Animal foraging, nutrition and digestion

  1. all animals must find food
      1. heterotrophic, respiring organisms
    1. all animals face same three problems:
      1. find food
      2. capture food
      3. consume and digest food
      4. eliminate wastes
  2. Basic nutritional needs
    1. beyond carbon and energy
      1. generally reflect limits of synthetic machinery
      2. proteins: essential and non essential amino acids
      3. vitamins: molecular components of biological functions
          4. somewhat similar among different animals
      4. essential elements
        1. non-carbon components of biological molecules
      5. electrolytes
        1. ionic solutes required for osmotic balance, membrane function
    2. In the United States, most nutritional needs are met by most individuals
  3. Predators and Herbivores
    1. predators eat other animals
      1. little problem meeting basic nutritional requirements
      2. difficulty is capturing food
    2. herbivores eat plants
      1. easy to capture food
      2. hard to meet nutritional needs
  4. Digestion
    1. physical break-up of food
      1. chewing, crops
    2. chemical processing of three main macromolecule types
      1. breaking macromolecules into component parts
      2. each requires particular set of enzymes
      3. carbohydrates (amylase)-> sugars
        1. examples: starch, sugar
      4. proteins (protease)-> amino acids
      5. fats (lipase)->glycerol and free fatty acids
  5. Digestion 
    1. Intracellular digestion
      1. macromolecules taken up via endocytosis
      2. examples: amoebae, Paramicium, some sponges
    2. Extra cellular digestion
      1. macromolecules digested outside of cells
        1. nutrients absorbed via active transport, diffusion
      2. advantage: keep digestive enzymes outside of cell
      3. disadvantage: surface area: volume limitations
    3. some example digestive tracks
      1. evolutionary trend towards increased complexity
  6. From starch to glucose to fat: an example
    1. mouth: amylase
      1. most digestion does not occur in the mouth
    2. stomach:
      1. highly acidic contents
      2. gastric juices primarily responsible for protein digestion
    3. small intestine
      1. most digestion and absorption of nutrients, water
      2. pancreatic amylase
      3. Na+/glucose co-transporter
      4. water movement
    4. Large intestine
      1. reabsorption of water
    5. Regulation of blood-glucose levels and hunger
      1. Insulin and glycogen
        1. regulation of blood glucose levels
      2. leptin
        1. regulation of fat deposition
      3. other hormones and pathways are still being explored
Study questions

1.    In what way is function of the vertebrate small intestine limited by the surface area : volume ratio?  What anatomical feature(s) have evolved to counter these limitations?  Where in the kidney would you expect to find similar anatomical feature(s)?

2.  Specialization upon a single part of a single species of plant (i.e., only young oak leaves, or only milkweed leaves) is much more common in insects than vertebrates.  Vertebrates tend to specialize on a plant part (i.e., fruit or nectar or leaves) and consume this part from a variety of plants (beever eat the bark from a wide variety of tree species).  Many vertebrates do not specialize at all:  deer will eat, in season, leaves, bark, and fruit.  Speculate on the difficulty or ease with which these vertebrate herbivores might meet their nutritional needs, compared to the difficulty for an insect.

3.  Predict differences in the surface area : volume ratio of the guts of herbivorous versus predatory insect larvae.  Hint:  consider the conversion efficiency of each food.  Why would it be best to test your prediction using larvae from closely related groups, such as two species of the same genus?

4.  In class, it was mentioned that a recent study showed that the allele for faulty leptin protein was equally common in slender and obese humans.  What does this imply for our understanding of the role of leptin in maintaining weight at the "set point" in humans?  What does this imply for our use of mice (where homozygosity for the faulty allele is causes obesity) as a model system for understanding human physiology?  

5.   Currently (and far into the past) there are arguments about diet and health:  some people advocate diets high in protein, others call for diets high in complex carbohydrates.  Others in the medical community call for decreased total calory intake.  Which of these makes the most sense in terms of your understanding of  the feedback loops in blood glucose and fat homeostasis?

See also:  content review #4, 5, 6;  concept review #1, 3, 4;  applying ideas #2, 4, 5, 6

Answers