Lecture 13 Outline (Ch. 41)
I.
Animal Nutrition Overview
II.
Food Intake
III. Digestive Compartments
IV. Adaptations
V.
Energy sources and stores
VI. Summary
What is/are the overall function(s) digestion?
Overview: The Need to Feed
• Food is taken in, taken apart, and taken up in the process
of animal nutrition
• In general, animals fall into three
categories:
– Herbivores eat mainly autotrophs
(plants, algae)
– Carnivores eat other
animals
– Omnivores regularly
consume animals as well
as plants or algal matter
3
Essential Parts of Diet
• Meat, eggs, cheese - provide all nine essential amino
acids ( “complete” proteins)
• Individuals eating only plant proteins need specific
plant combinations for all essential amino acids
Essential amino acids for adults
Methionine
Valine
Beans and
other legumes
Threonine
Phenylalanine
Leucine
Corn (maize)
and other grains
Isoleucine
Tryptophan
Lysine
4
Essential Parts of Diet
• Animals can synthesize most fatty acids they need
• The essential fatty acids are certain unsaturated fatty acids that
must be obtained from the diet
• Vitamins: organic molecules needed
in small amounts
• 13 essential vitamins for humans
• Fat-soluble & water-soluble
Vitamin A
B-complex
Vitamin D
Biotin/B7
Vitamin E
Vitamin C
(ascorbic acid)
Vitamin K
5
Minerals
• Minerals: inorganic nutrients, small amounts needed
Calcium
Phosphorus
Potassium
Sulfur
Chlorine
Sodium
Magnesium
Iron
A diet missing a certain essential part or not enough calories
overall leads to malnourishment or undernourishment
6
If a person is following a vegan diet, why is it
recommended to eat a variety of plant sources?
Remember, these are the parts of diet:
• Chemical energy (converted to ATP)
• Organic carbon and nitrogen
• Essential nutrients must be obtained
Food Intake
Ingestion: the act of eating
• Suspension feeders - many aquatic animals, which sift
small food particles from the water
• Substrate feeders are animals that live in or on their
food source
• Fluid feeders suck nutrient-rich fluid from a living host
• Bulk feeders eat relatively large pieces of food
8
Leaf miner caterpillar, substrate feeder
Baleen
Humpback whale, a suspension feeder
Caterpillar
Mosquito, a fluid feeder
Feces
9
Rock python, a bulk feeder
Label each region of the digestive tract below:
What are the function(s) of each region?
Food Intake
Digestion: process of breaking food down into molecules small enough to
absorb. In chemical digestion, enzymatic hydrolysis splits bonds in molecules
Small
molecules
Pieces
of food
Mechanical
digestion
Chemical digestion
Nutrient
(enzymatic hydrolysis) molecules
enter body
cells
Undigested
material
Food
1 Ingestion
2 Digestion
Absorption is uptake of
nutrients by body cells
3 Absorption
4 Elimination
Elimination is the passage of undigested
material out of the digestive compartment
Digestive Compartments
• Most animals process food (i.e. hydrolysis) in
specialized compartments
• Reduces risk animal digesting its own cells/ tissues
Tentacles
Food
Gastrovascular Cavity:
Mouth
Gastrovascular
cavity
For both digestion and
distribution of nutrients
Cells secrete digestive
enzymes
Epidermis
Gastrodermis
12
Digestive
Compartments
• More complex animals:
digestive tube with two
openings (mouth, anus)
“Tube within a tube”
Crop Gizzard
Intestine
Esophagus
Pharynx
Anus
Mouth
Typhlosole
Lumen of intestine
(a) Earthworm
Foregut
Midgut
Hindgut
Rectum
Anus
Esophagus
• Called alimentary canal
• Specialized regions,
carry out digestion and
absorption stepwise
Crop
Mouth
Gastric cecae
(b) Grasshopper
Stomach
Gizzard
Intestine
Mouth
Esophagus
Crop
Anus
(c) Bird
13
Digestive Compartments
Food moves by peristalsis
Tongue
Sphincter
Salivary
glands
Oral cavity
Salivary glands
Mouth
Pharynx
Esophagus
Esophagus
Sphincter
Liver
Stomach
Ascending
portion of
large intestine
Gallbladder
Gallbladder
Stomach
Duodenum of
small intestine
Pancreas
Small
intestine
Liver
Small
intestine
Small
intestine
Large
intestine
Pancreas
Large
intestine
Rectum
Anus
Rectum
Anus
Appendix
Cecum
A schematic diagram of the
human digestive system
• Mammalian alimentary canal and accessory
glands that secrete digestive juices through ducts
14
Oral Cavity, Pharynx, Esophagus
Food
Tongue
Epiglottis
up
Pharynx
Epiglottis
down
Larynx
Trachea
Esophagus
To To
lungs stomach
• Food  bolus, saliva
added, digestion
begins with amylase
and mucus
• Pharynx, junction
opens to both the
esophagus and the
trachea (windpipe)
Esophageal
sphincter
relaxed
Relaxed
muscles
Contracted
muscles
• Esophagus conducts Relaxed
muscles
Sphincter
relaxed
food pharynx to
stomach by peristalsis
• Epiglottis blocks
Stomach
entry to the trachea,
and larynx.
15
Digestion in the Stomach
• The stomach stores food and secretes gastric juice,
which converts a meal to acid chyme
5 µm
• Highly folded
• Gastric juice hydrochloric acid
(parietal cells) and
the enzyme pepsin
(chief cells)
• Pepsin initially
Gastric gland
secreted as
pepsinogen
Mucus cells
• Mucus protects
the stomach lining
from gastric juice
Esophagus
Sphincter
Stomach
Sphincter
Small
intestine
Folds of
epithelial
tissue
Epithelium
3
Pepsinogen
2
HCl
Pepsin
1
Cl–
H+
Chief cell
Parietal cell
16
Digestion in the Small Intestine
• The small intestine: longest section of alimentary canal
• Major organ of enzymatic
digestion and absorption
• 1st: duodenum
- acid chyme from
stomach mixes with
digestive juices from
pancreas, liver,
gallbladder, and the
small intestine itself.
- 2nd: jejunum
- 3rd: ileum
17
Digestion in the Small Intestine
liver/gallbladder
pancreas
bile aids digestion
and absorption
of fats
proteases trypsin &
chymotrypsin
amylase & lipase
bicarbonate
neutralizes the
acidic chyme
small intestine
lining of duodenum
(brush border)
produces several
digestive enzymes
jejunum and ileum
mainly absorb
18
water & nutrients
Carbohydrate digestion
Oral cavity,
pharynx,
esophagus
Polysaccharides Disaccharides
Salivary amylase
Smaller
Maltose
polysaccharides
Protein digestion
Proteins
Stomach
Pepsin
Small polypeptides
Small
intestine Pancreatic amylases
(enzymes Disaccharides
from
pancreas)
Pancreatic trypsin and
chymotrypsin
Smaller
polypeptides
Nucleic acid digestion
Fat digestion
DNA, RNA
Fat (triglycerides)
Pancreatic
nucleases
Nucleotides
Pancreatic lipase
Pancreatic carboxypeptidase
Glycerol, fatty acids,
monoglycerides
Small peptides
Small
intestine
(enzymes
from
epithelium)
Disaccharidases
Dipeptidases, carboxypeptidase, and
aminopeptidase
Nucleotidases
Nucleosides
Nucleosidases
and
phosphatases
Monosaccharides
Amino acids
Nitrogenous bases,
sugars, phosphates
19
Absorption in the Large Intestine
• The colon of the large intestine is connected to the
small intestine
• The cecum aids in
fermentation of plant
material,
- connects where the
small and large
intestines meet
• Human cecum
extension (appendix),
-minor role in immunity
Feces stored in rectum
until eliminated
20
Here’s our generalized digestive tract again:
What are the secretions and purpose from each region listed below:
Mouth Esophagus Stomach
& teeth
Small
intestine
Large
intestine
Absorption in the Large Intestine
• The colon houses strains of the bacterium Escherichia
coli, some of which produce vitamins
• Two sphincters between the rectum and anus control
bowel movements
– Internal smooth
muscle sphincter
(involuntary)
– External striated
muscle sphincter
(voluntary)
22
Mutualistic Adaptations
• Many herbivores have symbiotic microorganisms that
digest cellulose
• The most elaborate adaptations in ruminants
1
Rumen
2
Reticulum
Intestine
Esophagus
4
Abomasum
3
Omasum
23
Adaptations
• Herbivores
generally longer
alimentary
canals than
carnivores;
longer time
needed to digest
vegetation
Small intestine
Stomach
Small
intestine
• Coprophagy –
method to
recover more
nutrients by
ingesting feces
Cecum
Enzymes for
digesting
plant matter
Colon
(large
intestine)
Carnivore
Herbivore
24
Energy Sources and Stores
Pancreas
releases insulin
– cells uptake
sugars
Stimulus:
Blood glucose
level rises
after eating.
Homeostasis:
90 mg glucose/
100 mL blood
Pancreas releases
glucagon – liver
releases sugars
Stimulus:
Blood glucose
level drops
below set point.
If you eat a meal high in sugar, what happens?
Describe the steps
including changes
in blood sugar and
changes in hormones.
Energy Sources and Stores
• Animals store excess calories as glycogen in the liver
and muscles
• Energy secondarily stored as adipose, or fat, cells
• Fewer calories taken in than expended 
taken from storage and oxidized
• Excessive intake of food energy,
excess stored as fat
Fat cells
• Obesity contributes to
diabetes (type 2), colon
and breast cancer, heart
attacks, and strokes
fuel is
100 µm
27
Energy Sources and Stores
• The complexity of weight
control in humans is wellstudied
• Mice that inherit a defect in
the gene for leptin become
very obese
Ghrelin – secreted by stomach,
stimulates appetite
Insulin – secreted by pancreas,
suppresses appetite
Leptin – released by fat cells,
suppresses appetite
PYY – secreted by Sm. Intestine,
suppresses appetite
hypothalamus
Ghrelin
Insulin
Leptin
PYY
28
Obese mouse with mutant ob gene (left) – mutant
for leptin production – next to wild-type sibling mouse.
29
The gene db codes for the leptin receptor. If mice
are mutant for the db gene what happens?
1.
2.
3.
4.
They fail to make leptin – increased appetite
They fail to detect leptin – decreased appetite
They fail to detect leptin – increased appetite
They fail to make leptin – decreased appetite