Digestion and Metabolism
Overview
Digestion, Structures, and Processes
Scaling
Measurement of Metabolism (lab 2/28)
More about hormones later…
2/27 and 3/3/08
1
Overview of Digestion
Assimilation –
sequential
processes of
nutrient
absorption and
breakdown
Egestion –
expulsion of
undigested food
Figure 11.1
2
Feeding, Foods, and Energy
(Fig 11.2)
• Gross Energy (whatever is consumed)
 indigestible energy (feces)

• Digestible Energy

 unmetabolizable energy (urine)
• Metabolizable Energy

 Specific Dynamic Action (heat)
• Net Energy
3
Feeding, Energy, and Processing
Figure 11.3
• Role of salivary
amylase beginning
digestion
• Continued in
duodenum by
pancreatic amylase
and disacchridases
• Note lack of
interaction for
cellulose
4
Feeding, Energy, and Processing
Figure 11.5
• Begins in stomach
with pepsin
(low pH)
• Additional enzymes
and then dipeptidases
high pH
• However, some
proteins transported
directly into cells
•
endocytosis
5
Feeding, Energy, and Processing
Table 11.2
6
Feeding, Energy, and Processing
Figure 11.7
7
Feeding Structures
Many animals have specialized mouthparts
Siphons
Attachment organs
Tongues
Radula
Proboscis
Beaks
Jaws
9
Digestive Systems
Evolutionary
history: increasing
anatomical and
functional
specialization
Two-way gut
One-way gut with
specialized regions
Figure 11.13
10
Surface Area
Nutrients are hydrolyzed in the lumen of
the GI tract
Uptake of end products is slow
Efficiency of uptake is improved by
increasing surface area in two ways
Increasing gut length
Increasing surface undulations
Figure 11.18
11
Gastrointestinal Tract
Key functions and regions
Mechanical breakdown of food
mouth, pharynx, esophagus
Acidic compartment
stomach
Most digestion and absorption
upper or small intestines
Reclamation of water
lower or large intestines
Release of indigestible material
anus
12
Digestive Systems
Figure 11.13
13
Specialized Compartments
Specialized compartments increase the
efficiency of digestion
Compartments can vary in
pH
enzyme composition
and types of secretive and absorptive cells
Muscular valves (sphincters)
control the passage of food from one compartment
to the next
Complexity of gut morphology varies across
taxa
14
Gut Morphology
Figure 11.19
15
Regulation and Enzyme Production
Figure 11.27
Control of gastric
secretion of acid and
pepsinogen (pepsin
precursor)
Signals from
CNS (sensory)
Directly from food via
mechanoreceptors
(stretch) and
chemoreceptors
16
Regulation and Enzyme Production (2)
Figure 11.28
Control of intestinal
secretion
Via low pH of stomach
efflux
And also partially
digested materials
Secrete bicarbonate
ion to increase pH +
enzymes + bile (for
fats)
17