Animal Nutrition & Digestion Notes

Topic 7 Objectives: Animal Nutrition

• Reading: Chapter 41
• Distinguish between autotrophs and heterotrophs.
• Explain the advantages of a complete digestive system vs. an incomplete digestive system (specialization, batch vs. continuous flow).
• Distinguish the major functions of the digestive system (ingestion, digestion, absorption, secretion, excretion, motility).
• Give examples of how diverse mouthparts are related to the type of food eaten (e.g., insects, snakes, humans, cichlid fishes, etc.).
• Describe the structure and function of the major organs and tissues of the digestive system, and predict how the structure of these organs might be different in other organisms that eat different types of food (e.g., cows, snakes, and others). (mouth, esophagus, stomach, small intestine, large intestine, liver, pancreas)
• For the human digestive system, create a table describing how each major nutrient type (carbohydrate, protein, lipid) is digested and absorbed (in what part of the tract, by what enzyme(s), by what process).
• Explain how peristalsis moves chyme (partially digested food) through the digestive tract.
• Distinguish between the roles of bile and lipase in the digestion of fats (emulsify, catalyze).
• Describe how the stomach produces acid and how acid is involved in digestion (parietal cell, proton pump ($H^+$/$K^+$ ATPase), carbonic anhydrase, pepsin, etc.).
• Explain how inactive enzyme precursors are released and then activated in the gut (zymogen).
• Explain how the presence of chyme (partially digested food) in the digestive tract leads to the release of enzymes from the pancreas and bile from the liver, including the relevant hormones and the organs that release them.
• Draw a negative feedback loop for blood glucose regulation, identifying the roles of insulin and glucagon.
• Compare and contrast the causes, prevalence, and treatments of type I and type II diabetes mellitus.
• Predict the food habits of an animal (herbivore, omnivore, carnivore, nectarivore) based on the structure of its teeth and gastrointestinal tract.

Digestive Systems

• Heterotroph: An animal that gets chemical energy for synthesizing ATP and carbon-containing compounds from other organisms.
• Autotroph: Organisms (like plants) that make their own food.

Basic Processes:

• Ingestion
• Digestion
• Absorption
• Secretion
• Motility
• Excretion

Nutritional Requirements:

Animals:

• Amino acids, fatty acids, vitamins, minerals, chemical potential energy, nucleic acids, water

Plants:

• Amino acids, fatty acids, vitamins, minerals, chemical potential energy, nucleic acids, water

Excess Nutrients

• Excess nutrients are stored, converted to other nutrients, or excreted.
  • Amino acids: Stored as protein in muscles, converted to fat, or excreted.
  • Vitamins: Some storage (fat-soluble), mostly excreted.
  • Chemical energy: Stored as fat.

Feeding Modes

• Suspension feeding: Grabs food as it floats by.
• Deposit feeding: Earthworm eating soil.
• Suction Feeding
• Mass feeding: Prey/capture

Digestive Tracts

• Complete system: A continuous tube with specialized functions and two holes.
• Incomplete system: Does "batch flow" in hydra or anemone.
• In humans: Many folds - villi on organs for maximum surface area.
• Lumen: Is lined with epithelial tissues specialized for exchange.

Mouthparts:

• Mouthpart match type of food
  • crushes shells
  • tears fish scale
  • compacts algae

Ruminant Stomach

• 4-chambered stomach to digest cellulose
  • Rumen: acts as fermentation vat; has symbiotic bacteria and protists, cellulase.
    • Turning cellulose to glucose, then turning into ATP by fermentation.
    • Fatty acids are released as a by-product
  • Reticulum: Adjacent to the rumen. After partial digestion, food is regurgitated, chewed, and reswallowed
  • Omasum: Where food is sent, water, and minerals are absorbed
  • Abomasum: Contains digestive enzymes functions like other animal stomachs

Digestive Enzymes

Human Digestive Tract

• Mouth: Site of mechanical & chemical digestion, sorts food
• Esophagus: Transports food to the stomach
• Stomach: Site of mechanical & chemical digestion of proteins
• Small intestine: Site of chemical digestion and absorption of nutrients
• Large intestine: Absorbs water
• Appendix: Contains immune tissue w/ symbiotic bacteria
• Anus: Eliminates feces
• Salivary glands: Secrete enzymes that digest carbohydrates
• Liver: Secretes molecules that aid in fat digestion
• Gallbladder: Stores secretions from the liver, empties into the small intestine
• Pancreas: Secretes enzymes & other materials into the small intestine

Chemical Digestion

• Enzymes in the mouth begin chemical breakdown of carbohydrates & lipids
  • Salivary amylase cleaves bonds in starch to release dextrins & disaccharides (smaller polysaccharides)
    • Salivary glands in mouth secrete amylase
    • Mucus allows food to be swallowed
  • Tongue cells secrete lingual lipase - begins digestion of lipids - yielding diglycerides & triglycerides
  • Goes to stomach by muscle contractions called peristalsis
• Protein digestion begins in acid in stomach; lipids continue to be chemically digested in stomach, carbohydrates are not broken down further
• Contains ring-like muscles called sphincters
  • Acidic lumen (interior) - HCl secreted by parietal cells in living
  • Pepsinogen + HCl - Pepsinogen secreted by Chief cells in living + secretion of HCl by parietal cells
• Digestion of carbohydrates, proteins, & lipids is complete in the small intestine
  • Small polysaccharides -Disaccharide-monosaccharides - by pancreatic amylase
  • Bile is amphipathic
    • surrounds lipids in emulsification. Trypsinogen -trypsin- peptide amino acid.
    • smaller surface area to volume ratio
    • large droplet of triglyceride -> small droplet of monoglyceride + pancreatic lipase
• Small molecules that result are absorbed in small intestine with water, vitamins, and ions
• Remaining goes to large intestine in feces
  • Gut microbes break down cellulose -> sugars, fatty acids, vitamins

Feedback Regulation of Glucose

• High come glucose -> receptors -> pancreas -> secrete insulin
  • Inc Liver
• Low come glucose -> pancreas -> secrete glucagon
  • decreases glucotake

Diabetes

• Type 1: Not enough glucose produced
  • Insulin-dependent - pancreas isn't producing insulin
• Type 2: Non-insulin dependent - cells become insulin insensitive
  • diet, exercise, drugs

Absorption of glucose in the small intestine & Kidney epithelium

• ICF lumen mucosa ECF blood

Gas Exchange

• Fick's law of diffusion
  • Gases move down a gradient of partial pressure describes the amount of gas
  • $Rate of diffusion = k * A * (P<em>{gas}/ d) = k * A * ((P</em>{total} * Fractional concentration)/d)$
    • A = area
    • d = distance
• The blood in fish gills flows countercurrent to water.
• An increase in surface area and decreased distance leads to an increased rate of diffusion.
• Endotherms have a greater respiratory surface area than ectotherms.

Respiration

• Ventilation: The movement of air or water through a specialized gas exchange organ (lung/gill)
• Diffusion at respiratory surface: Where $O_2$ moves from the air or water into the blood.
  • $CO_2$ moves from blood into air or water along their concentration gradient
• Cellular respiration: The cells' use of $O<em>2$ & production of $CO</em>2$.
  • In humans, when $O<em>2$ levels are low & $CO</em>2$ levels are high, gas exchange occurs between blood & cells
• Circulation: Transport of dissolved $O<em>2$ & $CO</em>2$ throughout the body - along with nutrients, water, and other types of molecules - by the circulatory system
• Diffusion at tissues: Where $O<em>2$ moves from blood to tissues. $CO</em>2$ moves from tissues to blood along concentration gradients.
• ventilation -> diffusion @ respiratory surface -> circulation -> diffusion @ tissues

$O<em>2$/$CO</em>2$ in the Air

• The atmosphere consists primarily of nitrogen & oxygen.
  • The amount of $O_2$ in the atmosphere does not vary with elevation.
    • There are fewer molecules of $O_2$ & other atmospheric gases per unit volume of air at high elevations.
• When gases move by diffusion, they move according to a partial pressure/gases gradient.
  • At higher elevations: partial pressure of $O<em>2$ is lower, so fewer molecules of $O</em>2$ diffuse into tissues

In Water

• Water contains much less $O_2$ than the air & is much denser
  • Aquatic animals spend much more energy to ventilate.
• The amount of gas that dissolves in water depends on:
  1. Solubility of the gas in water: $O<em>2$ has low solubility in $H</em>2O$
  2. Temperature of water: As water temperature increases, the amount of gas dissolved decreases (warm water has less $O_2$).
  3. Presence of other solutes: Water with a higher concentration of solutes holds less dissolved gas.

Convection

• Flow of pressure through a tube
• $Q = (P<em>{in} - P</em>{out}) * \frac{\pi r^4}{8 \eta L}$
  • r = radius
  • L = length
  • η = viscosity of fluid

Circulatory System

• Blood, vessels, pump

Blood:

• Erythrocyte (carry $O_2$), Leukocyte (fight pathogens)
  • Only mammals have non-nucleated RBCs
  • 4 subunits transport $O_2$ by hemoglobin - in RBC
    • bound to 4 $O<em>2$ from lungs -> tissues. $\%$ unloading rate depends on partial pressure of $O</em>2$ in tissues
    • Right shift (Bohr shift) a small change in pH can change affinity of hemoglobin
      • helps hemoglobin let go of $O_2$
      • decrease in pH in blood unloads $O_2$ from hemoglobin
• Increase in temperature
• Increase in BPG- partial pressure of $O_2$ in high altitude mammals - higher saturation of hemoglobin (adaptation over gas

$CO_2$ transport

• $CO<em>2 + H</em>2O <-> H<em>2CO</em>3 <-> H^+ + HCO_3^-$ Alveolus
• 10% in plasma, 23% bound to hemoglobin, 70% as bicarbonate
• As blood moves throughout the body, pressure decreases
• Arteries: carry away from heart
• Veins: toward heart
• Capillaries: gas/nutrient exchange

Evolution of Vertebrate Circulation Patterns

• Fish: 1 circuit , 2-chambered heart
• Amphibians: 2 circuits 3-chambered heart
• Turtles, lizards, snakes: 2 circuits , 3-chambered heart
• Crocodilians: 2 circuits , 4-chambered heart
• Birds: 2 circuits , 4-chambered heart
• Mammals: 2 circuits , 4-chambered heart
• Endotherms require high metabolism.
• Two circulatory circuits
• Ventricle divided (partially or completely)
• Fully divided circulatory systems for high metabolism

Tracheal Systems

• Diffusion of materials between:
  • hemolymph
  • spiracles
  • gas + aqueous mixtures