Have a heart!
The original pump that is the drumbeat of our lives is an amazing structure. You've seen them on holiday cards, but now it's time for the real thing. A heart dissection is a fascinating experience that is at the core of our circulatory system, and our body as a whole. There our other dissection photos out there, but I wanted to make a clear walkthrough for teachers and students who are doing it.
What: Heart Dissection
Concepts: biology, anatomy, pumps
Time: ~45-60 minutes
Cost: ~$1.50 per heart
- One heart (pig, cow, or sheep from the butcher as in tact as possible)
- 4 x Dowels (or pencils)
- Blade (X-acto or otherwise)
- Pair of Gloves
A NOTE ON DISSECTIONS:
Dissecting animal organisms is a tricky subject which ultimately some will object to and that's okay. For us, we believe that with careful scientific exploration of animals who were treated in humane ways, we can learn and teach our students to be greater stewards of the environment, and especially toward the species they just learned about. There will always be some students who wish not to do a dissection, and we always allow whatever level of participation they choose in these experiences. Many prefer to just watch. Many of those eventually join in. But whatever it is, feel it out with your classroom or audience.
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Step 1: Feel the Beat
Check to see if those tickers are ticking!
The first thing to do is get moving to put that heart into high gear. As your body needs more oxygen to its muscles, the heart beats faster to circulate it. After 30 seconds of hopping around, it's time to check those arteries for a pulse.
The circulatory system is one big loop with many branches. We describe the tracks as veins (blood going to heart) and arteries (blood going away). A way I help students remember is that the heart thinks it's the most important organ in the body, so everything going to it is a "vein" because it's "vain." To feel our pulse, check one of the easy arteries and hold for 30 seconds.
You can do the radial artery (inside the wrist), the carotid artery (on the neck), or simply feel your chest. What does your heart sound like? How fast is it beating? What's the pattern?
A few students may be able to detect the WUMP-wump, WUMP-wump part of the beat (which they've probably heard in movies, too). This has to do with the fact that our heart has four chambers, which we'll get too soon. This comes from the two pairs of valves in the chambers of the heart.
Step 2: Check for Blood
Sure we've been told we're full of blood, but how do we know?
Maybe you've got a cut before, but you can see evidence even without an injury. Just look around.
Starting with looking at an eye, you can see both arteries and veins. The retinal arteries are thinner and brighter red than the veins. If you have a flashlight, you can also see blood in any narrow part of our skin like in our fingers and in our ears. For simple viewing, what do you think gives our tongues and gums that color?
Step 3: Have a Heart
Starting with a pig heart, there is a lot to notice before we start cutting. What do you see?
To start, let's orient our heart so that we're looking at the front. This is how it would sit inside the animal with them facing on us. We're going to refer to "left" as the animal's left, and right as the animal's "right," which is how things are described medically. That will be opposite the way we view them.
Looking at the front, you might notice a groove down the middle of the heart. This is the interventricular sulcus. This divides the ventricles, which we'll get into in a bit. If you flip it around, you might find a little bit of tissue, hanging like an ear flap. Those are the auricles, which help protect the atria inside.
Often hearts from the butcher will have a cut along one of the sides, which they do so the blood can drain out. You may see some coagulated blood (dark dark brown). What else can you find?
Step 4: Veins and Arteries
How many tubes go into and out of the heart? Try to find all four.
With a heart from the butcher, the first two you'll probably notice are the superior vena cava and the aorta. The superior vena cava is a vein that brings all of the blood from your upper body to your heart. There is also an inferior vena cava (which is often chopped off) that brings blood from the lower half of your body. The aorta is an artery that takes blood from your heart and pumps it through back toward your body. You can see these are thick as they are dealing with a lot of force. See where they lead.
Often in the front, you'll simply find two tubes without flaps which are the pulmonary veins and arteries. First, blood comes in from the vena cava on the right ventricle, then gets pumped out the pulmonary artery. After getting oxygen, it returns through the pulmonary vein, and then back out to the body.
These can be tricky, so use dowels or pencils to mark the four ins and outs.
Step 5: Making the Cut
There are many ways you can cut your heart, but the most informative will perhaps be directly down the interventricular sulcus. Find the line in the front of the heart, and make an incision that isn't too deep, only going through the top wall.
Lightly pull the two parts so it opens like a book, and take a look inside.
Step 6: A Four Bedroom House
The first thing to look for are the four rooms of the heart.
They match up with the two main arteries and veins we looked at, and are called atriums (top ones) and ventricles. Try putting your fingers through the arteries and veins to see if you can trace the path blood takes from the body, to the lungs, back from the lungs, and to the body.
We have four chambers, but if you want to do some investigating, you can learn about fish hearts, which only have two.
Step 7: The Pieces of the Heart
There are many things to look and learn about inside the heart. Some of the things you might try to find include:
- Valves -- the tricuspid and bicuspid valve are easily visible and divide the atriums from the ventricles.
- Chordae Tendinae -- the "heartstrings," which pull on valves to open or close them. Try it out with a pair of tweezers.
- Papillary Muscle -- just like in our limbs, tendons need muscles to pull them, and those are the densely packed papillary muscles. These are fascinating, as unlike our other muscles, they are not attached to the skeletal structure.
- Compare Ventricle Walls -- if you look at the right and left ventricles, one is much thicker than the other. Can you see which one? In the left ventricle, the heart has to contract to move blood throughout the whole body, so it has to have more muscle than the right, which brings blood a short distance to the lungs.
Keep going! See what else you can find!
Step 8: Keep Exploring
There's more inside the heart alone, and more to see when you compare them. When you look between hearts, you can start to notice differences between animals, individuals, the health of an animal by fat deposits and tissue, and much more.
Have fun, be respectful in dissection, and keep exploring and learning.