Respiratory Systems

1. Respiratory Systems • What is a respiratory system? How does it work? • What are the functions of respiratory systems? • What are the different respiratory strategies that animals use?

2. Definitions • Respiration– sequence of events that result in the exchange of oxygen and carbon dioxide between the external environment and the mitochondria • External respiration – gas exchange at the respiratory surface • Internal respiration – gas exchange at the tissues • Mitochondrial respiration – production of ATP via oxidation of carbohydrates, amino acids, or fatty acids. Oxygen is consumed and carbon dioxide is produced • Gas molecules move down concentration gradients

3. Mitochondrial respiration • Mitochondria consume O2 to produce ATP • Produce CO2 in process • Organisms must have mechanisms to obtain O2 from the environment and get rid of CO2 → External respiration

4. Respiratory strategies of animals • Unicellular and small multicellular organisms rely on diffusionfor gas exchange • Larger organisms must rely on a combination of bulk flow and diffusion for gas exchange, i.e., they need a respiratory system

5. Respiratory systems - physics • Diffusion • Diffusion is the movement of molecules from a high concentration to a low concentration • Slowover long distances • Fast over short distances

6. Respiratory systems - diffusion The Fick equation J= -DAdC/dx J = rate of diffusion (moles/sec) D = diffusion coefficient A = area of the membrane dC = concentration gradient dx = diffusion distance For gases, we usually use partial pressure rather than concentration

7. Respiratory systems - diffusion • Rate of diffusion will be greatest when the diffusion coefficient (D), area of the membrane (A), and energy gradients (dC/dx) are large, but the diffusion distance is small • Consequently, gas exchange surfaces are typically thin, with a large surface area J= -DAdC/dx For gases, we usually use partial pressure rather than concentration

8. Gas Pressure • Total pressure exerted by a gas is related to the number of moles of the gas and the volume of the chamber • Ideal gas law: PV = nRT P- total pressure; V- Volume; n – number of moles of gas molecules; R – gas constant (8.314472 J · K-1 · mol-1) T – temperature in Kelvin

9. Gas Pressure cont. • Air is a mixture of gases: nitrogen (78%), oxygen (21%), argon (0.9%) and carbon dioxide (0.03%) • Dalton’s law of partial pressures: in a gas mixture each gas exerts its own partial pressurethat sum to the total pressure of the mixture

10. Gases Dissolve in liquids • Gas molecules in air must first dissolve in liquid (water or extra-cellular fluid) in order to diffuse into a cell • Henry’s law: [G] = Pgas x Sgas

11. Gases Dissolve in liquids CO2 is much more soluble in water than is O2. Thus, at the same partial pressure, more CO2will be dissolved in a solution than will oxygen

12. Diffusion Rates Graham’s law • The relative diffusion of a given gas is proportional to its solubility in the liquid and inversely proportional to the square root of its molecular weight: Diffusion rate  solubility/MW • O2 32 atomic mass units • CO2 44 amu • In air “solubilities” are the same (1000 ml/L at 20oC) • Oxygen diffuses about 1.2 times faster than CO2 • However, CO2 is about 24 times more soluble in aqueous solutions than O2. So CO2 diffuses about 20 times faster than O2 in water

13. Diffusion Rates at a constant temperature Combining the Fick equation with Henry’s and Graham’s laws: Diffusion rate dPgas x A x Sgas / X x (MW) At a constant temperature the rate of diffusion is proportional to • Partial pressure gradient (dPgas) • Cross-sectional area (A) • Solubility of the gas in the fluid (Sgas) And inversely proportional to • Diffusion distance (X) • Molecular weight of the gas (MW)

14. Fluid Movement: Bulk flow • Bulk flow: Mass movement of water or air as the result of pressure gradients • Fluids flow from areas of high to low pressure • Boyle’s Law: P1V1 = P2V2 Temperature and the number of gas molecules remain constant

15. Bulk flow and Boyle’s law P2V2 P1V1 =P2V2 P1 =P2 P1V1 =P2V2 V2 P2 P1 =P2 Respiratory systems use changes in volume to cause changes in pressure!

16. Surface Area to Volume Ratio • As organisms grow larger, their ratio of surface area to volume decreases • This limits the area available for diffusion and increases the diffusion distance J= -DAdC/dx

17. Respiratory strategies of animals • Unicellular and small multicellular organisms rely on diffusionfor gas exchange • Larger organisms must rely on a combination of bulk flow and diffusion for gas exchange, i.e., they need a respiratory system

18. Respiratory Strategies Animals more than a few millimeters thick use one of three respiratory strategies • Circulating the external medium through the body • Sponges, cnidarians, and insects • Diffusion of gases across the body surface accompanied by circulatory transport • Cutaneous respiration • Most aquatic invertebrates, some amphibians, eggs of birds • Diffusion of gases across a specialized respiratory surface accompanied by circulatory transport • Gills (evaginations) or lungs (invaginations) • Vertebrates

19. Circulating the external medium through the body Parazoa and Cnidaria

20. Circulating the external medium through the body Tracheal system Series of narrow tubes leading from surface to deep within body Gases move in the tubes via a combination of diffusion and bulk flow

21. Cricket spiracle

22. Most animals have a circulatory system • Diffusion of gases across a specialized respiratory surface accompanied by circulatory transport O2 O2 Circulatory system External medium Respiratory surface Tissue

23. Cutaneous respiration Respiration through skin Found in some aquatic invertebrates and a few vertebrates Disadvantages: relatively low surface area Conflict between respiration and protection Salamander Lake Titicaca frog Annelid

24. External gills • Gills originate as outpocketings (evaginations) • Advantages: high surface area, exposed to medium • Disadvantages: easily damaged, not suitable in air Salamander Polychaete

25. Internal gills • Advantages: High surface area, protected • Disadvantages: not usually suitable in air

26. Lungs • Originate as infoldings (invaginations) • Advantages: High surface area, protected, suitable for breathing air • Disadvantages: not suitable in water

27. Ventilation • The active movement of the respiratory medium (air or water) across the respiratory surface • Ventilation of respiratory surfaces reduces the formation of static boundary layers i.e. improvesefficiency of gas exchange Types of ventilation • Nondirectional - medium flows past the respiratory surface in an unpredictable pattern • Tidal- medium moves in and out • Unidirectional - medium enters the chamber at one point and exits at another Animals respond to changes in environmental oxygen or metabolic demands by altering the rate or pattern of ventilation

28. Nondirectional ventilation Medium flows past the respiratory surface in an unpredictable pattern PO2 = 160mmHg O2 40 60 80 100 120 140 160 160 Flow

29. Effect of increased boundary layer

30. Tidal ventilation Medium moves in and out PO2 = 160mmHg Lung Blood vessel PO2 100mmHg 40 40 100 100 60 95 Flow 80 90

31. Gas exchange – unidirectional ventilation Medium enters the chamber at one point and exits at another With unidirectional ventilation, the blood can flow in three ways relative to the flow of the medium Medium Resp. surface Cocurrent flow Blood Medium Countercurrent flow Resp. surface Blood Medium Crosscurrent flow Resp. surface Blood

32. Orientation of Medium and Blood Flow PO2 of medium and blood will equilibrate

33. Orientation of Medium and Blood Flow PO2 of blood approaches that of the inhalant medium

34. Orientation of Medium and Blood Flow Initial-parabronchial (PI; ) and End-parabronchial values (PE). Mixed venous (Pv) blood; Arterial blood (Pa). Found in birds The PO2 of arterial blood is derived from a mixture of all serial air-blood capillary units and exceeds that of PE.

35. Ventilation and Gas Exchange Because of the different physical properties of air and water, animals use different strategies depending on the medium in which they live Differences • [Oair] 30x greater than [Owater] • Water is more dense and viscous than air • Evaporation is only an issue for air breathers Strategies • Unidirectional: most water-breathers • Tidal: air-breathers • Air filled tubes: insects

36. Ventilation and Gas Exchange in Water Strategies • Circulate the external medium through an internal cavity • Various strategies for ventilating internal and external gills

37. Ventilation in water- invertebrates

38. Sponges and Cnidarians • Circulate the external medium through an internal cavity • In sponges flagella move water in through ostia and out through the osculum • In cnidarians muscle contractions move water in and out through the mouth

39. Molluscs Two strategies for ventilating their gills and mantle cavity • Beating of cilia on gills move water across the gills unidirectionally • Blood flow is countercurrent • Snails and clams • Muscular contractions of the mantle propel water unidirectionally through the mantle cavity past the gills • Blood flow is countercurrent • Cephalopods (squid)

40. Crustaceans • Barnacles (filter feeding) or small species (copepods) lack gills and rely on diffusion • Shrimp, crabs, and lobsters, have gills derived from modified appendages located within a branchial cavity • Movements of the gill bailer propels water out of the branchial chamber; the negative pressure sucks water across the gills copepod

41. Echinoderms – sea stars, sea urchins, sea cucumbers • Most sea stars and sea urchins use their tube feet for gas exchange • Water is sucked in and exits through the madreporite • Sea stars also have external gill-like structures (respiratory papulae); cilia move water over the surface

42. Echinoderms, cont. • Brittle stars and sea cucumbers have internal invaginations • Brittle stars used cilia to move water into bursae • Sea cucumbers use muscular contractions of the cloaca and the respiratory tree to breathe water tidally though the anus

43. Jawless Fishes - Hagfish Hagfish • A muscular pump (velum) propels water through the respiratory cavity • Water enters the median nostril!!!! and leaves through a gill opening • Flow is unidirectional • Blood flow is countercurrent Lamprey and hagfish have multiple pairs of gill sacs

44. Ventilation - hagfish Gills sacs are arranged for counter current flow Water flow

45. Jawless Fishes - Lamprey Lamprey • Ventilation is similar to that in hagfish when not feeding • When feeding the mouth is attached to a prey (parasitic) • Ventilation is tidal though the gill openings

46. Elasmobranchs – sharks, skates and rays Steps in ventilation • Expand the buccal cavity • Increased volume sucks fluid into the buccal cavity via the mouth and spiracles • Mouth and spiracles close • Muscles around the buccal cavity contact forcing water past the gills and out the external gill slits Blood flow is countercurrent

47. Teleost Fishes Water flows in via the mouth, out via the opercular opening

48. Teleost Fishes V P

49. Fish Gills Fish gills are arranged for countercurrent flow

50. Ventilation and Gas Exchange in Air Two major lineages have colonized terrestrial habitats • Vertebrates • Arthropods (eeeekkkk) • Unidirectional ventilation of gills common in water-breathing animals • Tidal ventilation of lungs common in air-breathing animals