Evolution of the Circulatory System

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Evolution of the Circulatory System

• The effects of terrestrialization, predation, and
  size

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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.

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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.

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Circulatory Functions

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

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Blood Composition

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

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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.

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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.

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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.

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Circulatory Vessels

• Heart
• Arteries
• Capillaries
• Veins
• Lymphatics

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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.

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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.

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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.

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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.

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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.

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Evolution of the Heart

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

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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.

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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.

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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.

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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.

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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.

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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.

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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.

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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.

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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

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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.

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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.

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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.

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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.

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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.

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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.

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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.

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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).

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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.

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