Rat Dissection

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1) The length of the tail: 18.5 cm
2) The length of the body ( from the tip of the nose to the base of the tail: 22cm What is their relative proportion? 1.2:1
PART A (Overview) pg. 462-464
a) Draw a diagram of the rat when it is first cut opened and the internal organs are exposed. Identify and label the diaphragm, the stomach, the small intestine, the caecum, the heart, the left and right lung, the trachea and the esophagus. (Note: see Figure 22 on pg 470 for an example)

b) What structure divides the thoracic and abdominal cavities? The Diaphragm divides the thoracic and abdominal cavities.

c) What is the sex of your rat? Male.

Part C Digestive System pg 467
Skip the Salivary glands on pg 467 and continue with the Mouth on pg 468 d) Compare the length of the upper and lower pairs of incisors in the mouth. Which is longer? The upper incisor is longer than the lower incisor.

e) What does the surface of the tongue feel like? The tongue feels smooth and soft.

f) What are the functions of the tongue? The tongue is used to move the food around the mouth and to taste.

Esophagus: Carries bolus into stomach.

Epiglottis: Prevents food from entering the trachea.

Trachea: A tube which air passes from the mouth to the lungs.

g) Using a probe determine whether the esophagus or the trachea is more rigid. Can you explain why this might be so? The trachea is more rigid as the esophagus needs to be more flexible to adapt to the different size boluses.

h) To what organ is the esophagus attached? The Stomach.

i) What shape is the stomach? The stomach is j-shaped

J) Describe the interior wall of the stomach once you have cut it open. The interior wall of the stomach was thin. It was almost transparent, and was very flexible. It was like this so the rat could fit large amounts of food inside. The top portion of the stomach wall however, was thick and rough.

K) Measure the length of the small intestine and compare it to the body length of the rat. Length of the small intestine: 85 cm
Length of rat excluding tail: 22 cm
How do they compare? The length of the small intestine in comparison to the rest of the body was almost four times the size. Explain why the small intestine is so long relative to other organs of the body. The small intestine was so large in comparison to the rest of the body because food entering it needs to be mixed continuously for further digestion. Also, the small intestine is where most of the absorption of nutrients happens. What are the names given to the 3 parts of the small intestine? The small intestine is extremely long, and has three different parts. One part is called the duodenum. The duodenum is a short portion of the small intestine connecting the rest of the intestine to the stomach. It usually measures up to 25cm in length. Next, is the jejunum which is the middle part of the small intestine in all animals. Lastly, the ileum is mostly responsible for absorbing B12 from food sources, and it the smallest part of the small intestine. L) At the entrance of the colon is a large blind-ended sac called the caecum which joins into the ascending colon. Do humans have this structure? Yes

What is the purpose of the caecum? At the entrance of the colon, there is a sac called the “caecum”. Humans, in fact, do have a caecum, but it is known as the “appendix.” In humans, the appendix is not used, but in animals that are herbivores, like the rat, it is large and releases special bacteria in order to help in the digestion of cellulose.

Part E Respiratory System pg 477
M) The left lung has one lobe; the right lung has four lobes. Can you suggest a reason for the difference? The reason for the left lung only having one lobe is because the heart is more to the left in the rat’s chest, and therefore takes up space where the left lung should be.

N) Describe the texture of the lungs. The lung found inside the rat, were slippery and...
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