Examining the Systems of A Rat (Part 1, Day 1) Group Names______
Thinking
/Communication
/Application
/14
//15
//13
By the end of these three days, you should be able to:
- handle dissection equipment in a skillful manner
- recognize by name and state the functions of the structures for the following mammalian systems:
§ digestive
§ respiratory
§ circulatory
- recognize the differences and similarities between systems of human and rat
- gain skill in drawing biological drawings
- follow directions from a laboratory manual and follow a schedule
- work in a co-operative environment to gather information and put together a written lab report
Dissection involves the careful and systemic examination of the internal structures of an organism. A good dissection will reveal not only the location and structure of individual organs, but also how different organs relate to one another in the various systems of the body. To carry out a successful dissection, you should be familiar with the terms listed below.
TERM / MEANINGDorsal / Upper or back surface
Ventral / Under or belly surface
Lateral / Side
Anterior / Toward the front (head) end
Posterior / Toward the back end
Superficial / Near the surface
Proximal / Close to
Distal / Far from
Caution: Extreme care must be taken when using dissecting instruments, particularly scalpels. To the extent possible, make cuts away from your body. Wear plastic gloves and work in a well-ventilated area. Dispose of all materials as instructed by your teacher, and clean your work area.
GENERAL INSTRUCTIONS
1. During the dissection period, it is most important that ALL equipment and stations remain clean. Keep papers on the outside of the lab bench, dissection tray and rat in the middle, and any unused equipment on the inside lab bench towards the wall.
2. DO NOT throw any materials into the sinks. They rot, smell and scare the cleaning staff!
3. Read and follow ALL directions very carefully. Then if you still do not understand, ask the teacher.
4. Make sure you wrap a moist paper towel around your animal when it is not being used.
5. The word “DISSECTION” does not mean “CHOPPING UP”; rather it means “EXPOSING TO VIEW’. Never remove a part from the animal and then try to figure out what it was. Cut only when told to and only what is absolutely necessary.
6. You will be using the following dissection equipment:
i. Scissors for large cutting work
ii. Probe to lift tissues, push tissues aside and feel for tissue that can’t be seen
iii. Forceps to always hold tissues and to lift tissues (especially for cutting)
iv. Scalpel – the most favourite tool of biology students but scissors do almost the same job, are easier to use and cause less errors
v. Pins to pin back the skin/open the structure of the rat.
7. Since many of the structures will be similar to yours, as you study the rat, consider how the structure is similar to the human and note any differences that may exist between your own anatomy and that of the rat.
8. Sections that appear in bold and italics are for you to complete as part of a report. This report will be handed in on ______. Only one report per group is necessary.
You will have two periods to complete the dissection. Answer ALL questions that are asked and complete all diagrams, on blank paper, where indicated.
You are required to submit a completed lab report, one per group.
At the end of each day, drain all liquid from your tray into the sink - no parts! Place the parts of the rat into your plastic bag. Be sure to dampen a few paper towels with water and place around and on top of your rat. Make sure to label your rat and your plastic bag with your group names. Then place rat in the fume hood. Be sure to thoroughly clean all your dissecting equipment with soap and water, dry them and place back into their respective spots. Clean and dry your lab bench. You will be assessed on your ability to keep your station clean.
Rat External Anatomy-Part 1
Procedure: Obtain your rat. Rinse it off with water and place it in your dissecting pan to observe the general characteristics.
The rat's body is divided into six anatomical regions:
cranial region - head
cervical region - neck
pectoral region - area where front legs attach
thoracic region - chest area
abdomen - belly
pelvic region - area where the back legs attach
1. Note the hairy coat that covers the rat and the sensory hairs (whiskers) located on the rat's face, called vibrissae.
2. 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.
3. 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.
4. The ears are composed of the external part, called the pinna, and the auditory meatus, the ear canal.
5. Locate the teats on the ventral surface of the rat. Check a rat of another sex and determine whether both sexes have teats.
6. Examine the tail, the tails of rats do not have hair. Though some rodents, like gerbils, have hair on their tails.
7. Locate the anus, which is ventral to the base of the tale.
8. On female rats, just posterior to the last pair of teats, you will find the urinary aperture and behind that the vaginal orifice which is in a small depression called the vulva.
9. On males, you will find a large pair of scrotal sacs which contain testes. Just anterior to the scrotal sacs is the prepuce, which is a bulge of skin surrounding the penis. The end of the penis has a urogenital orifice, where both urine and sperm exit.
Procedure:
1) Place your rat on its side in a dissecting tray. Observe the major regions of the body: head, neck, trunk and tail.
In the space below, using a PENCIL, sketch a diagram of the rat. Using the terms above, sketch a diagram of your rat and label as many parts as possible. All labels should be drawn with a pencil and a ruler. (5 marks - C).
2) What is the sex of your specimen and how do you know? (2 marks – C)
3) Secure your specimen ventral (stomach) side up, with the legs spread laterally with string. Begin at the skin of the throat, and cut very shallowly (scissors work better than scalpels for this), make an incision the length of the body, then incisions at the collar bones, the posterior margin of the rib cage, and at the hips, cutting deep enough to reach the body cavities but not so deep as to damage the organs inside (Your teacher will show you what this looks like on picture before you start).
4) Free the resulting flaps of tissue, gently disconnecting it from underlying tissue with a blunt probe or careful cutting. You can pin the flaps aside or completely remove them.
Digestive System- Part 2
1) Look in the abdominal cavity. The abdominal organs may still be covered with a membrane, the peritoneum, but this usually comes off with the overlying layers. If necessary, wash the organs under the faucet and drain the body cavity. Try to expose as many digestive organs as you can.
2) Another membrane, the mesentery, surrounds and supports most of the digestive system and its related circulation, and in human males is a primary storage site for fat, causing "beer bellies" in some men. The primary fat storage site for most human females is usually in the sides and backs of the hips.
Why do you think that women do not store fat in their bellies, but rather in their sides? (Hint: think about what women do that men don’t) (2 marks - A).
3) Much of the anterior abdomen is occupied, especially on the right side, by the liver. The liver is the largest internal organ. Inspect it. The liver does many more things than making bile. It collects almost all of the blood circulated through the intestines and processes many of the chemicals picked up there (such as alcohol, which your liver detoxifies).
What are the dangers of taking in too much alcohol? Explain (2 marks - A).
4. Count the lobes (sections) of the liver. (Don't count the long, narrow spleen, which is lateral to the stomach on the left side).
How many lobes are there? (1 mark - T)
Tucked into a recess underneath is the gall bladder, where a secretion called bile, also produced in the liver, is stored. Bile is a salty fluid that, if it gets too concentrated, crystals can form – gallstones.
What is the function of bile? Explain (2 marks - T).
5. Remove the liver VERY CAREFULLY. Place the pieces of the liver in your tray and have your teacher initial the checklist.
Anterior to the liver, locate the sheet of muscle called the diaphragm.
6. Find the stomach. This organ has an incoming tube, the esophagus, anterior and an outgoing tube, the small intestine, posterior. The esophagus pierces the diaphragm and moves food from the mouth to the stomach. Is is distinguished from the trachea by its lack of cartilage rings. Locate the esophagus.Locate the pyloric sphincter and the cardiac sphincter.
Remove the stomach with about 0.5cm. of those tubes attached.
The stomach serves two major functions: it churns up the balls of food sent down the esophagus from the mouth (we chew the food up but stick it together into a ball - a bolus - to swallow it), reseparating the pieces, and it begins the chemical breakdown of the food with strong acids and with a powerful protein-digesting enzyme. The stomach (and much of the intestines) is lined with a mucus layer to protect the linings from the digestive secretions; in places where the mucus thins, self-digestion can happen, creating ulcers.
7. Cut open the stomach, but don't cut near the two tubes. Examine the interior of the stomach. You can place it under the dissection microscope if necessary. Have your teacher initial the checklist.
Describe the lining of the stomach and sketch what the lining looks like. (4 marks - C).
8. Fold the stomach back and look at the structures on the inside where the tubes connect. What do they look like? (1 mark - C)
The spleen is about the same color as the liver and is attached to the greater curvature of the stomach. It is associated with the circulatory system and functions in the destruction of blood cells and blood storage. A person can live without a spleen, but they're more likely to get sick as it helps the immune system function. LOCATE the spleen. Identify the spleen in front of your teacher and have your teacher initial the checklist.
The pancreas is a brownish, flattened gland found in the tissue between the stomach and small intestine. The pancreas produces digestive enzymes that are sent to the intestine via small ducts (the pancreatic duct). The pancreas also secretes insulin which is important in the regulation of glucose metabolism. LOCATE the pancreas by looking for a thin, almost membrane looking structure that has the consistency of cottage cheese. Identify the spleen in front of your teacher and have your teacher initial the checklist.
What are the functions of the pancreas? (3 marks-T)
Most of what's left in the abdominal cavity is the intestines, small and large. The intestines are held together by the mesentery membrane. This is a clear membrane, with many blood vessels inside. Draw a diagram of a section of the small intestine, with mesentery attached (3 marks - C).
Why would the mesentery have so many blood vessels? Explain (hint: think about the function of the small intestine – what happens there?) (2 marks - T)
Separate out the small intestine, (uncoil the small intestine until you have one complete long tube) clipping gently through the mesentery holding it together, until you have separated out a long single tube (you're going to measure them for question 10). At a certain, clearly recognizable point, the small intestine joins the large intestine, or colon, at the cecum.
What is the function of the large intestine? (2 marks - T)
The small intestine is made up of three parts – identify the three parts on your rat’s small intestine. What is the length of the small intestine in your rat? How long is the large intestine? (4marks - T)
11. Locate the cecum - a large sac in the lower thrid of the abdominal cavity, it is a dead-end pouch and is similar to the appendix in humans. It also is the point at which the small intestine becomes the large intestine.
12. Locate the rectum - the short, terminal section of the colon between the descending colon and the anus. The rectum temporarily stores feces before they are expelled from the body.
Analysis Questions, Day 1
1. Outline any special safety procedures that must be followed when performing a dissection: (3-A)
2. What is the function of the liver? Why do you think it is so large? (3-A)
3. Explain why the small intestine is so long relative to other organs of the body. (3-A)
Rat Anatomy ChecklistThroughout the course of the investigation, you will be to stop and have your instructor check your progress. At each checkpoint, you should have the box initialed by your instructor to ensure adequate progress. You will turn this sheet in at the end of the investigation.
1. Rat cut properly and pinned back. [ Instructor initials______]
2. Removal and dissection of liver. [ Instructor initials______]
3. Removal and dissection of stomach. [ Instructor initials______]
4. Identification of espohagus [Instructor initials______]
5. Removal and dissection of small intestine [ Instructor initials______]
6. Identification of spleen [Instructor initials______]
7. Identification of pancreas [ Instructor initials______]
8. Identification of caecum and large intestine. [ Instructor initials______]
9.Identificaiton of rectum[ Instructor initials______]
10. Proper dissection of digestive organs. [ Instructor initials______]
3 / 2 / 1
FOCUS - embraces lab as a learning opportunity, uses resources to enhance understanding, stays focused and self-directed
PARTICIPATION - shared equally in responsibilities, no absences
COMPLETION - all checkpoints achieved
RESPECT - attentive, curious, does not "play" with the specimen
SAFETY & CLEANUP - always wore goggles, cleaned up station, stored specimen appropriately
Quality of Dissection (well executed, specimen is in good shape) / 1234
Identification of Structures (location and function) / 1234
Attitudes (appropriate lab behaviour) / 1234
1