Evolution of the Circulatory System

1. Evolution of the Circulatory System The effects of terrestrialization, predation, and size

2. Circulatory Functions • Supplies all cells with needed substances, and remove byproducts of metabolism. • Brings O2 from the gills, skin, or lungs to cells. • Brings glucose, fats, and amino acids from organs to cells. • Removes CO2, nitrogenous wastes, and excess metabolic H2O.

3. Circulatory Functions • Maintains a stable and narrow internal body environment (homeostasis). • Uniformity of composition of interstitial fluids throughout the body. • Maintains a relatively uniform body temperature (exceptions are counter-current heat exchange systems in whales and arctic foxes.

4. Circulatory Functions • Fights disease. • Repair of injuries. • Circulation of hormones (accessory nervous system).

5. Blood Composition • Complex and stable series of salts. • Blood proteins (manufactured in the liver, raise the osmotic pressure of blood). • Albumin • Globulins • Fibrinogen.

6. Blood Composition • Blood cells. • Erythrocytes: red blood cells which are enucleate in most adult mammals (not camelids). They contain hemoglobin and are thus oxygen carrying cells. • Leukocytes: these white blood cells make up only 1% of the total blood cells. They fight infections and repair injuries. • Thrombocytes: serve in blood clotting.

7. Blood Forming Tissue • Since blood cells have a very short life span, it is necessary to replace them constantly (they live a few days to a few weeks). • Sites of blood formation. • Embryonic: kidney, liver, spleen, throat tissue, and thymus. • Adult fishes and amphibians: kidney, bone marrow, and spleen.

8. Blood Forming Tissue • Adult fishes and amphibians: kidney, bone marrow, and spleen. • Turtles: liver, bone marrow, and spleen. • Sharks: white cells formed in the gonads, bone marrow, and spleen.

9. Circulatory Vessels • Heart • Arteries • Capillaries • Veins • Lymphatics

10. An example of circulatory evolution: Hepatic Portal Syst. • Portal systems are bounded on both sides by capillary beds. • Hepatic portal system probably evolved to bring materials from the intestine directly to the liver. • Gives the liver first chance at materials for storage or transformation.

11. An example of circulatory evolution: Hepatic Portal Syst. • There are various problems with portal systems. Portal systems are inefficient. The blood received by portal organs is O2 poor, consequently the orgn must be also supplied with arterial blood, ie, 2 circulations in the organ. “Higher” vertebrates lose one of the portal systems.

15. Evolution of the Heart • Protochordate Heart. • Blood flow is unidirectional throughout the body. • Blood is forced through the body via peristaltic contraction of the heart. • Since there is only one respiratory structure (the integument) the system is very efficient.

16. Evolution of the Heart • Piscine stage • Since respiration is via capillary beds in the gills and not the integument, a more efficient high pressure pump is required. • The heart now has 2 functions, the collection of blood and the pumping of blood.

18. Evolution of the Heart • Piscine stage cont. • the sinus venosus is a thin-walled sac for blood collection. The walls are expandable to reduce back-pressure on the circulation. • The atrium is also a thin-walled sac, situated dorsal to the ventricle. • The muscular ventricle receives blood via gravity and slight contraction of theatrium. This is the major contractlie portion of the heart.

19. Evolution of the Heart • Piscine stage cont: • The conus arteriosus is lined with valves and evens out the flow of blood.

20. Evolution of the Heart • Early tetrapod heart • There is a new respiratory structure, the lung. Consequently the heart receives both O2 rich and O2 poor blood. This mixing of blood reduces the partial pressure of O2, and therefore reduces respiratory efficiency.

22. Evolution of the Heart • Lungfish have a partial solution: • Pulmonary blood enters the atrium separately from the systemic circulation. • A septum separates the 2 sides of the atrium. • This is actually a very good solution to the problem, as there is only a minimal mixing of O2 rich and O2 poor blood.

24. Evolution of the Heart • Modern amphibians are faced with essentially the same problem, or are they? • Again, pulmonary blood enters the atrium separately from the systemic circulation, but the inter-arterial septum does not extend into the ventricle.

25. Evolution of the Heart • Modern amphibians cont: • this apparent throwback has occurred in response to the respiratory behavior of modern amphibians They respire through the lungs and through the integument. Consequently both the systemic and pulmonary circulations are rich in O2 and there is no ‘need’ for ventricular separation of blood.

27. Evolution of the Heart • Later ectotherm stage: • The sinus venous is reduced but still serves as the site for origin of the heart beat. Note also the spiral valve in the conus arteriosus and its two trunks. • The conus arteriosus is gone. Actually it has been reduced and divided into trunks for the systemic and pulmonary circulation.

29. Evolution of the Heart • Later ectotherm stage cont: • The septum extends into the ventricle. • The R.S.A. gets O2 rich blood from the left side. • The L.S.A. and pulmonary arch get O2 poor blood from the right side, or so it would seem. • The L.S.A. in actuality gets only O2 rich blood.

31. Evolution of the Heart • Endotherm stage • Both birds and mammals have completely separated the atrium and ventricle to form a 4 chambered heart. However, the intraventricular septa are not homologous. • It should be noted that one ectotherm (not endotherm) has a 4 chambered heart: the crocodillians.

34. Evolution of the Lymphatic System • Function • Return capillary filtrate to the blood vascular system • This is problematical in terms of terrestrialization. • Increasing blood pressure resulting from terrestrialization. • More completely closed circulatory system with terrestrialization.

35. Evolution of the Lymphatic System • Six stages in the evolution of the lymph system • Venolymphatic stage • Pretetrapod stage • Early tetrapod stage • Higher ectotherm stage • Avian stage • Mammalian stage

36. Evolution of the Lymphatic System • Venolymphatic stage • The venous system is essentially only membranous sinuses. • No specialized lymph system. • Nature of venous system enables it to function as a lymph system.

37. Evolution of the Lymphatic System • Pretetrapod stage • Cardiac pressure is only effective transporting blood through the branchial capillaries. • Elsewhere, capillary pressure is via muscular activity and assumed to be low. • This results in low quantities of capillary filtrate (lymph) and thus a large percentage return through the capillary walls.

38. Evolution of the Lymphatic System • Pretetrapod stage cont: • Osteichthyes have a more complete elimination of venous sinuses. • 2 subvertebral ducts which empty into the anteior veins. • 2 lateral lymphatic ducts which empty into the illiac veins. • There are thus 4 openings to the venous system. • There is no forced movement of lymph. • Most lymph returns via the venous system.

40. Evolution of the Lymphatic System • Early tetrapod stage: • First serious problem in lymph return. • Branchial capillary system is lost and replaced with a pulmonary system. • Thus, cardiac pressure reaches all arterial capillaries of the aortic branches. • Capillary filtrate increases with blood pressure.

41. Evolution of the Lymphatic System • Early tetrapod stage cont: • Thus, the venous system can no longer handle the large quantity of lymph. • Anurans: • lymph is simply allowed to collect in lymph sinuses. • They have about ten pairs of lymph ‘hearts’.

42. Evolution of the Lymphatic System • Early tetrapod stage cont: • Caudata and Apoda • Increase number of lymph vessels • Decrease the number and size of lymph ‘hearts’. • They have about 100 pairs of lymph ‘hearts’. Each heart has an afferent and efferent ostium. They contain valves to prevent backflow. They empty directly into the venous system.

44. Evolution of the Lymphatic System • Higher ectotherm stage • Extensive lymphatic vessels. • They have reduced the number of lymph hearts to 2. • As in fish, there are only 4 entrances to the venous system.

45. Evolution of the Lymphatic System • Avian stage • Complete loss of lymph hearts. • Develop valves in lymph vessels (the valves essentially take over the function of the hearts, since body movement forces lymph flow).

46. Evolution of the Lymphatic System • Mammalian stage • Fusion of some lymph vessels. • Closure of 1 to 3 of the 4 venous ostia. • All valves go the same way. • Loss of some lymph vessels.