LABORATORY 7
VERTEBRATE CHORDATES
Dissection
of the Fetal Pig
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PREVIEW: Fetal Pig Dissection Video in the LRC before coming to lab.
In
this laboratory you will perform the dissection of the fetal pig, Sus scrofa. The fetal pig is representative of
mammals. Though you may not initially
feel that you have much in common with Sus scrofa, you share kingdom, phylum, and subphylum
with this organism. You will compare
this organism and its internal structure with another chordate vertebrate that
you dissected last week – the amphibian, Rana catesbiana.
The pig, like the frog,
is a tetrapod or a quadrupedal
vertebrate. Though there are many
differences, a great deal of the knowledge gained from the study of the fetal
pig is applicable to the human body. As
you work this week on the pig, think actively about similarities and
differences with your own body and with the lower vertebrate that you examined
last week.
There are two methods
employed when dissecting an entire animal.
The first is called a body system
approach. In this type of dissection
the animal is examined one system at a time.
There are some basic disadvantages involved with this method. Perhaps the main disadvantage is that as you
examine one system of the specimen, you destroy the next and have little
to examine or review later.
The second method is a body region approach. Here, each region -- head/neck, thorax,
abdomen, etc. - is dissected and all the structures in that region
identified. This allows the examiner to
view the anatomical relationships between all the organs in a region. It is important during such a dissection that
any structure which crosses from one region to the next be noted so that the
continuity of the structure can be observed.
The body region approach is
used in this exercise.
Since you will watch the
video on Fetal Pig Dissection before coming to class, you will be well
prepared for this dissection laboratory. Your instructor will give some general
directions and guiding advice. Use the
color photographs and pictures in your Atlas on pages 200-204 for comparison. You will not dissect the brain or spinal cord
and, since the muscles of the fetal pig are poorly developed at best, the muscular system
will not be studied in this laboratory. (Recall the several frog muscles that
you are to recognize and identify. Be
thankful that you are not
required to name the 650 striated skeletal voluntary muscles in
the human body.)
" PROCEDURE
1. Obtain a fetal pig and dissecting pan. Secure the pig in the dissecting pan with the
ventral surface up. You may use cotton
cord to tie the limbs and secure the pig as you did the frog last week..
2. Make
a midline incision through the skin and underlying muscles from the chin to the
umbilicus. Be careful not to cut through
the underlying organs.
3. Make transverse incisions at the throat and
about one-inch above the umbilicus. This
should be about the level of the diaphragm. Once the body cavity is open, sharp
dissection is usually not necessary. If
you will use blunt dissection technique you will salvage many more
structures. If the cavity contains
fluid, take your specimen to the sink, rinse it out, and drain the specimen
before continuing.
4. Open
the neck area and identify the following organs and vessels:
- common
carotid arteries -thymus
- internal
jugular -external
jugular vein
- submandibular
gland -esophagus
- trachea -
thyroid gland
- larynx -
right and left subclavian arteries
-
brachiocephalic artery
5. Open
the thorax and identify the following organs and vessels:
- anterior vena
cava - diaphragm
- posterior
vena cava - heart
- pulmonary
trunk - lungs
- right
pulmonary artery - left
pulmonary artery
- right
pulmonary veins - left
pulmonary vein
- aorta -
esophagus
- arotic
arch -
dorsal aorta
- trachea - primary
bronchi
- ductus
arterious -
coronary veins and arteries
6. The
technique for dissection of the abdominopelvic region
depends upon the sex of the specimen.
Make sure that you observe both sexes during the course of this
lab. You will see both again next week on your lab exam.
Male: -
Make two incisions angled from the umbilicus to the medial thigh.
-
This flap is now peeled back and the scrotal area dissected:
1) Locate
the inguial canal by tracing the vas deferens and
testicular artery to where they dive into the deep tissues.
2) Then
insert a blunt probe into the canal and enlarge the opening with a scalpel or
scissors.
3) The
contents of the scrotum can then be gently pulled out.
Female:
1) Continue the midline incision on either side of the
umbilicus all the way to the tail. 2)
Cut through the pubis symphysis.
7. Identify the following structures in the abdominopelvic area:
- peritoneum - kidney - liver
- renal artery - renal vein - testes
- gall bladder - ureter - epididymis
- urinary
bladder - ductus
deferens - urethra
- spleen - abdominal aorta - vagina
- femoral
artery - stomach - ovary
- duodenum - pancreas - horns of uterus
- large
intestine - small intestine - hepatic portal vein
- rectum -hepatic vein - umbilical artery
- inguinal
canal
& TERMINOLOGY
abdominopelvic cavity - ventral body
cavity caudal to the diaphragm
anterior vena cava - large vein
which drains structures anterior to the heart; equivalent to the superior vena
cava in humans; empties into the right atrium
aorta
- largest artery in the body; carries oxygenated blood out of the left
ventricle of the heart
aortic arch - the arch shaped
portion of the aorta as it curves posteriorly to
descend through the thoracic and abdominal cavities
body of the uterus - large, central portion of the uterus
brachiocephalic trunk - large branch
from the aortic arch divides into the common carotids and the right subclavian arteries in the pig; somewhat equivalent to the brachiocephalic artery in humans
common bile duct - formed where
the cystic duct and the hepatic duct join; empties into the duodenum; carries
bile to the duodenum
common carotid artery
- main blood supply to the head; in pigs both right and left arise from the brachiocephalic trunk; in humans the right common carotid
branches from the brachiocephalic artery and the left
from the aortic arch
common iliac artery
- terminal branches of the abdominal aorta
cystic duct - duct which carries
bile to and from the gall bladder
diaphragm
- muscular partition between the thoracic and abdominal cavity
dorsal aorta - that portion of the aorta found in the abdominal
region
ductus arteriosus
- direct connection between pulmonary trunk and the aorta; found only in fetal specimens
duodenum - first ( most proximal )
part of the small intestine ( bowel )
epididymis
- coiled tube which sits atop the testis from which arises the ductus deferens
esophagus
- muscular tube which carries food from mouth to stomach
gall bladder - muscular sac
found under the anterior edge of the liver; stores and concentrates bile;
receives and empties its contents via the cystic duct
heart
- pump for the circulatory system
horns of the uterus
- enlarged Y - shaped portion of the uterus in a pig; allows for litters with
many offspring
inguinal canal - opening through
which the spermatic cord passes from inside the abdominopelvic
cavity into the scrotum
internal & external jugular veins
- large veins which drain the head
kidney
- functional organ of the urinary system
large intestine -
distal part of the alimentary canal; in the pig it is usually found on the left
side of the abdomen
larynx
- cartilage reinforced entrance into the trachea; routes food into the
esophagus and air into the trachea
liver
- large brown organ in the right side of the abdomen in a pig; found in the
right upper quadrant of the abdomen in a human
lung
- functional organs of the respiratory system; found in the thoracic cavity
ovary
- female gonads; found in the pelvic area in a pig
ovarian artery - blood supply to
the ovary; branch from the abdominal aorta
pancreas - organ found just dorsal
to the stomach in a pig; gland with both endocrine and exocrine functions
peritoneum
- membrane which surrounds the abdominopelvic organs
and lines the abdominal wall
posterior vena cava - large vein
which drains structures posterior to the heart; equivalent to the inferior vena
cava in humans; empties into the right atrium
primary bronchi - terminal
branches of the trachea; air supply to each lung
pulmonary trunk - large artery
from the right ventricle which bifurcates into the pulmonary arteries and supplies the lungs
rectum -
distal part of the large bowel, just proximal to the anal canal
renal artery & vein
- blood supply and drainage for the kidney
small intestine - section of the
alimentary canal between the stomach and the large bowel; three sections- duodenum, jejunum, &
ileum
spleen
- moderately sized brown organ on the left side of the abdomen in a pig; found in the left upper quadrant in humans
stomach
- part of the alimentary canal between the esophagus and the small bowel; found slightly to the left and just
caudal to the diaphragm in the abdominal cavity of a pig
submandibular gland - one of three
pairs of salivary glands; found just under the mandible
testes
- male gonad; found within the scrotal sac
descending aorta - portion of the
aorta from the aortic arch distally to the diaphragm
thymus
- juvenile organ found in the ventral neck and cephalic portion of the thoracic
cavity
thyroid gland - small pea-sized
organ in the ventral neck just posterior to the larynx in a pig
trachea
- cartilage reinforced tube which carries air from the larynx to the primary
bronchi
umbilicus
- point where blood leaves and enters the fetal pig after going to the
placenta; there are large vessels which join the aorta and the posterior vena
cava from the umbilicus; these close after birth
ureters
- tubes which carry urine from kidneys to the bladder
urethra
- tube carrying urine from the bladder to the outside
urinary bladder - large ventrally
located sac which holds urine before excretion
vagina
- external entrance to the female reproductive tract
vas deferens - duct carrying
sperm from testes to prostate gland
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LABORATORY REPORT
· Identify
the specimen by genus and species, phylum, subphylum, and kingdom.
· Identify
the lab partners with whom you performed the dissection.
· Think
carefully about the systems and list those systems that are “nonfunctional” in
the fetal pig.
· You
have looked at components of several systems including the digestive,
circulatory, excretory, and reproductive.
Although you observed the components using the regional approach, it is
now time to group the organs that you observed by systems. List each structure listed for identification
under column headings: digestive system, circulatory system,
etc.
· As
you did last in last week’s laboratory report, record your insights about this
descriptive and exploratory laboratory exercise. How did you feel about lab?
· How
could this laboratory be improved? What
would make this laboratory more meaningful?
· For
practice in identification, label the following diagrams of the dissected pig.
A I Q
B J R
C K S
D L T
E M U
F N V
G O W
H P
A I Q
B J R
C K S
D L T
E M U
F N V
G O W
H P
$ LABORATORY EXAM II NEXT WEEK
You
should be prepared to:
1. Identify
animal tissues from microscope slides, atlas micrographs, or line drawings.
2. Identify
specialized structures of animal tissue and provide the function of each.
3. Identify
important structures and their functions that are associated with a given
tissue.
4. Identify
external features, organs, vessels within the dissected frog or frog models.
5. Compare
and contrast the skeleton of a frog and human.
6. Identify
organs and vessels within the dissected fetal pig or pig models.