Animal Nutrition and… The Digestive System!
-Luke Cheng
Part I: Food
Four different feeding mechanisms:
Suspension feeders: sift through water to obtain food (example: whales)
Substrate feeders: you live on what you eat (example: caterpillars)
Fluid feeders: you only drink stuff (mosquitoes, spiders, infant humans)
Bulk feeders: you eat large pieces of food (snake swallowing an entire antelope)
Glucose regulation (two enzymes from pancreas, an example of homeostasis):
Insulin--> causes liver and muscles to store glucose as glycogen
Glucagon--> causes the breakdown of glycogen into bloodstream
Things that animals GOTTA EAT:
Essential amino acids: Methionine, Valine, Threonine, etc. (lack of it: protein deficiency)
Essential Fatty Acids: unsaturated fatty acids such as linoleic acid
Vitamins (13 of them, these are ORGANIC nutrients):
Water soluble:
B1(thiamine): coenzyme used in removing CO2 from organic compounds
B2(riboflavin): Component of coenzymes FAD and FMN
Niacin: coenzyme component
B6(pyridoxine): coenzyme in amino acid metabolism
Pantothenic acid: coenzyme again
Folic acid (folacin): found in veggies, coenzyme for digestion
B12: coenzyme
Biotin: coenzyme for fat synthesis
Vitamin C: found in veggies, antioxidant, collagen synthesis, iron absorption,
lack of it leads to scurvy
Fat soluble vitamins:
A(retinol): visual pigments, maintenance of skin tissue, antioxidant
D: helps calcium and phosphorous absorption, promotes bone growth
Lack of this stuff leads to rickets in children
E(tocopherol): antioxidant, helps prevent damage to cell membranes
K(phylloquinone): for blood clotting
Minerals (Inorganic nutrients, there are lots of them…):
Calcium, Phosphorus: bone growth
Sulfur: amino acid component
Potassium: acid-base balance, nervous system
Chlorine, Sodium, Magnesium…
Iron: component of hemoglobin
Fluorine: for your teeth (and maybe bones)
Zinc, Copper, Manganese,
Iodine: thyroid hormones
Cobalt, Selenium, Chromium, Molybdenum…
Part II: Extracellular digestion in other animals
Earthworms: Mouth-Pharynx(throat)-Esophagus-crop-gizzard-intestine-anus(lol)
Grasshoppers: Mouth-crop-“gastic ceca”(weird pouches extending from midgut)-rectum-anus
Birds: Mouth-esophagus-Crop-stomach-gizzard-intestine-anus
(Gizzards contain sand that pulverizes food before going into the intestine)
Complete digestive tract/alimentary canal: a digestive tube extending between mouth and anus
Part III: The Human digestive system!
Oral cavity: salivary glands secret salivary amylase, which digests starches, teeth mash food
Epiglottis: a flap that blocks either windpipe or esophagus.
Esophagus: uses peristalsis (rhythmic waves of contraction by smooth muscles) to move food
Stomach: bolus of food gets churned in gastric juices, forms acid chyme, a mix of juice and food
Pepsinogen: inactive form of pepsin that is first secreted, then activated by acid (HCl)
Pepsin: hydrolysis of proteins into smaller polypeptides
Small Intestine: 6 meters long, enzymatic digestion, most absorption of nutrients.
Duodenum: chyme goes through pyloric sphincter into first segment of the s. intestine
Helper organs: they secrete enzymes that digest macromolecules in the duodenum
Pancreas: Chymotrypsin and trypsin, which breaks down proteins
Also secretes other proteases (suffix “-peptidase”):
Dipeptidase, carboxypeptidase, aminopeptidase.
Gallbladder: stores bile, which emulsifies fats into small micelles
Liver: produces bile.
Jejunum and then Ilium: absorbs nutrients using huge surface area created by villi (little
finger-like protrusions, and microvilli, which are ultra-tiny protrusions).
Note that all nutrient-rich blood goes down the hepatic portal vein to the liver first.
Large intestine: absorbs water, mostly, has cecum and appendix, both useless in humans
Rectum: stores your feces until you have a bowel movement (also stores bacteria like E. coli)
Anus: no digestive functions here, this is just a sphincter (a muscular ring-like valve) that lets
feces fall out.