Document Text Contents
Page 2
Digestion
and Nutrition
YOUR BODY
How It Works
Page 59
DIGESTION AND NUTRITION
has several important functions in the body. It regulates
carbohydrate, protein, and lipid metabolism and detoxifies
body wastes and drugs that have entered the body. In addition,
the liver eliminates bilirubin, a waste product of dead red
blood cells, by incorporating it into bile. This fluid, which is
stored in the gallbladder, helps digestion by emulsifying fats
into smaller molecules for absorption. Bile is composed of
bile salts, cholesterol, and phospholipids, as well as other
substances. The bile salts and lipids work to emulsify fats.
When needed, bile is released from the gallbladder into the
small intestine.
The pancreas produces hormones, digestive enzymes, and
58
Figure 6.3 Villi and microvilli (illustrated here) act to increase
the surface area of the small intestine, thus increasing the potential
for nutrient absorption. Villi are finger-like projections on the surface
of the intestine, and microvilli are smaller projections stemming
from the villi.
Page 60
bicarbonate to deliver to the duodenum to help digestion.
Insulin and glucagon are two pancreatic hormones that work
within the body to control blood glucose levels.
DIGESTION IN THE SMALL INTESTINE
When acidic chyme enters the duodenum, it triggers several
events. The acid, along with short proteins called peptides
and fatty acids in the chyme, causes cells at the beginning of
the duodenum to secrete intestinal fluid. About 1 to 2 quarts
of this digestive fluid is produced each day. The intestinal
juice, which contains some mucus, is alkaline and helps to
neutralize the acidic nature of chyme and protect the duo-
denum from the effects of the acid. The chyme also causes the
release of two hormones from the duodenum. The hormone
cholecystokinin (CCK) causes the gallbladder to constrict
and pump bile into the small intestine. CCK also causes the
pancreas to secrete digestive enzymes into the duodenum.
The hormone secretin causes the pancreas to secrete large
amounts of bicarbonate into the small intestine. The bicar-
bonate neutralizes most of the hydrochloric acid from the
stomach. After the neutralization occurs, the small intestine
contents are alkaline, creating the conditions needed for the
digestive enzymes to work.
Digestive enzymes break starch, proteins, triglycerides,
and nucleic acids into intermediate size pieces. Pancreatic
amylase breaks down starch. The bicarbonate from the
pancreas creates the alkaline conditions needed for amylase
and other enzymes to function. Amylase does not break
starch into glucose monosaccharide units, but into smaller
pieces, including the disaccharide maltose. Thus far in the
digestive process, the disaccharides, such as sucrose (from
table sugar and fruits) and lactose (from milk, such as the
chocolate shake in our example), that are ingested have not
been broken down. Dietary triglycerides are broken apart
by pancreatic lipase.
59The Stomach and Small Intestine
Page 118
117
Picture Credits
13: Lambda Science Artwork
20: © SIU/Visuals Unlimited
25: Lambda Science Artwork
27: Lambda Science Artwork
31: Lambda Science Artwork
34: Lambda Science Artwork
36: Lambda Science Artwork
42: Lambda Science Artwork
43: Lambda Science Artwork
47: Lambda Science Artwork
51: Lambda Science Artwork
53: © G.W. Willis, MD/Visuals Unlimited
58: Lambda Science Artwork
61: Lambda Science Artwork
65: Lambda Science Artwork
72: Lambda Science Artwork
77: AP Graphics
78: Courtesy USDA
79: Lambda Science Artwork
page:
Page 119
About the Author
Robert J. Sullivan Ph.D., MT (ASCP), is an Associate Professor of
Medical Laboratory Sciences at Marist College in Poughkeepsie, New
York. Dr. Sullivan teaches in both the medical laboratory science and the
biology curriculums. His research interests include the toxic effects of
heavy metals in alternative medicines, the use of medical laboratory
assays to evaluate the nutritional status of athletes, and international
issues in laboratory medicine.
118
Digestion
and Nutrition
YOUR BODY
How It Works
Page 59
DIGESTION AND NUTRITION
has several important functions in the body. It regulates
carbohydrate, protein, and lipid metabolism and detoxifies
body wastes and drugs that have entered the body. In addition,
the liver eliminates bilirubin, a waste product of dead red
blood cells, by incorporating it into bile. This fluid, which is
stored in the gallbladder, helps digestion by emulsifying fats
into smaller molecules for absorption. Bile is composed of
bile salts, cholesterol, and phospholipids, as well as other
substances. The bile salts and lipids work to emulsify fats.
When needed, bile is released from the gallbladder into the
small intestine.
The pancreas produces hormones, digestive enzymes, and
58
Figure 6.3 Villi and microvilli (illustrated here) act to increase
the surface area of the small intestine, thus increasing the potential
for nutrient absorption. Villi are finger-like projections on the surface
of the intestine, and microvilli are smaller projections stemming
from the villi.
Page 60
bicarbonate to deliver to the duodenum to help digestion.
Insulin and glucagon are two pancreatic hormones that work
within the body to control blood glucose levels.
DIGESTION IN THE SMALL INTESTINE
When acidic chyme enters the duodenum, it triggers several
events. The acid, along with short proteins called peptides
and fatty acids in the chyme, causes cells at the beginning of
the duodenum to secrete intestinal fluid. About 1 to 2 quarts
of this digestive fluid is produced each day. The intestinal
juice, which contains some mucus, is alkaline and helps to
neutralize the acidic nature of chyme and protect the duo-
denum from the effects of the acid. The chyme also causes the
release of two hormones from the duodenum. The hormone
cholecystokinin (CCK) causes the gallbladder to constrict
and pump bile into the small intestine. CCK also causes the
pancreas to secrete digestive enzymes into the duodenum.
The hormone secretin causes the pancreas to secrete large
amounts of bicarbonate into the small intestine. The bicar-
bonate neutralizes most of the hydrochloric acid from the
stomach. After the neutralization occurs, the small intestine
contents are alkaline, creating the conditions needed for the
digestive enzymes to work.
Digestive enzymes break starch, proteins, triglycerides,
and nucleic acids into intermediate size pieces. Pancreatic
amylase breaks down starch. The bicarbonate from the
pancreas creates the alkaline conditions needed for amylase
and other enzymes to function. Amylase does not break
starch into glucose monosaccharide units, but into smaller
pieces, including the disaccharide maltose. Thus far in the
digestive process, the disaccharides, such as sucrose (from
table sugar and fruits) and lactose (from milk, such as the
chocolate shake in our example), that are ingested have not
been broken down. Dietary triglycerides are broken apart
by pancreatic lipase.
59The Stomach and Small Intestine
Page 118
117
Picture Credits
13: Lambda Science Artwork
20: © SIU/Visuals Unlimited
25: Lambda Science Artwork
27: Lambda Science Artwork
31: Lambda Science Artwork
34: Lambda Science Artwork
36: Lambda Science Artwork
42: Lambda Science Artwork
43: Lambda Science Artwork
47: Lambda Science Artwork
51: Lambda Science Artwork
53: © G.W. Willis, MD/Visuals Unlimited
58: Lambda Science Artwork
61: Lambda Science Artwork
65: Lambda Science Artwork
72: Lambda Science Artwork
77: AP Graphics
78: Courtesy USDA
79: Lambda Science Artwork
page:
Page 119
About the Author
Robert J. Sullivan Ph.D., MT (ASCP), is an Associate Professor of
Medical Laboratory Sciences at Marist College in Poughkeepsie, New
York. Dr. Sullivan teaches in both the medical laboratory science and the
biology curriculums. His research interests include the toxic effects of
heavy metals in alternative medicines, the use of medical laboratory
assays to evaluate the nutritional status of athletes, and international
issues in laboratory medicine.
118
