices. Both together facilitates absorption of starch.
After ingestion, digestion of starch begins. During digestion process, soft mass of starch
enters stomach which mixed with chyme. There is no further digestion of starch because
bacteria in the stomach inactivate action of salivary amylase. Digestion include both
mechanical and chemical digestion. Mechanical digestion produces smaller starch particles.
Mechanical digestion also occurs after starch leaves mouth. Digestion starts in the mouth and
it continues in stomach and small intestine. Mechanical and chemical digestion occurs in co-
ordination with each other. Formation of soft mass through mechanical digestion is helpful in
providing more surface area for digestive juices which is chemical digestion process.
Segmentation mostly occurs in the small intestine. In segmentation there is local contractions
of circular muscle of the muscularis layer of the alimentary canal. These contractions produce
small segments in small intestine. Starch moves back and forth in these small intestine
segments. It results in subdividing, breaking up and mixing of starch. Movement of starch
back and forth in the intestinal lumen result in the mixing of digestive juices and facilitation
of absorption. Starch broken down in the small pieces need to enter in the bloodstream for its
utilization. Until food reaches bloodstream, its nutrients are not useful for the body. Entry of
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starch in the bloodstream occurs in the small intestine and this process is called as absorption.
Absorption of nutrients in the bloodstream occurs through epithelial cells of small intestine.
Epithelial cells of small intestine make up the mucosa. Defecation is the last step in the
digestion process and undigested starch is eliminated from the body during this process
(Brett, 10-14).
2.1a : The digestive system
2.1b Structure and Functions of Digestive System Organs
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