Animal Nutrition and Digestion

  • Animals eat other organisms- dead or alive

  • includes parasites

  • ingest and digest food

Essential Nutrients:

  • must be obtained from an animal’s diet

  • animals need these but can’t synthesize them themselves

  1. Essential Amino Acids- need 20 amino acids to synthesize proteins

    1. animals need need 8 amino acids, infants need 9- these + histadine

    2. protein deficiency is the most common type of malnutrition for humans

    3. Animal proteins- complete source of essential amino acids

    4. Plant proteins- “incomplete” but can be combined for complete complement, like corn+beans

  2. Essential Fatty Acids- animals can synthesize most fatty acids

    1. include unsaturated fatty acids

    2. typically obtained from seeds, grains, vegetables

    3. Ex: omega-3 and omega-6

  3. Vitamins-

    1. know water-soluble(B’s and C) vs fat-soluble (ADEK)

    2. required in very small amounts- overdose and underdose can cause problems

    3. 13 vitamins essential for humans

    4. moderate overdoses of water soluble is ok b/c expelled in urine

    5. excess amounts of fat soluble are stored in body fat

  4. Minerals-

    1. required in small amounts

    2. simple, inorganic nutrients

    3. large amounts of some minerals ingested can upset homeostatic balance

    4. know which ones you need a lot of vs less than 200 mg/day

Diet Classifications:

  • Not usually absolute, diet flexibility does exist

  • most animals are opportunistic

  1. Herbivore

  2. Omnivore

  3. Carnivore

    1. Sanguivore- consume blood

    2. Insectivore

Food Processing- 4 stages

  1. Ingestion- act of feeding

    1. filter feeding- sift small particles from their medium

    2. substrate feeding- animals living on/inside their food source, caterpillars, worms, maggots, beetles

    3. fluid feeding- mosquitoes, aphids, hummingbirds, ticks, suck up food

    4. bulk feeding- larger quantities of food, most mammals, reptiles, amphibians

    5. Adaptations- begin in mouth

      1. carnivores have incisors, canines, premolars, and molars spread out a bit

      2. omnivore- incisors, canines, premolars, molars all lines up close together

      3. herbivores- incisors and canines at front of mouth, premolars and molars far back

      4. snakes have modified teeth to inject venom

      5. frog and lizards’ tongue, proboscis

  2. Digestion- break food down into molecules small enough for body to absorb, most animals do this in compartments

    1. Intracellular digestion- food vacuoles fuse with lysosomes containing digestive enzymes, Porifera only do this

    2. Extracellular digestion

      1. Mechanical digestion- physical breakdown of large particles into smaller units, chewing/gut churning

      2. Chemical digestion- breaking down macronutrients into molecules that can be digested

    3. Different digestive systems:

      1. gastrovascular cavity- one opening for digestion and excretion

      2. Alimentary canal- contains compartments for digestion/absorption; two openings; more compartments for animals with more complex diets

        1. can eat more food b/4 earlier meal is fully digested

    4. human digestion starts in oral cavity→saliva=chemical digestion→tongue+teeth=mechanical digestion→ esophagus connects oral cavity to stomach

      1. stomach doesn’t digest itself b/c of strong mucosal lining secreted by epithelial cells lining stomach (replaced by mitosis every 3 days)

  3. Absorption

    1. Small intestine- increases surface area available for absorption

      1. main organ for digestion+absorption

      2. Functions: peristalsis + absorbs final products of digestion

      3. Components: Duodenum (connects to stomach)→ pancreas, liver, gallbladder produce enzymes and liquids that hang out in here; Jejunum- middle section; Ileum- connects to large intestine

    2. Adaptations:

      1. herbivores and omnivores have a longer alimentary canals than carnivores b/c more time for symbiotic microbes to digest cell walls+cellulose and more time to absorb nutrients from fibrous, protein poor foods

      2. Hindgut fermenters= symbiotic microbes in later parts of intestines (cecum), elongated intestine and ceca allow greater surface area

      3. Foregut fermenters= symbiotic bacteria, archaea, protists in stomach, have rumen instead of cecum

    3. know where different nutrients are digested

    4. Large intestine- reabsorb liquids and prepare feces for excretion

      1. components:

        1. Cecum- fermenting bacteria stored in herbivores; humans have a smaller one, have appendix as extension

        2. appendix- bank for gut bacteria

        3. colon- most liquid reabsorption occurs

        4. rectum - storage

        5. anus- opening+sphincter

  4. Nutritional Regulation-

    1. Liver- creates bile which is stored and concentrated in gallbladder

      1. bile is created from lipids brought to liver through lymphatic system

      2. regulates nutrient distribution + breaks down toxins that enter body

      3. monitors nutrients through the hepatic portal system that transports blood from the intestines to the liver

      4. 1st access to amino acids and sugars + releases materials back into blood stream, monitors glucose levels

    2. Pancreas- produces enzymes, alkaline solution that neutralizes chyme coming from stomach

      1. maintains glucose levels (endocrine function)

      2. secretes enzymes into duodenum to digest proteins, carbs, and fats (exocrine function)