Dissection of the Mammalian Respiratory System

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Introduction:

In this lab, you will be examining many characteristics of a rat’s anatomy. Dissections help researchers get a 3-dimensional picture of how the systems of a body work together. Now you’ll have the opportunity to see how the respiratory, digestive and circulatory system are arranged spatially.

The Classification of the Rat (Rattus norvegicus):

Kingdom: Animalia
Phylum: Chordata
Subphylum: Vertebrata
Class: Mammalia
Order: Rodentia
Family: Muridae
Genus: Rattus
Species: Norvegicus
Note:
Dissection does not mean “to cut up.” Rather, it means “to expose for viewing.” Therefore, please follow the instructions outlined in this lab for proper dissection technique and never cut more than is absolutely necessary to expose an organ. Raise structures that you wish to cut with forceps so that you can see what lies underneath. Approach the dissection in a step-like manner. Do not discard any organs until all sections are completed.

Materials:
*
* Preserved fetal pig
* Dissecting pan
* Scissors
* Scalpel
* Forceps
* Probe
* Twine

Instructions:
Part One: External Anatomy

1. Obtain your rat and observe the general characteristics. Key terms are underlined.

The rat’s body is divided into six anatomical regions:
i. Cranial region – head
ii. Cervical region – neck
iii. Pectoral region – area where front legs attach
iv. Thoracic region – chest area
v. Abdomen – belly
vi. Pelvic region – area where the back legs attach

2. Note the hairy coat that covers the rat and the sensory hairs (whiskers) located on the rat’s face, called vibrissae.

3. The mouth has a large cleft in the upper lip which exposes large front incisors. Rats are gnawing mammals, and these incisors will continue to grow for as long as the rat lives.

4. Note the eyes with the large pupil and the nictitating membrane found at the inside corner of the eye. This membrane can be drawn across the eye for protection. The eyelids are similar to those found in humans.

5. The ears are composed of the external part, called the pinna, and the auditory meatus, the ear canal.

6. Locate the teats on the ventral surface of the rat. Check a rat of another sex and determine whether both sexes have teats.

7. Examine the tail. The tails of rats do not have hair. Other rodents, like gerbils, do.

8. Locate the anus, which is ventral to the base of the tail.

9. Determine whether your rat is male or female by looking near the tail for the male or female genital organs.

Part Two: Respiratory System
The respiratory is responsible for the exchange of gases. The rat must take in oxygen for respiration processes and must rid itself of carbon dioxide waste.

1. You will carefully remove the skin and muscles of the rat to expose the organs beneath. Use scissors to cut through the abdominal wall of the rat following the incision marks as shown in Figure 1.

Figure [ 1 ]
2. Cut slowly and carefully; do not cut too deeply to prevent damaging the underlying structures. Keep the tip of your dissection tool pointed upwards. Note: when you cut through the thoracic cavity, you will encounter bone.

3. Once the incisions have been made, pin both skin flaps to the side of the rat.

4. Locate the trachea. The trachea is a tube that extends from the neck to the chest. It is white and lined with cartilage. The opening of the trachea is the glottis. The enlargement at the anterior end of the trachea is the larynx (voice box) which contains the vocal chords.

5. The trachea splits in the chest cavity into two bronchi. Each of these air tubes extends into the lungs and splits into smaller tubes called bronchioles. Using this information, locate the two lungs which lie on either side of the heart.

6. Locate the thin muscular diaphragm just above the liver. This muscle is responsible for drawing...
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