1 Lecture #11 – 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 Except……breaking news! Abstract – 6 April 2010 Background Several unicellular organisms (prokaryotes and protozoa) can live under permanently anoxic conditions. Although a few metazoans can survive temporarily in the absence of oxygen, it is believed that multi- cellular organisms cannot spend their entire life cycle without free oxygen. Deep seas include some of the most extreme ecosystems on Earth, such as the deep hypersaline anoxic basins of the Mediterranean Sea. These are permanently anoxic systems inhabited by a huge and partly unexplored microbial biodiversity. Results During the last ten years three oceanographic expeditions were conducted to search for the presence of living fauna in the sediments of the deep anoxic hypersaline L'Atalante basin (Mediterranean Sea). We report here that the sediments of the L'Atalante basin are inhabited by three species of the animal phylum Loricifera (Spinoloricus nov. sp., Rugiloricus nov. sp. and Pliciloricus nov. sp.) new to science. Using radioactive tracers, biochemical analyses, quantitative X-ray microanalysis and infrared spectroscopy, scanning and transmission electron microscopy observations on ultra-sections, we provide evidence that these organisms are metabolically active and show specific adaptations to the extreme conditions of the deep basin, such as the lack of mitochondria, and a large number of hydrogenosome-like organelles, associated with endosymbiotic prokaryotes. Conclusions This is the first evidence of a metazoan life cycle that is spent entirely in permanently anoxic sediments. Our findings allow us also to conclude that these metazoans live under anoxic conditions through an obligate anaerobic metabolism that is similar to that demonstrated so far only for unicellular eukaryotes. The discovery of these life forms opens new perspectives for the study of metazoan life in habitats lacking molecular oxygen.

5 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

6 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

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

8 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

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

10 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

11 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

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

13 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)

14 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

15 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

16 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

17 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

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

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

20 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

21 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

22 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

23 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

24 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

25 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

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