Respiratory System - BIO 126

• Respiration - process that results in exchange of gases (oxygen and carbon dioxide) between the atmostphere and body cells
• External respiration - gas exchange between the blood and the lungs
• Internal respiration - transport of gases through blood to and from tissue cells
• Physical Properties of Gases - Partial Pressure, Diffusion of Gases, Volume and Pressure
• Partial Pressure - individual pressure of a given volume of gas; Unit of measurement - atm, mass/area, torr, mmHg
• Atmosphere is composed of several gases - every gas present in a mixture has a particular partial pressure
• Diffusion of Gases - gases diffuse from areas of higher partial pressure to areas of lower partial pressure (along a pressure gradient)
• Rate of gas diffusion in steady state:

  $Rate =$$KA(P_1 - P_2) (1/d)$


  K = constant of proportionality, A = Surface area of diffusion plane, (P1 - P2) = difference in partial pressures inside a SPM, d = distance traveled by gas particles (minimum value is the thickness of the membrane)
• Any gas present within a confined volume exerts pressure inside the inner walls of the container; Volume and pressure exhibit an inverse relationship
• Respiratory media - bring respiratory gases to the respiratory tracts; air for terrestrial animals, water for aquatic animals
• Oxygen content in both air and water decrease as temperature increases
• Arrangement of respiratory media according to increasing oxygen content: seawater < freshwater < air
• Capacitance coefficient ($CC =$$\bigtriangleup concentration / \bigtriangleup partial pressure$) in air: CC(oxygen) = CC (carbon dioxide) -> P of oxygen taken from RM is same as P of carbon dioxide released
• Capacitance coefficient in water: CC (carbon dioxide) is 23x larger than CC (oxygen) -> Px of oxygen taken is much less than the Px of carbon dioxide released
• Rate of diffusion (measured by Krogh's coefficient) is faster in air than water -> KC for carbon dioxide is 6000x higher in air than in water
• Water is more dense and viscous than air, thus it is more challenging for aquatic organisms to extract gases from water
• Water has greater buoyant force than air to prevent fish gills from collapsing; In terrestrial animals, tracheal cartilage in trachea maintains integrity in high pressure
• Evaporation of water occurs faster in arid / dry conditions
• Modes of Gas Exchange - Concurrent, Countercurrent, Crosscurrent
• Concurrent Exchange - direction of respiratory medium is the same with the circulatory stream; oxygen tension decreases in medium and increases in blood; efficiency of gas exchange reduces by the end as partial pressure difference gets smaller (ex. mammals)
• Countercurrent exchange - direction of medium is against the circulatory stream; partial pressure remains constant throughout thus, pressure gradient is maintained (ex. fishes)
• Crosscurrent exchange - medium cuts across multiple pathways along circulatory system; highest oxygen tension is found at the start of the pathway and gradually depletes towards the end (ex. bird)
• Increasing efficiency in the modes of gas exchange: concurrent < crosscurrent < countercurrent
• Ventilation - Convection process by which the respiratory

  medium is brought across the surface of exchange membranes
• Passive ventilation - no energy expenditure needed for ventilation to occur (ex. fish facing upstream for water to flow across its respiratory structures)
• Active Ventilation - Energy expenditure is needed for ventilation to occur; has three types: nondirectional, unidirectional, bidirectional
• Nondirectional AV - random current flow of air and water across gas-exchange membrane (ex. gills in mudpuppy that wave back and forth)
• Unidirectional AV - air or water is pumped over the membrane in a one-way path (ex. sharks gulp water and pass it over their gills -> buccal pumping)
• Bidirectional AV - inhalation and exhalation occurs in different directions via same passages (ex. humans)
• Cutaneous Respiration - involves breathing through the skin, chief respiration of aquatic urodeles and some scaleless fishes
• Criteria for an ideal respiratory surface - high surface area, relatively moist, relatively thin, high pressure gradient inside and outside the surface
• Telmatobius - wrinkly skin increases surface area of the integument, increasing efficiency of cutaneous respiration
• Astylosternus - hairs / fingerlike papillae are used for respiration
• Respiration in hagfishes - unidirectional, water enters external nares, goes to the pharynx, then to the gill pouches, then exits through branchial pores in the pouches
• Respiration in lampreys - bidirectional, water enters and exits the gill pouches through the gill slits
• Respiration in sharks - shark gills are septal (has a gill septum that separates gill pouches); unidirectional (mouth / spiracle -> branchial arches)
• spiracle - first gill slit in sharks
• gill ray - connective tissue structure supporting the branchial arch
• gill filaments - gas exchange surfaces in a shark gill
• secondary lamella - individual gill filaments