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Developmental &
Physiological Aspects of
the Embryonic Chicken
Heart
Patrick Day
John Schreier
Biology 240W
Spring 2000
Introduction
Cellular migrations, fusions and specific
differentiations are all integral parts of the
development of the embryonic chicken
heart.
The embryonic chicken heart begins its
development on the ventral surface from
the fusion of paired pre-cardiac
mesodermal tubes. These tubes are
located on either side of the developing
foregut.
Introduction
These paired heart vesicles start to fuse at the
head (anterior end) and continue to fuse
posteriorly to form a continuous tube. This
happens between 25 to 30 hours of incubation.
After fusion is complete, the heart tube can be
identified from the anterior to posterior as
conotruncus, ventricle, atrium, and sinus
venosus.
The heart begins to beat after the paired heart
vesicles fuse. The sinus venosus in the fused
heart tube becomes the embryonic pacemaker.
Introduction
Blood flows fom the
sinus venosus to the
conotruncus.
The heart tube bends
to form an S-shape.
The ventricle bulges
to the right.
This happens after 33
hours of development.
Introduction
By 48 hours, the sinus
venosus and atrium
are moved to a
position anterior and
dorsal to the ventricle
and conotruncus.
Because the heart has
folded upon itself, the
ventricle is now Ushaped and the blood
flows posteriorly and
then makes a sharp
turn to flow anteriorly.
Introduction
After 72 hours, the atrium
prepares for division into
the right and left atria by
expanding.
At this time,
communication between
the sinus venosus and the
atrium is via the right side
of the atrium.
This is the first indication
that the sinus venosus is
becoming a part of the
future right atrium.
Introduction
When the atrium and ventricle each
divide into a pair of chambers, the
sinus venosus, which is incorporated
into the right atrium, gives rise to the
sinoatrial (SA) node or the mature
pacemaker.
The Experiment
We made the observation that the heart
rate of a chick embryo is relatively
constant when the embryo is kept in
sterile saline solution and at a steady
warm temperature of 37OC. After some
background research, it was found that
caffeine directly stimulates myocardial
tissue, the “pacemaker” of the heart, and
therefore has a direct effect on the rate
and force of contraction of the heart.
The Experiment
We hypothesized that the heart rate of the chicken embryo
will escalate with the addition of caffeine. We also
hypothesized that the heart rate will increase proportionally
with increasing concentrations of caffeine added.
We hypothesized this because caffeine inhibits the activity
of phosphodiesterase, which breaks down cyclic AMP.
This increase in the amount of cyclic AMP affects the
sympathetic nerves in the heart because it is a second
messenger that causes the SA node to tell the heart to beat
faster, which results in an increased force of ventricular
contraction and accelerated heart rate.
Methods
1. Three different 10 mL solutions of 3%,
0.3% and 0.03% caffeine respectively were
prepared.
2. The 72-hour chick embryo/egg was
then windowed as outlined in the lab
handout.
3. The in vivo heart rate was then
measured and recorded three times in
rapid succession.
4. Next, the first solution of 0.03% diluted
caffeine was added using a pipette to the
in vivo chick embryo.
Methods
5. The resulting heart rate was measured
and recorded six times in rapid
succession.
6. Steps 2-5 were then repeated using the
rest of the diluted solutions (0.3% and 3%)
and new in vivo chick embryos.
7. Next, a new 72-hr. chick embryo was
then explanted using the methodology
outlined in the lab handout.
8. The in vitro heart rate was then
measured and recorded three times in
rapid succession.
Methods
9. Next, the first solution of 0.03% diluted
caffeine was added using a pipette to the
in vitro chick embryo.
10. The resulting heart rate was then
measured and recorded six times in rapid
succession.
11. Steps 7-10 were repeated using the
rest of the diluted solutions (0.3% and 3%)
and new in vitro chick embryos.
Control Heart Rate
(in vivo, in vitro)
The control for the in vivo embryo
was 120 bpm (depicted with blue
horizontal line on graph).
The control for the in vitro embryo
was 103 bpm (depicted with red
horizontal line on graph).
Results (in vivo)
Results (in vitro)
Discussion
For the in vivo embryo, our
hypothesis was supported. The
heart rate increased with the
concentration of caffeine added
because it inhibits the enzyme
phosphodiesterase, which caused a
build up of cyclic AMP. This build up
excited the sympathetic nerves in the
heart and increased the heart rate.
Discussion
For the in vitro embryo, our hypothesis
was not supported. The results that were
observed were too erratic to be
considered supportive. Our interpretation
of this inconsistent data is that the
addition of the more concentrated caffeine
resulted in a sudden increase in heart
rate…so sudden it shocked the heart into
fibrillation and eventually cardiac arrest.
Future Experiments
To get more desired results, new and
improved experiments could be carried
out.
For example, the dilutions of caffeine
administered could be less potent and
segmented into a less dramatic increase
of concentration.
Another variation of the experiment above
could be to carry it out on a older chick
embryo (96hr). The advantage here is that
the heart would be more developed and
less prone to cardiac arrest.
References
McLaughlin, J.S. and E.R. McCain.
Developmental and Physiological
Aspects of the Chicken Embryonic
Heart. 10 Februaury 1999.
http://www.lv.psu.edu/jxm57/chicklab.
Sadler, M.J., J.J. Strain, and B. Caballero.
1999. Encyclopedia of Human
Nutrition, 1:A-D. San Diego: Academic
Press.