Evolutionary
y trends in the
circulatory system
1) Conversion from a single circuit to
u
circuit:
u
a double
– Fishes: single circuit:
• To g
gill capillaries
p
and body
y capillaries.
p
– Lungfishes and sarcopterygians:
• Pulmonary
y circuit: to lung
g capillaries.
p
• Systemic circuit: to body capillaries.
Evolutionary trends in the
circulatory
i
l t
system
t
2) Corresponding conversion of heart from a
single pump to a double pump:
– Single pump:
• Fishes.
– Partially subdivided pump:
• Lungfishes and coelacanths.
coelacanths
• All amphibians.
• Turtles, lizards & snakes.
– Double pump:
• Crocodilians and birds.
• Mammals.
Mammals
Evolutionary trends in the
circulatory system
3) Modification and reduction of aortic arches.
4) Addition of subcircuits.
– For example: portal systems.
5)) Reduction
u
and loss of
f other basic elements.
m
.
– For example:
• Truncus arteriosus.
• Sinus venosus.
General pattern of circulation in a fish
Carotid arteries
Heart
• Muscular tube.
• Divided into series of chambers:
– Each chamber formed from separate blood
island.
– Formed
d within
h splanchnic
l
h
hypomere.
h
• Composed of thick wall of cardiac muscle
(m c dium):
(myocardium):
– Lined with epithelium tissue (= endocardium).
– Surrounded by thin membrane of connective
tissue (= epicardium).
– Lies within fluid-filled p
pericardial cavity.
y
• Partitioned from coelom.
Heart
• Why is the heart considered to be a center of
emotion (with thanks to Aristotle)?
I give
i you my h
heart.
t
You broke my heart.
I’ve given my heart to another.
She has a soft heart.
It comes from the heart.
g with your
y
head rather than your
y
heart.
You’re thinking
• Cardiac muscle is intrinsically contractile.
• Rate of contractions mediated by vagus and
autonomic nerves.
Heart is a
peristaltic pump
with valves
Heart
• Two main pumping chambers:
h
– Atrium:
• Receives blood returning to heart.
heart
• Pumps anteriorly to ventricle.
– Ventricle:
• Pumps
P
blood
bl d anteriorly
t i l to
t ventral
t l aorta.
t
• Two accessory chambers:
– Sinus venosus (posterior):
• Stores blood returning to heart from veins.
– Truncus arteriosus (anterior):
• Strong
St
valves
l s tto resist
sist b
back-pressure
k
ss
f
from bl
blood
d
vessels.
• Equivalent to conus arteriosus of sharks and bulbus
arteriosus of bony fishes.
fishes
• Valves between chambers prevent back-flow.
Development
of the
heart
Heart cycle
• Systole:
– Atrium relaxes, fills with blood.
– Ventricle contracts
contracts, blood pumped into
aorta.
• Diastole:
– Atrium contracts, blood pumped into
ventricle
ventricle.
– Ventricle relaxes, fills with blood.
Systole
y
Diastole
Development of heart
• Chambers
ham rs develop
op from ant
anterior
r or to
posterior.
Each new
w chamber
m
beats more
m
rapidly.
p y.
• E
– Anterior chambers speed up to
synchronize.
• Sinus venosus becomes final regulator.
– Higher vertebrates: sinoatrial (SA) node.
• Located in posterior wall of right atrium.
• “Pacemaker”.
Major trends in the heart
• Longitudinal
L
it di l di
division
i i b
by septa,
t posterior
t i
to anterior.
• Strengthening of internal valves.
• Subdivision of truncus arteriosus into
separate trunks (arteries).
• Reduction of sinus venosus to cluster of
pacemaker cells (sinoatrial node, SA).
Aortic arches
• Six aortic arches develop
p between seven
primitive pharyngeal arches (pouches):
–
–
–
–
From ventral aorta, around pharynx.
To pair of radices.
Continue posteriorly to form dorsal aorta.
Continue anteriorly to form internal carotid
arteries.
• Basic pattern from which can derive all
patterns of aortic arches in vertebrates.
Ductus caroticus
Ductus arteriosus
Modified circulation in some airair-breathing fishes
Major trends in
the aortic arches
•
•
•
•
Isolation of carotid subcircuit.
Systemic circuit taken over by arch #4.
#4
Pulmonary circuit taken over by arch #6.
Pulmonary circuit isolated by loss of
ductus arteriosus.
Fetal circulation in mammals
• Lungs not functional in fetus:
– Blood shunted away from lungs.
– To
T and
nd f
from
m the
th placenta
pl
nt via
i umbilical
mbili l vessels:
ss ls:
• Umbilical artery to placenta from iliac artery.
placenta to inferior vena cava
• Umbilical vein from p
(post caval vein).
– Placenta forms from chorion and uterine tissue.
– Exchange of gases
gases, nutrient molecules
molecules, and urea by
diffusion across walls of chorionic villi.
– Oval opening between atria in heart shunts oxygenrich blood from right to left atrium.
atrium
– Any blood entering right atrium and pulmonary
artery shunted to aorta via the arterial duct
(d
(ductus
arteriosus).
i
)
• At birth:
– Flow through umbilical artery and vein cut off,
usually
ll b
by mother
th biting
biti umbilical
bili l cord.
d
• Remnants of umbilical blood vessels become
connective tissue.
– Oval opening in heart closes via a flap (valve),
which permanently attaches to the atrial wall.
– Arterial duct (ductus arteriosus) closes.
– Aquatic
A
ti organism
i
b
becomes a tterrestrial
t i l
organism.
Cardiovascular (circulatory)
system
• Blood-vascular
Bl d
l system:
t
– Closed circulatory system.
• Lymphatic system:
– Returns interstitial fluid to bloodvascular system.
Lymphatic system
• Functions:
– Provides for the return of fluids to the bloodvascular
s l ssystem.
st
• 99% of fluid that leaves the blood at the arterial end
p
y bed re-enters the capillaries
p
at the
of a capillary
venous end.
• Function of blood pressure vs osmotic pressure.
• Remaining 1% returned to blood by lymphatic vessels.
vessels
– Route of absorption of fats from the digestive tract.
f lymphocytes.
ymp
y
.
– Source of
• Presence in vertebrate groups:
– Absent in agnathans
g
and chondrichthyans.
y
– Present in bony fishes and all tetrapods.
Lymphatic
Lymphat c system
• Lymphoid
y p
masses (“lymph
y p glands”):
g
– Enlargements of lymph tissue.
• Include thymus gland, adenoids, tonsils, spleen
• Functions:
F
–
–
–
–
Filter bacterial and other foreign materials.
Lymphocyte production.
production
Antibody production.
Spleen
p
associated with erythrocytes.
y
y
• Destroys old cells, recovers iron.
• Excretes hemoglobin as bilirubin.
Endothermic
E
m f
fishes
• Most fishes are ectothermic.
– About the
h same temperature as the
h
surrounding water.
• Some
S me fishes are endothermic.
end thermic
– Able to maintain an elevated body
temperature
temperature.
• Endotherms often have higher rates of:
– Metabolism,
Metabolism growth,
growth reproduction.
reproduction
– Neural and visual function.
– Swimming speed,
speed endurance.
endurance
Endothermic
E
m f
fishes
• Endothermic fishes maintain elevated
body temperatures by conserving
heat generated by active swimming
muscles.
– Countercurrent system: rete mirabile.
– Blood from gills shunted to cutaneous
vessels near body surface.
– From there carried through heatexchanging system en route to warm the
swimming
i
i muscles.
l
Rete of the tuna
Endothermic fishes
• Examples:
– Tunas m
maintain temperatures
mp
from
f m 3-21°C
above ambient.
– Mackerel sharks and thresher sharks
maintain
i t i
3
3-7°C
7°C above
b
ambient.
bi t
– Marlins, sailfishes and swordfishes have
“brain
brain heaters
heaters”::
• Maintain elevated brain and eye temperatures.
• Superior
p
rectus losses contractile filaments,,
can generate heat without contracting.
• Hunt in cold water without decrease in brain
and visual functions.
functions
Marlin,
Makaira
Sailfish,
Istiophorus
h
Brain coolers in mammals
Evolutionary
y trends in the
circulatory system
1) Conversion from a single circuit to
u
circuit:
u
a double
– Fishes: single circuit:
• To g
gill capillaries
p
and body
y capillaries.
p
– Lungfishes and sarcopterygians:
• Pulmonary circuit: to lung capillaries.
• Systemic circuit: to body capillaries.
Evolutionary
y trends in the
circulatory system
2) C
Corresponding
di conversion
i of
f heart
h
t from
f
a
single pump to a double pump:
– Single pump:
• Fishes.
– Partially subdivided pump:
• Lungfishes and coelacanths.
• All amphibians.
• Turtles,
Turtles lizards & snakes.
snakes
– Double pump:
• Crocodilians and birds.
• Mammals.
Evolutionary trends in the
circulatory system
3) Modification and reduction of aortic arches.
4) Addition of subcircuits.
– For example: portal systems.
5)) Reduction
u
and loss of
f other basic elements.
m
.
– For example:
• Truncus arteriosus.
• Sinus venosus.