Transcript Animal Nutrition

Digestion & Nutrition
Chapter 41
We need to eat! 
• Since we as animals
cannot produce our own
food, we must EAT it.
• Classifying organisms by
what they eat…
– Herbivores: eat
autotrophs
– Carnivores: eat other
animals
– Omnivores: eat both
autotrophs and animals
– What are we??
Classifying Animals by HOW They
Get Their Food
• Suspension feeders:
– Sift small food particles
from the water
– Examples: clams,
oysters, whales
• Substrate feeders:
– Live on (or in) their food
source
– Example: leaf miners,
eat their way through
leaves
Classifying Animals by HOW They
Get Their Food
• Fluid-feeders
– Suck nutrient-rich
fluids from a living host
– Example: mosquitoes,
hummingbirds
• Bulk-feeders
– Eat relatively large
pieces of food
– That’s us! 
The 4 Stages of Food Processing
1. Ingestion
The act of eating
2. Digestion
The process of breaking down food into
molecules small enough for the body to
absorb (physical & chemical)
This involves hydrolysis, which you should
know well  PolymersMonomers
This has to occur in a specialized
compartment… why??
The 4 Stages of Food Processing
3. Absorption
– The animal’s cells absorb the small
molecules broken down during digestion
– Only monomers (monosaccharides, amino
acids, glycerol & fatty acids) can be
absorbed
4. Elimination
– Undigested material passes out of the
digestive compartment
Gastrovascular Cavities
• Gastrovascular
cavities are the
digestive systems in
simple animals
(Cnidarians,
Platyhelminthes)
• Incomplete
Digestive Systemone opening
Digestion in Alimentary Canals
• Complex animals
– An “Entrance” and an “Exit”
– This is a complete digestive system.
• Mouth = site of ingestion
• Anus = site of elimination
• What phyla have complete digestive
tracts?
• (Nematoda, Mollusca, Annelida,
Arthropoda, Echinodermata, Chordata)
Alimentary Canals/Complete
Digestive System
The Mammalian Digestive System
The Mammalian Digestive System
• Consists of:
–
–
–
–
–
–
Oral cavity (mouth)
Pharynx
Esophagus
Stomach
Small Intestine
Large Intestine
• Food moves through the digestive system by
peristalsis, rhythmic waves of contraction by
the smooth muscles
Accessory Organs
• Salivary glands
– Secrete saliva
• Liver
– Secretes bile
• Gallbladder
– Stores and concentrates bile
• Pancreas
– Secretes digestive enzymes
Oral Cavity
• The mouth
• Chewing cuts, smashes, and grinds food
to facilitate swallowing
• Saliva is secreted into the mouth by the
salivary glands
– Saliva contains salivary amylase
– This enzyme breaks down starch and
glycogen into smaller pieces
Specialized Teeth
• Structure of teeth
reflects feeding
behavior
• Antelope brush
teeth against dirt
as they eat; wear
down crown.
ANTELOPE
MOLAR
HUMAN
MOLAR
crown
crown
root
root
Pharynx
• The pharynx is
the intersection
that leads to
both the
esophagus
(digestive
system) and
the trachea
(respiratory
system)
• The epiglottis
makes sure
that food
doesn’t enter
the trachea
Esophagus
• The
esophagus
carries
food from
the
pharynx
into the
stomach
• Where is
your
stomach?
Stomach
• Our stomachs are stretchy – they expand to fit
our food! 
• The inside of the stomach contains gastric
juice, which has a pH of about 2
– HCl – kills most bacteria swallowed with food
-activates the enzyme pepsinogen
– Pepsin (active form) – breaks down proteins to
smaller polypeptides
– Why must pepsinogen be secreted in an
inactive form?????????
Stomach
• The pyloric
sphincter closes off
the stomach from the
small intestine, the
next stop on our tour
• The pyloric sphincter
lets in small amounts
of acid chyme at a
time
Small Intestine
• Most digestion and absorption occurs in
the small intestine
• In humans, the small intestine is about 6
meters long
– It’s called the “small intestine” because it has
a small diameter
Small Intestine
• First section of the small intestine is the
duodenum  responsible for digestion
– Acid chyme enters from the stomach
– Pancreatic enzymes and bile from the liver
are mixed with the food here.
Pancreatic Enzymes
• Secreted into duodenum
• Pancreatic amylase- breaks down polysaccharides to
disaccharides
• Trypsin and chymotrypsin- breaks down proteins to
smaller polypeptides
• Carboxypeptidase- breaks down proteins to amino acids.
• Lipase-breaks down lipids to fatty acids and glycerol
• Pancreatic nucleases-breaks down DNA & RNA to
nucleotides
Fat Digestion
• Liver produces bile
• Bile is stored in gallbladder, then
secreted into duodenum
• Bile emulsifies fats; breaks them into
small droplets
• This gives enzymes a greater surface
area to work on
Small Intestine
• The digestion occurs in the duodenum
• Disaccharidases- break disaccharides down
into monosaccharides.
• Aminopeptidases-break polypeptides down
into amino acids.
• Intestinal nucleases-break down nucleotides
into nucleotide bases and monosaccharides.
• The absorption of nutrients occurs in the
jejunum and ileum (sections 2 & 3 of small
intestine)
Small Intestine
• The jejunum and ileum have a brush
border
– The jejunum and ileum have villi (that look
like fingers) and microvilli. WHY??
– This gives them more surface area, which
facilitates absorption of nutrients
• Classic example of structure & function (form
follows function)!
The Small Intestine
Absorption of Nutrients
• What diffuses where?
• All nutrients except glycerol & fatty acids
diffuse directly into capillaries.
• Glycerol & Fatty Acids (from fats) diffuse
into LACTEALS (part of lymphatic system)
and eventually dump into the circulatory
system at ducts under the clavicles.
INTESTINAL LUMEN
Absorption
Mechanisms
carbohydrates
monosaccharides
Monosaccharides &
proteins
amino acids are
actively transported
across plasma
EPITHELIAL
CELL
membrane of
epithelial cells, then
from cell into internal
environment
Figure 41.11
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INTERNAL
ENVIRONMENT
amino acids
Fat Absorption
bile
salts
bile salts
+
micelles
fat globules
(triglycerides)
emulsification
droplets
fatty acids,
monoglycerides
triglycerides + proteins
EPITHELIAL
CELL
chylomicrons
Figure 41.11
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INTERNAL ENVIRONMENT
Hormones and Digestion
• Gastrin –secreted by stomach lining; causes acid
secretion.
• Secretin- causes pancreas to secrete bicarbonate
• Cholecystokinin (CCK)-controls secretion of pancreatic
enzymes & bile release from gall bladder
• GIP (glucose insulinotropic peptide)-causes cells to take
in more glucose by stimulating insulin secretion
Large Intestine (Colon)
• The major function of the colon is to reabsorb
water
• The wastes of the digestive tracts are called
feces, and they become more solid as they are
moved along the colon
– If it moves through too quickly, not enough
water is reabsorbed  diarrhea
– If it moves through too slowly, too much water
is reabsorbed  constipation
• The waste is stored in the rectum until it can be
eliminated through the anus
• Fecies are not considered “excretion.” Why
not?
Evolutionary Adaptations
• Evolutionary adaptations of the digestive
system exist among animals, primarily
based on their diet
• Herbivores have less specialized teeth
than do carnivores
• Herbivores have longer alimentary
canals than carnivores…why??
Evolutionary Adaptations
The Mammalian Digestive System
Food Pyramid
added fats and
simple sugars
milk, yogurt,
cheese group
fruit group
bread, cereal, rice,
pasta group
legume, nut, poultry,
fish, meat group
vegetable group
Carbohydrates
• Body’s main energy source
• Foods high in complex carbohydrates are
usually high in fiber; promote colon health
• Simple sugars lack fiber as well as
minerals and vitamins of whole foods;
intake should be minimized
• 4 Cal/g
Proteins
• 20 Total Amino Acids
• 8 Essential Amino Acids (Body can’t
make these, so they must be ingested in
foods)
• Plant proteins are incomplete; must be
combined to get all 8 essential a. acids.
• 4 Cal/g
Lipids
• Most fats can be synthesized
• Essential fatty acids must be obtained from food
• Fats should be about 30 percent of diet
• Excess saturated fats can raise cholesterol level
and contribute to heart disease
• 9 Cal/g
• So why do we want to cut lipids if we want to
lose weight?
Dietary Essentials
• Vitamins (Coenzymes: helps enzymes
function)
– Essential organic substances
• Minerals (Cofactors: help enzymes function)
– Essential inorganic substances