BIOLOGY EXPERIMENT
Lamb Heart
The heart is an oblong muscular organ, which is attached to the lungs and to the two major blood vessels of the body (the aorta and vena cava again) by a tangle of tubes at the top. There are also two “flaps” lying alongside the tube tangle which bear a vague resemblance to the external flaps of the ears, and which share their name: auricles. The probe in the following two pictures indicates the auricles.
A Lamb Heart
The Tube Tangle
If you wish to slice through a heart to expose the interior, which way should you slice? If the auricles indicate the “sides” of the heart, then a good choice for which way to slice is sideways, through each auricle, so you can see what is inside underneath each auricle. In the heart shown below, I sliced through one auricle, but missed the other. The second auricle is hidden behind the top of the heart on the right hand side.
The Interior of a Lamb Heart
The heart is hollow inside, with two chambers, one underneath each auricle. These are the ventricles. The larger of the two, with thicker more powerful walls, is normally on the left side of the body and is called the left ventricle, and the smaller of the two, with thinner walls, is the right ventricle. (If the heart is made to work by the muscular walls, which of the two chambers do you suppose has the harder job to do?) Within and underneath the auricles are two floppy chambers that look like either the upper portion of the ventricles, or maybe separate chambers atop each ventricle. These are the atria. (The right atrium is hidden in the picture above.) A little poking and lifting with a blunt probe (or an old pencil or pen) can reveal tough thin fabric flaps separating the ventricles from the atria. (When these flaps are lying flat against the walls, each atria and ventricle looks like a single chamber.) The visible tendon-like strings apparently hold down the edges of the flap for some reason. If you gently insert the probe through the various tubes in the top of the heart, it will emerge within one of the chambers. All of the tubes on top of the heart open into one of the chambers within.
(The flaps between the atria and ventricles are the mitral valve and the tricuspid valve–one-way valves that let blood flow from the atria to the ventricles, but not vice versa. The tendons–the chordae tendinae, or heart strings–are for holding the valve steady when it is closed so that it doesn’t blow inside out like an umbrella in the wind. The little lumpy muscles lining the interior walls that pull on these tendons are the papillary muscles.)
DISSECTION OF CHICKEN HEART (VIDEO)
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