Biol 111 – Comparative & Human Anatomy
Lab 6: Digestive, Respiratory, and Urogenital Systems of the Cat
Spring 2014
Philip J. Bergmann
Lab Objectives
1.
2.
3.
4.
To learn the component parts of the cat digestive, respiratory, and urogenital systems.
To study how the organs are suspended in the coelomic cavity.
To gain an appreciation for the integration of the digestive and respiratory systems.
To understand how the function of the digestive organs is related to their morphology,
location, and sequence.
5. To be able to determine the sex of a cat based on external and internal anatomy.
6. To gain an appreciation for the integration of the excretory and reproductive systems and
to learn their component parts.
7. To compare the covered systems to what you see in a number of vertebrates with odd body
shapes.
Material to Learn
1. Cat digestive and respiratory system
• Figures 7.39, 7.40 (Demo), 7.42 to 7.50
• Associated text: pp. 204-220
• OMIT: Figure 7.41
• OMIT: Any labeled blood vessels, nerves in the figures or text.
• OMIT: Any nervous or osteological structures that you don't already know in Figure 7.40.
• OMIT: Any muscles that you don’t already know, but know the diaphragm.
2. Cat urogenital system
• Figures 7.68, 7.69, 7.71, 7.72
• Associated text: pp. 239-244
• OMIT: Figure 7.70
Term list
Respiratory & Digestive
Anus
Ascending colon
Cecum
Central tendon
Descending colon
Diaphragm
Duodenum
Epiglottis
Esophagus
Falciform ligament
Gall bladder
Gastrosplenic ligament
Hard palate
Ileocecal junction
Ileum
Jejunum
Laryngopharynx
Liver
• Caudate lobe
• Right lateral lobe
• Right medial lobe
• Quadrate lobe
• Left medial lobe
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• Left lateral lobe
Lung
• Anterior lobe
• Middle lobe
• Posterior lobe
• Accessory lobe
Lymph node
Mediastinum
Mesentery
Mesocolon
Mesoduodenum
Mesogaster
Biol 111 – Lab 6: Cat GI, Resp, UG
Nasopharynx
Omental bursa
Omentum
Oral cavity
Oropharynx
Palatal rugae
Palatine tonsil
Pancreas
Parietal pericardium
Parietal peritoneum
Parietal pleura
Pericardium
Rectum
Small intestine
Soft palate
Spleen
Stomach
Tongue
Trachea
Transverse colon
Visceral pericardium
Visceral peritoneum
Visceral pleura
Urogenital structures
Adrenal gland
Crus of penis
Ductus deferens
Epididymis
Infundibulum
Inguinal canal
Kidney
Labia
Mesometrium
Mesovarium
Ovary
Penis
Renal cortex
Renal medulla
Renal papilla
Renal pelvis
Scrotum
Testis
Ureter
Urethra
Urinary bladder
Urogenital opening
Urogenital sinus
Uterine tube
Uterus (horns and body)
Vagina
Vas deferens
Background & Instructions
During today’s lab you will explore the digestive, respiratory, excretory, and reproductive systems
of the cat. As in the shark, the digestive and respiratory systems are closely integrated, as are the
excretory and reproductive systems. However, pay close attention to how the systems differ and
how their integration differs. The fact that the shark does gas exchange with water and the cat
with air is extremely important. The dissections are much easier and less time consuming than
those of the muscles, but there are more structures to know in the cat than the shark. Treat the cat
as building on the material that you learned for the shark. The structures shared by both animals
are in similar places and share similar functions.
1. Dissecting instructions
1. Start anteriorly and follow the digestive system from the mouth of the cat posteriorly. Use the
demo of the sagittal section through the cat head to find the structures in Figure 7.40. Do not cut
the skull of your cat. Pay particular attention to the subdivision of the pharynx and the path that
air would travel during respiration versus the path that food would travel during feeding.
2. Since the cat has its coelom subdivided more than the shark (see below), you will need to open
its various chambers separately. Start with the thoracic cavity. On the side that you dissected the
musculature of the cat, use your finger to locate the anteriormost rib. Use the large scissors
(blunt blade in and tilted up) to cut through this rib. Continue to cut posteriorly until you arrive
at the diaphragm. Since the mediastinum runs dorsally from the sternum, you need to avoid
damaging it as you cut through the ribs. Make your cut about 1 cm off the midline.
3. Cut about 0.5 cm anterior to the diaphragm dorsolaterally to make a triangular flap, similar to
that pictured at the top of Figure 7.42 of your lab manual.
4. Repeat this process on the other side, so that you have a left and right flap. You should have a
1 cm strip of tissue running from the throat to the diaphragm midventrally that contains the intact
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Biol 111 – Lab 6: Cat GI, Resp, UG
sternum and associated blood vessels. Finally, break the ribs on each side near their articulation
with the vertebrae by bending the body wall flap dorsally. You may have to break some of the ribs
one by one because they are quite hard. A demonstration of this part of the dissection will be
given in lab.
5. This gives you access to the lungs and heart. If needed, you can cut the midventral strip of
tissue just anterior to the diaphragm to gain a better view of the lungs and heart.
6. To open the peritoneal (abdominal) cavity, simply pinch a bit of the body wall between your
fingers or with forceps just off the midline of the abdomen. Then make a small snip with scissors
through the pinch – this is an easy way to make a clean cut in without damaging organs. Now use
your large scissors to cut anteriorly to, but not through, the diaphragm, and posteriorly to the
pelvis. Now cut laterally and parallel to the diaphragm and laterally a couple centimeters
anterior to the pelvis. These cuts will make two rectangular flaps, giving easy access to the
peritoneal cavity, containing much of the digestive and excretory systems.
7. Parts of the excretory and reproductive systems are still not visible because they are obscured
by the ventral portion of the pelvis. Palpate the bump formed by the two pubis bones, where they
meet anteriorly. This is the anterior end of the pubic symphysis. Use the scalpel to shave the
muscle tissue from this bump using a frontal cut to reveal the cartilaginous pubic symphysis.
8. Use the scalpel to cut dorsally (down) through the symphysis. Continue posteriorly, until you
have cut through the entire symphysis. You will have to cut through some muscles to do this. Be
careful to cut perfectly sagittally – cutting at an angle will embed the scalpel in the bone, which is
much harder to cut. Also be careful not to cut any of the structures underneath that you want to
study.
9. Grasp the cat by the thighs, near the origin of the femora, and bend them dorsally to break the
articulation between the sacrum and the innominate bones. This will open up an area for
examination of the excretory and reproductive organs. This part of the dissection will be
demonstrated in lab.
10. The remainder of this dissection is less involved and mainly involves cleaning fascia in the
pelvic region. Clean the fascia sufficiently to clearly view all of the structures. To reveal the
testis and associated structures in a male cat, make an incision with the small scissors (or
carefully with scalpel) through the scrotum. Trace the vas deference from the testis, into the body
cavity and to the urethra.
11. Finally, to examine the internal morphology of the kidney, remove the fascia and cut through
the kidney frontally to reproduce the view in figure 7.68. Do not cut through the kidney
completely, so that it remains attached to the rest of the cat via the ureter.
12. Since the reproductive system differs between sexes, make sure that you also examine a cat of
the opposite sex of the one you are working on.
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Biol 111 – Lab 6: Cat GI, Resp, UG
2. Digestive and respiratory integration
Although the cat is terrestrial, while the shark is aquatic, integration of the respiratory and
digestive systems remains at the anterior end. Since the cat lacks gill slits and the one-way
continuous flow of water through the pharynx that they allow, coordination between these two
systems is even stronger. Amniotes in general ventilate the lungs using thoracic muscles (body
wall muscles or a diaphragm) and ventilation must be coordinated with swallowing when the
animal is eating.
How do the components of the respiratory system differ between the shark and the cat?
In the cat, which structures are shared by the digestive and respiratory systems?
What structure is used by a mammal to prevent food and water from entering the trachea?
Examine the trachea. What is the function of the cartilaginous rings that you see embedded in
its wall?
How many lobes do the cat’s lungs have? Name them.
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Biol 111 – Lab 6: Cat GI, Resp, UG
3. Body cavities of the cat
In mammals the coelom is subdivided into four cavities. The pericardial and peritoneal cavities
remain, as you saw them in the shark last week. The pleural cavities house the lungs. The left
and right pleural cavities are separated by the mediastinum, a thin connective tissue membrane
that is dorsal to the sternum and ventral to the heart. The heart and pericardium are within the
mediastinum, slightly on the left side. The pericardium is the tough connective tissue sheath
surrounding the heart. The lungs are within the pleural cavities, lined by visceral pleura, while
the lining of these cavities along the body wall is called the parietal pleura. Likewise, the heart
is lined by visceral pericardium and is located inside the pericardial cavity. The abdominal
cavity, to be opened next, is the peritoneal cavity, with the visceral peritoneum lining the
organs, or viscera, and the parietal peritoneum lining the body wall.
How many cavities is your coelom divided into? Name them.
4. Digestive system
Again, in studying the digestive system, start at its anterior end (the mouth) and trace it caudally.
The esophagus is long and narrow, similar in shape to the trachea, but collapsed, so it may look
like a solid band of muscle. In the abdominal cavity you will find the large stomach, found on the
left side. Note the connective tissue membrane containing fat and attached to the greater curvature
of the stomach and draped over the intestines. This is a modified mesogaster into what is called
the omentum. It actually forms a pouch, called the omental bursa. You can gently lift this off of
the viscera and reflect it anteriorly. You do not need to tear or snip it off. Continue following the
GI tract posteriorly, finding the structures in the lab manual. Note the large liver, taking up a
considerable portion of the peritoneal cavity, and the gall bladder. The common bile duct runs
from the gall bladder to the duodenum. Near the duodenum, you will also find the diminutive
pancreas, which is thin and lobular.
Describe the position of the esophagus relative to the trachea.
What are the three sections of the small intestine called? What order do they go in? How can
you distinguish them?
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Biol 111 – Lab 6: Cat GI, Resp, UG
Name five mesenteries? What is each one connected to?
Your cat catches and eats a mouse. Trace the path of a mouse chunk from ingestion at the
mouth to the litter box. To do this, list all of the structures that the particle passes through and
be very specific.
5. Urogenital systems and integration
As in the shark, the excretory and reproductive systems are closely integrated because of common
developmental origins. The gonads arise from embryonic tissue near the kidney. The ovaries
remain in more-or-less their original position, while the testes descend through the inguinal
canals to the scrotum. The ductus deferens (vas deferens in humans) drains the testis and runs
through the inguinal canal and then to the urethra. In females, oviducts receive mature ova from
the ovaries and allow for their passage to the uterus. The uterus is separated from the vagina by
the cervix. Both the vagina and urethra exit into the urogenital sinus. In both sexes, ureters
drain the kidneys, moving urine to the urinary bladder. From the bladder, urine is voided via the
urethra.
Why would the male testis be situated outside of the body cavity in the scrotum?
What is the name of the duct that drains the following in a mammal?
Kidney:
Testis:
Ovary:
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Biol 111 – Lab 6: Cat GI, Resp, UG
Why would fishes lack urinary bladders but many amniotes have them?
In the female cat, list all the structures that are part of the reproductive system, and divide the
list into paired and unpaired structures. Ignore mesenteries for this question.
Paired
Unpaired
Trace the path that a sperm would travel from the testis in order to fertilize an ovum in the
uterine tube of a female cat. List every structure that the sperm would travel through.
Testis Epididimys 6. Comparison to the human, snake and turtle
On demonstration is a dissection of a water snake (Nerodia sp.) and a pond turtle (Chrysemys sp.).
Both animals have considerably modified body forms that mean that their viscera need to be
organized quite differently from the animals that you have dissected. The snake has evolved to be
limbless and to have a very elongate, slender body. This means that organs must be arranged in
such a way that they fit in the elongate body cavity. Trace the digestive tract of the snake. Also
examine what you can of its urogenital system. Remember that both gonads and kidneys are
paired structures. The kidneys appear as darker, lobular structures, while the gonads are anterior
to the kidneys and more cream colored. Do not worry about finding the lung of the snake because
it is most likely destroyed. Nevertheless, the snake has a reduced left lung and the right lung has
become elongate, spanning up to a third of the snake's body length.
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Biol 111 – Lab 6: Cat GI, Resp, UG
How is the gastrointestinal tract of the snake arranged so that it can fit in the body cavity?
How about the liver and gall bladder?
How are the kidneys and gonads arranged so that they better fit in the body cavity?
The turtle has a rigid shell, meaning that it cannot distend when the animal breathes, eats a large
meal, or is gravid (=pregnant). The shape of the shell, which is relatively high/domed, also means
that the viscera must be packed in a particular way to fit. Try tracing the digestive tract of the
turtle without disturbing the viscera so that they are not damaged (the demo will be displayed so as
to allow maximal ease of viewing). Also examine the gonads.
How are the organs of the gastrointestinal tract arranged so that they fit in the body cavity?
The lungs, which you probably will not be able to see, are in a position dorsal to the other
viscera. How does this differ from where you would expect them to be?
Why do you think the lungs are where they are?
What sex is the turtle on demo? How do you know? How much of the body cavity do the
gonads take up?
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Biol 111 – Lab 6: Cat GI, Resp, UG
We also have a model of a human torso with the viscera accessible and removable. Examine the
gastrointestinal tract of the human, comparing what you see to the situation in the cat.
How does the human GI tract differ from that of the cat? (Pay particular attention to the
relative sizes of the different organs.
Why do you think that you see these differences?
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Biol 111 – Lab 6: Cat GI, Resp, UG