Ch 46

• Physiological respiration


  The process by which animals exchange gases with their surroundings - how they take in O2 from the environment and deliver it to body cells, and remove CO2 from body cells and deliver it to the environment
• Cellular respiration


  All the oxidative reactions that lead to production of ATP in mitochondria of animal cells - where O2 is used and CO2 is released
• Physiological respiration


  Includes cellular respiration
• Respiratory medium


  • Water
  • Air
  • Both
• Respiratory surface


  • Body surface
  • Gills
  • Lungs
• The exchange of gases with the respiratory medium is called breathing, regardless of medium
• Atmospheric pressure


  Pressure exerted by the atmosphere on the body surfaces of animals, measured in mmHg (mm of mercury) or kPa
• Partial pressures


  The pressures exerted by each gas in air, in proportion to their amounts
• Atmospheric pressure changes - percentage of gases remains the same regardless of altitude, but lower atmospheric pressure results in lower partial pressures

  
• In all animals, exchange of O2 and CO2 across the respiratory surface occurs by simple diffusion
• Respiratory surfaces


  • They are thin
  • They have large surface areas
• Rate of diffusion becomes higher with larger concentration gradients and with increasing temperature
• Ventilation


  The flow of the respiratory medium (air or water) over the external side of the respiratory surface
• Perfusion


  The flow of blood or other body fluid on the internal side of the respiratory surface
• Gases must dissolve in water to enter and leave epithelial cells - the respiratory surface must be wetted, either directly by the respiratory medium or by a thin film of water
• Gills


  • They are evaginations of the body - they extend outward into the respiratory medium
• Lungs


  • They are invaginations of the body surface, deep in the body interior where they are less susceptible to drying out
• The respiratory system is responsible for gas exchange and consists of all parts of the body involved in exchanging air between the external environment and the blood
• Respiratory media


  • Water
  • Air
• Water as a respiratory medium

  Holds less oxygen than air, and O2 content is affected by temperature and solutes. It takes significantly more energy to move water than air over a respiratory surface
• Air as a respiratory medium

  Relatively high O2 content, low density, and low viscosity greatly reduce the energy required for ventilation. Gas molecules diffuse faster in air than in water. However, animals lose water during breathing
• External gills


  • They are gills that do not have protective coverings, extend out from the body in direct contact with water, and are exposed to mechanical damage and must be immersed in water to keep them from collapsing or drying
• Internal gills


  • They are located within a body chamber and have a cover that protects the gills from drying. Water must be brought to internal gills
• Animals with external gills

  • Certain annelids and mollusks, aquatic insects, larval forms of some bony fishes, and certain amphibians
• Cuttlefish gills


  • They use contractions of the muscular mantle to pump water over their gills
• Fish gills


  • The gills of bony fishes extend into a chamber covered by gill flaps or opercula, which help ventilate the gills
• Countercurrent exchange in fish gills

  Water flows over the gill filaments in a direction opposite to the flow of blood, maximizing the O2 and CO2 exchange with the water
• Tracheal system


  Air-conducting tubes in insects that are invaginations of the outer epidermis reinforced by rings of chitin
• Air enters and leaves the tracheal system at openings in the chitinous exoskeleton
• Countercurrent flow in fish gills

  1. Blood and water move in opposite directions

  2. Deoxygenated blood flows into filament

  3. Oxygenated blood flows out of filament
• Countercurrent exchange


  • Uses one-way flow of water over the gills to maximize O2 and CO2 exchange with water
  • Water flows over the gills in a direction opposite to the flow of blood under the respiratory surface
  • At any point along the gill filament, the water is more highly oxygenated than the blood - O2 diffuses from the water into the blood across the entire respiratory surface
  • Countercurrent exchange removes 80-90% of water's O2 content
• Tracheal system


  Air-conducting tubes (tracheae) that are invaginations of the outer epidermis of the animal reinforced by rings of chitin
• Insect breathing


  1. Air enters and leaves the tracheal system at openings in the chitinous exoskeleton (spiracles)

  2. Alternating compression and expansion of the body pumps air through the tracheal system

  3. Tracheae lead from the body surface and branch extensively to almost every cell inside the animal

  4. The finest branches (tracheoles) are dead-end tubes with very small fluid-filled tips that are in contact with cells of the body, forming the respiratory surface

  5. At places within the body the tracheae expand into internal air sacs that act as air reservoirs
• Positive pressure breathing


  Lungfishes and mature amphibians obtain air by gulping motion that forces air into the lungs
• Frog breathing


  1. Lowers the floor of its mouth and inhales through its nostrils

  2. Closes its nostrils, opens the glottis, and elevates the floor of the mouth, forcing air into the lungs

  3. Rhythmic ventilation assists in gas exchange

  4. Air is forced out when muscles in the body wall above the lungs contract and the lungs recoil elastically
• Bird lungs and air sacs

  • In addition to paired lungs, birds have nine pairs of air sacs that branch off the respiratory tract and allow air to flow in one direction through the lungs, rather than in and out
  • Within the lungs, air flows through fine, parallel tubes (parabronchi) that are surrounded by a capillary network - blood flows in the direction opposite to air flow (countercurrent exchange)
• Human respiratory system


  • Air enters through the nostrils and mouth
  • Air moves through the throat (pharynx) and 'voice box' (larynx) into the windpipe (trachea)
  • The trachea branches into two airways (bronchi) leading to the two lungs
  • Inside the lungs, the bronchi narrow and branch, becoming progressively narrower and more numerous
  • Terminal airways (bronchioles) lead into cup-shaped pockets (alveoli), where gas exchange occurs
• Bronchial system


  • The larynx, trachea, and larger bronchi are nonmuscular tubes encircled by rings of cartilage
  • The walls of the smaller bronchi and bronchioles contain smooth muscle cells that contract or relax to control the amount of air flowing to and from the alveoli
  • The epithelium of bronchi contain cilia and mucus-secreting cells that trap bacteria and airborne particles and move them upward into the throat - tobacco smoke paralyzes the cilia
• Ventilation anatomy


  1. A dome-shaped sheet of skeletal muscle (the diaphragm) separates the chest cavity containing the lungs from the abdominal cavity

  2. Lungs are covered by a double layer of epithelial tissue (the pleura) - a slippery fluid between the inner and outer layers allows the lungs to move freely within the chest cavity

  3. Contraction of the diaphragm and external intercostal muscles between the ribs brings air into the lungs by a negative pressure mechanism
• Ventilation physiology


  1. Lungs are elastic and resist stretching as they are filled - stretching stores energy, which can be released to expel air from the lungs

  2. When a person at rest exhales, the diaphragm and rib muscles relax - elastic recoil of the lungs expels the air

  3. When oxygen demand increases, air is expelled forcefully by contraction of abdominal wall muscles and internal intercostal muscles, reducing the volume of the chest cavity