CHAPTER 21
Nutrition & Digestion
Ingestion of Food
• Omnivore – ingests both plant &
animals (humans)
• Herbivore – ingests only plants
(cattle, deer, many aquatic species)
• Carnivore – ingests animals (lions,
sharks, hawks, spiders)
Sect 21.1
Sect 21.2
Methods of Ingestion
•Suspension feeders – extract food
particles suspended in water
•Substrate feeders – live in or on their
food source & eat their way through
•Fluid feeders – suck nutrient rich fluids
from their living hosts
•Bulk feeders – use tentacles, claws, or
jaws & teeth to kill & eat their prey
Stages of Food Processing
1. Ingestion–act of eating
2. Digestion – breaking
down food (polymers)
into molecules
(monomers) small
enough for the body
to absorb
3. Absorption – cells lining the
digestive tract take up (absorb)
small nutrient molecules
4. Elimination – undigested material
passes out the digestive
tract,…
(a chance to get some
reading done)
Human Digestive Tract
Oral Cavity
• Saliva
- buffers to protect teeth
- salivary amylase – digestive
enzyme that hydrolyzes starch
Sect 21.5
Oral Cavity (cont.)
• Teeth – cut, smash, grind solid food
- incisors: bite off food
- canines: tear loose a piece of food
- premolars & molars: grind, crush the
piece of food
•Tongue – used to taste & to
manipulate food while we chew – helps
shape food into a ball called a bolus
Sect 21.6
Pharynx
• Region commonly known as the
throat
• An intersection that leads either to
the esophagus or trachea
• As we swallow, the larynx (voice box)
moves upward & tips the epiglottis
(flap of cartilage) over the opening of
the trachea
Heimlich Maneuver
Sect 21.8
Esophagus
• Conducts food from the
pharynx down to the
stomach
• Peristalsis – wavelike
contraction of the smooth
muscles of the digestive
tract that squeezes the
bolus down to the stomach
(sect 21.4)
Sect 21.9
Stomach
• Highly elastic and can
stretch to accommodate
about 2 L of food & liquid
• Rugae are ridges or folds
in lining to allow for
expansion
• Gastric glands - release
gastric juice (breakdown
of protein begins)
Gastric Juice Contents
• Mucus – coats & lubricates stomach
lining
• HCl – acid that breaks apart the food
• Pepsinogen – inactive form of the
enzyme pepsin
- HCl converts pepsinogen into
pepsin (pepsin breaks down
proteins into smaller chains)
Stomach (cont.)
• Contraction of the muscles in stomach
wall aid chemical digestion
- contents of stomach are churned every 20
seconds
- mixture is called acid chyme
Sphincter Valves on Stomach
• Cardiac sphincter is
• Pyloric sphincter is
at the top of the
at the bottom of
stomach
the stomach
• Prevents backflow
• Regulates passage
into esophagus
of chyme into small
intestine
Stomach (cont.)
• Takes about 2-6 hours to empty
the stomach of a meal
• Mucus coats stomach & protects it
from the corrosive effects of
digestive juices
Stomach Ulcers
• Gastric ulcers are open sores that develop
on stomach wall
• Some ulcers develop from too much
pepsin &/or acid, or too little mucus
• Some ulcers develop from bacterial
infections that cause a loss of mucus &
damage the stomach lining
Sect 21.10
Small Intestine
• Most of the chemical digestion of
macromolecules in food take place
• Nutrients are absorbed into the blood
Sect
21.11
Pancreas
Pancreas produces
digestive enzymes
& an alkaline
solution rich in
bicarbonate
LIVER
Liver performs
wide variety of
functions:
-bile salts that
make fat more
susceptible to
enzyme attack
-gallbladder
stores bile until
it is needed
Parts of the Small Intestine
DUODENUM
-1st 25 cm
-Where acid chyme
mixes w/bile and
digestive enzymes
-Follow along w/
Table on p. 438
Carbohydrate Enzymes
• Pancreatic amylase –
hydrolyzes starch into a
disaccharide
• Different disaccharidases
– are specialized to
hydrolyze different
disaccharides
- maltase, sucrase,
lactase
Protein Enzymes
• Trypsin & Chymotrypsin – break
polypeptides into smaller chains
• Carboxypeptidase & Aminopeptidase –
splits off one amino acid at a time working
opposite ends of the polypeptide
• Dipeptidase – hydrolyzes fragments only 2
or 3 amino acids long
Nucleic Acid Enzymes
Nucleases – hydrolyze nucleic acids into
their component nucleotides
What are nucleic acids?
What is a nucleotide?
Fat Enzymes
• Fats are 1st coated
w/bile salts to keep
them separated from
one another - known
as emulsification
• Lipase then breaks
down fat droplets into
fatty acids & glycerol
Parts of Small Intestine
(Jejunum & Ileum)
Specialized in absorbing nutrients,
wrinkles w/in the small intestine give
it a large surface area, wrinkles are
covered by small, fingerlike projections
called villi
- each villus has tiny surface
projections called microvilli
- microvilli extend into the interior of
the intestine
•Tiny lymph vessels extend directly
into core of the villus along w/the
capillaries (lymph vessels & capillaries
pick up nutrients)
p. 439
- known as the lacteal
•Capillaries that drain nutrients away
from the villi converge into larger
blood vessels, which eventually lead
to the liver
•the liver converts many nutrients
into new substances that the body
needs
Large Intestines - Colon
-Is about 1.5 m long
& 5 cm in diameter
-connected to small
intestine at a
T-shaped junction
(a sphincter valve
regulates movement)
Sect 21.12
•One arm of the T is a blind pouch cecum
- appendix (a small fingerlike
projection of the cecum) has a minor
contribution to immunity
- appendix is prone to infection
itself
•Function of the colon is to reabsorb
water
•if water used during digestion is not
reclaimed, severe dehydration would
result
•wastes are called feces
•feces are stored in the rectum until
they can be eliminated
Sect 21.15
Healthful Diet
• ATP
• energy content in food is
measured in Kilocalories (1 kcal =
1000 calories)
• BMR (basal metabolic rate)
- about 1300 - 1800 cal a day
- minimal numbers, any activity
consumes kcal in addition to BMR
•Fad diets are often ineffective &
harmful
•balanced diet is adequate amounts of
all nutrients
•Recommended Dietary Allowance
(RDA) for nutrients - minimal standards
Sect 21.20
Sect 21.16
Essential Nutrients
• The body cannot make 9 of the
20 amino acids needed to make
proteins
- must be obtained from the
diet and cannot be stored in
excess
- meat & animal by-products
(eggs, milk, cheese)
Undernourished- deficient calories
Malnourished- missing essential
nutrients
Vegetarian Diet
- cannot make all aa
- must eat more than 1 type of plant
- beans & corn together
Nutrients (cont.)
• Most of the required fatty acids
are made from simpler
molecules
• some must be obtained from
our diet NOT A PROBLEM!!
Sect 21.18 &
21.23
Nutrients (cont.)
• Vitamin - organic nutrient that is
essential but required in small
amounts
- coenzymes (catalytic functions)
- water soluble vitamins (B, C)
- fat soluble vitamins (A, D, E, K)
Table on p.444
Sect 21.19
Nutrients (cont.)
• Minerals - chemical elements
other than C, H, O, N
ex: Calcium, Iron, Phosphorus,
Sodium
Table on p.445
•Food label provide important
nutritional information about
packaged foods
Sect 21.21
& 21.24
•choice of diet may reduce the risk of
cardiovascular disease & cancer
- diets rich in saturated fats high
cholesterol cardiovascular disease
Cholesterol
• Low-density lipoproteins - have a
tendency to cause blocked blood
vessels & high blood pressure
(found in saturated fats)
• High-density lipoproteins - may
decrease the risk of vessel
blockage (found in unsaturated
fats)