Bio 114 Chapters 34-35

• Animals are heterotrophs—they obtain the energy and nutrients they need from other organisms rather than making their own food as plants do
• Four processes needed to obtain energy from food

  • Ingestion
  • Digestion
  • Absorption
  • Elimination

  
• Four strategies for animal food-getting techniques

  • Suspension feeders
  • Deposit feeders
  • Fluid feeders
  • Mass feeders
• Natural selection has tightly matched the structure of animal mouthparts to their function in obtaining food
• Evolution is not progressive—animal mouthparts do not get "better" over time in the sense of being more complex, and adaptation is not perfect—some structures are actually maladaptive
• Adaptive radiation


  The diversification of a single ancestral lineage into many species, each of which lives in a different habitat or employs a distinct feeding method
• Two general designs of digestive tracts

  • Incomplete digestive tracts
  • Complete digestive tracts

  
• Complete digestive tracts


  • Animals can feed on large pieces of food
  • Chemical and physical processes can be separated within the canal, so that they occur independently of each other and in a prescribed sequence
  • Material can be ingested and digested continuously

  
• Digestion begins in the mouth, starting with the tearing and crushing activity of teeth during chewing
• Salivary amylase


  The most important catalyst in the breakdown of carbohydrates
• Lipase


  Enzyme that begins the breakdown of lipids
• Mucins


  Glycoproteins released by salivary glands that form the slimy substance called mucus
• Peristalsis


  Wave of muscle contractions that propel food from the esophagus to the stomach

  
• The esophagus has a prominent, widened segment called the crop where food can be stored and, in some cases, processed

  
• Crop


  Adaptation that allows birds to eat a large amount in a short time, then retreat to a safe location while digestion occurs
• Stomach


  • Tough, muscular pouch bracketed on both ends by valves called sphincters
  • Highly acidic lumen, with hydrochloric acid (HCl) as the predominant acid
• Pepsinogen


  Pepsin precursor that is converted to active pepsin by contact with the acidic environment of the stomach
• Parietal cells


  Source of HCl in gastric juice
• Mucous cells


  Secrete mucus that lines the gastric epithelium and protects the stomach from damage by HCl
• HCl secretion by parietal cells

  1. Carbonic anhydrase catalyzes formation of carbonic acid (H2CO3) from CO2 and H2O

  2. Carbonic acid dissociates into bicarbonate ion (HCO3-) and a proton

  3. Protons are actively pumped into the lumen of the stomach

  
• Ruminant stomach


  • Four-chambered stomach specialized for digesting cellulose rather than protein
  • Bacteria and protists in the rumen contain cellulase which frees up glucose and releases fatty acids

  
• Homeostasis


  The maintenance of relatively constant internal environment
• Achieving homeostasis


  1. Conformation

  2. Regulation
• Ruminant digestion


  1. Food first enters the rumen, which serves as a fermentation vat

  2. Ruminant regurgitates portions of the plant material into its mouth, forming a cud

  3. Swallowed cud goes to the omasum where water is removed

  4. Abomasum is the final chamber, which contains the ruminant's own digestive enzymes
• Conformational homeostasis


  Homeostasis that occurs by conformation to the external environment
• Regulatory homeostasis


  Homeostasis that requires a physiological mechanism that adjusts the internal state to keep it within limits that can be tolerated, regardless of the external conditions
• Small intestine


  • Six-meter-long tube where partially digested food mixes with secretions from the pancreas and liver
  • Enormous surface area for absorption of nutrients due to projections called villi and microvilli

  
• Homeostatic system


  • It has a sensor, an integrator, and an effector
  • It is based on negative feedback, in which effectors reduce or oppose the change in internal conditions
• Sensor


  A structure that senses some aspect of the external or internal environment
• Secretin


  Hormone produced in small intestine that induces flow of bicarbonate ions from pancreas to neutralize acid from stomach

  
• Integrator


  A component of the nervous system that evaluates the incoming sensory information and "decides" if a response is necessary to achieve homeostasis
• Cholecystokinin


  Hormone produced in small intestine that stimulates secretion of digestive enzymes from pancreas and secretion of molecules from liver involved in lipid digestion
• Effector


  Any structure that helps to restore the desired internal condition
• Gastrin


  Hormone produced by stomach cells that stimulates parietal cells to secrete HCl

  
• Ways animals exchange heat with their environment

  • Conduction
  • Convection
  • Radiation
  • Evaporation
• Na+-glucose cotransporter


  Transporter that brings glucose into epithelial cells along with sodium

  
• Conduction


  The direct transfer of heat between two physical bodies that are in contact with each other

  
• Convection


  A special case of conduction in which heat is exchanged between a solid and a liquid or gas rather than between two solids

  
• Pancreatic lipase


  Enzyme that breaks bonds in complex fats, releasing fatty acids and other small lipids
• Radiation


  The transfer of heat between two bodies that are not in direct physical contact