Animal Nutrition

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Herbivores generally have longer alimentary canals than carnivores, reflecting the longer time needed to digest vegetation.

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Alimentary canals of a carnivore (coyote) and herbivore (koala)

Cecum

Small intestine

Herbivore

Carnivore

Colon (large intestine)

Stomach

Small intestine

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Mutualistic ++ Adaptations

Many herbivores have fermentation chambers, where symbiotic microorganisms ++ digest cellulose.

The most elaborate adaptations for an herbivorous diet have evolved in the animals called ruminants.

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Ruminant digestion

Esophagus

Omasum

Abomasum

Intestine

Rumen

Reticulum

1

2

4

3

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Homeostatic mechanisms contribute to an animal’s energy balance

Food energy balances the energy from metabolism, activity, and storage.

Nearly all of an animal’s ATP generation is based on oxidation of energy-rich molecules: carbohydrates, proteins, and fats.

Animals store excess calories primarily as glycogen in the liver and muscles.

Energy is secondarily stored as adipose, or fat, cells.

When fewer calories are taken in than are expended, fuel is taken from storage and oxidized.

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Homeostatic regulation of cellular fuel

Homeostasis: 90 mg glucose/

100 mL blood

Stimulus: Blood glucose level rises after eating.

Stimulus: Blood glucose level drops below set point.

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Overnourishment and Obesity

Overnourishment causes obesity, which results from excessive intake of food energy with the excess stored as fat.

Obesity contributes to diabetes (type 2), cancer of the colon and breasts, heart attacks, and strokes.

The complexity of weight control in humans is evident from studies of the hormone leptin.

Mice that inherit a defect in the gene for an appetite regulation hormone, leptin, become very obese.

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Researchers have discovered several of the mechanisms that help regulate body weight.

Homeostatic mechanisms are feedback circuits that control the body’s storage and metabolism of fat over the long-term.

Hormones regulate long-term and short-term appetite by affecting a “satiety center” in the brain.

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