Download Rat Dissection Instructional Packet

RAT DISSECTION
ORDER: RODENTIA “to gnaw”
Day One Investigation
• External anatomy
• Opening thoracic and abdominal cavities
Day Two Investigation
• Abdominal Cavity
– Digestive System
– Urogenital System (Excretory & Reproductive)
• Thoracic Cavity
– Circulatory System
– Respiratory System
Observe External Anatomy
List 3 ways the rat is DIFFERENT
from humans.
List 3 ways the rat is SIMILAR to humans
1.
1.
2.
2.
3.
3.
Part I. External Anatomy
• Pre-Dissection Questions:
– Where do rats live?
– Would you typically see a rat during the day or night?
– What do rats eat?
– Do rats give birth to live young?
• What scientific term means to give birth to live young?
External Anatomy - Teeth
• All mammals have teeth that correspond to the type
of food they eat.
• The name RODENTIA comes from the Latin word
meaning “to gnaw”.
• Rodents such as the rat have 2 pairs of
CONTINUOUSLY GROWING INCISORS (front teeth)
which are kept at the
correct length by constant chewing.
• The mouth of the rat has a large cleft in the upper lip
which exposes the large front INCISORS – locate them.
• How long are they? Are they easily seen? Describe them
compared to the other teeth.
External Anatomy – Cranial Region
• Notice the rat has a hairy coat that covers the
entire body and sensory whiskers located on
the rat’s face.
• VIBRISSAE (whiskers) enable rats to feel their
way through tight spaces in the dark.
• Describe these whiskers:
External Anatomy – Cranial Region
• Locate 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 protections similar to eyelids found in
humans.
• What color eyes does your rat have?
External Anatomy – Cranial Region
• Locate the external EARS in rats are
surrounded by a PINNA, which is a flap of
cartilage covered by skin that can rotate to
direction of sounds heard by the ears.
• Locate the external NARES used for
respiration and odor detection.
External Anatomy – Abdominal Region
• Locate the TEATS (nipples) on the ventral
(stomach) side of the rat.
• Regardless if your rat is male or female – does
your rat have teats? ___________
• Remember a mammal, male or
female will have mammary glands,
nipples.
External Anatomy – Pelvic Region
• Locate the exit openings for the digestive,
excretory, and reproductive body systems.
• Like humans, male rats have 2 exit openings;
females have 3 exit openings.
In addition,
females have a
separate opening
for reproduction
and excretory
waste (urine).
Males have a
SHARED
urogenital
opening that
releases both
sperm and urine.
What Sex Is It?
• Because mammals are endothermic animals
creating lots of internal heat, and the ideal
temperature necessary for sperm production is a
few degrees cooler than body temperature, male
mammals, must have their TESTES suspended
outside their bodies in a sac (SCROTUM) to keep
them cooler.
• Testes outside the body in a scrotum are called
TESTICLES.
• Is your rat male or female? _____________
External Anatomy - Tail
• Examine the TAIL of your rat.
• What are some observations about the tail of
your rat?
• Rats do not have hair on their tails unlike many
other rodents that do like, gerbils, squirrels, and
chipmunks.
Part II: Dissection Preparation
Exposing the Abdominal &
Thoracic Cavities
STEP ONE – SKIN LAYER
• You will need to separate the skin from muscles for
your first cuts similar to the fish and amphibian
dissections.
• This time – START AT THE NECK AREA. There should be
an incision hole that you can use to begin.
• You will need to use your metal blunt ended probe to
separate the connective tissue of the skin from the first
layer of muscle. When you have gotten a section
separated you can begin to cut carefully down towards
the anus.
• YOU MUST CONTINUE USING THE PROBE TO TEASE
AWAY THE SKIN FROM THE MUSCLE AS YOU CUT TO
PREVENT CUTTING THE MUSCLE TISSUE! GO SLOWLY!
DO NOT CUT THE MUSCLES!
STEP TWO – CUTTING THROUGH MUSCLES
• Mammals are known as EUCOELOMATES. There is a
space you see surrounding the internal organs that is
called the “true coelom” – the body cavity is lined
with a membrane.
• Mammals have a DIAPHRAGM.
• This is a sheet of muscle that separates the body
cavity into two compartments:
– Thoracic Cavity – heart and lungs
– Abdominal Cavity – digestive, excretory, and reproductive
organs
• For this reason the rat must be dissected in
TWO STAGES!
DIGESTIVE SYSTEM DISSECTION
• Use your scissors to cut through the abdominal
wall of the rat following the incision marks in the
picture provided.
• Be careful not to cut too deeply and keep the tip
of your scissors always points upwards.
• Start at the lower abdomen and cut up towards
the diaphragm.
• To locate the diaphragm feels where the ribs are
located and it will be just next to them.
• Then make two incisions towards the back of the
rat like you see on your picture.
Abdomen cuts ONLY
Be careful!
Stop when get to the diaphragm!
This is what your
cuts should look
like – notice that
the chest area is
NOT CUT!
**PREGNANT FEMALES**
• Some of you may have the pregnant females
to dissect.
• Please take care with them as your classmates
will need to view these.
• Your TEACHER will carefully help you remove
the babies and set them aside for the class to
observe.
• Please do not attempt this without
assistance!!
DIGESTIVE SYSTEM
LIVER
• Locate the LIVER, which is a large, dark
colored organ just under the diaphragm. (you
can reference the photo on next slide).
– There are 3 lobes of the liver.
– The liver has many functions like digesting fats
from the bile produced. It also stores glycogen
for energy and transforms toxins.
– Rats do NOT have a GALLBLADDER because they
do not eat anything that would contain fats that
would require bile stored in the gallbadder.
STOMACH
• Locate the STOMACH.
• It is a curved organ usually located on the right side
(your right), just under the liver.
• Look at the top of the stomach and you should be able
to see the ESOPHAGUS.
• You should be able to see how the esophagus pierces
through the diaphragm muscle from thoracic cavity
and joins the stomach.
• Where the esophagus and stomach meet is called the
CARDIAC SPHINCTER. This controls the food going into
the stomach and prevents digesting food from
reentering back into the esophagus even if hanging
upside down.
Stomach
PANCREAS
• Next locate the PANCREAS. To find this you will need
to lift up the stomach.
• It will look like a thin membrane or a bumpy cottage
cheese like membrane (it won’t look like the nice leaf
structure we have seen previously).
• It will be found towards the bottom of the stomach
close to the beginning of the small intestines.
• It is always found in this location since it releases
enzymes into the small intestines to further digest
food.
• You can reference the photo on previous slide for
assistance.
SPLEEN
• Locate the SPLEEN. It will be about the same
color of the liver and you will find it attached
to the greater curvature (the outer margin of
the curve) of the stomach.
• It is shaped like a banana and is associated
with our circulatory system.
• You may again reference photo previously
shown.
SMALL INTESTINES
• Now locate the SMALL INTESTINES.
• It is a slender coiled tube that begins at the
bottom of the stomach at the Pyloric
Sphincter (a pinching will indicate it’s
location).
• The term “small” refers to its diameter tube
NOT its length.
• It consists of 3 sections: duodenum (mostly
straight), jejunum and ileum (both curly).
CECUM
• Following the Small Intestines, locate the CECUM.
• This is a pouch that connects the small and large
intestines together.
• Food is temporarily stored in the cecum so helpful
bacteria can digest the cellulose found in the cell
walls of plants.
• Since rats are considered a type of herbivore, what
type of digestive system do they have? (you may
need to look back in your notes, hint - focus on
what digestive system has the enlarged cecum)
________________________________
LARGE INTESTINES
• After locating the cecum, locate the LARGE
INTESTINES (also known as the COLON).
• It is actually a large greenish tube that extends
from the small intestines and leads to the anus.
• This is where the final stages of digestion and
water absorption occur.
• It has 4 sections:
–
–
–
–
Ascending colon (food moves up)
Transverse colon (short section parallel to diaphragm)
Descending colon (food moves back down)
Rectum (short terminal section that leads to anus –
this temporarily stores the feces before its expelled)
CHECKPOINT –
before moving on make sure to
confirm identification of digestive
organs with teacher! You will come
back to this cavity at the end to
identify two other systems.
THORACIC CAVITY DISSECTION
DISSECTING THE THORACIC CAVITY
• Now use your scissors to cut up into the thoracic
cavity.
• You will have to cut just above the diaphragm.
Sometimes cutting from the left or right sides
towards center helps.
• Be careful not to cut too deeply and keep the tip
of your scissors always points upwards.
• Make incisions like you see in diagram. Cut up
the neck area.
• You want to be able to see all the way up to the
trachea.
DIAPHRAGM
• Locate the DIAPHRAGM. Notice how the
muscle separates the two cavities.
• As discussed in class, why would this muscle
separating the heart and lungs from the
abdominal area be such a good adaption in
mammals?
HEART
• Locate the HEART. It is centrally located in
this cavity.
• The THYMUS GLAND may be visible at the
upper part of the heart.
• See photo on next slide for reference (use can
use this for lungs as well).
LUNGS
• Locate the LUNGS.
• They are spongy organs that lie on the left and
right side of the heart and should take up
most of the thoracic cavity.
• They lie closer to the back of the rat, you will
need to push the ribs to the side to find them.
• Now locate the TRACHEA and see how they
branch into the lungs.
• You may use the photo from the previous
slide.
CHECKPOINT –
before moving on make sure to
confirm identification of circulatory &
respiratory organs with teacher!
EXCRETORY SYSTEM
• The excretory and reproductive systems of
mammals work closely together.
• They many share the same “exit parts”, but
have different functions.
– Excretory system removes wastes
– Reproductive system produces gametes (sperm or
eggs)
KIDNEYS
• The primary organ of the excretory system are
the kidneys.
• They are large bean shaped structures located
toward the back of the abdominal cavity under
the intestines and found on both sides of the
spine. (lift up the intestines and lay them over to
one side to view them)
• Locate the KIDNEYS. Note all the veins and
arteries that connect the kidneys.
• Locate the URETERS attaching to the kidneys and
trace them to the URINARY BLADDER.
• Remove ONE kidney and cut it
lengthwise.
• What does the kidney look like
inside?
• The small yellowish glands in the
fat around the kidneys are the
ADRENAL GLANDS which
secrete adrenaline into the
blood during times of crisis (fight
or flight).
CHECKPOINT –
before moving on make sure to
confirm identification of excretory
organs with teacher!
REPRODUCTIVE SYSTEM
MALE REPRODUCTION
• If you do not have male, make sure to view
one!!
• If you do have a male, the major reproductive
organ is visible on the exterior – the TESTES
are located in the SCROTAL SAC.
• Carefully cut through the scrotal sac, and
locate the TESTICLES.
FEMALE REPRODUCTION
• Since the females are pregnant, identification of the
female organs will be difficult since we will be
removing the uterus that contain the babies.
• However, if you follow a short gray tube extending to
the URINARY BLADDER from the exterior, this is the
VAGINA. Following this up, the vagina divides into two
UTERINE HORNS.
• This duplex uterus is found in mammals that can
accommodate multiple embryos (babies - litters).
• In a simple uterus, like found in humans, there is only a
single chamber allowing for development of a single
embryo (although sometimes more in twins, etc).
Describe the little rat babies – describe all the detailed features you can see:
How many were found in the pregnant females?
CHECKPOINT –
before moving on make sure to
confirm identification the reproductive
system with teacher!
**MAKE SURE TO LOOK AT MALE &
FEMALE RATS –
AND MAKE SURE TO LOOK AT BABIES
AND PLACENTAS!