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As you read the chapter for this week, summarize the functions by classifying them into a chemical breakdown or mechanical breakdown using the following table. Please add rows as needed or even bullet points if easier.
Mechanical and Chemical Breakdown
Mechanical Breakdown Example: chewing in the mouth using the teeth
Chemical Breakdown Example: The salivary enzyme amylase in the saliva breaks down carbs in the mouth
Because learning changes everything. ®
HUMAN BIOLOGY
Seventeenth Edition
Sylvia S. Mader
Michael Windelspecht
Chapter
9
Digestive System
and Nutrition
© McGraw Hill LLC. All rights reserved. No reproduction or distribution without the prior written consent of McGraw Hill LLC.
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Learning Outcomes:
• State the function of each organ of the
gastrointestinal tract.
• List the accessory organs and name a function for
each.
• Describe the structure of the gastrointestinal tract
wall.
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Overview of the digestive system.
The organs are located within the gastrointestinal
(GI) tract.
Function—to hydrolyze, or break down, the
macromolecules found in food.
• The subunit molecules (monosaccharides, amino acids,
fatty acids, and glycerol) can cross plasma membranes
using facilitated and active transport.
The nutrients made available are transported by the
blood to our cells.
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Organs of the GI Tract and Accessory
Structures of Digestion (Figure 9.1)
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Digestion processes:
Ingestion—intake of food via the mouth.
Digestion—mechanically or chemically breaking
down foods into their subunits.
• Mechanical digestion—chewing in the mouth and
contractions of smooth muscles in the stomach.
• Chemical digestion—digestive enzymes hydrolyze
macromolecules into subunits.
• Begins in the mouth, continues in the stomach, and is
completed
in the small intestine.
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Digestion processes, continued.
Movement—food is passed from one organ to the
next, normally by contractions of smooth muscle
called peristalsis; indigestible must be expelled.
Absorption—movement of nutrients across the GI
tract wall into the blood; they are then delivered to
cells.
Elimination—removal of indigestible wastes.
• Defecation.
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Wall of the digestive tract.
Lumen—open area of a hollow organ or vessel; in the GI
tract, it contains food or feces.
Layers:
• Mucosa—innermost layer; produces mucus for protection; also
produces digestive enzymes.
• Submucosa—loose connective tissue; contains blood vessels,
lymphatic vessels, and nerves.
• Muscularis—made of two layers of smooth muscle (inner, circular
layer, and an outer, longitudinal layer) that move food along the GI
tract.
• Serosa—outer lining; is part of the peritoneum.
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The Layers of the Gastrointestinal Tract
Wall (Figure 9.2)
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Diverticulosis.
A condition in which the mucosa of any part of the
GI tract (usually the large intestine) pushes through
the other layers and forms pouches where food
collects.
Diverticulitis—when the pouches become infected.
• This happens in
10
–
25
% of people with diverticulosis.
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Inflammatory bowel disease (IBD)—chronic
diarrhea, abdominal pain, fever, and weight
loss.
Irritable bowel syndrome (IBS)—contractions of
the muscularis cause abdominal pain,
constipation, and diarrhea.
• The underlying cause is not known.
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List the digestive organs and accessory
structures of the digestive system.
Describe the processes that occur during the
digestive process.
Identify the four layers of the GI tract from the
lumen outward.
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Learning Outcomes:
• Identify the structures of the mouth, pharynx, and
esophagus and provide a function for each.
• Explain the series of events involved in swallowing.
• Summarize the diseases and conditions associated
with the mouth, pharynx, and esophagus.
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Mouth (oral cavity).
Receives food and begins mechanical and chemical digestion.
The roof of the mouth separates the nasal cavity from the oral
cavity.
• Two parts: a bony hard palate and a soft palate.
• The soft palate is made of muscle; ends in the uvula.
Tonsils—in the back of the mouth on either side of the
tongue.
• Lymphatic tissue; help protect from disease.
• There is a single pharyngeal tonsil in the nasopharynx, commonly
called the adenoids.
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Mouth (oral cavity), continued.
Three pairs of salivary glands secrete saliva, which
contains:
• Salivary amylase—begins carbohydrate digestion.
• Lysozyme—antibacterial enzyme.
Tongue.
• Covered in taste buds.
• Assists in mechanical breakdown, movement of food.
• Forms a bolus (mass of chewed food) and moves it toward
the pharynx.
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Teeth.
Mechanically digest food.
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smaller deciduous (baby) teeth, 32 adult teeth.
Two main divisions:
• Crown—the part of the tooth above the gum line.
• Root—the portion below.
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Teeth, continued.
• Enamel—extremely hard outer layer.
• Dentin—a thick layer of bonelike material.
• Pulp—nerves and blood vessels.
• Periodontal membranes—anchor the tooth to the
jawbone.
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Teeth, continued.
Dental caries—tooth decay, cavities.
• Occur when bacteria metabolize sugar and produce acids,
which erode the teeth.
• Can be painful when it reaches the nerves of the pulp.
Gingivitis—inflammation of the gums; can spread to
the periodontal membrane, causing loosening of the
teeth.
Periodontitis—loss of bone and loosening of the
teeth.
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The mouth and nasal passages lead to the
pharynx.
In turn, the pharynx opens into both the food
passage (esophagus) and air passage (trachea, or
windpipe).
• These two tubes are parallel to each other; the trachea is
in front of the esophagus.
• The esophagus is a muscular tube that leads to the
stomach.
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Swallowing.
Starts off voluntary, but once food or drink is pushed
back into the pharynx, it becomes an involuntary
reflex.
Food normally enters the esophagus because other
possible avenues are blocked.
• The soft palate moves back to close off the nasal passage,
and the trachea moves up under the epiglottis to cover
the glottis, the opening to the larynx.
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Peristalsis—contractions that push food through
the digestive tract.
Sphincter—a ring of muscle that acts as a valve.
When it contracts, it stops food from moving through;
when it relaxes, it allows food through.
That is, the lower esophageal sphincter is between the
esophagus and the stomach.
• Heartburn—failure of this sphincter; stomach contents move
from the stomach into the esophagus.
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Vomiting—when strong contractions of the
abdominal muscles and the diaphragm (the
muscle separating the thoracic and abdominal
cavities) force the contents of the stomach into
the esophagus and oral cavity.
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Describe the role of the mouth, pharynx, and
esophagus in digestion.
Detail how mechanical digestion and chemical
digestion occur in the mouth.
Explain what ordinarily prevents food from
entering the nose or trachea when you swallow.
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Learning Outcomes:
• Describe the structure of the stomach and explain
its role in digestion.
• Describe the structure of the small intestine and
explain its role in digestion.
• Explain how carbohydrates, lipids, and proteins are
processed by the small intestine.
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Stomach.
Stores food, starts digestion of proteins, and
controls movement of food into the small intestine.
Does not absorb nutrients.
• However, it does absorb alcohol, because alcohol is fat-
soluble and can pass through membranes easily.
There are three layers of muscle in the muscularis
layer (instead of two) to help in mechanical
digestion.
• Circular, longitudinal, and third oblique layer.
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(c): Steve Gschmeissner/Brand X Pictures/SPL/Getty Images 28
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Heartburn (GERD).
• The lining of the esophagus is thinner than the lining
of the stomach; if chyme enters the esophagus, it
produces a burning sensation.
• Can be caused by pregnancy and excess fat pushing
on the stomach.
• Gastroesophageal reflux disease (GERD)—chronic
heartburn.
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Stomach, continued.
The mucosa has deep folds called rugae.
The mucosa also has gastric pits, which contain
gastric glands.
• The gastric glands produce gastric juice, which contains:
• Pepsin—digests
proteins.
• Hydrochloric acid (HCl)—pH of 2.
• Kills bacteria and activates pepsin.
• Mucus.
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Stomach, continued.
Normally, the stomach empties in 2–6 hours.
Chyme—a mixture of food and gastric juice.
• Pyloric sphincter—allows only a small amount of chyme
to enter the small intestine at a time.
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The small intestine—named for its small
diameter compared with the large intestine’s.
The small intestine is very long, longer than the
large intestine.
• Averaging about 6 m (18 ft) in length, whereas the large
intestine is about 1.5 m (4.5 ft).
It consists of three regions:
• Duodenum.
• Jejunum.
• Ileum.
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The Small Intestine Is the Main Digestive Organ.
Pancreas—secretes digestive enzymes through a duct into
the duodenum, the first portion of the small intestine.
Another duct brings bile from the liver and gallbladder into
the duodenum.
Bile emulsifies fat.
• Mechanical digestion; causes fat droplets to disperse in water to
expose more of it to lipase.
• Produced by the pancreas, it hydrolyzes fats into glycerol and fatty
acids.
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The Small Intestine Is the Main Digestive Organ,
continued.
Pancreatic amylase—produced by the pancreas, secreted
into the duodenum.
• Digests carbohydrates.
Trypsin—produced by the pancreas, secreted into the
duodenum.
• Digests proteins, so is a protease—a class of enzymes that digest
proteins.
Pancreatic juice contains sodium bicarbonate, which
neutralizes acidic chime.
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Table 9.1a Major Digestive Enzymes: Carbohydrate Digestion
Enzyme Produced By Site of Action Optimum pH Function
Salivary amylase Salivary glands Mouth Neutral Begins the breakdown of starch to
maltose
Pancreatic amylase Pancreas Small intestine Basic Breakdown of starch to maltose
Maltase Small intestine Small intestine Basic Breakdown of maltose to glucose
Lactase Small intestine Small intestine Basic Breakdown of lactose to glucose
and galactose
Table 9.1b Major Digestive Enzymes: Protein Digestion
Enzyme Produced By Site of Action Optimum pH Function
Pepsin Gastric glands Stomach Acidic Breakdown of proteins to peptides
and amino acids
Trypsin Pancreas Small intestine Basic Breakdown of proteins to peptides
and amino acids
Peptidases Small intestine Small intestine Basic Breakdown of peptides to amino
acids
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Table 9.1c Major Digestive Enzymes: Nucleic Acid Digestion
Enzyme Produced By Site of Action Optimum pH Function
Nuclease Pancreas Small intestine Basic Breakdown of nucleic acids to
nucleotides
Nucleosidases Small intestine Small intestine Basic Breakdown of nucleotides to
phosphates, bases, and sugars
Table 9.1d Major Digestive Enzymes: Fat Digestion
Enzyme Produced By Site of Action Optimum pH Function
Salivary
lipase
Salivary glands Mouth Neutral Begins the breakdown of triglycerides
into fatty acids
Lipase Pancreas Small intestine Basic Breakdown of lipids to glycerol and fatty
acids
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Nutrients Are Absorbed in the Small Intestine.
The mucosa contains fingerlike projections
called villi (sing., villus).
The cells that cover the villi have microvilli.
• Give the villi a fuzzy “brush border.”
• Contain brush border enzymes that complete digestion.
These two structures greatly increase the surface
area of the small intestine for absorption of nutrients.
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Absorption in the Small Intestine
(Figure 9.6)
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(photos) (b): Al Telser/McGraw Hill; (c): Steve Gschmeissner/Science Photo Library/Getty Images 38
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Nutrients Are Absorbed in the Small Intestine,
continued.
Nutrients are absorbed into the villi, which contain blood
capillaries and a small lymphatic capillary called a lacteal.
• Monosaccharides and amino acids enter the blood capillaries of a
villus.
• Glycerol and fatty acids form lipoprotein droplets called
chylomicrons, which then enter a lacteal.
After nutrients are absorbed, they are eventually carried to
all the cells of the body by the blood.
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Digestion and Absorption of Organic
Nutrients (Figure 9.7)
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Lactose Intolerance.
Lactose is the primary sugar in milk.
Lactase—the brush border enzyme that digests lactose.
Characterized by diarrhea, gas, bloating, and abdominal
cramps after ingesting milk and other dairy products.
• Diarrhea occurs because the undigested lactose causes fluid retention
in the small intestine.
• Gas, bloating, and cramps occur when bacteria break down the
lactose anaerobically.
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Celiac Disease.
• Autoimmune response against a protein called
gluten, which is naturally found in grains such as
wheat, barley, and rye.
• The presence of gluten in the small intestine results
in an inflammatory response, which damages the
villi and microvilli of the small intestine.
• Can lead to abdominal pain, diarrhea, and
malnutrition.
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Describe the functions of the stomach and how
the wall of the stomach is modified to perform
these functions.
Detail the functions of the small intestine and
how the wall of the small intestine is modified to
perform these functions.
Summarize the differences in how
carbohydrates, proteins, and fats are digested
and absorbed by the small intestine.
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9.4 The Accessory Organs and Regulation
of Secretions
Learning Outcomes:
• Explain the functions of the pancreas, liver, and
gallbladder during digestion.
• List the secretions of the pancreas, liver, and
gallbladder.
• Summarize how secretions of the accessory organs
are regulated.
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Pancreas.
Located behind the stomach.
Most pancreatic cells produce pancreatic juice,
which enters the duodenum via the pancreatic duct.
• Contains sodium bicarbonate and digestive enzymes.
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Accessory Organs of the Digestive System
(Figure 9.8)
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Pancreas, continued.
Also an endocrine gland; secretes the hormone
insulin when the blood glucose levels rise.
Type 1 diabetes—not enough insulin.
• Normally diagnosed in childhood.
Type 2 diabetes—the body’s cells are insulin-
resistant.
• Normally occurs in adulthood.
• Risk factors: obesity, inactivity, family history.
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Liver.
The largest gland in
the body.
Lies mainly in the upper right abdominal cavity,
under the diaphragm.
Lobules—structural and functional units.
The hepatic portal vein brings blood to the liver
from the GI tract.
• The lobules filter this blood, removing poisonous
substances.
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Table 9.2 Functions of the Liver
1. Destroys old red blood cells; excretes bilirubin, a breakdown product of
hemoglobin in bile, a liver product
2. Detoxifies blood by removing and metabolizing poisonous substances
3. Stores iron (Fe raised to the 2 plus power), the water-soluble vitamin B12, and the fat-soluble
vitamins A, D, E, and K
4. Makes plasma proteins, such as albumins and fibrinogen, from amino
acids
5. Stores glucose as glycogen after a meal; breaks down glycogen to glucose
to maintain the glucose concentration of blood between eating periods
6. Produces urea after breaking down amino acids
7. Helps regulate blood cholesterol level, converting some to bile salts
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Liver, continued.
Stores vitamins.
Involved in blood glucose homeostasis.
• Stores glucose as glycogen; when blood glucose is low, it
releases glucose by breaking down glycogen.
• Converts glycerol and amino acids to glucose.
• As amino acids are converted to glucose, urea is formed.
Produces plasma proteins.
Regulates blood cholesterol levels.
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Liver, concluded.
Produces bile, which contains bile salts, water,
cholesterol, and bicarbonate.
• Contains bilirubin, a green pigment formed from the
breakdown of hemoglobin.
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Gallbladder.
• Pear-shaped organ just below the liver.
• Stores bile.
• Gallstones—made of a stone-like material.
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Liver disorders: hepatitis and cirrhosis.
Liver disease can cause bile pigments to leak into
the blood, causing jaundice.
• Yellowish tint to the whites of the eyes and the skin.
.
• Inflammation of the liver.
• Has different forms.
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Hepatitis
Hepatitis, continued.
Hepatitis A—usually acquired from sewage-
contaminated drinking water and food.
Hepatitis B—usually from sexual contact, but also
from blood transfusions or contaminated needles.
• More contagious than the AIDS virus and is spread in the
same way.
• Vaccines are available for hepatitis A and B.
Hepatitis C—usually acquired by infected blood.
• Can lead to chronic hepatitis, liver cancer, and death.
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Cirrhosis.
Chronic disease; first, liver becomes fatty, and then
filled with fibrous scar tissue.
Often seen in people with obesity and alcohol use
disorder, due to malnutrition and the excessive
alcohol (a toxin) the liver is forced to break down.
The liver can regenerate and recover if the rate of
regeneration exceeds the rate of damage.
• During liver failure there may not be enough time to let
the liver heal so will need a liver transplantation.
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Secretion of digestive juices is controlled by the
nervous system and digestive hormones.
When you look at or smell food, the parasympathetic
nervous system stimulates gastric secretion.
A meal rich in protein causes the stomach to produce
the hormone gastrin.
• Increases the secretory activity of gastric glands.
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Hormonal Control and Regulation of
Digestion (Figure 9.9)
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Nervous system and hormonal control,
continued.
Secretin—secreted by the duodenum.
• Release is stimulated by HCl (present in chyme).
Cholecystokinin (CCK)—released by the duodenum
when proteins and fat are present.
• Causes the liver to increase production of bile and causes
the gallbladder to contract and release stored bile.
• These hormones increase the production of pancreatic
juice.
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Name and describe the functions of three main
accessory organs that assist with the digestive
process.
Discuss what could occur if each of the
accessory organs of digestion did not function
properly.
Detail why the regulation of digestive secretions
is important to the overall process of digestion.
Describe what could occur without regulation.
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Learning Outcomes:
• Describe the structure and function of the large
intestine.
• List the disorders of the large intestine and provide a
cause for each.
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Large intestine—includes the cecum, the colon,
the rectum, and the anal canal.
Larger in diameter than the small intestine, but it is
shorter in length.
Cecum—the first portion.
• Vermiform appendix—projection off of the cecum.
• Fights infections.
• Appendicitis—inflamed appendix; can cause peritonitis, a
life-threatening infection of the peritoneum.
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The Regions of the Large Intestine
(Figure 9.10)
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Large intestine, continued.
Colon—includes the ascending colon, which goes up
the right side of the body; transverse colon, which
crosses the abdominal cavity; descending colon,
which passes down the left side; and the sigmoid
colon, which enters the rectum, the last portion of
the large intestine.
• The rectum opens at the anus, where defecation, the
expulsion of feces, occurs.
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Functions of the large intestine.
Does not produce digestive enzymes.
Does not absorb nutrients except certain vitamins.
Absorbs water from feces to prevent dehydration.
Absorbs vitamins produced by intestinal flora, the
bacteria that inhabit the intestine.
• Bacteria break down indigestible material and produce B-
complex vitamins and vitamin K.
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Functions of the large intestine, continued.
Forms feces.
• ¾ water, ¼ solid wastes.
• Bacteria and dietary fiber (indigestible remains) make up
the solid wastes.
• Bacteria digesting the indigestible materials causes the
odor of feces and accounts for the gas.
• Stercobilin, a breakdown product of bilirubin, and
oxidized iron cause the brown color of feces.
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Functions of the large intestine, concluded.
Defecation—ridding the body of feces.
• Peristalsis forces feces into the rectum.
• Stretching of the rectal wall initiates nerve impulses to the
spinal cord.
• Then the rectal muscles contract and the anal sphincters
relax, allowing the feces to exit the body through the anus.
• Can inhibit defecation by contracting the external anal
sphincter, which is made of skeletal muscle.
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Diarrhea—increased peristalsis and failure to absorb
water from feces, due to either an infection or nervous
stimulation.
Constipation—dry, hard feces; may be controlled with
water and fiber.
Hemorrhoids—enlarged, inflamed blood vessels of the
anus due to chronic constipation, pregnancy, aging, anal
intercourse.
Diverticulosis—pouches; weak spots in the muscularis
layer.
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Irritable bowel syndrome (IBS), or spastic.
colon—the muscularis contracts powerfully but
without normal coordination.
• Symptoms: abdominal cramps, gas, constipation, and
urgent, explosive stools.
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Inflammatory bowel disease (IBD)—includes:
Ulcerative colitis—affects the large intestine and rectum.
• Results in diarrhea, rectal bleeding, abdominal cramps, and urgency to
defecate.
Crohn’s disease—usually in the small intestine.
• Ulcers in the intestinal wall; they are painful and bleed as they erode
the submucosal layer, where there are nerves and blood vessels.
• Can’t absorb nutrients in the affected areas.
• Symptoms: diarrhea, weight loss, abdominal cramping, anemia,
bleeding, and malnutrition.
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Polyps and cancer.
Polyps—small growths in the colon lining.
• Can be benign or cancerous.
• If colon cancer is detected while still confined to a polyp, the
expected outcome is a complete cure.
• Increased dietary fat raises the risk of colon cancer.
• Fiber in the diet inhibits colon cancer, and regular
elimination reduces the time that the colon wall is exposed
to cancer-promoting agents in the feces.
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Describe the parts of the large intestine, and
provide the function for each.
Explain the role of the large intestine in the
digestive tract.
Describe how constipation and diarrhea are
related to the large intestine.
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Learning Outcomes:
• Calculate a BMI value and interpret its relationship
to your overall health.
• Identify the role of each class of nutrient in the
human body.
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Obesity—significantly overweight.
One of the greatest health problems in the United
States.
• Almost 42% of adults and 18.5% of children are obese.
• Excess body fat is associated with a higher risk for
premature death, type 2 diabetes, hypertension,
cardiovascular disease, stroke, osteoarthritis, and certain
types of cancer.
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Defining obesity.
Having a body mass index (BMI) of 30 or greater.
• Weight in kilograms (kg) is divided by the height in
2m .
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Table 9.3 BMI Values
Classification BMI Values
Healthy 18.5 to 24.9
Overweight 25.0 to 29.9
Obese 30.0 to 39.9
Extremely (morbid) obese 40.0 and higher
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Source: Adapted from “Clinical Guidelines on the Identification, Evaluation, and Treatment of Overweight and Obesity in Adults: The Evidence Report.” 76
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Classes of nutrients.
Nutrient—a required component of food that
performs a physiological function in the body.
• Provides energy, promotes growth and development, and
regulates cellular metabolism.
• Includes carbohydrates, proteins, lipids, minerals, and
vitamins.
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Carbohydrates—are either simple or complex.
Glucose—simple sugar.
Complex carbohydrates are digested to glucose.
Although body cells can use fatty acids as an energy
source, brain cells require glucose.
Any product made from refined grains, such as white
bread, cake, and cookies, should be minimized in the
diet.
• During refinement of grains, fiber is removed, along with
vitamins and minerals.
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Carbohydrates, continued.
• Sources of complex carbohydrates, such as beans,
peas, nuts, fruits, and whole-grain products, are
good sources of vitamins, minerals, and fiber.
• Insoluble fiber adds bulk to the feces and stimulates
movements of the large intestine, preventing
constipation.
• Soluble fiber combines with bile salts and
cholesterol in the small intestine and prevents them
from being absorbed.
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Can carbohydrates be harmful?
High intake of refined carbohydrates and
fructose sweeteners contribute to obesity.
In addition, they have a high glycemic index,
because they quickly increase blood glucose.
• When blood glucose levels rise rapidly, the pancreas
produces a lot of insulin to bring the level down.
• Chronically high insulin levels may lead to insulin
resistance, type 2 diabetes, and increased fat deposition.
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Reducing High-Glycemic-Index
Carbohydrates (Table 9.4)
Table 9.4 Reducing High-Glycemic-Index Carbohydrates
To Reduce Dietary Sugar
• Eat fewer sweets, such as candy, soft drinks, ice cream, and pastries.
• Eat fresh or frozen fruits or fruits canned without heavy syrup. Avoid
artificial fruit juices.
• Use less sugar—white, brown, or raw—and less honey and syrups.
• Avoid sweetened breakfast cereals.
• Eat less jelly, jam, and preserves.
• When cooking, use spices, such as cinnamon, instead of sugar to flavor
foods.
• Do not put sugar in tea or coffee.
• Avoid processed foods made from refined carbohydrates, such as white
bread, rice, and pasta, and limit potato intake.
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Proteins—made of 20 different amino acids.
There are eight essential amino acids—must be attained
through the diet.
Complete proteins—contain all essential amino acids;
usually derived from animal sources.
• Non-animal sources of complete proteins are tofu, soymilk, and other
processed food from soybeans.
Incomplete proteins—plant sources; need to combine them
to get all essential amino acids.
• Must ingest essential amino acids every day; they are not stored in
the body.
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Can proteins be harmful?
An overabundance of protein intake can result in
dehydration during exercise.
• Can also lead to calcium loss in urine, which can lead to
kidney stones.
Eating red meat can lead to cardiovascular disease
since it is high in saturated fats.
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Lipids—include fats, oils, and cholesterol.
Saturated fats.
• Usually of animal origin.
• Solid at room temperature (unsaturated fats are usually
liquid at room temperature).
• That is, butter, fat in meat, coconut oil, and palm oil.
Unsaturated fats.
• Don’t promote cardiovascular disease.
• That is, corn oil and safflower oil are high in
polyunsaturated fatty acids.
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Lipids, continued.
Polyunsaturated oils contain the essential fatty acids
linoleic acid and linolenic acid.
Olive oil and canola oil have more monounsaturated
fatty acids than others.
Omega-3 fatty acids preserve brain function and
protect against heart disease.
• Flaxseed, cold-water fish are excellent sources.
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Saturated and Unsaturated Fatty Acids
(Figure 9.14)
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Can lipids be harmful?
The risk for cardiovascular disease is increased by a
diet high in saturated fats and cholesterol.
• Saturated fats contribute to the formation of
atherosclerotic plaques that limit blood flow.
• Cholesterol is carried in the blood by two transport
proteins: high-density lipoprotein (HDL) and low-density
lipoprotein (LDL).
• HDL (the “good” lipoprotein) ends up in the liver, where the
cholesterol is metabolized.
• LDL (the “bad” lipoprotein) ends up being deposited in the
tissues.
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Can lipids be harmful? continued.
Trans fatty acids (trans fats) arise when unsaturated
fatty acids are hydrogenated to produce a solid fat.
• Found in commercially packaged goods, such as cookies
and crackers.
• If something contains partially hydrogenated vegetable oil, it
contains trans fats.
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Table 9.5a Reducing Lipids in the Diet
To Reduce Saturated Fats and Trans Fats in the Diet
• Choose poultry, fish, or dry beans and peas as a protein source.
• Remove skin from poultry, and trim fat from red meats before cooking;
place on a rack, so that fat drains off.
• Broil, boil, or bake rather than fry.
• Limit your intake of butter, cream, trans fats, shortenings, and tropical
oils (coconut and palm oils).
• Use herbs and spices to season vegetables instead of butter, margarine,
or sauces. Use lemon juice instead of salad dressing.
• Drink skim milk instead of whole milk and use skim milk in cooking and
baking.
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Table 9.5b Reducing Lipids in the Diet
To Reduce Dietary Cholesterol
• Avoid cheese, egg yolks, liver, and certain shellfish (shrimp and lobster).
Preferably, eat white fish and poultry.
• Substitute egg whites for egg yolks in both cooking and eating.
• Include soluble fiber in the diet. Oat bran, oatmeal, beans, corn, and
fruits, such as apples, citrus fruits, and cranberries, are high in soluble
fiber.
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Minerals are divided into major minerals and
trace minerals.
Major minerals are needed at quantities greater
than
100
mg per day; trace, less than 100 mg.
Major minerals—in cells and body fluids; are
structural components of tissues.
Trace minerals are often part of larger molecules.
• That is, iron is present in hemoglobin, and iodine is a part
of thyroid hormones.
• That is, zinc, copper, and manganese are present in
enzymes.
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Table 9.6a Minerals: Major (More than 100 mg/Day Needed)
Mineral Functions Food Sources Health Concerns Deficiency Health Concerns Toxicity
(Ca raised to the 2 plus power) Strong bones and teeth,
nerve conduction, muscle
contraction, blood clotting
Dairy products, leafy
green vegetables
Stunted growth in children,
low bone density in adults
Kidney stones, interferes
with iron and zinc
absorption
Phosphorus (P O 4 raised to the 3 minus power) Bone and soft tissue growth;
part of phospholipids, ATP,
and nucleic acids
Meat, dairy products,
sunflower seeds,
food additives
Weakness, confusion, pain
in bones and joints
Low blood and bone calcium
levels
Potassium (K raised to the plus power) Nerve conduction, muscle
contraction
Many fruits and
vegetables, bran
Paralysis, irregular
heartbeat, eventual death
Vomiting, heart attack,
death
Sulfur (S raised to the 2 minus power) Stabilizes protein shape,
neutralizes toxic substances
Meat, dairy products,
legumes
Not likely In animals, depresses
growth
(Na raised to the plus power) Nerve conduction, pH and
water balance
Table salt Lethargy, muscle cramps,
loss of appetite
Edema, high blood pressure
Chloride (Cl raised to the minus power) Water balance Table salt Not likely Vomiting, dehydration
Magnesium (Mg raised to the 2 plus power) Part of various enzymes for
nerve and muscle
contraction, protein
synthesis
Whole grains, leafy
green vegetables
Muscle spasm, irregular
heartbeat, convulsions,
confusion, personality
changes
Diarrhea
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Table 9.6b Minerals: Trace (Less than 100 mg/Day Needed)
Mineral Functions Food Sources Health Concerns Deficiency Health Concerns Toxicity
Zinc (Zn raised to the 2 plus power) Protein synthesis, wound
healing, fetal development
and growth, immune
function
Meats, legumes, whole
grains
Delayed wound healing,
stunted growth, diarrhea,
mental lethargy
Anemia, diarrhea, vomiting,
renal failure, abnormal
cholesterol levels
Iron (Fe raised to the 2 plus power) Hemoglobin synthesis Whole grains, meats,
prune juice
Anemia, physical and mental
sluggishness
Iron toxicity disease, organ
failure, eventual death
Copper (Cu raised to the 2 plus power) Hemoglobin synthesis Meat, nuts, legumes Anemia, stunted growth in
children
Damage to internal organs if
not excreted
Iodine (I raised to the minus power) Thyroid hormone synthesis Iodized table salt, seafood Thyroid deficiency Depressed thyroid function,
anxiety
Selenium (S e O 4 raised to the 3 minus power) Part of antioxidant enzyme Seafood, meats, eggs Vascular collapse, possible
cancer development
Hair and fingernail loss,
discolored skin
Manganese (Mn raised to the 2 plus power) Part of enzymes Nuts, legumes, green
vegetables
Weakness and confusion Confusion, coma, death
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Minerals, continued.
• Occasionally individuals do not receive enough iron,
calcium, magnesium, or zinc in their diets.
• Adult females need more iron in their diet than
males because they lose hemoglobin each month
during menstruation.
• A varied and complete diet usually supplies enough
of each type of mineral.
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Calcium
Calcium.
• In bones, teeth.
• Needed for nerve impulse conduction, muscle
contraction and blood clotting.
• Calcium supplements prevent osteoporosis—a
degenerative bone disease common in the elderly.
•
is needed with calcium to prevent bone
loss.
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Sodium
Sodium—regulates water balance.
• Important in the movement of materials across the
plasma membrane as well as the conduction of a
nerve impulse.
• The recommended amount of sodium intake per day
is 1,500 mg, but the average American takes in more
than 3,400 mg.
• Excess sodium can worsen hypertension.
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Table 9.7 Reducing Dietary Sodium
To Reduce Dietary Sodium
• Use spices instead of salt to flavor foods.
• Add little or no salt to foods at the table, and add only small amounts of
salt when you cook.
• Eat unsalted crackers, pretzels, potato chips, nuts, and popcorn.
• Avoid hot dogs, ham, bacon, luncheon meats, smoked salmon, sardines,
and anchovies.
• Avoid processed cheese and canned or dehydrated soups.
• Avoid brine-soaked foods, such as pickles and olives.
• Read nutrition labels to avoid high-salt products.
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Vitamins—organic compounds.
• Used for metabolism.
• Need to ingest, since they are not produced in high
enough quantities by the body.
• Are often parts of coenzymes.
• There are 13 vitamins, two types: fat soluble and
water soluble.
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Table 9.8 Fat-Soluble Vitamins
Vitamin Functions Food Sources Health Concerns
Deficiency
Health Concerns
Toxicity
Vitamin A Antioxidant synthesized from
beta-carotene; needed for
healthy eyes, skin, hair, and
mucous membranes and for
proper bone growth
Deep yellow/orange and
leafy, dark green
vegetables; fruits; cheese;
whole milk; butter; eggs
Night blindness,
impaired growth
of bones and
teeth
Headache, dizziness,
nausea, hair loss,
abnormal
development of
fetus
Vitamin D Group of steroids needed for
development and maintenance
of bones and teeth and for
absorption of calcium
Milk fortified with vitamin
D, fish liver oil; also made
in the skin when exposed
to sunlight
Rickets,
decalcification
and weakening of
bones
Calcification of soft
tissues, diarrhea,
possible renal
damage
Vitamin E Antioxidant that prevents
oxidation of vitamin A and
polyunsaturated fatty acids
Leafy green vegetables,
fruits, vegetable oils, nuts,
whole-grain breads and
cereals
Unknown Diarrhea, nausea,
headaches, fatigue,
muscle weakness
Vitamin K Needed for synthesis of
substances active in clotting of
blood
Leafy green vegetables,
cabbage, cauliflower
Easy bruising and
bleeding
Can interfere with
anticoagulant
medication
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Table 9.9 Water-Soluble Vitamins (top)
Vitamin Functions Food Sources Health Concerns
Deficiency
Health Concerns
Toxicity
Vitamin C Antioxidant; needed for forming
collagen; helps maintain
capillaries, bones, and teeth
Citrus fruits, leafy green
vegetables, tomatoes,
potatoes, cabbage
Scurvy, delayed
wound healing,
infections
Gout, kidney
stones, diarrhea,
decreased copper
Thiamine
(vitamin B1)
Part of coenzyme needed for
cellular respiration; also promotes
activity of the nervous system
Whole-grain cereals, dried
beans and peas, sunflower
seeds, nuts
Beriberi, muscular
weakness, enlarged
heart
Can interfere with
absorption of
other vitamins
Riboflavin
(vitamin B2)
Part of coenzymes, such as FAD;
aids cellular respiration, including
oxidation of protein and fat
Nuts, dairy products, whole-
grain cereals, poultry, leafy
green vegetables
Dermatitis, blurred
vision, growth failure
Unknown
Niacin
(nicotinic
acid)
Part of coenzyme NAD; needed
for cellular respiration, including
oxidation of protein and fat
Peanuts, poultry, whole-grain
cereals, leafy green
vegetables, beans
Pellagra, diarrhea,
mental disorders
High blood sugar
and uric acid,
vasodilation, etc.
Folacin
(folic acid)
Coenzyme needed for production
of hemoglobin and formation of
DNA
Dark, leafy green vegetables;
nuts; beans; whole-grain
cereals
Megaloblastic
anemia, spina bifida
May mask B12
deficiency
FAD = flavin adenine dinucleotide
NAD = nicotinamide adenine dinucleotide
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Table 9.9 Water-Soluble Vitamins (bottom)
Vitamin Functions Food Sources Health Concerns
Deficiency
Health Concerns
Toxicity
Vitamin B6 Coenzyme needed for synthesis
of hormones and hemoglobin;
CNS control
Whole-grain cereals,
bananas, beans, poultry,
nuts, leafy green vegetables
Rarely, convulsions,
vomiting,
seborrhea,
muscular weakness
Insomnia,
neuropathy
Pantothenic
acid
Part of coenzyme A needed for
oxidation of carbohydrates and
fats; aids in the formation of
hormones and certain
neurotransmitters
Nuts, beans, dark green
vegetables, poultry, fruits,
milk
Rarely, loss of
appetite, mental
depression,
numbness
Unknown
Vitamin B12 Complex, cobalt-containing
compound; part of the
coenzyme needed for synthesis
of nucleic acids and myelin
Dairy products, fish, poultry,
eggs, fortified cereals
Pernicious anemia Unknown
Biotin Coenzyme needed for
metabolism of amino acids and
fatty acids
Generally in foods,
especially eggs
Skin rash, nausea,
fatigue
Unknown
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Antioxidants—decrease the rate of oxidation
or transfer of electrons.
Cellular metabolism generates free radicals, which
damage cells and tissues.
The most common free radicals in cells are
superoxide 2(O ) and hydroxide (OH ).
Vitamin C, E, and A are considered antioxidants
because they defend the body against free radicals.
• Are common in fruits and vegetables.
102
2(O ) (OH ).
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Vitamin D
Vitamin D.
Skin cells contain a precursor that is converted to
vitamin D after UV exposure.
Vitamin D is modified first in the kidneys and then in
the liver until finally it becomes calcitriol.
• Promotes the absorption of calcium by the intestines.
Lack of vitamin D leads to rickets in children.
• Bowing of the legs, caused by defective mineralization of
the skeleton.
• Most milk is fortified with vitamin D to prevent rickets.
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Basal metabolism—the number of calories a body
burns at rest to maintain normal body functions.
• Depending on exercise levels, someone may need
more calories beyond the basal metabolic rate.
• A person cannot become overweight without taking
in more calories than needed.
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Limit the number of calories to an amount used
daily.
• Woman—maximum number of daily calories
(without exercise) is 2,000.
• Man—maximum 2,500 calories.
• The MyPlate graphic shows how someone should
distribute those calories among the food groups.
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The MyPlate Dietary Recommendations
(Figure 9.15)
Access the text alternative for slide images.
U.S. Department of Agriculture 106
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A diet should include foods from all food groups.
Eat more of these foods: fruits, vegetables, whole grains, and
fat-free or low-fat milk products.
• Choose dark green vegetables, orange vegetables, and leafy
vegetables.
• Dry beans and peas are good sources of fiber and an excellent protein
source as well.
• Limit potatoes and corn.
• When eating grains, choose whole grains, such as brown rice, oatmeal,
and whole-wheat bread.
• Choose fruit as a snack or a topping for foods, instead of sugar.
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A diet should include, continued.
Choose lean meats, such as poultry, and fish high in omega-3
fatty acids, such as salmon, trout, and herring, in moderate-
sized portions.
• Include oils rich in monounsaturated and polyunsaturated fatty acids
in the diet.
Eat less of foods high in saturated or trans fats, added sugars,
cholesterol, salt, and alcohol.
Be physically active every day.
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Eating disorders have social, cultural, emotional,
and biological roots.
Anorexia nervosa—psychological disorder; a fear of
getting fat.
• Usually results in self-induced starvation, high physical
activity, and may include purging.
Bulimia nervosa—eat large amounts of high-calorie
food (binge-eating) followed by purging to avoid weight
gain.
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Eating disorders, continued.
Binge-eating disorder—overeating without purging.
• Stress, anxiety, anger, and depression can contribute.
• Common in the obese.
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Eating disorders, concluded.
Muscle dysmorphia—thinks his or her body is
underdeveloped.
• Excess body-building.
• A preoccupation with diet and body form.
• May spend hours in the gym every day.
• Unlike anorexia nervosa and bulimia, affects more men
than women.
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Briefly describe and give an example of each
class of nutrients.
Discuss why carbohydrates and fats might be the
cause of the obesity epidemic today.
Explain the difference between a vitamin and
mineral.
112
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- human Biology Seventeenth Edition
- Organs of the GI Tract and Accessory Structures of Digestion (F
- The Layers of the Gastrointestinal Tract Wall (Figure 9.2)
- Absorption in the Small Intestine (Figure 9.6)
- Digestion and Absorption of Organic Nutrients (Figure 9.7)
- 9.4 The Accessory Organs and Regulation of Secretions
- Accessory Organs of the Digestive System (Figure 9.8)
- Hormonal Control and Regulation of Digestion (Figure 9.9)
- The Regions of the Large Intestine (Figure 9.10)
- Reducing High-Glycemic-Index Carbohydrates (Table 9.4)
- Saturated and Unsaturated Fatty Acids (Figure 9.14)
- The MyPlate Dietary Recommendations (Figure 9.15)
9.1 Overview of Digestion 1
9.1 Overview of Digestion 2
Processes of Digestion
Stages of Digestion
Wall of the Digestive Tract 1
Wall of the Digestive Tract 2
Bowel Disease
Check Your Progress 9.1
9.2 The Mouth, Pharynx, and Esophagus
The Mouth 1
Structures of the Mouth (Figure 9.3a) 1
The Mouth 2
The Mouth 3
The Mouth 4
Structures of the Mouth (Figure 9.3b) 2
The Mouth 5
The Pharynx and Esophagus
Swallowing
The Process of Swallowing (Figure 9.4)
Peristalsis 1
Peristalsis 2
Check Your Progress 9.2
9.3 The Stomach and Small Intestine
The Stomach 1
Structure of the Stomach (Figure 9.5)
The Stomach 2
The Stomach 3
The Stomach 4
The Small Intestine 1
The Small Intestine 2
The Small Intestine 3
Major Digestive Enzymes (Table 9.1) 1
Major Digestive Enzymes (Table 9.1) 2
The Small Intestine 4
The Small Intestine 5
Lactose Intolerance
Celiac Disease
Check Your Progress 9.3
The Accessory Organs 1
The Accessory Organs 2
The Accessory Organs 3
Functions of the Liver (Table 9.2)
The Accessory Organs 4
The Accessory Organs 5
The Accessory Organs 6
Liver Disorders
Hepatitis
Cirrhosis
Regulation of Digestive Secretions 1
Regulation of Digestive Secretions 2
Check Your Progress 9.4
9.5 The Large Intestine and Defecation
The Large Intestine 1
The Large Intestine 2
Functions of the Large Intestine 1
Functions of the Large Intestine 2
Functions of the Large Intestine 3
Disorders of the Colon and Rectum 1
Disorders of the Colon and Rectum 2
Disorders of the Colon and Rectum 3
Disorders of the Colon and Rectum 4
Check Your Progress 9.5
9.6 Nutrition and Weight Control 1
9.6 Nutrition and Weight Control 2
Defining Obesity
BMI Values (Table 9.3)
The Body Mass Index Chart (Figure 9.11)
Classes of Nutrients
Carbohydrates 1
Carbohydrates 2
Carbohydrates 3
Proteins 1
Proteins 2
Lipids 1
Lipids 2
Lipids 3
Lipids 4
Reducing Lipids in the Diet (Table 9.5) 1
Reducing Lipids in the Diet (Table 9.5) 2
Minerals 1
Minerals (Table 9.6) 1
Minerals (Table 9.6) 2
Minerals 2
Calcium
Sodium
Reducing Dietary Sodium (Table 9.7)
Vitamins
Fat-Soluble Vitamins (Table 9.8)
Water-Soluble Vitamins (Table 9.9) 1
Water-Soluble Vitamins (Table 9.9) 2
Antioxidants
Vitamin D
How to Plan Nutritious Meals 1
How to Plan Nutritious Meals 2
How to Plan Nutritious Meals 3
How to Plan Nutritious Meals 4
Eating Disorders 1
Eating Disorders 2
Eating Disorders 3
Check Your Progress 9.6
End of Main Content
