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Digestion and Metabolism

OverviewDigestion, Structures, and Processes

ScalingMeasurement of Metabolism (lab

2/28)More about hormones later…

2/27 and 3/3/08

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Overview of Digestion

Assimilation –sequential processes of nutrient absorption and breakdownEgestion – expulsion of undigested food

Figure 11.1

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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

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Feeding, Energy, and Processing

• Role of salivary amylase beginning digestion

• Continued in duodenum by pancreatic amylaseand disacchridases

• Note lack of interaction forcellulose

Figure 11.3

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Feeding, Energy, and Processing

• Begins in stomach with pepsin (low pH)

• Additional enzymesand then dipeptidaseshigh pH

• However, some proteins transporteddirectly into cells• endocytosis

Figure 11.5

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Feeding, Energy, and Processing Table 11.2

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Feeding, Energy, and Processing Figure

11.7

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Feeding Structures

Many animals have specialized mouthparts

SiphonsAttachment organsTongues

RadulaProboscis

BeaksJaws

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Digestive Systems

Evolutionary history: increasing anatomical and functional specialization

Two-way gutOne-way gut with specialized regions

Figure 11.13

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Surface Area

Nutrients are hydrolyzed in the lumen of the GI tractUptake of end products is slowEfficiency of uptake is improved by increasing surface area in two ways

Increasing gut lengthIncreasing surface undulations

Figure 11.18

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Gastrointestinal Tract

Key functions and regionsMechanical breakdown of food

mouth, pharynx, esophagusAcidic compartment

stomachMost digestion and absorption

upper or small intestinesReclamation of water

lower or large intestinesRelease of indigestible material

anus

Digestive Systems

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Figure 11.13

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Specialized Compartments

Specialized compartments increase the efficiency of digestionCompartments can vary in

pHenzyme compositionand 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

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Gut Morphology

Figure 11.19

Regulation and Enzyme Production

Control of gastric secretion of acid and pepsinogen (pepsin precursor)Signals from

CNS (sensory)Directly from food via mechanoreceptors (stretch) and chemoreceptors

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Figure 11.27

Regulation and Enzyme Production (2)

Control of intestinal secretion

Via low pH of stomach effluxAnd also partially digested materials

Secrete bicarbonate ion to increase pH + enzymes + bile (for fats)

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Figure 11.28