Download Lab Exercise 10

Class Set
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 the 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 a few taxonomic categories. 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. 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 anatomical reference terms indicating location and position of structures.
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 organ system.
Define all the terms that are bolded and underlined.
Anatomical Terms: (Figures 10.1)
The anatomical terms in Table 10.1 will allow you to describe the relative position of organs to each other in the
specimen. When you study this table you will notice that each anatomical term has an opposite term.
Anatomical Term
Definition/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
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
Figure 10.1 Anatomical Positions of Fetal Pig
External Features of Fetal Pig: (Figure 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.
Structures located on the Head Region:
1. 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.
2. 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.
3. Pinnae are the external ears. They are also composed of cartilage, just as the human ear. The external-auditory
meatus is the opening for the external auditory canal which leads to the tympanic membrane (eardrum), and to the
middle ear.
4. Eyes are used for seeing and sensing light.
5. Mouth is the beginning of digestive tract where chewing occurs and where saliva mixes with the food.
6. Teeth tear and chew food to help break it down.
7. Tongue manipulates food for chewing and swallowing; a taste organ.
Structures located on the Trunk Region:
8. Umbilical Cord 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.
9. Anus 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.
10. Legs, which there are four, including 2 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
Determining the Gender of the Pig (Figures 10.3)
Males do not have a urogenital papilla (view the caudal region). In the male, the urogenital tract opens near the
umbilical cord. In the female, both the urogenital tract and the digestive tract exit at the anal region. Only the
female has a urogenital papilla; it is located near the anus
Male: Urogenital opening
Female: Genital papilla
Figures 10.3 Determining the Gender
Internal Anatomical Structures:
To study the internal structure of the fetal pig you must expose the ventral side of the pig by tying a string around
one of the pig's forelegs. Pass the string under your dissecting pan and tie it to the other foreleg. Stretch the string
tightly so that it will hold the pig's legs apart. Repeat with the back leg (figure 10.4).
Figure 10.4 - Tying a string to expose the ventral side of the pig
Use forceps to lift the skin under the chin. With the scissors follow the line pattern shown in Figure 10.5 and
make incisions to expose the various organs for study.
Figure 10.5 Incision line patterns to study the internal Structures
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 sheetlike 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.
Larynx
Trachea
Thoracic
cavity
Heart
Lung
Diaphragm
muscle
Stomach
Liver
Spleen
Colon
Pancreas
Kidney
Small intestine
Figure 10.7a - Labeled Organs
Abdominopelvic
cavity
Larynx
Trachea
Thoracic
cavity
Heart
Left lung
Right lung
Diaphragm muscle
Liver
Stomach
Spleen
Pancreas
Figure 10.7b - Enlarged Labeled Organs