Obtaining & Processing Nutrients & Relation of Animal Body Evolution to Digestion Kenneth L. Campbell Professor of Biology University of Massachusetts at Boston

Obtaining & Processing Nutrients

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. Amino acids Fats Sugars Nucleic Acid Components Minerals Vitamins

Teeth: break food into smaller particles & mix in saliva Saliva: adds water, buffer salts & often enzymes that begin sugar digestion Stomach: adds HCl & pepsin, a proteolytic enzyme Apocrine pancreas & bile: add enzymes & detergents for degrading protein, fats, sugars, & nucleic acids Small intestine: absorbs simple sugars, amino acids, fats, nucleosides, vitamins, & ions Cecum: often acts as a fermenter allowing bacteria to break down complex sugars Large intestine: absorbs water, ions, & small molecules Colon: absorbs water, stores feces Where does this occur?

Review: What do each of these organs do? Stomach Small Intestine ColonCecum Large Intestine Pancreas & Bile Saliva Teeth

P262%20Web%20Pages/ EX-14%20Digestive% 20Histology/aa.GIF / va/anatomy/case6/gi4.gif Smooth muscle layers Mucosa: HCl & pepsin Stomach Histology Small Intestine Histology miller/013634fig8-24.gif

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. hsc.usf.edu/2005/ lipoprotmet.jpg

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. hsc.usf.edu/2005/ lipoprotmet.jpg

The Liver is Central to Processing of Sugars. 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.

Glucose Homeostasis 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: Liver Fat Muscle Brain 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.

Glucagon acts on liver to stimulate glucose production & release, & on fat to cause fat breakdown. Glucagon rises when glucose falls. Adrenaline, cortisol, & growth hormone also make blood glucose rise. But insulin-like- growth factor I acts like insulin. Pancreas Hormones Control the Glucose Balance Insulin acts on body cells to allow them to take in circulating glucose. Insulin levels rise when glucose rises. InsulinGlucagon Islets of Langerhans

Relation of Animal Body Evolution to Digestion

Evolutionary Adaptations for Digestion Form & function of the gut. 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 HCO 3 -2 & PO 4 -3 in herbivores. Venoms & proteases in some reptiles & invertebrates.

Digestive Tracts of Carnivores: Simple stomach, short small intestine, simple, short large intestine for extraction of high quality foods.

Digestive Tracts of Herbivores: 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.

Digestive Tracts of Omnivores: These are hybrid, systems: simple stomachs, moderately long small intestines, & well- developed, but simple, large intestines.

Digestion is an extraction & breakdown process optimized to provide metabolic building blocks & energy source molecules. Evolutionary adaptations match each animal’s anatomy & physiology to it’s food sources & quality. Summary: