Download Background:

Background:
Mammals are vertebrates having hair on their body and mammary glands to nourish
their young. They belong to a groups of recently evolved mammals called Placentals.
The placental mammals, unlike monotremes that lay eggs and marsupials that have
their young complete their development in a pouch, give birth to fully formed offspring.
In many cases thier young are able begin taking care of themselves just hours after being
born.
The developing young, or fetus, of a placental mammal grows inside the female's uterus
while attached to a membrane called the placenta. The placenta provides a place where
fetal blood and maternal blood can come very close to each other and allow diffusion of
nutrients into the fetuses blood and wastes out of the fetuses blood. (Maternal and Fetus
blood does not mix). The placenta will be the source of food and oxygen for the fetus and
the means by which waste will be removed the entire time it remains inside the mother.
The dissection of the fetal pig in the laboratory is important because pigs and humans
have a very similar internal anatomy. Pigs are so similar to us that pig tissue, such as
heart valves, have often been used to treat disease in humans. The goal of this lab is for
you to become more familiar with your anatomy and physiology. Knowing more about
your anatomy and physiology can help you become a participant in your own health
management. This can increase your chances of having good health and decrease the
probability of being misdiagnosed when seeking medical attention from a health
professional.
Objectives:
* Identify important external structures of the fetal pig.
* Identify major structures associated with a fetal pig's digestive, respiratory, circulatory,
excretory, endocrine, and reproductive systems.
* Compare the functions of certain organs in a fetal mammal with those of an adult
mammal.
Clean up:
Clean up your materials and work area after each day. Wrap the pig in damp paper towels
and put it in the plastic bag. Obtain a piece of masking tape and label your bag with your
names. Store your fetal pig in the box it came from. Leave your lab bench cleaner and/or
more organized than it was then when you came into the class.
Part A - External Anatomy
1. Obtain a fetal pig and rinse off the excess preservative by holding it under running
water. Lay the pig on its side in the dissecting pan and locate dorsal, ventral, anterior,
posterior, & lateral surfaces.
2. A fetal pig has not been born yet, but its approximate age since conception can be
estimated by measuring its length. Measure your pig's length from the tip of its snout to
the base of its tail and record this on your data sheet (number 1 on data sheet). Use the
length/age chart on the data sheet to determine the age of your fetal pig & record this
(number 2 on the data sheet).
3. Examine the pig's head. Locate the eyelids and the external ears or pinnae. Find the
external nostrils (nares). Label these parts on figure 1, external fetal pig diagram.
Examine the exterior of the fetal pig for hair. Describe what was found (number 3 on data
sheet).
4. Study the pig's appendages and examine the pig's toes. Count and record the number of
toes and the number of hooves the pig has on one appendage (number 4 on data sheet).
Label the toes and hooves on figure 1, external fetal pig diagram.
5. Locate the umbilical cord. With scissors, cut across the cord about 1 cm from the body.
Examine the 3 openings in the umbilical cord. The largest is the umbilical vein, which
carries blood from the placenta to the fetus. The two smaller openings are the umbilical
arteries which carry blood from the fetus to the placenta. Label the umbilical cord on
figure 1, external fetal pig diagram.
6. Lift the pig's tail to find the anus. Anterior from the anus along the ventral surface of
the pig study and note the tiny bumps called mammary papillary. These are present in
both sexes. Count the number of mammary papillary and record it on the data sheet
(number 5 on the data sheet). In the female these structures connect to the mammary
glands and will be used to nurse theri young. Label both of these structures on figure 1,
external fetal pig diagram.
7. Determine the sex of your pig by locating the urogenital opening through which liquid
wastes and reproductive cells pass. In the male, the opening is on the ventral surface of
the pig just posterior to the umbilical cord. In the female, the opening is ventral to the
anus and reveals a a small structure called the Genital papilla. Record the sex of your
pig (number 6 on the data sheet).
8. With scissors, make a 3-cm incision in each corner of the pig's mouth. Your incision
should extend posteriorly through the jaw. Spread the jaw open and examine the tongue.
9. Observe the palate on the roof of the mouth. The anterior part of the palate is the hard
palate, while the posterior part is the soft palate.
10. Locate the epiglottis, a cone-shaped structure at the back of the mouth. What is the
function of this structure (number 7)?
11. Dorsal to the glottis, find the opening to the esophagus. Examine the tongue and note
tiny projections called sensory papillae. What is the function of these structures (number
8)?
12. Examine the teeth of the pig. Canine teeth are longer for tearing food, while incisor
are shorter and used for biting. Pigs are omnivores, eating plants and animals. Draw a
picture of the canines and incisors on the data sheet (number 9).
Part B: The Incision
1. Place the fetal pig ventral side up in the dissecting tray.
2. Tie a string securely around a front limb. Run the string under the tray, pull it tight, and
tie it to the other front limb. Repeat this procedure with the hind limbs to hold the legs
apart so you can examine internal structures.
3. Study the diagram at the left. The
lines numbered 1-4 show the first set
of incisions that you will make. To
find the exact location for the incision
marked 3, press along the thorax with
your fingers to find the lower edge of
the ribs. This is where you will make
incision 3.
4. With scissors, make the incisions
in order, beginning with 1. It will be
necessary to cut through the rib cage
but while doing so be sure to keep the
tips of your scissors pointed upward
because a deep cut will destroy the
organs below. Also, remember to cut
away from yourself.
5. After you have made your
incisions through the body wall, you
will see the peritoneum, a thin layer
of tissue that lines the body cavity. If
no internal organs are clearly visible
you did not cut deep enough and the
peritoneum is still in tact. Cut through
the peritoneum along the incision lines. What is the function of the peritoneum?
6. Spread the flaps of the body wall apart. Look carefully for the umbilical vein and
notice that it is directly connected to a large brownish red organ (possibly blue if the
umbilical vein popped and leaked blue latex). This is the liver. Blood returning from the
placenta goes first to the fetal liver so that excess nutrients can be stored and then placed
into the blood stream during those times when the mother has not eaten. Cut the umbilical
vein, which extends to the liver.