Lecture #10 – Animal Circulation and Gas Exchange Systems

1. Lecture #10 – Animal Circulation and Gas Exchange Systems

2. Key Concepts: • Circulation and gas exchange – why? • Circulation – spanning diversity • Hearts – the evolution of double circulation • Blood circulation and capillary exchange • Blood structure and function • Gas exchange – spanning diversity • Breathing – spanning diversity • Respiratory pigments

3. Animals use O2 and produce CO2 • All animals are aerobic • Lots of oxygen is required to support active mobility • Some animals use lots of oxygen to maintain body temperature • All animals produce CO2 as a byproduct of aerobic respiration • Gasses must be exchanged • Oxygen must be acquired from the environment • Carbon dioxide must be released to the environment

4. Animals use O2 and produce CO2 • Circulation systems move gasses (and other essential resources such as nutrients, hormones, etc) throughout the animal’s body • Respiratory systems exchange gasses with the environment

5. Circulation systems have evolved over time • The most primitive animals exchange gasses and circulate resources entirely by diffusion • Process is slow and cannot support 3-D large bodies • Sponges, jellies and flatworms use diffusion alone

6. Critical Thinking • Why isn’t diffusion adequate for exchange in a 3D large animal???

7. Critical Thinking • Why isn’t diffusion adequate for exchange in a 3D large animal??? • Surface area / volume ratio becomes too small • Remember, area is a square function; volume is a cubic function

8. Critical Thinking • But…..plants rely on diffusion for gas exchange…..how do they get so big???

9. Critical Thinking • But…..plants rely on diffusion for gas exchange…..how do they get so big??? • Their living tissue is close to the surface and exposed to air – either in the open atmosphere or in the soil atmosphere

10. Circulation systems have evolved over time • The most primitive animals exchange gasses and circulate resources entirely by diffusion • Process is slow and cannot support 3-D large bodies • Surface area / volume ratio becomes too small • Sponges, jellies and flatworms use diffusion alone

11. Virtually every cell in a sponge is in direct contact with the water – little circulation is required Diagram of sponge structure

12. Jellies and flatworms have thin bodies and elaborately branched gastrovascular cavities Again, all cells are very close to the external environment This facilitates diffusion Some contractions help circulate (contractile fibers in jellies, muscles in flatworms) Diagram of jellyfish structure, and photos

13. Circulation systems have evolved over time • Most invertebrates (esp. insects) have an open circulatory system • Metabolic energy is used to pump hemolymph through blood vessels into the body cavity • Hemolymph is returned to vessels via ostia – pores that draw in the fluid as the heart relaxes Diagram of open circulatory system in a grasshopper

14. Circulation systems have evolved over time • Closed circulatory systems separate blood from interstitial fluid • Metabolic energy is used to pump blood through blood vessels • Blood is contained within the vessels • Exchange occurs by diffusion in capillary beds Diagram of a closed circulatory system, plus a diagram showing an earthworm circulatory system

15. Open systems…. Use less metabolic energy to run Use less metabolic energy to build Can function as a hydrostatic skeleton Most invertebrates (except earthworms and larger mollusks) have open systems Closed systems…. Maintain higher pressure Are more effective at transport Supply more oxygen to support larger and more active animals All vertebrates have closed systems Open vs. Closed…both systems are common

16. All vertebrates have a closed circulatory system • Chambered heart pumps blood • Atria receive blood • Ventricles pump blood • Vessels contain the blood • Veins carry blood to atria • Arteries carry blood from ventricles • Capillary beds facilitate exchange • Capillary beds separate arteries from veins • Highly branched and very tiny • Infiltrate all tissues in the body We’ll go over these step by step

17. Chambered heart pumps blood • Atria receive blood • Ventricles pump blood • One-way valves direct blood flow Diagram of a chambered heart

18. Critical Thinking • Atria receive blood; ventricles pump • Given that function, what structure would you predict???

19. Critical Thinking • Atria receive blood; ventricles pump • Given that function, what structure would you predict??? • Atria are soft, flexible chambers • Ventricles have much more muscular walls

20. Chambered heart pumps blood • Atria receive blood • Soft walled, flexible • Ventricles pump blood • Thick, muscular walls • One-way valves direct blood flow Diagram of a chambered heart

21. Vessels contain the blood • Arteries carry blood from ventricles • Always under pressure • Veins carry blood to atria • One-way valves prevent back flow • Body movements increase circulation • Pressure is always low Diagram showing artery, vein and capillary bed

22. Note that blood vessel names reflect the direction of flow, NOT the amount of oxygen in the blood • Arteries carry blood AWAY from the heart • Arterial blood is always under pressure • It is NOT always oxygenated • Veins carry blood TO the heart Diagram of blood circulation pattern in humans

23. Capillary beds facilitate exchange • Capillary beds separate arteries from veins • Highly branched and very tiny • Infiltrate all tissues in the body • More later Diagram showing artery, vein and capillary bed

24. All vertebrates have a closed circulatory system – REVIEW • Chambered heart pumps blood • Atria receive blood • Ventricles pump blood • Vessels contain the blood • Veins carry blood to atria • Arteries carry blood from ventricles • Capillary beds facilitate exchange • Capillary beds separate arteries from veins • Highly branched and very tiny • Infiltrate all tissues in the body

25. Key Concepts: • Circulation and gas exchange – why? • Circulation – spanning diversity • Hearts – the evolution of double circulation • Blood circulation and capillary exchange • Blood structure and function • Gas exchange – spanning diversity • Breathing – spanning diversity • Respiratory pigments

26. Evolution of double circulation – not all animals have a 4-chambered heart Diagram showing progression from a 1-chambered heart to a 4-chambered heart. This diagram is used in the next 12 slides.

27. Fishes have a 2-chambered heart • One atrium, one ventricle • A single pump of the heart circulates blood through 2 capillary beds in a single circuit • Blood pressure drops as blood enters the capillaries (increase in cross-sectional area of vessels) • Blood flow to systemic capillaries and back to the heart is very slow • Flow is increased by swimming movements

28. Two circuits increases the efficiency of gas exchange = double circulation • One circuit goes to exchange surface • One circuit goes to body systems • Both under high pressure – increases flow rate

29. Amphibians have a 3-chambered heart • Two atria, one ventricle • Ventricle pumps to 2 circuits • One circuit goes to lungs and skin to release CO2 and acquire O2 • The other circulates through body tissues • Oxygen rich and oxygen poor blood mix in the ventricle • A ridge helps to direct flow • Second pump increases the speed of O2 delivery to the body

30. Most reptiles also have a 3-chambered heart • A partial septum further separates the blood flow and decreases mixing • Crocodilians have a complete septum • Point of interest: reptiles have two arteries that lead to the systemic circuits • Arterial valves help direct blood flow away from pulmonary circuit when animal is submerged

31. Critical Thinking • What is a disadvantage of a 3 chambered heart???

32. Critical Thinking • What is a disadvantage of a 3 chambered heart??? • Oxygen rich and oxygen poor blood mix in the ventricle • Less than maximum efficiency

33. Mammals and birds have 4-chambered hearts • Two atria and two ventricles • Oxygen rich blood is completely separated from oxygen poor blood • No mixing  much more efficient gas transport • Efficient gas transport is essential for both movement and support of endothermy • Endotherms use 10-30x more energy to maintain body temperatures

34. Mammals and birds have 4-chambered hearts • Mammals and birds are NOT monophyletic • What does this mean???

35. Mammals and birds have 4-chambered hearts • Mammals and birds are NOT monophyletic • Mammals and birds evolved from separate reptilian ancestors Phylogenetic tree showing the diversification of vertebrates

36. Mammals and birds have 4-chambered hearts • Mammals and birds are NOT monophyletic • Four-chambered hearts evolved independently • What’s this called???

37. Mammals and birds have 4-chambered hearts • Mammals and birds are NOT monophyletic • Four-chambered hearts evolved independently • Convergent evolution

38. Review: evolution of double circulation

39. Key Concepts: • Circulation and gas exchange – why? • Circulation – spanning diversity • Hearts – the evolution of double circulation • Blood circulation and capillary exchange • Blood structure and function • Gas exchange – spanning diversity • Breathing – spanning diversity • Respiratory pigments

40. Blood Circulation • Blood vessels are organs • Outer layer is elastic connective tissue • Middle layer is smooth muscle and elastic fibers • Inner layer is endothelial tissue • Arteries have thicker walls • Capillaries have only an endothelium and basement membrane

41. Critical Thinking • Arteries have thicker walls than veins • Capillaries have only an endothelium and basement membrane • What is the functional significance of this structural difference???

42. Critical Thinking • Arteries have thicker walls than veins • Capillaries have only an endothelium and basement membrane • What is the functional significance of this structural difference??? • Arteries are under more pressure than veins • Capillaries are the exchange surface

43. Form reflects function… • Arteries are under more pressure than veins • Capillaries are the exchange surface Diagram showing artery, vein and capillary bed

44. Blood pressure and velocity drop as blood moves through capillaries Graph showing relationships between blood pressure, blood velocity, and the cross-sectional area of different kinds of blood vessels – arteries to capillaries to veins. This same graph is on the next 3 slides.

45. Total cross-sectional area in capillary beds is much higher than in arteries or veins; slows flow

46. Velocity increases as blood passes into veins (smaller cross-sectional area); pressure remains dissipated

47. One-way valves and body movements force blood back to right heart atrium

48. Critical Thinking • What makes rivers curl on the Coastal Plain???

49. Critical Thinking • What makes rivers curl on the Coastal Plain??? • Velocity is controlled by gravity in rivers • The Coastal Plain is just a few meters above sea level – little gravity to force forward momentum • The water slows; the rivers meander • The functional equivalent to blood meandering through a capillary bed

50. Capillary Exchange • Gas exchange and other transfers occur in the capillary beds • Muscle contractions determine which beds are “open” • Brain, heart, kidneys and liver are generally always fully open • Digestive system capillaries open after a meal • Skeletal muscle capillaries open during exercise • etc…