Nutrition and Digestion
Chapter 18
The Body’s Needs
• Nutrients- substances in food that provide energy
and materials for cell development, growth, and
repair
• Your body needs energy for every activity it
performs
– How much depends on age, weight, activity level
– We measure the energy in food with calories
• Calorie- the amount of heat necessary to raise
the temperature of 1 kg of water 1 degree
Celsius.
Classes of Nutrients
• Six kinds of nutrients available in food
– Protein
– Carbohydrates
– Fats
– Vitamins
– Minerals
– water
Proteins
• Large molecules that contain carbon, hydrogen, oxygen,
nitrogen, and sometimes sulfur
• Needed for repair and replacement of body cells and for
growth
• A molecule of protein is made of amino acids
– Body needs 20 different amino acids to make thousands of
proteins
– 8 of those amino acids not found in body, so they have to be
supplied by the food we eat. Called essential amino acids
• Complete proteins, like eggs, milk cheese, and meat, contain all 8
essential amino acids
• Incomplete proteins missing one or more amino acids
• How can vegetarians or vegans get all the essential amino acids?
Carbohydrates
• Main source of energy for body. Contains
carbon, hydrogen, and oxygen. There are
three types
– Sugars table sugar, fruits, honey, milk. Called
simple carbohydrates
– Starch potatoes and foods from grains (pasta).
Made of many simple sugars in long chains, so
called a complex carbohydrate
– Fiber found in cell wall of plant cells. Food like
whole-grain bread, beans, peas, vegetables, fruit
Fats
• Necessary because they provide energy and
help body absorb vitamins. Also known as
lipids
– A gram of fat releases twice as much energy as a
gram of carbohydrate
– During digestion, fat broken down into fatty acids
and glycerol
– Excess energy from foods you eat stored as fat
Classification of Fats
Unsaturated
• Liquid at room temperature
• Vegetable oils
• Fats found in seeds,
avocado
Saturated
• Found in meat, animal
products, some plants.
• Usually solid at room
temperature
• Associated with high blood
cholesterol
– Cholesterol is part of cell
membrane in all cells, but too
much dietary cholesterol can
leave deposits in walls of
blood vessels leading to
heart attack or stroke
Vitamins
• Organic nutrients needed in small quantities for
growth, regulating body functions, and
preventing some diseases
– Most food supply some, but no one food supplies
them all
– A well balanced diet usually gives your body all the
vitamins it needs
• Two types
– Water soluble dissolve easily in water, not stored by
body, must be ingested daily
– Fat soluble dissolve in fat, stored by body
Minerals
• Inorganic nutrients (NO CARBON) that
regulate many chemical reactions in the body
– Build cells, send nerve impulses, carry oxygen to
cells
• 14 minerals body uses
– Calcium and phosphorus used in greatest amount
Water
• Next to oxygen, most important factor for
survival
– We can survive weeks without food but only few
days without water because cells need water to
carry out their jobs
• Human body 60% water
– Water is lost through perspiration, when you
exhale, and when you urinate that water must
be replaced every day
Healthy Eating
• http://www.choosemyplate.gov/
Digestion
• Process that breaks down food into small
molecules so they can be absorbed and
moved into the blood
– From blood, food molecules are transported
across cell membrane to be used by cells
– Mechanical digestion- takes place when food is
chewed, mixed, churned
– Chemical digestion- occurs when chemical
reactions occur that break down large molecules
of food into smaller ones
Enzymes
• Type of protein that speeds up the rate of a
chemical reaction in the body
– Can reduce amount of energy needed for
chemical reaction to begin
• Examples
– Amylase produced by glands near mouth and
helps speed up breakdown of complex
carbohydrates
– Pepsin in stomach, helps break down proteins
Pancreas
• Organ that releases several enzymes through
tube in small intestine.
– Break down starches into glucose
– fats into fatty acids
– break down proteins
Digestive Tract
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Mouth
Esophagus
Stomach
Small intestine
Large intestine
Rectum
anus
Accessory Organs
• Food doesn’t pass through them, but are
important to digestive process
• Liver
• Gallbladder
• Pancreas
• Tongue
• Teeth
• Salivary glands
Mouth
• Mechanical and chemical
digestion begin in mouth
• Mechanical
– When you chew your food
and mix with tongue
• Chemical
– Saliva is watery substance
that contains mucus and
amylase (the enzyme).
Food mixed with saliva
becomes soft mass and
moved to back of mouth
by tongue
Esophagus
• A muscular tube about 25
cm long.
– No digestion takes place
here
– Mucus glands keep food
moist
– Smooth muscles in walls
move food downward with
a squeezing action
peristalsis
– Epiglottis structure that
prevents food from going
down windpipe when you
swallow
Stomach
• Muscular bag where both mechanical and chemical
digestion take place
– Mechanical food is mixed in stomach by peristalsis
– Chemical food is mixed with enzymes and strong
digestive solutions, such as hydrochloric acid
• Specialized cells in walls of stomach release about 2L of
hydrochloric acid a day.
– The acid works with enzyme pepsin to digest protein
– Acid also destroys bacteria from food
– Stomach walls protected from acid by mucus
• Food moves through stomach in 2-4 hours and is
changed to chyme thin, watery liquid
Inside the Stomach
Small Intestine
• First part is duodenum most
digestion takes place here.
– Inside is Bile a greenish fluid
from liver added to break up
large fat particles
• Chemical digestion of carbs,
proteins, and fats occurs when
digestive solution from
pancreas mixed in. mix
contains bicarbonate ions and
enzymes
– Insulin also added, which is a
hormone that allows glucose to
pass from bloodstream into
cells
Small Intestine
• Absorption of food takes place
• Villi fingerlike projections on the ridges and
folds of intestine wall.
– Increase surface area of small intestine so
nutrients in chyme have more places to be
absorbed
• Peristalsis continues and nutrients move into
blood vessels inside villi
Large Intestine
• Chyme enters as thin
watery mixture
– Main job of large intestine is
to absorb water from
chyme/undigested mass
• Peristalsis slows down, and
chyme may stay there for 3
days
• Muscles in rectum (last
section of large intestine)
and the anus control release
of semi solid wastes from
body in form of feces
Bacteria
• Bacteria in large intestine feed on undigested
material like cellulose while making us
vitamins we need
• Breakdown of intestinal materials by bacteria
produces gas