NUTRITION AND DIGESTION
I.
Animals ingest their food in a variety of ways
OMNIVORES  ingest both plants and animals
HERBIVORES  plant eaters
CARNIVORES  meat eaters
SUSPENSION FEEDERS  extract food particles suspended
in the surrounding water
e. SUBSTRATE FEEDERS  live on or in their food source and
eat their way through the food
f. FLUID FEEDERS  obtain food by sucking nutrient-rich
fluids from a living host
g. BULK FEEDERS  ingest relatively large pieces of food
a.
b.
c.
d.
II.
Overview: Food processing occurs in four stages
a. INGESTION  the act of eating
b. DIGESTION  the breaking down of food into molecules
small enough for the body to absorb
i. MECHANICAL DIGESTION  broken into smaller
pieces
ii. CHEMICAL DIGESTION  “hydrolysis”; breaking
chemical bonds; polymers  monomers
c. ABSORPTION  the cells lining the digestive tract take up
(absorb) small nutrient molecules
d. ELIMINATION  undigested material passes out of the
digestive tract
III.
Digestion occurs in specialized compartments
a. GASTROVASCULAR CAVITY  a digestive compartment
with a single opening (HYDRAS)
b. ALIMENTARY CANAL  a tube between two openings (a
mouth and an anus)
i. PHARYNX  throat
ii. ESOPHAGUS  a channel that leads to a crop, gizzard,
or stomach
iii. CROP  a pouch-like organ in which food is usually
softened and stored temporarily
iv. STOMACHS and GIZZARDS  pouch-like and may
store food temporarily, but they are more muscular than
crops and actively churn and grind the food
v. INTESTINE  region of the digestive tract between the
stomach or gizzard and the anus
vi. ANUS  the opening through which undigested
materials are expelled
IV.
The human digestive system consists of an alimentary canal and
accessory glands
a. MAIN PARTS
i. Mouth, oral cavity, tongue, pharynx, esophagus,
stomach, small intestine, large intestine, rectum, anus
b. DIGESTIVE GLANDS (accessory glands)
i. Salivary glands, pancreas, liver (gallbladder)
c. PERISTALSIS  rhythmic waves of contraction of smooth
muscles in the walls of the digestive tract
d. PYLORIC SPHINCTER  a muscular ring regulates the
passage of food out of the stomach and into the small
membrane
V.
Digestion begins in the oral cavity
a. MECHANICAL DIGESTION  teeth
b. CHEMICAL DIGESTION  saliva
c. TONGUE  “bolus”
VI.
The food and breathing passage both open into the pharynx
a. TRACHEA  “windpipe”
VII. The esophagus squeezes food along to the stomach
a. ESOPHAGUS  a muscular tube that conveys food boluses
from the pharynx to the stomach
i. 2 layers of muscle
1. Circular
2. Longitudinal
ii. Action of these muscles is involuntary and causes
peristalsis
VIII. The stomach stores food and breaks it down with acid and
enzymes
a. GASTRIC GLANDS  secrete mucus, HCl, and pepsinogen
b. GASTRIN  a hormone released that stimulates secretion of
gastric juice
c. ACID CHYME  a mixture of the gastric juice and food
IX.
Bacterial infections can cause ulcers
a. GASTRIC ULCERS  open sores in the lining of the stomach
X.
The small intestine is the major organ of chemical digestion and
nutrient absorption
a. PANCREAS  produces digestive enzymes and an alkaline
solution rich in bicarbonate alkaline solution neutralizes acid
chyme as it enters the small intestine
b. LIVER
i. BILE  no digestive enzymes, but emulsifies fats
making them more susceptible to enzyme action
ii. GALLBLADDER  stores bile
c. DUODENOM  first 25 cm of small intestine
i. Where acid chyme from stomach mixes with bile and
pancreatic enzymes
d. VILLI  small finger-like projections, line the wall of the
small intestine
i. MICROVILLI  line the villi
XI.
The large intestine reclaims water
a. LARGE INTESTINE = COLON
i. Main function is to absorb water from the alimentary
canal
b. APPENDIX  small, fingerlike extension; contains a mass of
white blood cells and has a minimal role in immunity
c. FECES  indigestible material
d. RECTUM  terminal portion of colon where feces is stored
XII. Adaptations of vertebrate digestive systems reflect diet
a. Herbivorous animals have longer digestive tracts
b. RUMINANT MAMMALS  have a more elaborate system for
cellular digestion
XIII. Overview: A healthful diet satisfies three needs
a. Fuel to power all body activities
b. Organic raw materials needed to make the animal’s own
molecules
c. Essential nutrients, or substances the animal cannot make for
itself from any raw material but must obtain in prefabricated
form from food
XIV. Chemical energy powers the body
a. KILOCALORIES  the energy content of food measurement
b. BASAL METABOLIC RATE (BMR)  the number of
kilocalories a resting animal requires to fuel the essential
processes for a given time
XV. Body fat and fad diets
a. ESSENTIAL FATTY ACIDS  must be obtained in our diet
b. RECOMMENDED DIETARY ALLOWANCES (RDAs) 
minimal standards established by nutritionists for preventing
nutrient deficiencies
XVI. Vegetarians must be sure to obtain all eight essential amino acids
a. ESSENTIAL AMINO ACIDS  must be obtained from the
diet
XVII. A healthful diet includes 13 vitamins
a. VITAMIN  an organic nutrient that is essential but required
in much small quantities than the essential amino acids
(*COENZYMES)
XVIII. Essential minerals are required for many body functions
a. MINERALS  chemical elements other than carbon,
hydrogen, oxygen, and nitrogen
XIX. What do food labels tell us?
XX. Diet can influence cardiovascular disease and cancer
a. LOW-DENSITY LIPOPROTEINS (LDLs)  correlate to
blocked blood vessels
b. HIGH-DENSITY LIPOPROTEINS (HDLs)  decrease risk of
blockage