Comparative Anatomy: Dissection - Classroom Science Resources

• Inside the right ventricle, identify the valve at the beginning of the pulmonary
artery. (The pulmonary artery to the lungs can be seen curving out
of the right ventricle toward the left side of the heart.)
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Eye protection should be used during dissection activities. Students
Program Summary
By using X-rays, CAT scans, and other powerful instruments, doctors today are
able to tell an awful lot about what’s going on inside a person’s body. But
even these advanced techniques don’t tell a doctor the whole story.
Sometimes, learning about the systems of the human body — the muscles,
should be encouraged to wash their hands after handling specimens.
bones, organs, and cells that keep us functioning — requires hands-on research.
Latex gloves should be available for student use. Food should not be
By studying human anatomy, scientists have found that every one of us is an
allowed in the laboratory. Scalpels and scissors must be sharp for effec-
incredibly complex system made up of many smaller systems. For a great part
tive use. Students should be taught to use dissection equipment properly.
of human history, human dissection has been forbidden and abhorred, but
Always emphasize the dangers of working with sharp instruments.
without human dissection, no real knowledge of the internal structures of
the human body could have been gathered.
Many advances in medicine are due first and foremost to anatomical understanding.
Discuss the benefits of studying vertebrates/invertebrates. (i.e.,
Mammals, like cats and pigs, are studied because they are like humans; but we
don’t like to study them because they are like humans.)
Dissecting is an activity that requires precise motor skills that must be
developed. Students should understand the reason for dissecting. It is an
activity that should be treated very seriously. Proper attitudes toward dissection
will increase the value of the activity and encourage sensitivity of
students toward living things. Dispose of all waste in accordance to
school policy.
Microscopic anatomy, called histology, involves observations of dissected
tissue.The earliest histologists used naturally occurring dyes to stain their
sections.With the invention of chemical dyes, a greater array of stains became
available, allowing scientists to see cellular structures that were once invisible.
Vocabulary
gross anatomy — The study of major body structures that are visible to the
naked eye.
comparative anatomy — The study of the body structures of different
Investigation
Provide students with sheep hearts to dissect and compare to models of a
human heart.
• Place the heart on the table with the apex toward you and with the anterior
side uppermost. If a thin membrane (pericardium) still covers the heart,
remove it. Note the apex (tip) of the heart and the base (broader end).
• Measure the length, diameter and mass of the heart.
species of animals in order to understand their similarities and differences.
taxonomy — The scientific classification of living and extinct organisms.
x-rays — Invisible electromagnetic radiation with wavelengths shorter than
visible light. X-rays are produced when high energy charged particles collide
with other charged particles or with atoms.
CAT (computerized axial tomography) scan — A technique to derive
a three-dimensional image of a cross section of deep tissue within the body
by sweeping different sections of the patient with x-rays.
• Observe the structures at the base of the heart. Find the opening of the large
arteries and veins.
• Find the groove in which the coronary artery of the heart lies (coronary
sulcus).
• With a pair of scissors, cut through the side of the aortic arch and locate the
superior and inferior vena cava. From there, follow the route that blood
would take through the heart, from the right atrium to the right ventricle to
the pulmonary artery (to the lungs), back to the left atrium and finally to the
left ventricle.
• Pass your fingers or a blunt probe up between the tricuspid valves into the
right atrium. Find the two openings by which the blood enters from the
dissection — To separate into pieces for scientific examination.
Animal Welfare Act — A law that promotes the humane care and treatment
of laboratory animals.
artery — A vessel that carries blood away from the heart.Arteries generally
carry oxygenated blood. In mammals, the exception is the pulmonary artery,
which carries deoxygenated blood to the lungs.
histology — The study of tissue organization on a cellular level.
anterior — Anatomical term used to describe the front of a structure.
posterior — Anatomical term used to describe the back of a structure.
apex — Tip.
superior and inferior vena cava. Notice the absence of valves at the openings
pericardium — The membrane that surrounds the heart and holds it in
of these veins.
place.
• With a pair of scissors, cut through the aorta and continue down through
aortic arch — The curved top portion of the aorta, the blood vessel carry-
the thick muscular wall of the left ventricle. At the base of the aorta observe
ing blood from the heart to all the organs and other structures of the body.
the left semilunar valve.
atrium — The chamber of the heart that collects blood returning from the
• Compare the inside surface of the right atrium and ventricle.Within the
rest of the body. In all vertebrates but fish, there are two atria, left and right.
right ventricle, observe the little muscular bundles on the wall called tribec-
The right atrium collects deoxygenated blood from the body and passes it to
ulae carnae. Note the chordae tendinea, which are attached at one end to
the right ventricle.The left atrium collects oxygenated blood from the lungs
the valves and at the other end to the papillary muscles. (Continued)
and passes it to the left ventricle. (Continued)
ventricle — The chamber of the heart that is responsible for pumping
blood out to the rest of the body. In mammals and birds, there are two ventricles,
left and right.The right ventricle pumps deoxygenated blood to the
lungs via the pulmonary artery; the left ventricle pumps oxygenated blood
to the body via the aorta.
coronary — Relating to the heart, or to one of the two arteries that originate
in the aorta and supply blood directly to heart tissue.
inferior vena cava — A large blood vessel carrying blood to the heart
that carries oxygen-poor blood to the right atrium from the lower half of
the body.
superior vena cava — A large vein that carries oxygen-poor blood to
the right atrium of the heart from the upper parts of the body.
pulmonary artery — Relating to the lungs. Sometimes this term is used
to denote the pulmonary valve, which is the valve that prevents back-flow
of blood from the pulmonary artery into the right ventricle.
pulmonary veins — Vessels that bring blood from the lungs to the
heart.
mitral valve — The valve that separates the left atrium and the left ventricle
and prevents back-flow from the ventricle to the atrium. Derived
from “miter,” which it resembles. (A miter is a tall, pointed hat with peaks
in front and back which is worn by a bishop.)
tricuspid valve — The valve that separates the right atrium and the right
ventricle and prevents back-flow from the ventricle to the atrium. It is
composed of three leaf-like parts.
sulcus — The groove found at the boundary of the atria and ventricles.
tribeculae carnae — Cardiac muscle that contribute significantly to the
contractile action of the ventricular walls.
chordae tendinae — Muscular fibers that attach the cardiac valves to
the papillary muscles.
microtome — An instrument used to cut very thin sections of tissue for
viewing under a microscope.
paraffin — A waxy substance often used to fix tissue before it is sectioned.
rejection — The process by which foreign tissue, such as a transplanted
organ, is attacked by the recipient’s immune system.
Christiaan Barnard (1922–2001) — The South African surgeon who
performed the first human heart transplant in 1967.
Discussion Topics
• Compare the thickness of the walls of the left and the right ventricle.
Discuss the function of each ventricle and come up with reasons for the
difference in thickness.
• Provide students with information on organ donation and transplantation
issues.
• A girl’s heart usually beats between 78 and 80 times per minute.A boy’s
heart is slower than that — about 70 to 72 times per minute.What are
some possible reasons for this difference?
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