Download NSCC NTR150 Ch03 Human Body

Chapter 3 - The Human Body:
Are We Really What We Eat?
taught by
Norman D. Sossong, MD, PhD
NSCC – NTR150 – Spring 2008
MyPyramid Edition
Nutrition: An Applied Approach
Janice Thompson Melinda Manore
3
The Human Body:
Are We Really What We Eat?
PowerPoint® Lecture Slides prepared by
AMY MARION
New Mexico State University
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Why Do We Eat?
Food provides us with
• Energy for body processes
• Heat for body temperature regulation
• Building blocks for growth and maintenance of
body tissues
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Why Do We Want to Eat?
Food is intimately connected to our sense of
taste, but also stimulates our senses of
• Sight
• Smell
• Taste
• Touch (Texture)
• Hearing
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Why Do We Want to Eat?
Appetite: psychological desire to eat certain
foods.
• Strong cravings even when we’re not hungry
are due to appetite.
Hunger: physiological sensation that prompts us
to eat.
Satiety: the feeling of being full.
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Why Do We Want To Eat?
The signals that prompt us to eat include
• Nerve receptors in the stomach & small
•
•
intestines send signals to the brain to indicate if
the stomach is full or empty.
Blood glucose levels trigger the release of
hormones called insulin and glucagon
The hypothalamus region of the brain receives
these signals.
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Why Do We Want To Eat?
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Why Do We Want To Eat?
Hormones: chemicals produced in specialized
glands that travel in the bloodstream to target
organs in other parts of the body.
• Some hormones stimulate food intake.
• Examples:
•
• Neuropeptide Y
• Galanin
Some hormones produce a feeling of satiety.
• Examples:
•
•
•
Leptin
Cholecystokinin
Serotonin
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Why Do We Want To Eat?
Foods have differing effects on our feelings of
hunger:
• Proteins have the highest satiety value
• Carbohydrates have a lower satiety value than fats
• Bulky foods provide a sense of satiety
• Solid foods are more filling than semi-solid foods
• Beverages (liquids) are less filling than semi-solid
foods
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Organization of the Body: Atoms & Elements
Atoms
The smallest units of matter
The smallest units of an element
Element
• Any substance that cannot be broken down to
•
any other substance by ordinary chemical
means
Pure chemicals that cannot be separated into
simpler chemicals
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Periodic Table of the Elements
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The Elements of Life
92 naturally occurring elements are on the earth
Only 11 are found in living organisms in more than trace
amounts
•
“trace amounts” = < 0.01%
These 11 elements have atomic #s < 21
•
And hence have low atomic masses
Oxygen, hydrogen, carbon, and nitrogen = 96.3% of weight of
human body
Approximately 90% of the atoms (and about 75% of the
weight) of organisms are oxygen and hydrogen, reflecting the
predominant role of water (H2O) in living systems
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Organization of the Body: Molecules
Atoms bond to each other to form molecules.
Molecule
• = a group of atoms held together by energy in a
stable association or by chemical bonds
Compound
• = a molecule that contains atoms of more than one
•
element in proportions than never vary
for example: water is H2O, carbon dioxide is CO2
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Organization of the Body: Macromolecules
Carbohydrates, proteins, fats and vitamins are
usually very large molecules.
Carbohydrates, proteins, and fats are especially
large and are called macromolecules.
The goals of digestion:
• Break macromolecules down to smaller
•
molecules
Absorb the smaller molecules into the cells of
the body
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Organization of the Body: Small to Large
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Organization of the Body: Cells
Molecules are the building blocks of cells.
Cells: the smallest unit of life.
Molecules that result from the digestion of food
are used to build the cells of the body.
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Organization of the Body: Cell Membrane
Cell membrane =
plasma membrane:
outer layer
enclosing each cell
of the body.
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The Cell Membrane as Part of the Cell
Structure
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Phospholipid
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Cell Membrane
Phospholipid Bilayer
• Composed of 2
layers of
phospholipids
• Phospholipid
“tails” face each
other toward the
interior of the
membrane
• Phospholipid
“heads” line the
interior and
exterior surfaces
of the
membrane
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Organization of the Body: Cell Membrane
•
•
•
•
Composed of 2
layers of
phospholipids
Phospholipid “tails”
face each other
toward the interior of
the membrane
Phospholipid “heads”
line the interior and
exterior surfaces of
the membrane
Cholesterol is
embedded in the
membrane
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Phospholipid Bilayer & Cholesterol
Cholesterol
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Organization of the Body: Cell Membrane
The cell membrane is selectively permeable
allowing it to control the passage of materials
into and out of the cell.
The cell membrane encloses
• cytoplasm – the liquid within the cell
• organelles – tiny structures that perform many
different cellular functions
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Organization of the Body: Organelles
Organelles
• Nucleus
• Endoplasmic reticulum
• Ribosomes
• Mitochondria
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Organization of the Body: Tissues
Cells join together to form tissues.
Tissue: group of cells acting together to perform
a common function.
• For example: muscle tissue, nerve tissue
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Organization of the Body: Organs
Different tissues combine to form organs.
Organ: a sophisticated organization of tissues
that perform a specific function
• For example: stomach, heart, brain
Organ systems are groups of organs working
together for a particular function.
• For example: gastrointestinal system
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Digestion and Absorption
by
Norman D. Sossong, MD, PhD
for NSCC:
NTR150 – Spring 2008
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What Happens to the Food We Eat?
The food we eat undergoes three processes:
1. Digestion
2. Absorption
3. Elimination
These processes occur in the gastrointestinal
tract.
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Overview of the GI Tract
Anatomical Overview
Wall of the GI Tract
Functional Overview
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The Gastrointestinal Tract
Organization
•
•
Mouth  anus
Accessory organs
• Salivary glands, liver, pancreas, gallbladder
Functions
• Ingestion
• Transport
• Secretion
• Digestion
• Absorption
• Elimination
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What Happens to the Food We Eat?
Gastrointestinal (GI) tract:
series of organs arranged
as a long tube.
The GI tract includes:
• Organs such as the
•
stomach, intestines
Sphincters: muscles
that control the passage
of material from one
organ to the next
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Layers of Gastrointestinal Wall
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The Muscular Layers
of The Gastrointestinal Wall
Outer Layer
= longitudinal fibers
Pacemaker in greater curvature  3/minute
Inner Layer
= circular fibers
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The Functions of the Digestive System (or)
Gastrointestinal (GI) Tract
Ingestion
Transport
Secretion
Digestion
Absorption
Elimination
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The Functions of the Digestive System (or)
Gastrointestinal (GI) Tract
Ingestion
• = the active, voluntary process of placing food (or other
•
material) in the mouth or GI tract
Normally takes place in the mouth
Transport
Secretion
Digestion
Absorption
Elimination
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The Functions of the Digestive System (or)
Gastrointestinal (GI) Tract
Ingestion
Transport = Propulsion
• Deglutition = Swallowing (voluntary)
• Peristalsis (involuntary)
• Segmentation
Secretion
Digestion
Absorption
Elimination
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The Functions of the Digestive System (or)
Gastrointestinal (GI) Tract
Ingestion
Transport = Propulsion
• Deglutition = Swallowing (voluntary)
• Peristalsis (involuntary)
• Segmentation
Secretion
Digestion
Absorption
Elimination
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Digestion
Digestion: the process of breaking large food
molecules down to smaller molecules.
Digestion includes:
• Mechanical digestion: the physical breakdown
•
of food.
Chemical digestion: enzymatic reactions that
break down large food molecules.
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Digestion: The Mouth
Digestion begins in the mouth.
• Chewing is the mechanical digestion that
•
breaks food into smaller pieces
Some chemical digestion takes place
• Salivary amylase is an enzyme produced by the
salivary glands that begins the chemical digestion
of carbohydrates.
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Digestion: Chewing
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Deglutition (Swallowing)
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Deglutition (Swallowing)
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Digestion: The Mouth
The epiglottis
covers the
opening to the
trachea during
swallowing.
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Digestion: Swallowing
Food travels from the mouth to the stomach through the
esophagus.
Peristalsis is the muscular contractions moving food
through the GI tract.
Esophagus
Peristalsis &
Segmentation
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Esophageal Swallowing
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Esophageal Swallowing
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Digestion: Stomach
The gastroesophageal sphincter separates the
esophagus from the stomach.
Digestion in the stomach includes
• Extensive mechanical digestion to mix food
•
with gastric juice
Chemical digestion of proteins and fats
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Digestion: Stomach
Gastric juice contains
• Hydrochloric acid (HCl) – to denature proteins
•
•
•
and activate pepsin
Pepsin – an enzyme to digest protein
Gastric lipase – an enzyme to digest fat
Mucus – to protect the stomach lining
Chyme: semi-solid product of mechanical and
chemical digestion in the stomach.
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Digestion: The Stomach
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Digestion: Small Intestine
From the stomach, chyme is slowly released
through the pyloric sphincter to the small
intestine.
Chemical digestion continues in the small
intestine using pancreatic enzymes and bile.
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Digestion: Accessory Organs
Accessory organs of the GI tract include
• Liver – produces bile which emulsifies fats
• Pancreas
• produces many digestive enzymes
• produces bicarbonate to neutralize chyme
• Gall bladder – stores bile
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Digestion: Accessory Organs
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Absorption
Absorption: the process of taking molecules
across a cell membrane and into cells of the body.
• A small amount of absorption occurs in the
•
stomach.
Most absorption of nutrients occurs in the small
intestines.
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Absorption
The lining of the GI tract has special structures to facilitate
absorption.
Villi are folds in the
lining that are in close
contact with nutrient
molecules.
The brush border is
composed of
microvilli which
greatly increase the
surface area.
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Elimination
Undigested food components move through a
sphincter called the illeocecal valve to the large
intestines.
In the large intestine:
• Very little digestion takes place
• Material is stored 12-24 hours prior to
•
elimination
Water and some nutrients are absorbed
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Elimination
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Disorders Related to Digestion
The lining of the stomach is designed to cope
with hydrochloric acid but other regions of the
GI tract are not.
Heartburn is caused by hydrochloric acid in the
esophagus.
GERD, or gastroesophageal reflux disease, is
painful, persistent heartburn.
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Disorders Related to Digestion
Peptic ulcers are regions of the GI tract that have
been eroded by HCL and pepsin.
The bacterium Helicobacter pylori contributes to
the production of both gastric and duodenal
ulcers.
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Disorders Related to Digestion
Celiac disease
• Complete intolerance for gluten, a protein
•
•
•
found in wheat, rye, barley.
Can damage the small intestine leading to poor
absorption of nutrients.
Requires a diet lacking wheat, rye, barley.
There may be a genetic component to the
disease.
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Disorders Related to Digestion
Irritable bowel syndrome (IBS) is a disorder that
interferes with normal colon function.
Symptoms of IBS include
• Abdominal cramps and bloating
• Either diarrhea or constipation
IBS is more common in women than in men.
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Disorders Related to Digestion
Diarrhea
• Can be caused by food intolerances, infection
•
•
of the GI tract, stress, or bowel disorders
Can lead to severe dehydration
Is more dangerous for children and the elderly
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End of Lecture on GI Tract
Overview of Digestion
Digestion
•
= process of breaking food down into particles small
enough to be absorbed into the blood
•
•
These particles are the building blocks of the various types
of foods
Mechanical
•
•
Mastication = chewing
Segmentation = mixing in the GI tract
• Chemical
Chemical breakdown
•
•
Enzymes
Other secretions
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The Functions of the Digestive System (or)
Gastrointestinal (GI) Tract
Ingestion
Transport = Propulsion
Secretion
Digestion
Absorption
Elimination
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Overview of Absorption
Absorptive mechanisms
•
•
•
Passive diffusion
Facilitated diffusion
Active transport
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The Functions of the Digestive System (or)
Gastrointestinal (GI) Tract
Ingestion
Transport = Propulsion
Secretion
Digestion
Absorption
Elimination = Defecation
•
= elimination of indigestible (and/or unabsorbed)
substances from the body via the anus in the form of feces
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Schematic Summary of
Gastrointestinal Tract
Activities
Ingestion
Propulsion
Digestion
Absorption
(Metabolism)
Defecation
Assisting Organs
Salivary glands
•
•
Moisten food
Supply enzymes
Liver
•
Produces bile
Gallbladder
•
Stores and secretes bile
Pancreas
•
•
Secretes bicarbonate
Secretes enzymes
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Putting
It
All
Together:
Mouth
Digestion
• Enzymes and Absorption
•
•
•
Salivary amylase acts on starch
Lingual lipase acts on fat
Saliva
• Moistens food for swallowing
Esophagus
• Transports food to stomach
• Esophageal sphincter
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Salivary Glands
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Saliva
Function
• Cleans the mouth
• Dissolves food chemicals so they can be tasted
• Moistens food and aids in compacting it into a bolus
• Contains enzymes that begin the chemical breakdown
of starchy foods
Composition
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Composition of Saliva
Water: 97% to 99.5%
pH = 6.75 – 7.00 (acidic, but variable)
Electrolytes
• Sodium
• Potassium
• Chloride
• Phosphate
• Bicarbonate
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Composition of Saliva (cont.)
Proteins
• Salivary amylase: a digestive enzyme
• Mucin: a glycoprotein that when dissolved in water
• Lubricates the oral cavity
• Hydrates foodstuffs
• Lysozyme:
a bacteriostatic enzyme
Metabolic wastes
• Urea
• Uric acid
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Putting It All Together:
Digestion and Absorption
After leaving the mouth,
digestion is continued in the stomach
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The Stomach Walls
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Stomach Glands
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Putting It All Together:
Digestion and Absorption
Stomach
•
•
•
•
•
Hydrochloric acid
•
•
Prepares protein for digestion
Activates enzymes
Pepsin
•
Begins protein digestion
Gastric lipase
•
Some fat digestion
Gastrin (hormone)
•
Stimulates gastric secretion and movement
Intrinsic factor
•
Needed for absorption of vitamin B12
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Putting It All Together:
Digestion and Absorption
Small intestine
• Sections of small intestine
• Duodenum, jejunum, ileum
• Digestion
• Bicarbonate neutralizes
stomach acid
• Pancreatic & intestinal
enzymes
• Carbohydrates
• Fat
• Protein
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Putting It All Together:
Digestion and Absorption
Small intestine
• Absorption
• Folds, villi, microvilli expand
absorptive surface
• Most nutrients absorbed here
• Fat-soluble nutrients go into
lymph
• Other nutrients into blood
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Putting It All Together:
Digestion and Absorption
Large Intestine
• Digestion
• Nutrient digestion already complete
• Some digestion of fiber by bacteria
• Absorption
• Water
• Sodium, potassium, chloride
• Vitamin K (produced by bacteria)
• Elimination
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Functions of Colon
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Nutrient Absorption
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Regulation of GI Activity
Nervous system
• Regulates GI activity
• Local system of nerves
• Central nervous system
Hormonal system
• Increases or decreases GI activity
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Hormonal Regulation of Digestion
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Circulation
of Nutrients
Vascular system
Lymphatic system
Excretion and
elimination
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Nutrition and GI Disorders
Constipation
•
•
Hard, dry, infrequent stools
Reduced by high fiber, fluid intake,
exercise
Diarrhea
• Loose, watery, frequent stools
• Symptom of diseases/infections
• Can cause dehydration
Diverticulosis
• Pouches along colon
• High fiber diet reduces formation
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Benefits of Fiber
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Fiber Content in Foods
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Nutrition and GI Disorders
Gastroesophageal Reflux Disease (GERD)
•
Reduced by smaller meals, less fat
Irritable Bowel Syndrome (IBS)
Colorectal cancer
•
Antioxidants may reduce risk
Gas
Ulcers
•
Bacterial cause
Functional dyspepsia
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Common GI Ailments
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The Fate of a
Piece of Pizza
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