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Chapter 41: Animal Nutrition
1. Why do we eat?
- Fuel (chemical energy)
- To get organic material for biosynthesis (carbon skeletons)
- Essential nutrients (substances that can’t be made from scratch)
2. What are the 4 main feeding mechanisms of animals?
- Suspension feeders
- Substrate feeder
- Fluid feeders
- Bulk feeders
Figure 41.2 Four Main Feeding Mechanisms of Animals
SUSPENSION FEEDERS
SUBSTRATE FEEDERS
Feces
Baleen
Caterpillar
FLUID FEEDERS
BULK FEEDERS
Chapter 41: Animal Nutrition
1. Why do we eat?
2. What are the 4 main feeding mechanisms of feeding?
3. When our bodies need energy, what is the order of fuel usage?
3rd
1st )
(fat- 2nd
proteincarbs4. How is appetite regulated in the body?
- Hormones
source
fcn
- PYY
S. intestine
suppresses appetite
(after meals)
- Insulin pancreas
suppresses appetite
↑blood sugar=↑insulin
- Ghrelin stomach
triggers hunger
↓weight = ↑ghrelin
(+)
makes dieting difficult
- Leptin adipose
suppresses appetite
- ↑ Fat = ↑ leptin = ↓ appetite
- ↓ Fat = ↓ leptin = ↑ appetite
Figure 41.5 A few of the appetite-regulating hormones
Secreted by the stomach
wall, ghrelin is one of the
signals that triggers feelings
of hunger as mealtimes
approach. In dieters who lose
weight, ghrelin levels increase,
which may be one reason
it’s so hard to stay on a diet.
Produced by adipose (fat)
tissue, leptin suppresses
appetite as its level increases.
When body fat decreases,
leptin levels fall, and appetite
increases.
Ghrelin
Insulin
The hormone PYY,
secreted by the small
intestine after meals,
acts as an appetite
suppressant that
counters the appetite
stimulant ghrelin.
Leptin
PYY
A rise in blood sugar level
after a meal stimulates
the pancreas to secrete
insulin (see Figure 41.3).
In addition to its other
functions, insulin suppresses
appetite by acting on the brain.
Chapter 41: Animal Nutrition
1. Why do we eat?
2. What are the 4 main feeding mechanisms of feeding?
3. When our bodies need energy, what is the order of fuel usage?
3rd
1st )
(fat- 2nd
proteincarbs4. How is appetite regulated in the body?
- Hormones
source
fcn
- PYY
S. intestine
suppresses appetite
(after meals)
- Insulin pancreas
suppresses appetite
↑blood sugar=↑insulin
- Ghrelin stomach
triggers hunger
↓weight = ↑ghrelin
makes dieting difficult
- Leptin adipose
suppresses appetite
- ↑ Fat = ↑ leptin = ↓ appetite
- ↓ Fat = ↓ leptin = ↑ appetite
5. What happens if there is a mutation in the leptin system?
Figure 41.6 A ravenous rodent
Chapter 41: Animal Nutrition
1.
2.
3.
4.
5.
6.
Why do we eat?
What are the 4 main feeding mechanisms of feeding?
When our bodies need energy, what is the order of fuel usage?
How is appetite regulated in the body?
What happens if there is a mutation in the leptin system?
What are essential nutrients & what are the 4 classes?
- Nutrients our bodies cannot make
- Essential amino acids (8)
- Essential fatty acids – certain unsaturated FAs – linoleic acid
- Vitamins
- Minerals
Figure 41.10 Essential amino acids from a vegetarian diet
Essential amino acids for adults
Methionine
Valine
Threonine
Phenylalanine
Corn (maize)
and other grains
Leucine
Isoleucine
Tryptophan
Lysine
Beans
and other
legumes
Table 41.1 Vitamin Requirements of Humans
Table 41.2 Mineral Requirements of Humans
Chapter 41: Animal Nutrition
1.
2.
3.
4.
5.
6.
Why do we eat?
What are the 4 main feeding mechanisms of feeding?
When our bodies need energy, what is the order of fuel usage?
How is appetite regulated in the body?
What happens if there is a mutation in the leptin system?
What are essential nutrients & what are the 4 classes?
- Nutrients our bodies cannot make
- Essential amino acids (8)
- Essential fatty acids – certain unsaturated FAs – linoleic acid
- Vitamins
- Minerals
7. What is the difference between malnourished & undernourished?
- Under – get all essentials…just not enough
- Mal – missing some essentials
8. How is food processed?
Figure 41.12 The four stages of food processing
Small
molecules
Pieces
of food
Mechanical
digestion
Chemical digestion
(enzymatic hydrolysis)
Nutrient
molecules
enter body
cells
Undigested
material
Food
1 INGESTION
2 DIGESTION
3 ABSORPTION
4 ELIMINATION
Chapter 41: Animal Nutrition
1.
2.
3.
4.
5.
6.
7.
8.
9.
Why do we eat?
What are the 4 main feeding mechanisms of feeding?
When our bodies need energy, what is the order of fuel usage?
How is appetite regulated in the body?
What happens if there is a mutation in the leptin system?
What are essential nutrient & what are the 4 classes?
What is the difference between malnourished & undernourished?
How is food processed?
What is the path that food takes through us?
Mouthesophagusstomachsmall intestinelarge intestinerectumtoilet
Figure 41.15 The human digestive system
Salivary
glands
Oral cavity
Parotid gland
Sublingual gland
Esophagus
Pyloric
sphincte
r
Liver
Ascending
portion of
large intestine
Mouth
Pharynx
Esophagus
Submandibular gland
Stomach
Gallbladder
Gallbladder
Liver
Pancreas
Small intestine
Large intestine
Rectum
Appendix
Stomach
Small
intestines
Pancreas
IIeum
of small
intestine
Cecum
Salivary
glands
Cardiac
orifice
Tongue
Anus
Duodenum of
small intestine
Large
intestines
Rectum
Anus
A schematic diagram of
the human digestive system
Chapter 41: Animal Nutrition
1.
2.
3.
4.
5.
6.
7.
8.
9.
Why do we eat?
What are the 4 main feeding mechanisms of feeding?
When our bodies need energy, what is the order of fuel usage?
How is appetite regulated in the body?
What happens if there is a mutation in the leptin system?
What are essential nutrient & what are the 4 classes?
What is the difference between malnourished & undernourished?
How is food processed?
What is the path that food takes through us?
Mouthesophagusstomachsmall intestinelarge intestinerectumtoilet
10. Let’s find out what happens along the way?
Figure 41.16 From mouth to stomach: the swallowing reflex
and esophageal peristalsis (layer 1)
Bolus of food
Tongue
Epiglottis
up
Pharynx
Glottis
Larynx
Trachea
To lungs
Esophageal
sphincter
contracted
Esophagus
To stomach
Figure 41.16 From mouth to stomach: the swallowing reflex
and esophageal peristalsis (layer 2)
Bolus of food
Tongue
Epiglottis
up
Pharynx
Glottis
Larynx
Trachea
To lungs
Esophageal
Epiglottis
sphincter
down
contracted
Esophagus
To stomach
Glottis up
and closed
Esophageal
sphincter
relaxed
Figure 41.16 From mouth to stomach: the swallowing reflex
and esophageal peristalsis (layer 3)
Epiglottis
up
Bolus of food
Tongue
Glottis
down
and open
Epiglottis
up
Pharynx
Glottis
Larynx
Trachea
To lungs
Esophageal
Epiglottis
sphincter
down
contracted
Esophageal
sphincter
relaxed
Esophageal
sphincter
contracted
Esophagus
To stomach
Glottis up
and closed
Relaxed
muscles
Contracted
muscles
Relaxed
muscles
Figure 41.21 Flowchart of enzymatic digestion in the human
digestive system
Protein digestion
Carbohydrate digestion
Nucleic acid digestion
Fat digestion
Oral cavity, Polysaccharides Disaccharides
pharynx,
(starch, glycogen) (sucrose, lactose)
esophagus
Salivary amylase
Smaller polysaccharides,
maltose
Stomach
Proteins
Pepsin
Small polypeptides
Lumen of
small intestine
Polysaccharides
Pancreatic amylases
Maltose and other
disaccharides
Polypeptides
Pancreatic trypsin and
chymotrypsin (These proteases
cleave bonds adjacent to certain
amino acids.)
Smaller
polypeptides
DNA, RNA
Pancreatic
nucleases
Nucleotides
Disaccharidases
Dipeptidases, carboxypeptidase, and
aminopeptidase (These proteases split
off one amino acid at a time, working from
opposite ends of a polypeptide.)
Monosaccharides
Amino acids
bile salts prevents small droplets from coalescing into
larger globules, increasing
exposure to lipase.)
Pancreatic lipase
Amino acids
Small peptides
Bile salts
Fat droplets (A coating of
Pancreatic carboxypeptidase
Epithelium
of small
intestine
(brush
border)
Fat globules (Insoluble in
water, fats aggregate as
globules.)
Glycerol, fatty
acids, glycerides
Nucleotidases
Nucleosides
Nucleosidases
and
phosphatases
Nitrogenous bases,
sugars, phosphates
Figure 41.17 The stomach and its secretions
Esophagus
Cardiac orifice
5 µm
Stomach
Interior surface of stomach.
The interior surface of the
stomach wall is highly folded
and dotted with pits leading
into tubular gastric glands.
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.
Pyloric
sphincter
Small
intestine
Folds of
epithelial
tissue
Epithelium
3
Pepsinogen
2
HCl
Pepsin (active enzyme)
1 Pepsinogen and HCI
are secreted into the
lumen of the stomach.
1
2 HCl converts
pepsinogen to pepsin.
Mucus cells secrete mucus,
which lubricates and protects
the cells lining the stomach.
Chief cells secrete pepsinogen, an inactive form of the
digestive enzyme pepsin.
Parietal cell
Parietal cells secrete
hydrochloric acid (HCl).
Chief cell
- stomach epithelium secretes gastric juice
- parietal cells secrete HCl & chief cells secrete pepsinogen
- pH = 2
3 Pepsin then activates
more pepsinogen,
starting a chain
reaction. Pepsin
begins the chemical
digestion of proteins.
Figure 41.19 The duodenum
Liver
Bile
Gallbladder
Stomach
Acid chyme
Intestinal
juice
Pancreatic juice
Pancreas
Duodenum of
small intestine
Figure 41.21 Flowchart of enzymatic digestion in the human
digestive system
Protein digestion
Carbohydrate digestion
Nucleic acid digestion
Fat digestion
Oral cavity, Polysaccharides Disaccharides
pharynx,
(starch, glycogen) (sucrose, lactose)
esophagus
Salivary amylase
Smaller polysaccharides,
maltose
Stomach
Proteins
Pepsin
Small polypeptides
Lumen of
small intestine
Polysaccharides
Pancreatic amylases
Maltose and other
disaccharides
Polypeptides
Pancreatic trypsin and
chymotrypsin (These proteases
cleave bonds adjacent to certain
amino acids.)
Smaller
polypeptides
DNA, RNA
Pancreatic
nucleases
Nucleotides
Disaccharidases
Dipeptidases, carboxypeptidase, and
aminopeptidase (These proteases split
off one amino acid at a time, working from
opposite ends of a polypeptide.)
Monosaccharides
Amino acids
bile salts prevents small droplets from coalescing into
larger globules, increasing
exposure to lipase.)
Pancreatic lipase
Amino acids
Small peptides
Bile salts
Fat droplets (A coating of
Pancreatic carboxypeptidase
Epithelium
of small
intestine
(brush
border)
Fat globules (Insoluble in
water, fats aggregate as
globules.)
Glycerol, fatty
acids, glycerides
Nucleotidases
Nucleosides
Nucleosidases
and
phosphatases
Nitrogenous bases,
sugars, phosphates
Figure 41.20 Protease activation
Pancreas
Membrane-bound
enteropeptidase
Inactive
trypsinogen
Other inactive
proteases
Lumen of duodenum
Trypsin
Active
proteases
Chapter 41: Animal Nutrition
1. Why do we eat?
2. What are the 4 main feeding mechanisms of feeding?
3. When our bodies need energy, what is the order of fuel usage?
4. How is appetite regulated in the body?
5. What happens if there is a mutation in the leptin system?
6. What are essential nutrient & what are the 4 classes?
7. What is the difference between malnourished & undernourished?
8. How is food processed?
9. What is the path that food takes through us?
10. Let’s find out what happens along the way?
11. What hormones control digestion?
- CCK – cholecystokinin
- Secretin
- Gastrin
- Enterogastrone
Figure 41.22 Hormonal control of digestion
Enterogastrone secreted by the
duodenum inhibits peristalsis and
acid secretion by the stomach,
thereby slowing digestion when
acid chyme rich in fats enters the
duodenum.
Liver
Enterogastrone
Gallbladder
CCK
Amino acids or fatty acids in the
duodenum trigger the release of
cholecystokinin (CCK), which
stimulates the release of digestive
enzymes from the pancreas and bile
from the gallbladder.
Gastrin
Stomach
Pancreas
Gastrin from the stomach
recirculates via the bloodstream
back to the stomach, where it
stimulates the production
of gastric juices.
Secretin
Duodenum
CCK
Key
Stimulation
Inhibition
This ensures enzymes are only present when needed.
Secreted by the duodenum,
secretin stimulates the pancreas
to release sodium bicarbonate,
which neutralizes acid chyme
from the stomach.
Chapter 41: Animal Nutrition
1. Why do we eat?
2. What are the 4 main feeding mechanisms of feeding?
3. When our bodies need energy, what is the order of fuel usage?
4. How is appetite regulated in the body?
5. What happens if there is a mutation in the leptin system?
6. What are essential nutrient & what are the 4 classes?
7. What is the difference between malnourished & undernourished?
8. How is food processed?
9. What is the path that food takes through us?
10. Let’s find out what happens along the way?
11. What hormones control digestion?
12. How & where are nutrients absorbed?
- Facilitated diffusion & active transport of monomers
- Microvilli of small intestine
Figure 41.23 The structure of the small intestine
Microvilli
(brush border)
Vein carrying blood to
hepatic portal vessel
Blood
capillaries
Epithelial
cells
Muscle layers
Villi
Epithelial cells
Large
circular
folds
Lacteal
Key
Nutrient
absorption
Intestinal wall
Villi
Lymph
vessel
Chapter 41: Animal Nutrition
1. Why do we eat?
2. What are the 4 main feeding mechanisms of feeding?
3. When our bodies need energy, what is the order of fuel usage?
4. How is appetite regulated in the body?
5. What happens if there is a mutation in the leptin system?
6. What are essential nutrient & what are the 4 classes?
7. What is the difference between malnourished & undernourished?
8. How is food processed?
9. What is the path that food takes through us?
10. Let’s find out what happens along the way?
11. What hormones control digestion?
12. How & where are nutrients absorbed?
13. How & where are fats absorbed?
- Fats are emulsified by bile salts
- Absorbed into the lacteal w/in the villi – lymph system
Figure 41.24 Digestion and absorption of fats
Fat globule
1 Large fat globules are
emulsified by bile salts
in the duodenum.
Bile salts
Digestion of fat by the pancreatic
enzyme lipase yields free fatty
acids and monoglycerides, which
then form micelles.
2
Fat droplets
coated with
bile salts
Micelles made
up of fatty acids,
monoglycerides,
and bile salts
3 Fatty acids and monoglycerides leave micelles
and enter epithelial cells
by diffusion.
Chylomicrons containing fatty
substances are transported out
of the epithelial cells and into
lacteals, where they are carried
away from the intestine by lymph.
4
Epithelial
cells of
small
intestine
Lacteal
Chapter 41: Animal Nutrition
1. Why do we eat?
2. What are the 4 main feeding mechanisms of feeding?
3. When our bodies need energy, what is the order of fuel usage?
4. How is appetite regulated in the body?
5. What happens if there is a mutation in the leptin system?
6. What are essential nutrient & what are the 4 classes?
7. What is the difference between malnourished & undernourished?
8. How is food processed?
9. What is the path that food takes through us?
10. Let’s find out what happens along the way?
11. What hormones control digestion?
12. How & where are nutrients absorbed?
13. How & where are fats absorbed?
- Fats are emulsified by bile salts
- Absorbed into the lacteal w/in the villi – lymph system
14. What is the purpose of the large intestine?
- Absorption of water – makes feces solid
- Home of endosymbiotic bacteria
Chapter 41: Animal Nutrition
1. Why do we eat?
2. What are the 4 main feeding mechanisms of feeding?
3. When our bodies need energy, what is the order of fuel usage?
4. How is appetite regulated in the body?
5. What happens if there is a mutation in the leptin system?
6. What are essential nutrient & what are the 4 classes?
7. What is the difference between malnourished & undernourished?
8. How is food processed?
9. What is the path that food takes through us?
10. Let’s find out what happens along the way?
11. What hormones control digestion?
12. How & where are nutrients absorbed?
13. How & where are fats absorbed?
14. What is the purpose of the large intestine?
15. What are some evolutionary adaptations of the vertebrate digestive system?
- Teeth shape
- Intestinal length
- Symbiotic adaptations for fermentation in herbivores
- Storage chambers
Figure 41.26 Dentition and diet
Incisors
Canines
(a) Carnivore
(b) Herbivore
(c) Omnivore
Molars
Premolars
Figure 41.27 The digestive tracts of a carnivore (coyote) and herbivore
(koala) compared
Small intestine
Small
intestine
Stomach
Cecum
Colon
(large
intestine)
Carnivore
Herbivore
Figure 41.28 Ruminant digestion
1 Rumen. When the cow first chews and
swallows a mouthful of grass, boluses
(green arrows) enter the rumen.
2 Reticulum. Some boluses
also enter the reticulum. In
both the rumen and the
reticulum, symbiotic prokaryotes
and protists (mainly ciliates) go
to work on the cellulose-rich
meal. As by-products of their
metabolism, the microorganisms
secrete fatty acids. The cow
periodically regurgitates and
rechews the cud (red arrows),
which further breaks down the
fibers, making them more
accessible to further microbial action.
Intestine
Esophagus
4 Abomasum. The cud, containing great numbers of microorganisms,
finally passes to the abomasum for digestion by the cow‘s own
enzymes (black arrows).
3 Omasum. The cow then reswallows
the cud (blue arrows), which moves to
the omasum, where water is removed.