1) Describe the process of food digestion within the gastrointestinal tract. In your answer, make sure to address the following questions: (19 marks total)
a) Where does chemical digestion begin? What is the first enzyme to access food that is ingested? What macromolecule does this enzyme digest? Where is this enzyme produced/secreted? (4 marks)
Both chemical and mechanical digestion begins in the mouth as food materials are broken down into more absorbable units. Food material is transported down the gastrointestinal tract though muscle contractions, a process known as peristalsis. An enzyme known as Amylase, whose main function is to break down carbohydrates, is produced in the salivary glands and pancreas and is the first enzyme to access ingested food materials. These digestive enzymes are called alpha amylase and pancreatic amylase respectively. The carbohydrates in question are broken down from larger disaccharides into smaller monosaccharaides. After salivary amylase breaks down food materials the bolus is moved down the esophagus through mechanical contraction and enters the stomach through the esophageal sphincter.
b) Does the stomach produce any enzymes or other factors that can be used to break down food? If so, what macromolecules do these factors digest and what cells produce these factors? (5 marks)
The stomach houses several specialized cell types with distinct functions. Among these cell types are mucous neck cells (which secrete mucus and bicarbonate), parietal cells (which secrete gastric acid or HCl and the intrinsic factor), enterchromatfin like cell (which secrete histamines), Chief cells (which secrete pepsin[ogen] and gastric lipase), D cells (which secrete somato...
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...ons which are removed by the lymphatic system for lymphatic digestion.
d) In what form are carbohydrates absorbed in the gastrointestinal tract? How are they absorbed? (2 marks)
In the gastrointestinal tract carbohydrates are absorbed as monosaccharides. To absorb glucose and galactose transporters are used. Amylase will break carbohydrates into disaccharides’, which will be broken down further into monosaccharides by enzymes associated with the intestinal epithelium (maltase, sucrose, lactase). These monosacharides will then enter into their respective transporters. Glucose and galactose are brought into epithelial cells using the Sodium Glucose Transporter, while the Glucose Transporter lets fructose enter down its own gradient. The monosacharides leave the cell on its opposite side to be transported into the bloodstream.
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