Herbivores
 Carnivores
 Omnivores

1.
2.
3.
Fuel
Raw organic materials
Essential nutrients
Largest portion of energy production
of ATP
 Mostly from cell respiration

› Organic molecules  monomers= fuel
› Rich organic molecules
1. Carbs
2. Fats
3. Proteins
= the maintenance of stable, internal
conditions w/specific limits
 GLUCOSE REGULATION
›
›
›
•
Excess calories used for biosynthesis
Body stores energy in “depots”
Regulated by hormones
When energy needed is more than energy
consumed  fuel in storage depots is
oxidized
• Liver glycogen
• muscle
1) When blood
glucose
level rises, a gland
called
the pancreas secretes
insulin,
a hormone, into the
blood.
STIMULUS:
Blood
glucose
level rises
after eating.
4) Glucagon promotes
the breakdown of
glycogen in the
liver and the
release of glucose
into the blood,
increasing blood
glucose level.
2) Insulin enhances the
transport of glucose into body
cells and stimulates the liver
and muscle cells to store
glucose as glycogen. As a
result, blood glucose level
drops.
Homeostasis:
90 mg glucose/
100 mL blood
STIMULUS:
Blood glucose
level drops
below set point.
3) When blood
glucose level drops
the pancreas
secretes the hormone
glucagon which
opposes the effect of
insulin.
Undernourishment- deficient in calories,
glycogen and fat used up
 Overnourishment- body hoards fat
instead of using for fuel

Feedback circuits control the body’s
storage and metabolism of fat
 Hormones regulate appetite through
“satiety center” in the brain
 Most weight regulating hormones=
polypeptides (proteins)

› Ex: hormone leptin- long term appetite
regulator in mammal
 Feedback inhibition= produced by adipose =
leptin =appetite
Ingestion: A heterotrophic mode of nutrition
in which other organisms or detritus are
eaten whole or in pieces
Digestion: The process of breaking down
food into molecules small enough for the
body to absorb
Enzymatic hydrolysis: The process in
digestion that splits macromolecules from
food by the enzymatic addition of water
Absorption: The uptake of small
nutrient molecules by an
organism’s own body; the 3rd main
stage of food processing following
digestion
Elimination: The passing of
undigested material out of the
digestive compartment
Intracellular digestion: The joining of
food vacuoles and lysosomes to allow
chemical digestion to occur within the
cytoplasm of a cell
Extracellular digestion: The breakdown
of food outside cells.
Gastrovascular cavity: An extensive
pouch that serves as the site of
extracellular digestion and a
passageway to disperse materials
throughout most of an animal’s body
Complete digestive tract/alimentary
canal: A digestive tract consisting of a
tube running between a mouth and an
anus

1)
2)
WHY?
Polymers are too large to pass through
cell membranes.
Macromolecules that make up an
animal aren’t organized in the same
way as those that make up food.

•
•
•
•
•
Polysaccharides and disaccharides 
simple sugars
Fats  glycerol and fatty acids
Proteins  amino acids
Nucleic acids nucleotides
HOW are these broken down?
Enzymatic hydrolysis!
Digestive compartments!
-vacuoles
 2 TYPES OF DIGESTION
Intracellular digestion-pinocytosis and
phagocytosis
Extracellular Digestion

Pinocytosis
Phagocytosis
Occurs within compartments continuous
with the outside of animal’s body 
alimentary canal
 Mammals have specialized regions to
carry out digestion
 We can ingest additional food before
earlier meals are completely digested
(inefficient and difficult for animals
w/gastrovascular cavities)

 It’s
continuous with the outside
environment via the mouth and
anus, nutrients haven’t entered
the body yet by crossing the
membrane.

Alimentary canal
Peristalsis-Rhythmic waves of contraction of smooth muscles

Accessory glands-

that push food along digestive tract
 Sphincters-ring-like valves consisting of modified muscles in a
muscular tube, such as tract; closes off the tube like a draw string
› 3 pairs of salivary glands
› Pancreas= gland w/ dual functions: the nonendocrine portion
secretes digestive enzymes and an alkaline solution into the
small intestine; the endocrine portion secretes the hormones
insulin and glucagon in the blood
› Liver=largest organ in the body; produces bile, prepares
nitrogenous wastes for disposal, detoxifies poisonous
chemicals in the blood
› Gallbladder= an organ that stores bile and releases it as it is
needed into the small intestine





Oral cavity: the mouth of an animal
Salivary amylase: a salivary gland enzyme
that hydrolyzes starch and glycogen
Bolus: a lubricated ball of chewed food
Pharynx: an area in the vertebrate throat
where air and food passages cross
Epiglottis: a cartilaginous flap that blocks
the top of the windpipe, the glottis, during
swallowing, which prevents the entry of
food or fluid into the trachea
Esophagus: a channel that conducts food,
by peristalsis, from the pharynx to the
stomach
Small Intestine: the longest section of the
alimentary canal; the principal site of the
enzymatic hydrolysis of food molecules and
the absorption of nutrients
Duodenum: the 1st section of the small
intestine, where acid chyme from the
stomach mixes with digestive juices from
the pancreas, liver, gallbladder, and
gland cells of the intestinal walls
 Bile: a mixture of substances that is
produced in the liver, stored in the
gallbladder, and acts as a detergent to
aid in the digestion and absorption of
fats

Microvillus: one of many fine, fingerlike
projections of the epithelial cells in the
lumen (cavity) of the small intestine that
increase its surface area
 Lacteal: a tiny lymph vessel extending
into the core of an intestinal villus and
serving as the destination for absorbed
chylomicrons
 Chylomicrons: one of the small
intracellular globules composed of fats
are mixed with cholesterol and coated
with special proteins


Hepatic portal vein: a large circulatory
channel that conveys nutrient-laden
blood from the small intestine to the liver,
which regulates the blood’s nutrient
content
Let the digestion begin!
1)
2)
3)
4)
Chew-mechanical
digestion, increase
surface area of food
for…
Salivation-chemical
digestion begins!
Bolus is formed
Bolus goes down
pharynx (we
swallow)


Epiglottis blocks
opening to windpipe
so we don’t choke
(see motion of
Adam’s apple) and
food goes down
esophagus by
peristalsis
Swallowing is at first
voluntary, but then
involuntary waves of
muscle contraction
push the bolus into
the stomach
4) The
esophageal
sphincter relaxes,
allowing bolus
down
esophagus.
2) The
swallowing
reflex is
triggered when
a bolus of food
reaches the
pharynx.
1) When a person isn’t
swallowing , the
esophageal sphincter
muscle is contracted,
the epiglottis is up,
and the glottis is open,
allowing air flow
through the trachea
to the lungs
55) After the food
3) The larynx, the
upper part of the
respiratory tract,
moves upward
and tips the
epiglottis over
the glottis,
preventing food
from entering the
trachea.
had entered the
esophagus, the
larynx moves
downward and
opens the breathing
passage.
6) Peristalsis
moves the bolus
down into
stomach.
Figure 41.16
Stomach- stores food, prepares for
digestion, in upper abdomen
 Gastric juice- digestive fluid, acidic

› Pepsin- enzyme in gastric juice that begins
hydrolysis of proteins
› Pepsinogen- inactive pepsin first secreted by
cells located in gastric pits of stomach
› Acid chyme- nutrient rich broth; a mix of
recently swallowed food and gastric juice
Pyloric sphincter- opening from stomach to
small intestine
 Cardiac orifice opening- opening from
stomach to esophagus

Esophagus
Cardiac orifice
Stomach
5 µm
Pyloric
sphincter
Small
intestine
Folds of
epithelial
tissue
Interior surface of stomach.
The interior surface of the
stomach wall is highly folded
and dotted with pits leading
into tubular gastric glands.
Epithelium
3
Pepsinogen
1
Pepsin (active enzyme)
2
Gastric gland. The gastric
glands have three types of cells
that secrete different components
of the gastric juice: mucus cells,
chief cells, and parietal cells.
HCl
1
2 HCl converts
pepsinogen to pepsin.
Mucus cells secrete mucus,
which lubricates and protects
the cells lining the stomach.
3
Pepsin then activates
more pepsinogen,
starting a chain
reaction. Pepsin
begins the chemical
digestion of proteins.
Chief cells secrete pepsinogen, an inactive form of the
digestive enzyme pepsin.
Parietal cell
Figure 41.17
Parietal cells secrete
hydrochloric acid (HCl).
Pepsinogen and HCI
are secreted into the
lumen of the stomach.
Chief cell
Secretes gastric juice through epithelium
stomach lining
1.
Parietal cells secrete HCL acid->
pepsinogen-> pepsin in lumen
-


2.
*positive feedback inhibition
Many suggestive enzymes secreted in
inactive form
Coating of mucus secreted by epithelial cells
Smooth muscles mix stomach contents
-> acid chyme
-
Cardiac orifice opens for bolus
Pyloric sphincter helps regulate chyme
into the intestine
2- 6 hrs to empty
1) Duodenum
A) Pancreatic enzymes include protein-digesting
enzymes in inactive form but are activated once
they’re in the duodenum (like
pepsinogenpepsin)
B) Epithelial lining of the duodenum called the
brush border secretes digestive enzymes, some
which are secreted into the lumen of the
duodenum, other digestive enzymes bind to the
surface of epithelial cells
C) Digestion is completed as peristalsis moves
chyme and digestive juices while still in the
duodenum
Pancreas
Membrane-bound
enteropeptidase
Inactive
trypsinogen
Other inactive
proteases
Lumen of duodenum
Trypsin
Active
proteases
2) Absorption
A) villi and microvilli increase rate of
absorption
villi absorb nutrientsmicrovillilactealbloodstream
B) nutrients are absorbed across the
intestinal epithelium and then the
unicellular epithelium of capillaries/lacteal
Vein carrying blood to
hepatic portal vessel
Microvilli
(brush border)
Blood
capillaries
Epithelial
cells
Muscle layers
Key
Nutrient
absorption
Villi
Intestinal wall
Large
circular
folds
Lacteal
Villi
Lymph
vessel
Epithelial cells
3) Hormones help control secretion of digestive
juices
4) Active and Passive transport of nutrients across
epithelial cells
A) fructose moves by facilitated diffusion down
concentration gradient from lumen of
intestine  epithelial cells  capillaries
B) amino acids, peptides, vitamins, glucose are
pumped against concentration
gradient=intestine can absorb a higher
proportion of nutrients
Amino acids + sugars epithelium  capillaries 
bloodstream
converge to hepatic portal vein  liver  heart
b) Liver regulates amount of nutrients (i.e.
glucose)in blood
C) Glycerol+fatty acidsepithelial
cellsrecombined into fat w/in epithelial
cellsform chylomicronslactealsvessels of
lymphatic systemlarge veins that return blood to
heart

Large intestine/colon- connected to the small
intestine at a T shaped junction where a sphincter
controls the movement of material; functions
mainly in water absorption and formation of feces
Cecum- one arm of the T-pouch
 Appendix- cecum’s finger-like extension;

contains a mass of white blood cells that
contribute to immunity
Feces- wastes of the digestive tract
 Rectum- terminal portion of the colon

Recovers water that has entered the
alimentary canal as solvent of digestive
juices
 Feces becomes solid by peristalsis

› Constipation results b/c too much water
absorbed by intestine=moves slowly
› Feces exit out rectum