Biology- The digestive system
Digestive System:
As with any system we are learning in this course, the structural anatomy and functions of each are the basis of your learning.
Otherwise known as the alimentary canal, the best way to learn the digestive system structures and their functions is to follow some food through the process from beginning to end.
Where does the food go?
As food enters the mouth, both mechanical and chemical digestion begins. First the food is physically broken down by the mechanical process of mastication (chewing), into smaller particles, creating a bolus with the tongue against the soft plate. During this phase, the salivary glands mix the food with salivary amylase beginning the chemical digestion of starches. The bolus then enters the pharynx (throat) first then is routed to the esophagus. These two tubes are simply passageways for the food to be carried to the holding tank, known as the stomach. Neither have any specific digestive function.
A mere 10% of absorption takes place in the stomach. Substances like alcohol, aspirin and the like are taken up into the blood immediately. This is the reason one feels the effects of such drugs so rapidly. Nutrients however, are not absorbed by the stomach at all. Rugae, which are the folds and creases of the stomach, contain muscles which contract in four different directions to aid in churning the food and mixing it with the digestive enzymes excreted there. These enzymes, hydrochloric acid, pepsinogen and mucin, are what begin the chemical breakdown of proteins. This churned food is called, chyme.
At approximately 10 cc’s at a time, this liquefied chyme is released into the duodenum (the first part of the small intestine), where the final 90% of absorption will take place.
The duodenal area is probably the busiest part of the alimentary canal. If not, certainly one of the most crucial parts essential for life. In this main intersection, there are ducts secreting substances from the pancreas (as
As with any system we are learning in this course, the structural anatomy and functions of each are the basis of your learning.
Otherwise known as the alimentary canal, the best way to learn the digestive system structures and their functions is to follow some food through the process from beginning to end.
Where does the food go?
As food enters the mouth, both mechanical and chemical digestion begins. First the food is physically broken down by the mechanical process of mastication (chewing), into smaller particles, creating a bolus with the tongue against the soft plate. During this phase, the salivary glands mix the food with salivary amylase beginning the chemical digestion of starches. The bolus then enters the pharynx (throat) first then is routed to the esophagus. These two tubes are simply passageways for the food to be carried to the holding tank, known as the stomach. Neither have any specific digestive function.
A mere 10% of absorption takes place in the stomach. Substances like alcohol, aspirin and the like are taken up into the blood immediately. This is the reason one feels the effects of such drugs so rapidly. Nutrients however, are not absorbed by the stomach at all. Rugae, which are the folds and creases of the stomach, contain muscles which contract in four different directions to aid in churning the food and mixing it with the digestive enzymes excreted there. These enzymes, hydrochloric acid, pepsinogen and mucin, are what begin the chemical breakdown of proteins. This churned food is called, chyme.
At approximately 10 cc’s at a time, this liquefied chyme is released into the duodenum (the first part of the small intestine), where the final 90% of absorption will take place.
The duodenal area is probably the busiest part of the alimentary canal. If not, certainly one of the most crucial parts essential for life. In this main intersection, there are ducts secreting substances from the pancreas (as