Dissection

Dissection is the act of cutting open an organism to study its internal anatomy. Dissection is commonly practised among students of all ages in their science classes to learn how an organism works and how its anatomy is organised.

What can be dissected?

Anything once alive can be dissected, such as frogs, flowers, or even humans.

How can hibiscus flowers be dissected?

Although most do not consider flowers as something they can dissect, they can be dissected and are often easier to get a hold of for dissection than an animal.

Depending on the gender of a flower, they will have different anatomy and thus be dissected differently (Table 1):

Table 1. Dissection of female and male hibiscus flowers.

Parts and purposes of a flower

How can a heart be dissected?

A heart dissection aims to look at the different parts that make up the heart. A good resource for learning the parts of the heart can be found here.

Materials

Dissecting a heart allows students to understand the workings of an animal's heart and involves various materials:

• Gloves
• Apron
• Scalpel
• Safety goggles
• Dissection tile
• Heart

Risk assessments of the heart dissection:

• Proper usage of laboratory supplies (especially scalpels)
• Biological hazards
• Maintaining a safe lab environment
• Follow the proper steps for the dissection

The dissection steps

The steps to a heart dissection:

1. Keep the heart on the dissection tile to maintain a clean workspace.

2. Analyze the heart and take note of the different parts of it. Most of the heart consists of ventricles which help pump blood from the heart to the rest of the body.

3. The top portion of the heart is the atria, and it looks almost like a flabby piece of skin. There will be the left atrium and the right atrium.

4. Begin the dissection by taking the scalpel and cutting parallel to the line that runs across the heart. This cut will go up through the wall of the right ventricle. Note: you can tell which side of the ventricle is because the left side is thicker than the right.

5. Peel back the cut right ventricle to analyse the thickness and look at the tendinous cords (they look like strings).

6. Cut down the left ventricle wall and look at the thickness (much thicker than the right ventricle). Also, you can look at the blood vessels in the heart.

7. If a pencil or other object is stuck through one of the blood vessels from inside the left ventricle, you should see the top of it come out of the top of the heart. The pencil will come out of the pulmonary artery (carries blood from the right side of the heart to the lungs) when inserted on the right side, and if it comes out of the left, it is in the aorta (takes blood throughout the entire body).

8. You can locate two other blood vessels; the right side also has the vena cava (which circulates deoxygenated blood from the upper half of the body), while the left side has the pulmonary vein (collects oxygenated blood from the lungs and brings it into the heart).

Diagram of the heart

Dissecting a rabbit for a practical

Sometimes, a student is given a whole body for dissection to analyse all of the different organs and how they work together in the body.

Materials:

• Gloves
• Apron
• Scalpel
• Safety goggles
• Dissection tile
• Scissors
• Forceps (these can be used to help grab and move organs)
• Rabbit
• Bone shears

The muscular system

1. To best observe the muscles, the rabbit is skinned. Create a small incision between the shoulder blades with the scalpel, then cut from the incision towards the tail using the scissors. Also, make cuts around each limb and the tail.

2. Begin to pull the skin off of the body gently. If any muscles are holding onto the skin, cut them off, but make sure not to damage the body.

3. As you peel off the skin, take note of the muscles on the rabbit and how they had connected to the skin.

The digestive system

1. Next, the goal is to view the digestive system. Place the rabbit on its back and cut from the muscular abdomen wall to the most posterior rib.

2. Make two additional incisions from the linea alba to the backside of the rabbit. Fold the flaps of skin and muscle laterally. You are now looking at the digestive system.

3. One of the first things you will notice is a thin layer of muscle called the diaphragm. It helps organisms breathe in and out.

4. Below the diaphragm is a reddish organ which is the liver. The liver helps filter blood and regulate blood sugar.

5. If you lift the right side of the liver, you will find the greenish coloured gallbladder—the gallbladder stores bile.

6. You will see the stomach below the diaphragm if you lift the entire liver. If you open the stomach, you can potentially still find some food that the rabbit last ate.

7. Next to the small intestines, you will find the pancreas. It is small and pinkish in colour, making enzymes used in digestion.

8. The small intestines connect to the large intestines. The large intestines consist of the cecum (absorbs leftover fluids and salts from digestion), colon (creates stool), and appendix (protects healthy gut bacteria).

The respiratory system

1. Next, we are going to look at the respiratory system. Cut from the diagram to the base of the neck and fold back the skin. Make a shallow cut towards the chin and use a blunt tool to move away any tissue to view the larynx and trachea.

2. You should also be able to see the lungs of the rabbit.

The circulatory system

1. Next, we will look at the circulatory system. Remove the thymus gland to get a better view of the heart. Then remove the pericardium, a type of membrane, from around the heart.

2. Use steps 1-8 from the above section to analyze the heart (How can a heart be dissected?)

The urogenital system

1. The second to last system is the urogenital system. Remove the rabbit’s liver and push the visceral organs to the right.

2. Locate the bean-shaped kidneys and cut one of them in half lengthwise with a scalpel. Inside the kidney is the renal medulla which regulates the urine concentration.

3. The ureter is connected to the kidney, and it transports urine to the bladder.

4. The urine will be removed from the body using the urethra. This urethra placement will depend on the gender of the rabbit.

This next step will vary based on the gender of the rabbit:

1. If male: cut open the scrotum to view the white round testes and then cut one of the testes in half. Inside are coiled tubules that produce semen known as seminiferous tubules.

2. If female: Cut open the ovaries and see where egg cells are produced. Egg cells then go through the fallopian tubes and into the uterus.

The nervous system

1. The final system is the nervous system. Place the rabbit on its stomach and begin to remove all coverings from its neck and back of the skull.
2. Put bone shears into the base of the skull and carefully cut around the top of the skull. Remove this cut piece of skull and look at the brain. To view the ventral surface, the brain will need to be removed.
3. The cerebellum (motor control) is located at the back of the brain, and the cerebrum (receives and gives information from sense organs, aka eyes or nose) is near the front. The cerebrum is the largest part of the brain.