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Regulation of Nutrient Intake Part 1
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Covers how different organisms regulate nutrient intake, following on from a previous lecture.
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Comparative Anatomy and Physiology of AnimalsLecture 18 Regulation of nutrient intake 2 16/12/20
Post ingestive processing
- Animals regulate what nutrients it requires via feeding choices.
- After ingestion, amounts of nutrients delivered to tissues can be modified by changing
efficiency of digestion and absorption from the gut (by adjusting digestive enzyme secretion,
varying rate of passage, and changing the shape and size of the gut), or by differential
utilisation of absorbed nutrients.
Adjusting digestive enzyme secretion
- Until recently, it was believed that the function of the gut was to maximise digestion and
absorption of contents.
- The prevailing view was that enzyme secretion was stimulated by the presence of nutrients
in the gut and that the higher the concentration of nutrients, the greater the amount of
digestive enzymes secreted.
- The abundance of the nutrient transporters that absorb digested nutrients across the gut
lining has been shown to be positively related to the concentration of nutrients in the diet.
- As a result, most available nutrients are extracted from food in the gut, without wasting
energy maintaining unnecessary digestive and absorptive capacity when nutrient levels are
low, or food is scarce.
- This view was challenged recently by a study on locusts. Contrary to expectation, the
secretion of digestive enzymes did NOT increase along with their respective nutrients. On
the diet that was highest in protein relative to carbohydrates, the protease activity was
reduced. In the diet where carbohydrates were high relative to protein, the carbohydrase
activity was reduced.
- Nutrients at correct ratio for animal’s requirements (balanced P:C for locusts) - intake target
can be met by eating.
- Compensatory feeding cannot correct dietary imbalance – every extra mouthful gives more
unbalanced food!
- If complementary food not available, postingestive processing can help to correct imbalance
and bring animal closer to its intake target.
Varying rate of passage
- Faster transit can reduce rate of nutrients absorbed
from gut.
- Also change balance of nutrients absorbed.
- If A<B in diet, but absorbed faster, at t, A>B in blood.
- If intake target is A>B then flushing gut after t would
match intake target.
- Achieved by eating again, new food pushes out old
food, or by gut nutrient sensors changing gut motility.
- Control of motility, and thus transit time, by gut
nutrient sensors is well known in vertebrates and is
linked to release of hormones that also cause changes in the release of digestive enzymes.
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