BPK 105 Study Guide - Final Guide: Hepatic Portal System, Intestinal Villus, Intestinal Epithelium
27 Apr 2018
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Module 11 - Review Questions - Part 5
9. Describe the digestion and absorption of carbohydrates through the entire digestive
system. Include the site, stimulation and function of important secretions and describe
the details of absorption across the cell membrane. [7 marks]
- Ingested carbohydrates consist primarily of starches, cellulose, sucrose (table sugar),
and small amounts of fructose (fruit sugar) and lactose (milk sugar). Starches, cellulose,
sucrose, and fructose are derived from plants, and lactose is derived from animals.
- Polysaccharides are large carbohydrates, such as starches, cellulose, and glycogen,
that consist of many sugars linked by chemical bonds.
- Starch is an energy-storage molecule in plants. Cellulose forms the walls of plant cells.
Glycogen is an energy-storage molecule in animals and is contained in muscle and in
the liver.
- When uncooked meats are processed or stored, the glycogen is broken down to
glucose, which is further broken down, so that little, if any, glycogen remains. Therefore,
almost all dietary carbohydrates come from plants. Starch is broken down by enzymes.
Cellulose is a polysaccharide that is not digested but is important for providing fiber in
the diet.
Process:
- Salivary amylase begins the digestion of carbohydrates in the mouth (figure 16.23). The
carbohydrates then pass to the stomach, where digestion continues until the food is well
mixed with acid, which inactivates salivary amylase.
- In the duodenum, pancreatic amylase continues the digestion of carbohydrates, and
absorption begins. The amylases break down polysaccharides to disaccharides.
- A group of enzymes called disaccharidases that are bound to the microvilli of the
intestinal epithelium break down the disaccharides to monosaccharides.
- The monosaccharides glucose, galactose, and fructose are taken up through the
intestinal epithelial cells (figure 16.24).
- Cotransport of the major monosaccharide, glucose, and Na+ is driven by a Na+
concentration gradient that is established by the sodium-potassium pump.
- Diffusion of Na+ down its concentration gradient provides the energy to transport
glucose across the cell membrane.
- This mechanism is also used for galactose transport, while fructose is taken up by
facilitated diffusion (see chapter 3).
- Once inside the intestinal epithelial cell, monosaccharides are transported into the
capillaries of the intestinal villi and are carried by the hepatic portal system to the liver.
Document Summary
Module 11 - review questions - part 5: describe the digestion and absorption of carbohydrates through the entire digestive system. Include the site, stimulation and function of important secretions and describe the details of absorption across the cell membrane. Ingested carbohydrates consist primarily of starches, cellulose, sucrose (table sugar), and small amounts of fructose (fruit sugar) and lactose (milk sugar). Starches, cellulose, sucrose, and fructose are derived from plants, and lactose is derived from animals. Polysaccharides are large carbohydrates, such as starches, cellulose, and glycogen, that consist of many sugars linked by chemical bonds. Starch is an energy-storage molecule in plants. Glycogen is an energy-storage molecule in animals and is contained in muscle and in the liver. When uncooked meats are processed or stored, the glycogen is broken down to glucose, which is further broken down, so that little, if any, glycogen remains. Therefore, almost all dietary carbohydrates come from plants.
