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Lecture 14: Vertebrate Heart Structure and Function (Why do animals need a…
Lecture 14: Vertebrate Heart Structure and Function
Facts
120 Australians die of cardiovascular disease each day
Between 2006-2015, the incident of cardiovascular disease in Australia has remained the same
The human heart starts beating
3 weeks
after fertilisation (when a woman takes the urine test)
Why do animals need a circulatory system?
1.
To transport
oxygen
and
nutrients
around the body to tissues and organs
2.
To remove waste products
3.
To achieve cell-cell communication via
hormones
(i.e. hormone action)
4.
To regulate temperature and reproduction
e.g. blood vessels carry nourishment to the foetus
Circulatory systems evolved along with
increased metabolic demands
in more complex and larger animals
It went to a point where diffusion was not viable anymore
As an organism increases in size, the SA to V ratio
decreases
There would be
less surface area
for substances to diffuse through, slowing down the diffusion rate
Circulatory systems
2
types
Open circulatory system (e.g. in small animals such as
arthropods
)
Blood (
haemolymph
) flow freely within body cavities
Haemolymph makes
direct contact
with all tissues and organs
A
tubular
heart pumps the haemolymph to different regions of the body via
blood vessels
The blood vessels are
open-ended
so haemolymph flows out and bathes the tissues
All components
of haemolymph leave the blood vessels
The haemolymph drains
slowly
back into the
heart
Haemolymph enters back into the heart when
relaxed
via
ostia
(openings)
The ostia act as
valves
, ensuring
one-way flow
of blood
Closed circulatory system (e.g. in an
annelid worm
)
Blood
(circulating fluid) is
contained
in a continuous series of blood vessels
A
heart
(connecting vessels for an annelid worm) pumps the circulating fluid to different regions of the body via
blood vessels
The blood vessels are
not open
so blood (transport fluid) is kept
separate
from
interstitial fluid
(fluid that bathes/surrounds our cells)
Specific
components of the circulating fluid are
filtered
out of the
capillaries
to penetrate tissues
Small solutes and water leave
Larger molecules and blood cells
remain
Blood returns back into the heart via
veins
, with
valves
to ensure one-way flow of fluid
Advantages
1.
Faster, more efficient and higher pressure transport and delivery of fluid to tissues
2.
A closed circulatory system can
control the distribution
of food to specific tissues, via
changing vessel resistance
3.
Larger molecules can be
delivered
to specific tissues more efficiently
Nutrients
Hormones
4.
Through evolution (over time), we now have a circulatory system that keeps oxygenated blood
separated
from deoxygenated blood
e.g in
humans
Evolution of vertebrate heart chambers
1.
Fish
One
/single circulation
One atrium
One ventricle
Specialisation of vessels
Arteries
Veins
Blood pumped over the
gills
to become
oxygenated
However, the blood leaves the gills at
very low pressure
Blood enters the systemic capillary beds and gills at
very low pressure
This limits efficiency of delivery of
nutrients
and
oxygen
to tissues
This
reduces
the metabolic rate of fish relative to other organisms
Anatomy of a
teleost fish
heart and chambers
Sinus venosus
Preliminary collecting chamber
Filled primarily from the
hepatic veins
No
muscular wall
Leads into the atrium
Bulbus arteriosus (aka.
conus arteriosus
in elasmobranchs)
Final chamber
Filled with blood from the single
ventricle
(which followed the atrium)
Elastic
in nature (can recoil)
Reduces extreme pulsing of blood leaving the ventricle
Gives a more constant, even flow of blood
Windkessel effect
:red_flag:
2.
Air-breathing fish
Two
circulations
Pulmonary
Systemic
Partially divided
atrium and ventricle
Left side
Receives
oxygenated
blood from
lungs
Right side
Receives
deoxygenated
blood from the
body
Gill bypasses
Low resistance
Bypass to the
lungs
Direct link to
dorsal aorta
Oxygenated
blood separated from
deoxygenated
blood
Blood can be
oxygenated
in
air
or
water
Hence,
air
-breathing fish
3.
Amphibians
3
-chambered heart
Left atrium
Receives
oxygenated
blood from
lungs
Right atrium
Receives
deoxygenated
blood from the
body
One ventricle
Potential for some
mixing
of blood
However, a
septum
directs blood movement and maintains separation
≥ 90%
of the time
Partial separation of pulmonary and systemic circuits allows for
different pressures
, controlling distribution fo blood to tissues
Higher
pressure in systemic circuit
Blood needs to be pumped around the body
Low
pressure in pulmonary circuit due to exchange surface
4.
Reptiles
3-
(or
4-
) chambered heart
2
aortae :warning:
Left aorta takes
oxygenated blood
from the atrium (which came from the
lungs
) to the
body
Right aorta takes
mixed blood
coming from both ventricles
When reptiles do not breathe (i.e. underwater), blood bypasses the lungs and flows directly to the
systemic
circuit via the
right aorta shunt
This prevents total flows around the whole circulatory system
Direction of blood flow is controlled by
resistance
in the
pulmonary circuit
This resistance is
lower
when the reptile is
breathing
5.
Birds and mammals
4-
chambered heart
Separate
pulmonary and systemic circuits
Advantages
1.
Pulmonary and systemic circuits can operate at
different pressures
2.
Systemic circuit
always
receives blood with
high O2 content
3.
Gas exchanged is
maximised
4.
Lower/more stable metabolic rate???? :warning:
Mammalian (human heart)
Foetal heart
Foramen ovale and ductus arteriosus are
open
Foramen ovale
Allows blood to travel from the
right
atrium to the
left
atrium
The blood flowing from the pulmonary artery can
bypass
the pulmonary circuit and go directly into the
aorta
This creates high resistance? :warning:
Newborn heart
Foramen ovale and ductus arteriosus are
closed
This happens on the 1st day of being born