PowerLecture: Chapter 7

1
PowerLectureChapter 7

• Digestion and Nutrition

2
Learning Objectives

• Understand the structure and function of the
  component parts of the human digestive system.
• Describe how digestion functions in homeostasis.
• Explain how the human body manages to meet the
  energy and nutritional needs of the various body
  parts even though the person may be feasting
  sometimes and fasting at other times.

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Learning Objectives (contd)

• Summarize the daily nutritional requirements of a
  25-year-old man who works at a desk job and
  exercises very little. State what he needs in
  terms of energy, carbohydrates, proteins, and
  lipids, and name at least six vitamins and six
  minerals that he needs to include in his diet
  every day.

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Impacts/Issues

• Hormones and Hunger

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Hormones and Hunger

• Sixty percent of Americans are considered
  overweight or obese.
• Adipose cells store fat to help us through times
  when food might be scarce (which is not often for
  most of us in todays world!)
• The hormones leptin and ghrelin may have effects
  on hunger and eating.
• The digestive system works with other organ
  systems to maintain homeostasis.

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How Would You Vote?

• To conduct an instant in-class survey using a
  classroom response system, access JoinIn Clicker
  Content from the PowerLecture main menu.
• Should fast-food items be required to carry
  health warnings?
• a. Yes, obesity is becoming an epidemic and
  warning labels will help alleviate the crisis.
• b. No, it is up to individuals to use common
  sense and avoid too much fat or too many
  calories.

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Section 1

• The Digestive System An Overview

8
The Digestive System An Overview

• The digestive system (gastrointestinal tract or
  GI tract) is a 6-9 meter long tube where food
  processing takes place to bring nutrients into
  the body.
• Food is transported through the lumen of the tube
  from the mouth to the anus.
• Specialized regions include the mouth, pharynx,
  esophagus, stomach, small intestine, large
  intestine, rectum, and anus.

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The Digestive System An Overview

• The digestive tube has four layers.
• The mucosa is the epithelial lining that faces
  the lumen of the gut.
• Underlying the mucosa is the submucosa, a layer
  of connective tissue containing blood and lymph
  vessels plus nerve networks.
• A smooth muscle layer (longitudinal and circular)
  lies outside the submucosa.

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The Digestive System An Overview

• The serosa forms the outer covering it is a thin
  serous membrane.
• Circular arrays of smooth muscle make up the
  sphincters, which close off a passageway to
  control forward movement of the tracts contents.

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lumen
mucosa
submucosa
circular muscle cells
smooth muscle layer
longitudinal muscle cells
serosa
Fig. 7.2, p. 121
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The Digestive System An Overview

• Digestive system operations contribute to
  homeostasis in key ways.
• Mechanical processing and motility include
  movements that break up, mix, and transport
  ingested food material.
• Secretion is the release of needed enzymes and
  other fluids.
• Digestion is the chemical breakdown of food
  matter to molecules small enough to cross the gut
  lining.

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The Digestive System An Overview

• Absorption is the passage of digested nutrients
  into the blood and lymph.
• Elimination is the expulsion of undigested and
  unabsorbed residues from the end of the GI tract.

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food, water intake
oxygen intake
elimination of carbon dioxide
DIGESTIVE SYSTEM
RESPIRATORY SYSTEM
nutrients, water, salts
carbon dioxide
oxygen
CIRCULATORY SYSTEM
URINARY SYSTEM
water, solutes
elimination of food residues
elimination of excess water, salts, wastes
rapid transport to and from all living cells
Fig. 7.3, p. 121
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Major Components
Accessory Organs
Mouth (Oral cavity)
Salivary Glands
Pharynx
Esophagus
Stomach
Liver
Gallbladder
Pancreas
Small intestine
Large intestine (colon)
Rectum
Anus
Fig. 7.1, p.120
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Section 2

• Chewing and Swallowing Food Processing Begins

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Chewing and Swallowing Food Processing Begins

• Processing starts with the teeth and salivary
  gland enzymes.
• Mechanical breakdown of food begins in the mouth
  (oral cavity).
• Teeth (32 in adults, 20 in children) chew the
  food.
• Each tooth has an enamel coat (crown), a dentin
  core, and an inner pulp.
• Incisors bite off chunks, cuspids tear, and
  molars and premolars grind food.

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molars (12)
premolars (8)
canines (4)
incisors (8)
lower jaw
upper jaw
Fig. 7.4a, p. 122
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enamel
crown
dentin
pulp cavity (contains nerves and blood vessels)
gingiva (gum)
root canal
periodontal membrane
root
bone
Fig. 7.4b, p. 122
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Chewing and Swallowing Food Processing Begins

• Salivary glands secrete a fluid (saliva) into the
  mouth.
• Parotid glands lie just in front of the ear
  submandibular glands are located in the lower
  jaw sublinguals are under the tongue.
• Saliva contains salivary amylase to begin
  carbohydrate digestion, bicarbonate to neutralize
  acids, and mucins to help form the food into a
  bolus.

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parotid gland
submandibular gland
sublingual gland
Fig. 7.4c, p. 122
22
Chewing and Swallowing Food Processing Begins

• The tongue presses food against the hard palate
  of the roof of the mouth to aid mixing, then
  muscle contractions force the bolus into the
  pharynx (throat) and then into the esophagus.

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Chewing and Swallowing Food Processing Begins

• Swallowing has voluntary and involuntary phases.
• The tongue (with the help of the palate) pushes
  the bolus into the pharynx where receptors
  initiate the swallowing reflex into the
  esophagus.
• The epiglottis closes off the trachea to prevent
  choking.
• Muscle contractions called peristalsis move the
  food along the tract to the stomach.

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VOLUNTARY PHASE
INVOLUNTARY PHASE
hard palate
food bolus
epiglottis
Contracted muscles close off esophagus.
Larynx rises trachea closes, and muscle
contractions squeeze food into esophagus.
trachea (airway) open
Fig. 7.5a, p. 123
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muscles relaxed
muscles relaxed
Circular muscles contract, squeezing bolus
toward the stomach.
bolus
Lower esophageal sphincter opens and food enters
stomach.
stomach
Fig. 7.5bc, p. 123
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Section 3

• The Stomach Food Storage, Digestion, and More

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The Stomach Food Storage, Digestion, and More

• The stomach is a muscular sac that stores and
  mixes food, secretes substances to dissolve and
  degrade food, and controls the rate at which
  food enters the small intestine.
• Cells of the stomach
• lining secrete intrinsic
• factor, required for
• absorption of vitamin B12.

Figure 7.6a
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serosa
esophagus
1
longitudinal muscle
circular muscle
pyloric sphincter
2
oblique muscle
submucosa
3
mucosa
duodenum
Fig. 7.6, p. 124
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The Stomach Food Storage, Digestion, and More

• Gastric juice includes hydrochloric acid,
  pepsinogens, and mucus the hormone gastrin
  stimulates secretion of these materials.
• HCl dissolves bits of food to form a thick
  mixture called chyme it also converts pepsinogen
  (inactive) to pepsin (active), and kills
  microbes.
• Pepsin begins the digestion of proteins.
• Normally, mucus and bicarbonate ions protect the
  stomach lining however, a bacterium
  (Helicobacter pylori) can interfere with mucus
  production, resulting in a peptic ulcer.

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The Stomach Food Storage, Digestion, and More

• Peristaltic contractions churn the chyme and keep
  the pyloric sphincter at the stomachs exit
  closed, but small amounts of chyme are released
  at intervals into the small intestine.
• Depending on the acidity and fat content of
  chyme, it can take the stomach 2-6 hours to
  empty an empty stomach forms folds called rugae.
• Water and alcohol are two of the few substances
  absorbed across the stomach wall.

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Section 4

• The Small Intestine A Huge Surface Area for
  Digestion and Absorption

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The Small Intestine A Huge Surface Area for
Digestion and Absorption

• The vast majority of nutrients are absorbed in
  the small intestine.
• The key to the small intestines ability to
  absorb is the structure of its wall.
• The mucosa is highly folded.
• Absorptive surface area is increased by
  fingerlike projections of the intestine lining
  called villi, which bear even smaller microvilli,
  giving each cell a brush border.

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submucosa
serosa (thin connective tissue layer)
mucosa
thick layer of circular muscle
thin layer of longitudinal muscle
Extensive circular folds of mucosa
Fig. 7.7a, p. 125
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Villi (many fingerlike, epithelium-covered
projections from the mucosa)
epithelium
blood capillaries
lymph vessel
connective tissue
vesicles
artery
vein
lymph vessel
Villi on one of the folds, longitudinal section
One villus
Fig. 7.7cd, p. 125
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microvilli at free surface of absorptive cells
ctyoplasm
mucus secretion (goblet cell)
hormone secretion
phagocytosis lysozyme secretion
absorption
Fig. 7.7e, p. 125
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Section 5

• Accessory Organs The Pancreas, Gallbladder, and
  Liver

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Accessory Organs The Pancreas, Gallbladder, and
Liver

• The pancreas produces a variety of digestive
  enzymes.
• The pancreas lies near the stomach it contains
  both exocrine and endocrine glands.
• Four kinds of digestive enzymes are producedone
  kind for each of the four major categories of
  food (carbohydrates, proteins, lipids, and
  nucleic acids).
• Hormones that regulate blood sugar and
  bicarbonate to neutralize the pH of chyme are
  also produced.

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main pancreatic duct
stomach
duodenum
pancreatic hormones secreted into blood
endocrine portion of pancreas (Islets of
Langerhans)
gland cells
exocrine portion of pancreas enzymes secreted
into duodenum
Fig. 7.8, p. 126
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Accessory Organs The Pancreas, Gallbladder, and
Liver

• The gallbladder stores bile.
• The gallbladder is a small sac that stores bile
  produced by the liver.
• Bile is emptied into the small intestine when
  food is present to aid in the digestion and
  absorption of fats.
• The liver is a multipurpose organ.
• The liver is one of the largest organs in the
  body.

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Accessory Organs The Pancreas, Gallbladder, and
Liver

• The bile secreted by the liver contains bile
  salts, which are derived from cholesterol.
• Bile salts help emulsify fats by breaking large
  fat globules into smaller bits.
• Excess cholesterol is also emulsified if the
  level of cholesterol is much higher than the
  amount of bile salts present, however, gallstones
  can form.
• The liver processes nutrient-laden blood from the
  small intestine blood enters the liver via the
  hepatic portal vein.

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inferior vena cava
hepatic vein
liver capillary beds
stomach
liver
gallbladder
(spleen)
hepatic portal vein
pancreas
ascending colon of large intestine
descending colon of large intestine
small intestine
appendix
rectum
Fig. 7.9, p. 127
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Accessory Organs The Pancreas, Gallbladder, and
Liver

• The liver has many important functions
• It converts glucose to glycogen, a storage form.
• It produces plasma proteins.
• It forms urea.
• It makes bile, which is useful in fat
  emulsification.
• It detoxifies harmful substances.
• It degrades worn-out red blood cells.
• It aids in the immune response by removing
  foreign particles.
• It absorbs and stores factors needed for red
  blood cell production.

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Table 7.1, p. 127
44
Section 6

• Digestion and Absorption in the Small Intestine

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Digestion and Absorption in the Small Intestine

• Roughly 9 liters of fluid enters the duodenum
  (the first section of the small intestine) each
  day.
• Nutrients are released by chemical and mechanical
  means.
• Secretions from the pancreas (pancreatic juice)
  are added to chyme in the duodenum.
• Trypsin and chymotrypsin digest proteins to
  peptide fragments peptidases break the fragments
  down into amino acids.
• Bicarbonate from the pancreas buffers the acid
  from the stomach.

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Table 7.2, p. 128
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Digestion and Absorption in the Small Intestine

• Bile salts speed up fat digestion by
  emulsification triglycerides tend to form large
  globules, but when smaller fat droplets become
  coated with bile salts, the negative charges on
  the droplets repel and cause them to stay
  separated.
• Repeated segmentation contractions create an
  oscillating movement that mixes the food.

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p. 128
49
Digestion and Absorption in the Small Intestine

• Different nutrients are absorbed by different
  mechanisms.
• Monosaccharides (glucose), amino acids, and some
  nucleotides cross the gut lining by active
  transport and enter the bloodstream.
• Absorption of fatty acids and monoglycerides is
  aided by bile salts.
• Free fatty acids diffuse into the gut epithelium,
  aided by micelle formation.
• Fats combine with proteins to form particles that
  enter lymph vessels called lacteals, which drain
  into the blood.

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Lumen of intestine
carbohydrates
monosaccharides
amino acids
proteins
Epithelial Cell
Internal Environment
Fig. 7.10, p. 129
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bile salts
bile salts


Micelles
Fat Globules (triglycerides)
fatty acids, monoglycerides
Emulsification
triglycerides proteins
Fig. 7.10, p. 129
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Section 7

• The Large Intestine

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The Large Intestine

• The large intestine begins as a blind, cup-shaped
  pouch (cecum) where it joins the small intestine.
• It continues as the colon (ascending, transverse,
  and descending).
• It ends in the sigmoid colon, which connects
• with the rectum.

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The Large Intestine

• The colon concentrates and stores fecesa mixture
  of undigested and unabsorbed material, water, and
  bacteria.
• Sodium is actively transported out of the colon
  and water follows by osmosis.
• About 30 percent of the feces is bacteria that
  produce vitamins and intestinal gases.

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The Large Intestine

• The appendix projects from the cecum it has no
  known function.
• Feces can become trapped in the appendix, causing
  inflammation called appendicitis.
• If the appendix bursts, released bacteria can
  cause peritonitis in the abdominal cavity.
• When feces distend the rectal wall, defecation
  occurs feces move into the anal canal and
  eventually out of the body through the anus.

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transverse colon
ascending colon
descending colon
fat deposit
ileum of small intestine
cecum
appendix
rectum
anal sphincter
anal canal
anus
Fig. 7.11, p. 130
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Table 7.5, p. 140
58
Section 8

• Managing Digestion and the Processing of Nutrients

59
Managing Digestion and the Processing of Nutrients

• Nerves and hormones regulate digestion.
• Distention of the gut wall after a meal
  stimulates the release of signals from sensory
  receptors, which respond with muscle action and
  enzyme secretion.
• Four major gastrointestinal hormones regulate
  digestion
• Gastrin, produced by the stomach lining,
  stimulates secretion of acids into the stomach to
  aid digestion of protein somatostatin inhibits
  acid production.
• Secretin, from the intestinal lining, stimulates
  the pancreas to release bicarbonate.

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sight, smell, taste of food
emotional states
CENTRAL NERVOUS SYSTEM
LONG REFLEX PATHWAYS
smooth muscle or gland
gut wall
sensory receptors
nerve network
Stimulus
Response
gut lumen
change in food volume, composition in lumen
gut wall moves or substances secreted into lumen
Fig. 7.12, p. 130
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Managing Digestion and the Processing of Nutrients

• Cholecystokinin (CCK) enhances the actions of
  secretin and stimulates gallbladder contractions
  both CCK and secretin slow the rate of gastric
  emptying.
• GIP (glucose insulinotropic peptide) is released
  in the presence of glucose and fat, and
  stimulates insulin secretion for glucose uptake.
• Blood carries the absorbed nutrients to the liver
  for delivery throughout the body.

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Other body tissues
Brain
Glucose
Glucose
Fats
Liver
Fats
Amino acids
Amino acids
Glucose
Glucose
Muscle
Small intestine
Fig. 7.13, p. 131
63
Section 9

• Digestive System Disorders

64
Digestive System Disorders

• The GI tract is open to many kinds of
  disease-causing organisms.
• Bacteria, viruses, and other pathogens can enter
  the GI tract through contaminated food and water.
• One common result of GI tract infection is
  diarrhea (watery feces) where too little water is
  absorbed by the intestines loss of water can
  lead to dangerous dehydration.

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Digestive System Disorders

• Food poisoning can result when bacteria such as
  Salmonella or E. coli O157H7 colonize the gut
  following consumption of contaminated food.

Figure 7.14a-b
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Digestive System Disorders

• Tooth decay (dental caries) results when lack of
  brushing leaves food residues on the teeth that
  support bacterial growth untreated, gingivitis
  (inflammation of the gums) or periodontal disease
  (inflammation of the periodontal membrane) can
  also occur.
• Helicobacter pylori, introduced as a cause of
  peptic ulcers, has also been linked to gastritis
  (inflammation of the intestines) and stomach
  cancer.

Figure 7.14c-d
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Digestive System Disorders

• Colon disorders range from inconvenient to
  life-threatening.
• Constipation occurs when food residues remain in
  the colon for too long, resulting in hard, dry
  feces that are difficult to eliminate.
• Bulk (soluble and insoluble fiber) in the diet is
  important for moving material through the large
  intestine at the proper speed.
• Too little bulk can result in the formation of
  diverticula, knoblike sacs protruding from the
  intestinal wall (this condition is called
  diverticulosis) if the knobs become inflamed
  this is called diverticulitis and can lead to
  ruptures of the diverticula.

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Fig. 7.15, p. 133
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Digestive System Disorders

• The most common bowel disorder is irritable bowel
  syndrome (IBS) as a result of disturbances to
  peristalsis, individuals alternate between
  diarrhea and constipation.
• Colon cancer is the second most common cancer
  diagnosed in the United States polyps forming in
  the colon wall can turn malignant and spread.

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Digestive System Disorders

• Malabsorption disorders prevent some nutrients
  from being absorbed.
• A malabsorption disorder is anything that
  interferes with the uptake of nutrients across
  the lining of the small intestine.
• Lactose intolerance results
• from a deficiency of lactase.
• Persons suffering from
• cystic fibrosis do not produce
• the pancreatic enzymes
• necessary for normal digestion
• and absorption of nutrients.

Figure 7.17
71
Digestive System Disorders

• Crohns disease is an inflammatory disease that
  can so severely damage the intestinal lining that
  portions of the tract must be removed.

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Video The Problem with Pork
CLICKTO PLAY

• From ABC News, Biology in the Headlines, 2005 DVD.

73
Section 10

• The Bodys Nutritional Requirements

74
The Bodys Nutritional Requirements

• Complex carbohydrates are best.
• Complex carbohydrates are the main source of
  energy taken into the body they are also the
  best types of carbohydrates to intake.
• They are degraded to glucose, the main source of
  energy available to individual cells.
• Fruits, vegetables, and grains are also high in
  fiber needed for bulk in the feces.

Figure 7.17
75
The Bodys Nutritional Requirements

• Refined sugars represent empty calories because
  they do not contribute to our nutritional needs.
• Eating such sugars leads to surges in blood sugar
  levels and changes to how fat is utilized for
  energy by the body.
• Too much sugar eventually increases fat storage
  and increases the risk of heart disease and type
  2 diabetes.

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The Bodys Nutritional Requirements

• There are good fats and bad fats.
• Phospholipids and cholesterol are important
  components of membranes fats are energy
  reserves, provide insulation and cushioning, and
  store vitamins.
• Essential fatty acids are those not made by the
  body itself and which must be acquired through
  food whole foods and vegetable oils provide
  plenty of them in the diet.
• Animal fats and trans fats are also common in our
  food, but eating too much of them can damage the
  cardiovascular system.

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The Bodys Nutritional Requirements

• Proteins are vital to life.
• Of the 20 different amino acids in proteins,
  eight are essential amino acids and are not made
  by the body they must be supplied in the diet.
• Most animal proteins are complete, possessing
  ratios of amino acids that match our needs
  nearly all plant proteins are incomplete, meaning
  they lack one or more of the essentials.

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isoleucine leucine lysine methionine phenylalanine
threonine tryptophan valine
essential amino acids
total protein intake
Fig. 7.16, p. 134
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The Bodys Nutritional Requirements

• Guidelines for healthy eating.
• The classic food pyramid has been replaced with
  a set of nutritional guidelines published by the
  Food and Drug Administration.
• These guidelines call for 55 of daily calories
  to come from complex carbohydrates and further
  recommend limiting fat intake to 20-30 of daily
  calories.
• More whole grains, legumes, dark green and orange
  vegetables, fruits, and milk products should be
  added to our diets.

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p. 135
81
The Bodys Nutritional Requirements

• The Mediterranean diet is an example of an
  alternative diet that meets the goal of lowering
  heart disease and other ills it emphasizes whole
  grains, fruits and vegetables, and reduced meat
  intake.
• Other alternative diets, such as those that
  promote high protein, have little scientific data
  to support their effectiveness.

Figure 7.17
82
Section 11

• Vitamins and Minerals

83
Vitamins and Minerals

• Humans need small amounts of at least 13 organic
  molecules called vitamins to assist in cellular
  metabolism these vitamins must come from a
  balanced diet.
• Inorganic substances called minerals (Ca, Mg, K,
  Fe, for example) are also needed.
• A balanced diet will normally meet all
  requirements for these substances excessive
  intake is at least wasteful and at worst harmful.

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Table 7.3, p. 136
85
Table 7.3, p. 136
86
Table 7.4, p. 137
87
Section 12

• Calories Count Food Energy and Body Weight

88
Calories Count Food Energy and Body Weight

• Obesity is an excess of fat in the bodys adipose
  tissue the World Health Organization has
  declared obesity a major global health concern.
• A male is obese if his body
• is 20 body fat.
• A female is obese if her
• body is 24 body fat.

89
Calories Count Food Energy and Body Weight

• One indicator of obesity-related health risk is
  the body mass index (BMI) the BMI is a number
  that relates body weight with height.
• The basal metabolic rate (BMR) is the amount of
  energy needed to sustain the body at rest the
  number of kilocalories needed to maintain
  acceptable body weight can be calculated
  relative to your amount of physical activity and
  age.

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Weight Guidelines for Women
Weight Guidelines for Men
Starting with an ideal weight of 100 pounds for a
woman who is 5 feet tall, add five additional
pounds for each additional inch of height.
Examples
Starting with an ideal weight of 106 pounds for a
man who is 5 feet tall, add six additional pounds
for each additional inch of height. Examples
Height (feet)
Weight (pounds)
Height (feet)
Weight (pounds)
52 53 54 55 56 57 58 59 510
511 6
110 115 120 125 130 135 140 145 150 155 160
52 53 54 55 56 57 58 59 510
511 6
118 124 130 136 142 148 154 160 166 172 178
Fig. 7.18, p. 138
91
Calories Count Food Energy and Body Weight

• Genes, weight control, and exercise.
• The hormones leptin and ghrelin influence
  appetite, hunger, storage of fat in the body, and
  other weight-related factors hormone production,
  as well as other genetic factors, differ between
  different individuals.
• To lose weight, caloric intake must be balanced
  with calories burned this usually requires
  dietary controls paired with exercise.
• Emotions also affect weight anorexia nervosa and
  bulimia are eating disorders related to emotional
  problems.

92
Table 7.5, p. 139
93
Fig. 7.20, p. 142