Human The Body: Are We Really
What We Eat?
Why do we want to eat?
Food stimulates our senses
Psychosocial factors arouse our appetite
Various factors affect hunger and satiation
Signals from the brain
Hormones
The amount and type of food we eat
Why Do We Want to Eat?
Appetite: psychological desire to eat certain
foods.
Strong cravings even when were not hungry
are due to appetite.
Hunger: physiological sensation that prompts
us to eat.
Satiety: the feeling of being full.
2002DavidRyan
Influences on Food Choices
Past family history of food choices
Knowledge or familiarity
Cultural background
Personal or religious beliefs
Personal preferences
Smell
Taste
Visual appeal
Availability
Cost
Curiosity
Perceived healthfulness
Convenience of preparation
Frequency of previous consumption
Peer-pressure
Sounding good at time of selection
The Human Body: Are We Really
What We Eat?
Why do we want to eat?
Food stimulates our senses
Psychosocial factors arouse our appetite
Various factors affect hunger and satiation
Signals from the brain
Hormones
The amount and type of food we eat
Why Do We Want to Eat?
Psychology, not physical
hunger, controls most
eating behaviors
Why Do We Want to Eat?
Eating Meals with Others
Are 44% larger than if eaten alone
More carbohydrates
More protein
More fat
More alcohol
Why Do We Want to Eat?
Factors Affecting Meal Size
The more people present, the larger the meal
The more people present, the more time spent
eating
Eating with a person who normally eats large meals
will increase your food consumption by between
25% and 69%
If a female is eating a meal with a desirable male,
she will eat less ice cream than if eating alone!
Why Do We Want to Eat?
People served themselves 38%
more ice cream when they
used big bowls than when
they used smaller bowls
Why Do We Want to Eat?
People ate 32% more popcorn
from big buckets than from
medium-size buckets, even if
the popcorn was stale!
Why Do We Want to Eat?
People eating from regular bowls ate
about 11 ounces of soup. People
eating from bottomless bowls ate
about 17 ounces some up to 24
ounces.
People eat with their eyes not
their stomachs!
Why Do We Want to Eat?
Why do we want to eat?
Food stimulates our senses
Psychosocial factors arouse our appetite
Various factors affect hunger and satiation
Signals from the brain
Hormones
The amount and type of food we eat
Why Do We Want to Eat?
The signals that prompt us to eat include:
Nerve receptors in the stomach 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.
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.
Some hormones produce a feeling of satiety.
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 or liquids
Are We Really What We Eat?
Atoms: the smallest units of matter.
Atoms bond to each other to form molecules.
Molecules: groups of atoms bonded in
specific configurations.
for example: water is H2O, carbon dioxide is
CO2
Organization of the Body
Carbohydrates, proteins, fats and vitamins
are usually very large molecules.
The goals of digestion:
Break these large molecules down to smaller
molecules
Absorb the smaller molecules into the cells of
the body
Organization of the Body
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.
Organization of the Body
Cell membrane: outer layer enclosing each
cell of the body.
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
Organization of the Body
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
Organization of the Body
Cells join together to form tissues.
Tissue: group of cells acting together to
perform a common function.
For example: muscle tissue, nerve tissue
Organization of the Body
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 a for particular function.
For example: gastrointestinal system
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.
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
What Happens to the Food We Eat?
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.
What Happens to the Food We Eat?
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.
What Happens to the Food We Eat?
The epiglottis covers the opening to the
trachea during swallowing.
Food travels from the mouth to the stomach
through the esophagus.
Peristalsis is the muscular contractions
moving food through the GI tract.
What Happens to the Food We Eat?
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
What Happens to the Food We Eat?
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.
What Happens to the Food We Eat?
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.
What Happens to the Food We Eat?
Accessory organs of the GI tract for digestion
include:
Liver produces bile which emulsifies fats
Pancreas
produces many digestive enzymes
produces bicarbonate to neutralize chyme
Gall bladder stores bile
What Happens to the Food We Eat?
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.
What Happens to the Food We Eat?
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.
What Happens to the Food We Eat?
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
What Happens to the Food We Eat?
Accessory organs of the GI tract for
absorption include:
Lymphatic System transports most fats and
fat-soluble vitamins
Liver as blood leaves the GI system it is
transported to the liver via the portal vein
Receives products of digestion, then releases
them into bloodstream as needed
Processes and stores monosaccharides,
triglycerides (fats) and amino acids, and plays a
major role in regulating these energy nutrients.
Disorders Relating 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.
Disorders Relating 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.
Disorders Relating 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.
Disorders Relating 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.
Disorders Relating 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