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 O 2 and produce CO 2 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 CO 2 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 O 2 and produce CO 2 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 Diagram of sponge structure Virtually every cell in a sponge is in direct contact with the water – little circulation is required

12 Diagram of jellyfish structure, and photos 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)

13 Diagram of open circulatory system in a grasshopper Circulation systems have evolved over time  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 Most invertebrates (esp. insects) have an open circulatory system

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

15 Open vs. Closed…both systems are common 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

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

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

21 Diagram showing artery, vein and capillary bed 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

22 Diagram of blood circulation pattern in humans 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

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

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

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 CO 2 and acquire O 2  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 O 2 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 Phylogenetic tree showing the diversification of vertebrates Mammals and birds have 4-chambered hearts Mammals and birds are NOT monophyletic Mammals and birds evolved from separate reptilian ancestors

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

44 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. Blood pressure and velocity drop as blood moves through capillaries

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…

51 Diagram showing sphincter muscle control over capillary flow. Micrograph of a capillary bed. Bed fully open Bed closed, through- flow only Note scale – capillaries are very tiny!!

52 Capillary Transport Processes: Endocytosis  exocytosis across membrane Diffusion based on electrochemical gradients Bulk flow between endothelial cells  Water potential gradient forces solution out at arterial end  Reduction in pressure draws most (85%) fluid back in at venous end  Remaining fluid is absorbed into lymph, returned at shoulder ducts

53 Capillary Transport Processes: Endocytosis  exocytosis across membrane Diffusion based on concentration gradients Bulk flow between endothelial cells  Water potential gradient forces solution out at arterial end  Reduction in pressure draws most (85%) fluid back in at venous end  Remaining fluid is absorbed into lymph, returned at shoulder ducts

54 Bulk Flow in Capillary Beds Remember water potential: Ψ = P – s Remember that in bulk flow P is dominant  No membrane  Plus, in the capillaries, s is ~stable (blood proteins too big to pass) P changes due to the interaction between arterial pressure and the increase in cross- sectional area

55 Diagram showing osmotic changes across a capillary bed Bulk Flow in Capillary Beds Remember: Ψ = P – s

56 Capillary Transport Processes: Endocytosis  exocytosis across membrane Diffusion based on concentration gradients Bulk flow between endothelial cells  Water potential gradient forces solution out at arterial end  Reduction in pressure draws most (85%) fluid back in at venous end  Remaining fluid is absorbed into lymph, returned at shoulder ducts