Download Lab Exercise 10

Fetal Pig Dissection
Introduction:
A fetal pig has not been born yet. The specimens that we use in this biology class were salvaged from
pregnant sow being slaughtered for food. After removal, the fetal pigs were embalmed with a
preservative. They are not raised specifically for dissection purposes. If it was not for the intervention of
certain biological needs, these fetal pigs would have been discarded.
There is an appropriate reason why we study the anatomy (structures) of the fetal pig. In comparison
to many other laboratory mammals, that are studied, the pig’s anatomy is very similar to that of a
human. This is why many of drugs that are used by humans were previously tested on pigs. Humans
and pigs both belong to the same class; however, they only differ in classification.. The classification
that both the human and pig belong to are; Kingdom Animalia, Phylum Chordata, Subphylum
Vertebrata, and Class Mammalia. Mammals are vertebrates having hair on their body and mammary
glands to nourish their young The difference between pigs and humans is that pigs are classified in the
order Artiodactyla and humans are grouped with the order Primates. If we examine a mammal before
it is fully developed we get to see how it adapts, survives, and thrives in the uterus before birth.
Objectives:
Upon completion of this exercise, you should be able to:
1.
2.
3.
4.
5.
Define and use specific reference terms of location and positions.
Describe the major cavities, their subdivisions, their boundaries, and the
organs contained in each.
Become familiar with the major internal organs of the fetal pig.
Describe which organs belong to a specific system.
Define all the terms that are bolded and underlined.
Terms of Location and position: (Figures 10.1)
The scientific terms in Table 10.1 will allow you to describe the relative position of organs to each other
in an animal. When you study this table you will notice that each scientific term has an opposite term.
Scientific Term
Scientific Meaning
Superior
above or toward the upper surface or back
Inferior
below or toward the lower surface
Anterior
nearer the front side or head
Posterior
nearer the back side or tail
Medial
in toward the midline
Scientific Term
Scientific Meaning
Lateral
out to the side, away from the midline
Cranial (head)
in front or toward the head
Caudal (tail)
in back or toward the tail
Ventral
nearer or toward the belly
Dorsal
nearer or toward the back
Table 10.1 of Location and position
Figures 10.1 Anatomical Positions of Fetal Pig
External Features of Fetal Pig: (Figures 10.2)
The head is located at the anterior side of the body. It is connected to the torso by the neck and has many
of the same features for its face as humans do.
Following parts are located on the head:
The snout of the pig has a blunt tip, ending with a disc-like, flexible but firm structure composed of
cartilage. The tip of the nose is also strengthened by bone. This permits the pig to use the snout to push,
lift weights and dig.
External nostrils are opening in the cartilaginous disc of the snout. They open into the nasal cavity.
Here the inhaled air is warmed, filtered and humidified.
Pinnae are the external ears. They are also composed of cartilage, just as the human ear. The externalauditory meatus is the opening for the external auditory canal which leads to the tympanic membrane
(eardrum), and to the middle ear.
Eyes located on the head that are used for seeing and sensing light.
Mouth is the beginning of digestive tract where chewing occurs and where saliva mixes with the food.
Teeth tear and chew food to help break it down. Teeth in the fetal pig may not be visible. Tongue
manipulates food for chewing and swallowing; a taste organ.
Following parts are located on the trunk: Umbilical Cord -This structure, identifies the animal as a
fetus. It extends from the mid-ventral abdominal surface to the placenta. It functions in the procurement
of food and oxygen for the fetus from the mother, and the movement of wastes from fetus to mother.
Anus -This is the terminal opening of the digestive tract for eliminating solid waste from the body of the
pig. It is located just ventral to the base of the tail in both males and females. Simply lift the tail to find
the anus.
The pig has four legs, two front legs with elbows, wrists and toes. Then two back legs with knees,
ankles, and toes. Forelimbs and hind limbs helps with walking and balance.
Figures 10.2 External Features of Fetal Pig
Anatomical Features of Fetal Pig:
To study the internal structure of the fetal pig you must expose the ventral side of the pig by pinning
back each of the pig’s legs. (figure 10.4).
Figure 10.4 – Pinning the legs to expose the ventral side of the pig
Using figure 10.5, make incision with the scissors to expose the various organs of an animal for study.
Figure 10.5 Making the incisions lines, to study the internal Structure of the Fetal Pig
Oral Cavity: The tongue often protrudes from the anterior opening of the oral cavity. The tongue is a
highly manipulative, muscular structure that contributes to chewing, swallowing, and sensing food.
Chemical sensation occurs at sensory papillae, visible on the tongue. Taste cells within buds of the
papillae. The two nares (commonly called nostrils) allow air into the nasal cavity for olfactory
sensation and respiration. Palates - the hard palate makes up the anterior part of the roof of the mouth
and soft palate is at the posterior. Visible here are the beginning of the teeth.
The pharynx is the region encompassing the base of the tongue and the junction of the passageways for
food (esophagus) and air (trachea). The epiglottis, small flap of tissue at rear of pharynx, covers the
opening to the trachea during swallowing to prevent food entry into the trachea. The respiratory
system is an organ system that removes carbon dioxide from the blood and replaces it with
oxygen. This is done by alveoli within the lungs. During inspiration, fresh air enters the respiratory
system through the paired external nares (nostrils) and the oral cavity to the pharynx. The function of
the larynx is to move air from the pharynx to the trachea. It is part of the respiratory tract. The larynx
also contains the vocal cords and voice box. Air then travels into the trachea (windpipe), then through
the bronchi and bronchioles reach the alveoli. During expiration, air flows in the opposite direction.
(Figure 10.6)
Figure 10.6 Wind pipe and food pipe
Thoracic cavity (Figures 10.7 and b): The thoracic cavity is protected by the rib cage and contains the lungs
and heart. Lungs, encapsulated by a pleural membrane and heart encased in its transparent pericardial
membrane. Lungs have multiple lobes and are found on either side of the heart. Gently push the heart to the
side to see the shiny white tube, esophagus traveling down behind it. This carries food from the mouth
to the stomach. The diaphragm is a sheet-like muscle that separates the thoracic cavity from the
abdominal cavity.
Abdominal cavity (Figures 10.7): It is dominated by the liver (large, brown organ at anterior of cavity)
and the intestine.
The liver is the large black/brown multi-lobed organ at the top of the abdominal cavity. It secretes bile,
Bile flows into the gall bladder (imbedded in the underside of the liver lobe) for short-term storage. The
bile is then released into the duodenum (anterior section of the small intestine) via a duct. Bile serves
as an emulsifier of fats to increase fat breakdown.
The Stomach is located on the right side, tucked under the liver. The spleen is found along the left
external margin of the stomach. It is an immune system organ that fights infection and also breaks
down expired red blood cells. Pancreas produces hormones -- insulin and glucagon -- that control the
level of glucose in the blood. Enzymes from pancreas exit through pancreatic duct and enter the
duodenum of the small intestine
Small intestine is a large mass of coiled tube where digestion of food and absorption of nutrients
occurs. The large intestine (the colon is one region of it) is responsible for the absorption of water and
vitamins. The rectum is the distal-most section of the large intestine. Undigested materials as feces exit
through Anus.
The digestive system is a continuous canal from the mouth to the anus. It is the path where the nutrient
materials we intake travel and eventually turns into solid waste.
The urinary System controls the composition of the blood, while forming and eliminating liquid
wastes. Most of the action in this system takes place in two fairly large organs called the kidneys. They
are large bean-shaped structure (one on each side) located behind the abdominal organs. The function of
kidney is to maintain water balance, filter blood and produce urine. Each kidney empties its urine into its
ureter.
There are three major components that make-up the cardiovascular system. The first we will discuss is
the blood, which flows within the tubes or vessels (arteries, veins, capillaries) of the circulatory system.
The functions of blood are transportation of gases and nutrient, regulation, and protection. The second
focus is on the heart (large pump), which is a mass of cardiac muscle and other muscular tissues. The
force for the bloods movement, through out the body, is supplied by contractions of the heart. The next
focus will be on the blood vessels, which forms a closed circuit of tubes that allows blood to be
transported to and from the cells of the body.
The function of the respiratory system is gas exchange (intake and elimination of gases). The
respiratory system is intertwined with the cardiovascular system. Cells continuously need oxygen for
metabolism and need to remove carbon dioxide to prevent rapid cell death.