Final answer:
Goblet cells are necessary for GI tract function because they protect the lining with mucus. They secrete a gel-forming mucin which is the major component of mucus, acting as a protective barrier and lubricant. They do not produce bile, secrete digestive enzymes, or absorb nutrients.
Step-by-step explanation:
Goblet cells are necessary for GI tract function because they protect the lining with mucus. These cells are modified simple columnar epithelial cells that secrete a gel-forming mucin, which is the major component of mucus. The presence of mucus in the digestive tract plays a crucial role in lubrication which facilitates the passage of food through the GI tract. Moreover, mucus acts as a barrier, protecting the lining of the GI tract from digestive enzymes and the abrasive effect of food particles. Additionally, it aids in the defense against pathogens by limiting their contact with epithelial cells of the intestines.
It's important to note that goblet cells do not produce bile for digestion, secrete digestive enzymes, or absorb nutrients. These functions are carried out by other cells and structures within the GI tract. For instance, bile is produced by the liver, digestive enzymes are secreted by both the pancreas and intestinal glands, and the absorption of nutrients is primarily the role of the columnar epithelial cells within the intestines.