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Biology 188 General Biology II March 31, 2003 Obtaining & Processing Nutrients & Relation of Animal Body Evolution to Digestion Kenneth L. Campbell Professor of Biology University of Massachusetts at Boston.
March 31, 2003
Obtaining & Processing Nutrients
Relation of Animal Body Evolution to Digestion
Kenneth L. Campbell
Professor of Biology
University of Massachusetts at Boston
This presentation is made possible by a grant entitled“Shortcourses in Endocrinology at Minority Undergraduate Institutions”from the National Institute of General Medical Sciences (NIGMS) to The Minority Affairs Committee of the Endocrine Society
What are nutrients? Why are they being extracted?Nutrients are those parts of food that provide sources of energy, molecular building blocks, or ions and small molecules needed to support biochemical functions.
Teeth: break food into smaller particles & mix in salivaSaliva: adds water, buffer salts & often enzymes that begin sugar digestion Stomach: adds HCl & pepsin, a proteolytic enzymeApocrine pancreas & bile: add enzymes & detergents for degrading protein, fats, sugars, & nucleic acidsSmall intestine: absorbs simple sugars, amino acids, fats, nucleosides, vitamins, & ions Cecum: often acts as a fermenter allowing bacteria to break down complex sugarsLarge intestine: absorbs water, ions, & small moleculesColon: absorbs water, stores feces
Where does this occur?
What do each of
these organs do?
HCl & pepsin
Fats are often broken down after being absorbed by the small intestine. They are moved as complexes wrapped in specific proteins. The earliest complexes have the most fat relative to protein and are the least dense.
Converts many simple sugars, several amino acids, acetate & glycerol to glucose ( =gluconeogenesis) then secretes it into blood.
Stores glucose as a macromolecule, glycogen, & hydrolyzes glycogen to glucose.
Makes fat from fatty acids & glycerol, & breaks fat down to acetate & glycerol.
Stores amino acids as protein, & can break proteins down to amino acids.
The body must control glucose levels because all cells use glucose to make ATP, the energy currency of cells. Some tissues like brain almost never burn any other fuel molecule. But too much glucose damages cells by getting attached to certain proteins and changing their function. Key tissues in this balancing act are:
Pancreas (endocrine cells)
After meals glucose from liver is mainly stored as glycogen in liver & muscle & as fat in fat cells. When more energy is needed between meals, glycogen, fat & protein (last) are broken down & liver uses the parts to make glucose.
Hormones (insulin, glucagon, adrenalin, cortisol) signal the change from storage to synthesis.
Hormones Control the
Insulinacts on body cells to allow them to take in circulating glucose. Insulin levels rise when glucose rises.
Adrenaline, cortisol, & growth hormone also make blood glucose rise. But insulin-like-growth factor I acts like insulin.
Glucagonacts on liver to stimulate glucose production & release, & on fat to cause fat breakdown.Glucagon rises when glucose falls.
Shape & arrangement of teeth:
From Wessells & Hopson, Biology, (Random House:1988), 817, 822, 819.
Carnivore Omnivore Herbivore
Contents of saliva:
Contains amylases in cloven hoofed animals, rodents, rabbits, dogs, & primates.
High content of HCO3 -2& PO4 -3 in herbivores.
Venoms & proteases in some reptiles & invertebrates.
Form & function of the gut.
Simple stomach, short small intestine, simple, short large intestine for extraction of high quality foods.
Ruminants, efficiently extract nutrients from low quality foods by symbiosis with bacteria in complex stomach.
On similar feed, equids extract easily digested materials in foregut, & get more calories by fermentation in complex hindgut.
These are hybrid, systems: simple stomachs, moderately long small intestines, & well-developed, but simple, large intestines.
Evolutionary adaptations match each animal’s anatomy & physiology to it’s food sources & quality.