Download Chapter 1 Homework - due Tuesday, Sept

Answers to Review Questions - Chapter 48
1. Imagine you have just taken a bite of steak. List in sequence the structures
through which it passes in its journey through the digestive system. What
happens in each structure?
Assuming it is mostly protein, the steak would be chewed in the mouth
(mechanical digestion), then passed to the pharynx for swallowing, then through
the esophagus into the stomach where the chemical digestion of the protein
begins. In particular, pepsin converts the protein to short polypeptides, which
then flow into the small intestine. In the small intestine, further chemical
digestion occurs. Trypsin and chymotrypsin convert the polypeptides into
shorter chains, which are then converted to amino acids by carboxypeptidase,
peptidases, and dipeptidases. The amino acids are then absorbed into the
bloodstream and are carried to the liver. Any remaining waste products would
then pass into the large intestine and eliminated through the anus.
2. What are the four layers of the digestive tract? What significant
features/components are found in each?
Mucosa - innermost layer consisting of epithelial tissue and underlying connective
tissue
Submucosa - surrounds mucosa - consists of connective tissue housing blood and
lymph vessels and nerves.
Muscle layer (muscularis) - two sublayers of smooth muscle surrounding the
submucosa.
Visceral peritoneum (a.k.a. serosa or adventitia) - outer connective tissue "coat"
of the digestive tract
3. What are the predominant active enzymes found in each of the following regions
of the digestive tract? What function does each enzyme perform?
a) mouth
Enzyme - salivary amylase; breaks down polysaccharides into
disaccharides.
b) Stomach
Enzyme - pepsin; breaks down proteins (long polypeptides) into short
polypeptides.
c) small intestine
Enzymes:
Pancreatic amylase - breaks down polysaccharides into
disaccharides
Pancreatic lipase - breaks down fats into fatty acids and glycerol
Trypsin, chymotrypsin - break down polypeptides into short
polypeptides.
Peptidases - break down short polypeptides into amino acids.
Maltase, lactase, sucrase - break down disaccharides into
monosaccharides.
4. What does the liver produce to aid in digestion? How does this material assist
digestion?
The liver produces bile, which contains bile salts. These salts function to
emulsify (break up) large fat droplets into smaller fat droplets. This increases the
surface area on which the enzymes may act to digest the lipids.
5. What are chylomicrons?
Chylomicrons are protein-covered fat droplets that transport triacylglycerols to
the lymph and then to the blood.
6. List the essential amino acids (see chapter 3). Why are they "essential"?
Leucine, isoleucine, lysine, phenylalanine, tryptophan, valine, methionine,
threonine, histidine (and arginine in children).