Download Evolution of the Circulatory System

Evolution of the Circulatory
System
The effects of terrestrialization,
predation, and size
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.
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 countercurrent heat exchange systems in whales
and arctic foxes.
Circulatory Functions

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Fights disease.
Repair of injuries.
Circulation of hormones (accessory
nervous system).
Blood Composition

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Complex and stable series of salts.
Blood proteins (manufactured in the
liver, raise the osmotic pressure of
blood).
– Albumin
– Globulins
– Fibrinogen.
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.
Blood Forming Tissue

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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.
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.
Circulatory Vessels
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Heart
Arteries
Capillaries
Veins
Lymphatics
An example of circulatory
evolution: Hepatic Portal Syst.

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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.
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.
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.
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.
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.
Evolution of the Heart

Piscine stage
cont:
– The conus
arteriosus is lined
with valves and
evens out the
flow of blood.
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.
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.
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.
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.
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.
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.
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.
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.
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
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.
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.
Evolution of the Lymphatic
System
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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.
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.
Evolution of the Lymphatic
System
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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’.
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.
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.
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).
Evolution of the Lymphatic
System
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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.