Transcript File

Pig Dissection
• http://faculty.clintoncc.suny.edu/faculty/Mic
hael.Gregory/files/Bio%20102/Bio%20102
%20Laboratory/Fetal%20Pig/Fetal%20Pig.
htm
Directional and Anatomical
Terminology
• Anatomists and morphologists rely on a
set of terms to describe structural
positions, These may not all be
immediately obvious to you, so you should
practice using them. The terms are
generally presented to you in pairs, as
terms are often used to indicate opposing
directions.
Planes of section.
• We can figuratively (or actually) section
(=cut) our subject using planes. There are
several particular planes of section that
are useful for the purposes of discussing
anatomy.
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
16.
Anterior - near or toward the head
Posterior - near or toward the tail
Dorsal - referring to the back
Ventral - referring to the belly
Lateral - referring to the side
Median - referring to the midline
Cranial - referring to the head
Caudal - referring to the tail
Proximal - toward the attached end of a structure
Distal - toward the free end of a structure
Longitudinal - in the axis from head to tail
Transverse - across the longitudinal axis
Pectoral - chest or shoulder area
Pelvic - hip region
Inferior- toward or closer to the tail (caudal region)
Superior- toward or closer to the head region
Page Pig Book Use color on every page!
1
2
3
4
5
6
7
8
9
10
Points
Title Page Names of authors (max of 2)
10
Be creative, use color and make it fun!!!
Basic Anatomical terms
37
Diagram showing 16 terms from the lab color 5pts
External anatomy: Diagram of head, neck, trunk, tail. 29 Label=Thorax, Abdomen, Sacral What is
inside and out of these sections? How can you tell male from female?
color=5pts
Internal Anatomy Diagram with parts labeled and umbilical cord drawing
Circulatory System: Purpose, flow of blood, structures/functions, diagrams of arteries and veins X
section, Heart diagram, path of blood flow,
color coded Red = oxygenated Blue= deoxygenated
Respiratory System: Purpose, flow of air, structures and functions. Diagram of inspiration and
expiration
Digestive System: Purpose, path of food, structures and functions
Excretory System: Purpose, organs of excretion. Diagram of a cross section of the
kidney. Path of flow of nitrogen waste as it is formed and removed from the pig’s body
Reproductive System: Purpose, structures and functions Female: structures and how do they
work. Male and how do they work
Nervous System: Purpose, How is it broken into parts?
Anterior - near or toward the head
Posterior - near or toward the tail
or back
Dorsal - referring to the back
Ventral - referring to the belly
Lateral - referring to the side
Median - referring to the midline
Cranial - referring to the head
Caudal - referring to the tail
Proximal toward the
attached end of
a structure
Distal - toward
the free end of a
structure
Longitudinal - in the axis from
head to tail
Transverse - across the
longitudinal axis
• is an imaginary plane that divides the body
into superior and inferior parts. It is
perpendicular to the coronal and sagittal
planes.
Pectoral - chest or shoulder area
Pelvic - hip region
Inferior- toward or closer to the tail
(caudal region)
Superior- toward or closer to the
head region
• As with vertebrate directional terms, superior
and inferior can be used in a relative sense in
humans, but can not be uniformly applied to
other organisms with varying normal anatomical
positions. For example, the shoulders are
superior to the navel, but inferior to the eyes in
humans. In any tetrapod, the shoulders are
cranial to the belly, but caudal to the eyes.
sagittal section
• The sagittal section, or plane, divides the
subject into left and right portions.
Mid-sagittal
• The mid-sagittal section splits the subject
exactly into left and right sides.
transverse
• A transverse plane, also known as an
axial plane or cross-section, divides the
body into cranial and caudal (head and
tail) portions.
Directional Terms:
• Anatomists rely on a set of directional
terms to explain the orientation of subject
material. Although some of the terms are
unfamiliar, with practice they will become
easier to use, and you will see that
“proximal to” is lesser cumbersome than
“up the extremity and closer to the middle
of the body.”
left and right
• stated relative to the subject, not relative
to the people viewing it
anterior (cranial)
• towards the front (head) of the animal
posterior (caudal)
• towards the back (tail) of the animal
superior
• higher on the subject- typically used on
bipeds such humans
inferior
• lower on subject- also used on subjects
such as humans
dorsal
• towards the back
Ventral
• towards the belly
medial
• towards the mid-sagittal section
lateral
• away from the mid-sagittal section
proximal
• towards the mid-sagittal section along a
limb
distal
• away from the mid-sagittal section along a
limb
External Anatomy
• The body consists of the following regions:
head, neck, trunk, and tail. The 2 pairs of
appendages present on the trunk are the
fore legs and hind legs. The cord
projecting from the ventral surface is the
umbilical cord. This cord connects the fetal
pig to the placenta within the uterus of the
mother pig.
Pig Book
1Title Page
Names of authors (max of 2) Be
creative, use color and make it fun!!!
2Basic Anatomical terms Diagram showing 16 terms
from the lab
3External anatomy: Diagram of head, neck, trunk,
tail. Thorax (what is inside?) Abdomen (what is
inside?) Sacral (what is here?) How can you tell
male from female?
4Internal Anatomy Diagram with parts labeled and umbilical cord
drawing
5Circulatory System: Purpose, flow of blood, structures/functions,
diagrams of arteries and veins X section, Heart diagram, path of
blood flow, color coded Red = oxygenated Blue=
deoxygenated
6Respiratory System: Purpose, flow of air, structures and functions.
Diagram of inspiration and expiration
7Digestive System: Purpose, path of food, structures and functions
8Excretory System: Purpose, organs of excretion. Diagram of a
cross section of the kidney. Path of follow of nitrogen waste as it
is formed and removed from the pig’s body.
9Reproductive System: Purpose, structures and functions
Female: structures and how do they work.
Male and how do they work
10Nervous System: Purpose, How is it broken into parts?
Fetal Pig Dissection
• Objectives: Upon completion of this lab
students should
• Be able to identify, and know the names
and functions major structures of the fetal
pig's external anatomy.
• Be able to identify, and know the names
and functions of the major structures of the
fetal pig's internal gross anatomy.
• The fetal pigs that we will use in lab
were purchased from a Biological
supply company. They obtain fetal pigs
from processing plants - the unborn pigs
are removed from the uteri of
slaughtered sows.
• The period of pregnancy (gestation) in pigs
is about 17 weeks (compared to 40 weeks
in humans).
• The fetal pigs we will use in class are 3-4
weeks from birth. You will work in groups on
the fetal pigs. Each group of students will
be given a fetal pig to be used for the labs
on pig dissection.
• Attach a tag with your names (in pencil) to
one of the hind legs for future identification.
• Note the slit in the skin in the neck region of
the pig. (ours were not injected)
• This is the area where the circulatory
system of the pig was injected with latex
(red latex in the arterial system, blue latex
in the venous system) to make it easier to
see and trace the blood vessels.
Page 2
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
16.
Anterior - near or toward the head
Posterior - near or toward the tail
Dorsal - referring to the back
Ventral - referring to the belly
Lateral - referring to the side
Median - referring to the midline
Cranial - referring to the head
Caudal - referring to the tail
Proximal - toward the attached end of a structure
Distal - toward the free end of a structure
Longitudinal - in the axis from head to tail
Transverse - across the longitudinal axis
Pectoral - chest or shoulder area
Pelvic - hip region
Inferior- toward or closer to the tail (caudal region)
Superior- toward or closer to the head region
External Anatomy
• Page 3 draw a diagram of the main parts
• Place the pig on its side in the pan and note
that the body consists of the following regions:
• head, neck, trunk, and tail.
• The 2 pairs of appendages present on the trunk
are the fore legs and hind legs. The cord
projecting from the ventral surface is the
umbilical cord.
• This cord connects the fetal pig to the placenta
within the uterus of the mother pig.
• The head bears the mouth and jaws, the
snout (nose), the external nostrils (nares),
the eyes, and the external ears. Feel the
relatively thick neck in the fetal pig. This
thickness is due to the presence of welldeveloped neck muscles that will
eventually be used for rooting.
• The cranial portion of the trunk is called the
thorax (chest) and is encased by the ribs. Feel
the ribs under the skin and determine the
posterior border of the thorax. The thorax
contains the lungs, heart, and major blood
vessels.
• The fore legs are found in the thoracic region.
The parts of each of these appendages as well
as those of the hind legs (in the sacral region) are
the upper leg, lower leg, wrist, foot, and toes
(digits).
• Examine the digits present on the legs and note
that only 2 of the 5 digits found in most terrestrial
vertebrates are present. The first toe
(corresponding to our thumb) has been lost; the
second and fifth toes are reduced, with only the
third and fourth toes being fully developed.
• The caudal portion of the trunk is called the
abdomen.
• In contrast to the thorax, the ventral portion
of the abdomen is soft. The umbilical cord
is located near the posterior end of the
abdomen. There are 2 rows of teats
(mammary papillae), one on either side of
the umbilical cord. The stomach, intestine,
kidneys, and other viscera (soft internal
organs) are found within the abdominal
cavity.
• The sacral region includes the hind legs,
pelvic bones, and their attachment to that
area of the vertebral column.
• The anus (posterior opening of the digestive
tract) is located under the tail.
• In female pigs, the vulva (openings of the
reproductive and urinary tracts) is found just
below the anus.
• In male pigs, the external opening of the
penis is located posterior to the umbilical
cord. The scrotum (scrotal sacs) are found
on either side of the midline of the anus.
Page 3
Internal Anatomy
Page 4
• For the dissection of the fetal pig you will need
string, a scissors, a sharp scalpel, a blunt probe, a
forceps, and dissecting pins.
• The definition of dissecting is to separate the body
into parts for the purpose of study. This means
that your scissors and scalpel should be used
sparingly and with care. The most useful
dissecting instrument is a blunt probe, which can
be used to separate organs from membranes.
1.
2.
3.
Place the pig on its dorsal surface in the dissecting pan.
Tie a string around one fore leg and passing the string
under the pan tie the other end to the other fore leg. The
string should be tied tight enough to spread the forelegs
apart.
Tie a string in the same fashion to the hind legs. Do not
remove the string from the appendages at the end of the
lab; simply slip the strings out from under the pan at the
end of each lab period.
Mark a line on the skin with a permanent marker from the
tip of the lower jaw to a point 12 millimeters (mm), (about
2 inch), in front of the umbilical cord. Divide the line
around the umbilical cord and mark a pair of parallel lines
about 12 mm apart back to the posterior boundary of the
abdominal wall. Make sure that you understand where to
draw these lines - if you are not sure ask the lab
instructor.
4.
5.
Examination of the Skin: Use your scalpel to cut
through the skin and into the underlying connective
tissue along the line extending from in front of the
umbilical cord to the tip of the jaw. Recall that the
dermis of the skin is a dense connective tissue, while
the subcutaneous layer is a loose connective tissue.
Use your probe to separate the thick layer of skin
(epidermis and dermis) from the underlying loose
connective tissue for about 25 mm (1 inch) on one side
of the incision in the region posterior to the fore legs.
Use your scissors to cut out a piece of skin about an
inch square from that area.
Examine the skin and note its leathery texture. The skin
of pigs contains a large number of hair follicles, which
will only appear as whitish lines in the skin of your fetal
pig. Examine the slide of skin when you are finished
with the gross dissection of the fetal pig in this lab.
ABDOMINAL REGION
1. In order to open the body cavity, use your
scissors to cut completely through the body
wall beginning just in front of the umbilical
cord (follow the line cut previously). As you cut
anteriorly you will cut through the sternum
(breastbone) - keep the tip of your scissors up
so that you do not damage the underlying
structures.
2. Next, use your scissors to make the parallel
posterior cuts through the body wall.
3.
Umbilical Structures: A cord will be seen in the abdominal
cavity extending anteriorly from the umbilical cord. This cord
is the umbilical vein, which carries fetal blood from the
placenta to the liver. Cut this vein about half way between
the liver and the umbilical cord. Keep the position of this
vein in mind as it will be traced later. Pull the flap of the
body wall containing the umbilical cord posteriorly to expose
the underside of the flap. On the underside note the 3 cords
entering the body cavity by way of the umbilical cord. The
lateral pair are the umbilical arteries which carry fetal
blood to the placenta. The large sac in the center is the
urinary bladder. The duct extending from the urinary
bladder into the umbilical cord is the allantoic duct. This
duct carries nitrogenous wastes from the bladder to the
placenta. The fetus receives oxygen and food from the
mother by way of the placental circulation and gives up
carbon dioxide and nitrogenous wastes.
4. Cut off about 12 mm of the umbilical cord in
order to observe in cross-section the 3 blood
vessels and the allantoic duct. The blood
vessels in the umbilical cord consist of 2
umbilical arteries (may show red latex) with
relatively thick walls and an umbilical vein
with a thinner wall. A fourth small vessel, the
allantoic duct, is from the urinary bladder.
5. Make a drawing of a cross-section of the
umbilical cord showing the 4 vessels label your drawing.
6. Make a pair of lateral incisions through the body
wall on each side in front of the hind legs (see
figure one) to expose the abdominal cavity.
Wash out the abdominal cavity with tap water to
remove the coagulated blood present. When
examining the viscera (soft internal organs) with
your fingers be careful not to tear any of the
structures. The body cavity (coelom) in which
the thoracic and abdominal organs are located is
completely lined with an epithelial layer called
the peritoneum.
Organs are also covered with a layer of peritoneum.
This layer of epithelium is derived from the
mesoderm germ layer. A double layer of
peritoneum is called a mesentery. Mesenteries
serve to suspend and hold structures together in
the coelom.
•
•
Once you have opened the abdomen and washed
out the cavity and locate the organs listed in the
paragraphs below.
The most obvious structure in the abdominal cavity
is the liver. The liver is composed of 5 lobes which
are attached only at the dorsal and anterior
margins. Posterior to the liver are the small
intestine and the thicker coiled large intestine
(colon). The small and large intestines are
suspended from the mid-dorsal body wall by a
mesentery. Blood vessels and nerves are found
between the two layers of peritoneum making up
the mesentery. Carefully lift and push the small
intestine forward and find where the posterior part
of the small intestine enters the large intestine.
mesentery
• Put the intestines back in their normal positions and
lift the liver forward to see the soft, white-walled
stomach anterior to the intestines. The dark-colored
spleen is located along its left posterior border and
attached to the stomach by peritonium.
• A light-colored granular structure, the pancreas, is
found in the mesentery between the stomach and
the first portion of the small intestine. The gall
bladder may be seen by lifting up the extreme right
lobe of the liver. It appears as a small upside down
sac under the lobe. The duct from the gall bladder,
the bile duct, opens into the duodenum (first
portion of the small intestine). The pancreatic duct
also opens into the duodenum at about the same
location as the bile duct. Is it possible to find and
trace the path of these ducts in your fetal pig?
• Behind the peritoneal lining of the dorsal
part of the abdominal cavity are the
relatively large kidneys. Cut the
peritoneum along the lateral border of the
left kidney and pull it off toward the midline.
• Locate the muscular diaphragm, which
separates the abdominal and thoracic
cavities. The diaphragm is thin in the
center but thicker at the periphery.
Pancreas
THORACIC REGION
• In order to see the organs in the thoracic
cavity, it is necessary to cut the
attachment of the diaphragm to the body
wall on both sides.
1.
2.
3.
4.
5.
Cut the diaphragm away from the body wall on both sides of the pig.
Force the thoracic cavity open with your fingers to expose the lungs and
heart. The lungs appear as solid bodies since they do not contain air in
the fetus. The lobes of the left and right lungs, and the heart are
surrounded by peritoneum - note the peritoneum as you force the thoracic
cavity open. This means that each organ is enclosed in a separate sac.
The sac enclosing the hearts is called the pericardial sac, and the sac
enclosing each lung is called a pleural sac.
Force the thoracic cavity open further to examine the lungs more closely.
Note that the left lung is divided into 3 lobes and the right lung into 3 lobes
plus a fourth lobe that passes ventral to a large vein and is directly
posterior to the heart.
The 2 large lobes of whitish granular tissue concealing part of the heart
and the anterior blood vessels is the thymus gland. The thymus extends
anteriorly for a short distance into the neck region. This gland is relatively
large in young animals but degenerates after sexual maturity.
The thyroid gland is a small gland located against the trachea just in front
of the thorax. This gland is brownish in color in preserved fetal pigs.
Slide of Human Skin
• The skin is composed of 2 layers; an outer, thin epidermis and
an inner, thick dermis. Examine the slide under scanning and
low power, and identify these 2 layers. Refer to the handout.
• The dermis consists of a dense connective tissue. Identify the
nuclei of the fibroblasts and the fibers in your section. Blood
vessels are present in the dermis but not in the epidermis. Can
you identify a blood vessel in your section? It is sometimes
possible to see the red blood cells within the small blood
vessels of the dermis.
• Sweat glands and hair follicles are present in the dermis and
extend up through the epidermis. Find a section through a hair
follicle and the associated sebaceous (oil) glands.
• The sebaceous glands and follicles are derived from the
epidermis. The subcutaneous layer is under the dermis.
This is a loose connective tissue containing many fat cells.
Identify the fat cells in your section.
Circulatory System
Page 5
• The flow of blood in the circulatory system
is as follows:
• heart-->arteries-->arterioles-->capillaries->venules-->veins--> heart
• Arteries and arterioles are thick-walled
vessels that carry blood away from the heart,
whereas veins and venules are relatively
thin-walled vessels that carry blood toward
the heart. Arterioles subdivide in the various
tissues of the body to ultimately form
capillaries. Capillaries eventually come
together to form venules. The small, thinwalled capillaries are the functional units
of the circulatory system. The exchange of
materials between blood and the cells takes
place at the capillaries.
• Blood transports oxygen from the lungs to the
body tissues and returns carbon dioxide to
the lungs. The right auricle and the right
ventricle are involved in transporting blood to
the lungs (pulmonary circulation) and the left
auricle and left ventricle are involved in
transporting blood to the body tissues
(systemic circulation). In other words, the
right side of the heart pumps deoxygenated
blood to the lungs and the left side of the
heart receives oxygenated blood from the
lungs and pumps it to the body tissues.
• Examine the demonstration slide of an artery
and vein sometime during the lab period.
A. Examination of the Heart
• Locate a pair of thickened white strands, which are
present on either side of the pericardial sac. These
are the phrenic nerves. Tease these nerves away
from the pericardium and observe their distribution to
the diaphragm.
• Remove the pericardial sac from around the heart be careful to not cut blood vessels or nerves in the
process. Note that the pericardial membrane is
strongly attached where the blood vessels enter and
leave the heart. Identify the 4 chambers of the heart:
the thin-walled right atrium (auricle), the thin-walled
left atrium (auricle), the thick-walled right ventricle
and the thick-walled left ventricle. Note the coronary
artery and the coronary vein which are present in the
diagonal groove between the 2 ventricles.
1. Major Arteries and Veins Heart
• Veins
• Several veins from the head, neck, shoulders and fore
legs join to form the superior vena cava (anterior vena
cava, precava), which enters the anterior portion of the
right atrium. These veins are located ventral to the
arteries supplying the same regions, but the veins are
thin-walled and more difficult to trace. Pressing on the
auricle with your fingers will force fluid into the veins and
may help in tracing them. The muscles extending from
the sternum to the larynx and head may have to be
removed in order to expose the veins.
• The inferior vena cava (posterior vena
cava, postcava) enters the posterior portion
of the right atrium. Find where this vein
penetrates the center of the diaphragm,
passes through a groove in the small
median lobe of the lung, and into the right
atrium (it may be necessary to lift up the
posterior portion of the heart). This vein
returns all the blood from the posterior part
of the body to the heart.
• Hidden partially
behind the
pulmonary artery,
the aorta is a large
vessel that
branches into the
brachiocephalic(3)
and the left
subclavian artery
(7)
1. Pulmonary Artery
Arteries
• Two large arterial trunks leave the ventricles
anteriorly. The most ventral trunk is the
pulmonary trunk, which transport blood directly
to the lungs. This artery will be traced later. The
other trunk, the aortic arch, gives off 2 main
arteries, which send branches to the fore legs,
shoulder, neck, and head regions. Lift the left
lung to trace the aortic arch dorsally. It turns
posteriorly and runs along the dorsal midline as
the dorsal aorta and eventually delivers blood to
the entire posterior part of the body.
Other Closely Associated
Structures
• Ventral to the dorsal aorta is a thick, white tube,
the esophagus, which leads from the pharynx
through the diaphragm and into the stomach.
Along the esophagus run 2 main branches of the
vagus nerve. The vagus nerves innervate the
thoracic and abdominal viscera. Another pair of
nerve cords, bearing a series of small swelling
along their course, may be seen behind the
peritoneum dorsal and lateral to the aorta on
either side. These are the main trunks of the
sympathetic nervous system.
B. Systemic Circulation
• You will identify the main branches of the
systemic arteries and veins, including the
hepatic portal system. This will be done in
order to understand where the major
organs obtain their blood supply and
where the blood goes after leaving them
Systemic Arteries -Diagram
• The brachiocephalic artery (innominate) is the
first major artery branching off the aortic arch.
Find this artery, which branches to give rise first to
the right subclavian artery and then to the right
and left common carotid arteries. The carotids
carry all blood going to the head region. In the
head they branch into the external carotids, which
supply the face, and the internal carotids, which
supply the skull cavity and brain (we will not trace
these arteries). The second major artery to arise
from the aortic arch is the left subclavian artery note that the left subclavian artery arises directly
from the aortic arch.
• Separate one of the nerve cords which run
parallel to the common carotids in a
common sheath. The nerves are the main
trunks of the vagus nerve and sympathetic
nervous system. These were seen before
as separate nerves in the thoracic region.
Trace the nerves on one side to the point
where they separate.
• The dorsal aorta gives off a series of small
segmental arteries dorsally between the ribs,
and one or more small arteries ventrally to the
esophagus. In order to trace the aorta into the
abdominal cavity, cut directly through the
diaphragm to the aorta. At the point where the
aorta penetrates the diaphragm, the celiac artery
arises from the aorta sending branches to the
spleen, pancreas, stomach, and liver. The
anterior mesenteric artery branches from the
aorta and is found posterior to the celiac artery.
The anterior mesenteric artery sends branches to
the small intestine and the coiled portion of the
large intestine.
• Dissect the left kidney free from the dorsal
body wall and turn it to the right to expose
more of the dorsal aorta. Locate the renal
artery. Put the kidney back in its original
position and continue to explore the aorta
posteriorly. If your fetal pig is a female, be
careful not to damage the ovaries, oviduct,
and uterus during the upcoming exercises.
These structures are suspended by
mesenteries within the posterior region of
the abdominal cavity.
• The posterior mesenteric artery (inferior
mesenteric) runs ventrally from the aorta to the
colon. A pair of genital arteries arise laterally to
supply the reproductive organs. A pair of
relatively large iliac arteries arise next and
extend laterally to the hind legs. Slightly posterior
to these, locate the umbilical arteries which
supply blood to the bladder and placenta. After
birth the umbilical arteries degenerate into a pair
of small vessels supplying only the urinary
bladder. The most posterior extension of the
aorta, the tiny caudal artery, will be seen when
the reproductive system is examined.
Systemic Veins • Dorsal to the iliac arteries are the iliac
veins which unite to form the postcava.
As the postcava runs anteriorly it receives
the segmental veins from the body,
genital veins from the reproductive
structures, and renal veins from the
kidneys. Note that the postcava turns to
the right around the dorsal aorta and
comes to lie almost ventral to it at the level
of the renal veins.
• From this point on the postcava is not easily
followed since it is embedded dorsally in the
extreme right lobe of the liver. Turn the intestines
and liver to the left, and scrape the liver tissue
away from the point where the postcava enters
the liver to the point where it penetrates the
diaphragm. In the anterior part of the liver, it
receives several hepatic veins - at least one from
each lobe - and also a small connection from the
umbilical vein. This connection, which is difficult
to find in the liver tissue, is lost after birth. The
umbilical vein distributes itself to the lobes of the
liver, where it is continuous with parts of the
hepatic portal vein.
• The hepatic portal vein begins in capillaries in
the small and large intestines, and ends in
capillaries in the liver. The liver capillaries collect
into the hepatic vein already mentioned. Find the
hepatic portal vein as it leaves the center coil of
the large intestine dorsally. It soon receives a
large branch from the small intestine, and later a
smaller one from the spleen, pancreas, and
stomach. Shortly thereafter, the hepatic portal is
joined by the umbilical vein and branches into the
lobes of the liver. The entrance of the postcava
and precava into the right atrium has already
been observed.
C. Heart and Pulmonary
Circulation
• Removal of the Heart
• If removal and dissection of the heart is done properly, the
heart will retain its normal shape and the observations given
below can be repeated. Keep the heart in the plastic bag with
your fetal pig for review.
• Determine where the precava enters the right atrium and
cut this vein. Lift the heart forward to find the postcava and
cut this vein about 12 mm from the atrium. Find the
pulmonary veins from the left lung and trace their entry into
the left atrium. Cut the pulmonary veins, which will expose
the left pulmonary artery. Cut the left pulmonary artery at
the surface of the lung. The aorta and its branches are now
the only remaining vessels attached to the heart. Cut the
brachiocephalic (innominate) and left subclavian arteries
between the aorta and their first branches. Cut the aortic arch
about 25 mm beyond the left subclavian artery, and remove
the heart from the body.
Flow of Blood through the Heart
• This next part should be done with a
sheep heart, if available. If no sheep
hearts are available, make sure you
know the main structures that reside in
the heart as well as the flow of blood
through the heart.
• Find the roots of the precava and postcava. Cut
through a line connecting them to open the right
atrium. You can now look directly into the right
ventricle through the tricuspid valve, which is
usually open. Make a straight cut through the wall
of the atrium, the tricuspid valve, and the outer
muscular wall of the right ventricle. Examine the
cavity of the ventricle and the remaining flaps of
the tricuspid valve. Make another cut through the
ventral wall of the right ventricle and into the
pulmonary artery in one continuous line.
Examine the tricuspid valve from behind, and the 3
semi-lunar valves at the base of the pulmonary
artery.
• Probe into the right and left pulmonary arteries from the
pulmonary trunk. The blood passes from the arteries into the lung
capillaries which unite eventually into the pulmonary veins. Find the
entrances of the pulmonary veins into the left atrium (on either
side of the cut ends of the pulmonary arteries). Cut on a line
between the pulmonary veins, and on through the left atrium, the
same as you did through the right. Look first at the bicuspid valve,
usually closed, guarding the entrance to the left ventricle.
• Cut through the bicuspid valve and the outer wall of the left
ventricle to the tip of the heart. You must look behind the remaining
wall of the bicuspid valve to see the entrance to the aortic arch. Cut
through this valve and on out through the wall of the aorta. Note in
the base of the aorta, the 3 semi-lunar valves. Just above 2 of
these valves will be found the openings of right and left
coronary arteries, which supply blood to the tissues of the heart.
Respiratory System
Page 6
• The mammalian respiratory system takes in air
rich in oxygen (inhalation, inspiration) and
releases air rich in carbon dioxide (exhalation,
expiration). The exchange of O2 and CO2 in the
lungs is at the level of the blood capillaries and
the alveoli (air sacs). Air entering the mouth or
nostrils passes into the pharynx. The pharynx is
located at the back of the oral cavity and is the
region where the food and air passageways
cross. Air passes ventrally into the larynx and
food passes dorsally into the esophagus.
Procedure
1. To expose the pharynx insert your scalpel into the corner of the mouth and cut back
to the jaw bone on each side. This cuts the muscles that hold the jaws closed.
2. Separate the jaws by pushing down on the tongue and inspect the oral cavity and
tongue. The tongue is attached at the back of the oral cavity. Note the small,
undeveloped teeth in the upper and lower jaws. The ridged roof of the mouth is the
hard palate, which separates the oral cavity from the nasal cavities. Posterior to the
hard palate, the roof of the mouth becomes smooth and is called the soft palate.
3. Use your scissors to cut completely through the midline of the lower jaw and tongue.
This will separate the lower jaw into 2 equal halves. Separate the halves of the jaw
and examine the posterior region of the pharynx. Find the flap of tissue attached to
the ventral side of the pharynx. This is the epiglottis and serves to cover the glottis
(opening of the pharynx into the larynx) during swallowing.
4. Use your scissors to continue the mid-ventral cut into the larynx and trachea.
Determine the relationship of the larynx to the esophagus. Expose the trachea
back into the thorax as far as the right lung. Cut the trachea open for a short distance
in order to see the rings of cartilage in the tracheal wall. These rings serve to hold
the trachea open.
5. Cut the bronchial tubes (which connect the trachea to the lungs) close to the lung
and remove the right lung from the chest cavity by cutting any remaining
mesenteries. Identify at the root of the lung the cut ends of the pulmonary veins and
arteries and the bronchial tubes. Note the thickness of the wall and the diameter of
the vessels and tubes. Also, note that the median lobe of the lung, which partially
surrounds the postcava, is actually a part of the right lung.
VENTILATION
• Bronchial tubes in the lungs contain smooth
muscle, but no skeletal muscle, therefore, the
expansion and contraction of lungs during
breathing results from movement of the ribs,
diaphragm, and other muscles.
• During inspiration the thoracic cavity is expanded
by:
• Contraction of the intercostal muscles between the
ribs. Contraction of these muscles enlarges the thoracic
cavity by lifting the ribs upward and outward.
• Contraction of the muscles of the diaphragm.
Contraction of these muscles lowers the diaphragm to
enlarge the thoracic cavity. The enlargement of the
thoracic cavity results in decreased air pressure in the
lungs. Air enters the lungs from the outside to equalize
the pressure.
• During expiration the thoracic cavity returns
to normal by:
• Gravity, which pulls the ribs down when the
intercostal and diaphragm muscles relax.
• Contraction of the abdominal muscles (and
certain chest muscles other than the
intercostals), which force the diaphragm up and
the thoracic cavity down. Rapidly exhale some
air in order to feel the chest constrict and the
abdominal muscles tighten.
Digestive System
Page 7
• The mammalian digestive system is
concerned with processing and absorbing
food and water for the body. The system
begins with the mouth and ends with the
anus. Ingested food is digested and the
products are absorbed in the digestive
tract; undigested material is expelled from
the anus.
Procedure
1. Examine the region of the pharynx - locate the origin of the
esophagus and follow it posteriorly. Cut through the diaphragm
to find the point where the esophagus joins the stomach. The
sac-like stomach is a somewhat J-shaped organ. It is divided
into 2 regions; a larger cardiac region into which the
esophagus opens and a smaller pyloric region which opens
into the small intestine.
2. Note the greater curvature of the stomach and open the
stomach by cutting along this curvature. Examine the stomach
internally and note that a gross difference between the cardiac
and pyloric regions is not evident.
3. Cut through the pyloric valve and into the anterior portion of
the small intestine, the duodenum. Note the heavy muscle in
the wall of the pyloric valve; this is called the pyloric sphincter.
This sphincter controls the amount of partially digested food
passing into the small intestine from the stomach.
4. The first 50-75 mm of the small intestine is
called the duodenum. Recall that the
pancreatic duct and the bile duct empty into
the duodenum. Begin the removal of the
small intestine by carefully cutting the
mesentery holding the coils together. This
will allow a gradual unwinding of the
intestine. Estimate the length of the small
intestine in your fetal pig. The small
intestine in man is approximately 20 feet
long. The portion of the small intestine
following the duodenum is the jejunum,
which is about 2 of the length of the
intestine. The remainder of the intestine is
called the ileum.
5. Cut open a short length of the ileum and
examine the lining. Note that the lining is
folded to form macroscopic folds. The folds
are covered with numerous small finger-like
projections, which are barely visible to the
naked eye. These projection are called villi.
The folds and villi serve to greatly increase
the surface area of the intestine.
6. Locate where the small intestine unites
with the large intestine. Extending to the left
of this junction is a blindly ending pouch
(12-25 mm long), the cecum. Unravel the
large intestine and estimate the length of
this portion of the digestive tract.
Excretory System
Page 8
• Nitrogenous waste products produced by cell
metabolism are removed from the blood stream
by the kidneys. The kidneys, urinary bladder,
and associated ducts make up the excretory
system. The process of removing nitrogenous
wastes from the blood is called excretion.
Recall that blood is supplied to each kidney by a
renal artery. The blood leaves each kidney by a
renal vein.
Procedure
1. Remove the left kidney and cut it lengthwise into 2 equal halves. The kidney
will appear in gross section to be composed of 3 regions: an outer
granulated region, the cortex; a radially striated layer, the medulla; and an
inner cavity, the renal pelvis. Each kidney contains over 1 million functional
units called nephrons (renal tubules). The blind end of each nephron is
located in the cortex where it forms a cup-like structure called a Bowman's
capsule. The capsule encloses a ball of capillaries, the glomerulus. A renal
corpuscle is a glomerulus surrounded by a Bowman's capsule. The
nephrons extend through the medulla to the renal pelvis where the urine is
collected.
2. The renal pelvis empties into the urinary bladder through the ureter. The
ureter runs posteriorly to the urinary bladder. Expose this duct without
damaging the structures crossing over it. These include the umbilical
arteries and the reproductive ducts in both sexes, and the ovaries just
posterior to the kidneys in females. The bladder empties to the outside
through another duct, the urethra. This duct will be observed when the
reproductive system is dissected. In the case of the fetus, wastes are
transported via the allantoic duct to the placenta, where they are removed by
the mother's blood.
Reproductive Systems
Page 9
• The reproductive and excretory systems of
vertebrates have a close connection with one
another. In the males, the same duct transports
the sperm and urine. The male and female
reproductive organs of vertebrates have the
same embryonic origin; it is during development
that they become different in structure and
function. The male and female reproductive
systems are composed of the sex glands
(gonads) and their associated ducts and
glands.
• Each student will be responsible for
knowing both the male and female
reproductive systems.
Female Reproductive System
• The female gonads are the 2 ovaries, which are located
posterior to the kidneys. Each ovary is suspended in the
abdominal cavity by a mesentery. A small convoluted
tube, the oviduct, is located lateral to each ovary. This
tube is also called the Fallopian tube. The oviduct
continues on each side as a slightly larger tube forming
one of the 2 horns of the uterus. Pig embryos develop
in the uterine horns, which become greatly enlarged at
maturity and during pregnancy. The 2 horns of the uterus
unite to form the body of the uterus, which lies dorsal to
the urethra. In humans the fetus develops in the body of
the uterus and there are no uterine horns.
Procedure
1. In order to separate the hind legs, use your scalpel to cut through from
the ventral midline between the legs,. The cut will pass through muscles
and through the pelvic bones. Be careful when you are cutting the
pelvic bone it is easy to cut structures you need to identify. One
way to do this is to cut half way through the pelvic bone and spread the
legs apart to break the bone the rest of the way. Then use your blunt
probe to push away the muscles and other tissue. If you have any
trouble doing this ask for help from your lab instructor.
2. Three tubes will be exposed which are from ventral to dorsal - the
urethra, part of the reproductive tract, and the rectum. The urethra
and the reproductive tract unite about 12 mm before the vulva and form
a common passage, the vestibule (urogenital canal). The tube
connecting the vestibule and the body of the uterus is called the vagina.
3. Open the vestibule and vagina along one side and locate the opening of
the urethra and the constriction of the vagina at the base of the uterus.
4. Expose the rectum and open it by cutting anteriorly starting with the
anal opening. Locate the anal sphincter muscle, which is located at the
distal end of the large intestine. Find the caudal artery which is against
the spinal column and dorsal to the rectum.
Operation of the Female
Reproductive System:
• Ova develop in follicles within the ovaries. When
fully developed, the ova are released from the
follicles and enter the oviduct, where fertilization
may take place. After fertilization, cleavage of the
zygote begins and eventually the embryo
becomes implanted in the uterine horn (or uterus
in humans). The placenta is formed from uterine
tissue and from 2 extraembryonic membranes
(chorion and allantois) formed by the embryo.
Fetal development continues in the uterine horn
(uterus in humans), until birth. During birth, the
offspring pass through the uterine horn to the
body of the uterus, to the vagina, and to the
vestibule on their way out of the body.
Male Reproductive System
• The location of the male gonads, the testes, depends on
the age of the fetus. The testes begin their development
in the same location as the ovaries, but prior to birth start
to descend into the scrotal sacs (scrotum). They will be
found somewhere along this path in your fetal pig. The
sperm ducts (vas deferens) will be seen looping over
the umbilical arteries and the ureters, and then joining
together dorsal to the urinary bladder. Posteriorly, the
sperm duct pass through the abdominal wall on either
side of the midline via the inguinal canals. Identify
these structures before you complete the following
procedure.
Procedure
1. Cut through the skin of one of the scrotal sacs and extend the cut to the point find
where the sperm duct leaves the abdominal cavity. This will open the inguinal
canal and the testis will be exposed.
2. Open the sac that surrounds the testis. The convoluted tubule looping around the
testis is the epididymis, which empties into the single sperm duct.
3. Cut through the skin slightly to one side of the ventral midline to expose the slender
penis extending from the anal region to the urinary orifice. The central tube of the
penis is the urethra. This tube arises from the urinary bladder.
4. To expose the remaining structures of the reproductive system, it will be necessary
to cut through the tissues in the midline between the legs and break the pelvic bone
(refer to step 1 for the female reproductive system). The legs can be spread
apart as the cut is deepened to the level of the urethra. The urethra appears
somewhat thicker in males than in females due to the presence of accessory
glands that are closely associated with the urethra. The Bulbourethral glands,
which are about 12 mm long, are lateral to the urethra. The seminal vesicles are
located where the ductus deferans and the urethra unite.
5. Dissect the urethra and the accessory glands away from the rectum to determine
where the sperm ducts enter the urethra. The urethra transports both sperm and
urine in the male reproductive system.
6. Expose the rectum (which is located just dorsal to the urethra) and open it by
cutting anteriorly starting at the anal opening. Locate the anal sphincter muscle
which is located at the distal end of the large intestine. Is it possible to find the small
caudal artery which is located against the spinal column and dorsal to the rectum?
Operation of the Male
Reproductive System
• In the male reproductive system, sperm
(spermatozoa) are formed in the seminiferous
tubules of the testes. Sperm produced in these
tubules are stored in a connecting tubule, the
epididymis. The sperm, together with secretions
from the accessory glands (Bulbourethral
glands, seminal vesicles), form the semen.
Semen is released via the urethra in a process
called ejaculation. After the semen is deposited
in the vagina of the female, some of the sperm
eventually reach the distal end of the Fallopian
tube where fertilization of the ova may take
place.
Female reproductive organs
Nervous System
Page 10
• The nervous system is made up of the central nervous
system (brain and spinal cord) and the peripheral
nervous system (cranial, spinal, and autonomic nerves).
The nervous system can be subdivided into 2 distinct parts
based on function. One part of this system is the somatic
(voluntary) nervous system. It is under conscious control
and is composed of nerve cells of the brain, nerve cells
receiving stimuli from major sense organs, and nerve
cells that stimulate striated muscles. The other part of
the nervous system is the autonomic nervous system,
which is not under voluntary control. The autonomic
system controls activities such as digestion, excretion,
secretion, and circulation. The organs that are controlled
by this system are the heart, smooth muscles, and
glands. Activities of these organs are also influenced by
hormones.
• The autonomic nervous system is subdivided
into the sympathetic and parasympathetic
nerve systems. Both of these systems innervate
the internal organs, and the actions of these 2
systems oppose one another. In general, the
sympathetic nervous system stimulates the heart
and decreases the activity of the digestive
system and associated organs. On the other
hand, the parasympathetic system tends to
decrease heart activity and stimulate activity of
the digestive system and associated organs.
• Procedure
• First remove the remaining skin from the head and
neck of your pig and cut off the ears. Remove what
remains of the upper and lower lips.
• Turn the pig on its side with the left side up.
• Dissect away the membrane of the dorsal surface
of the lower jaw in order to see the teeth still
present in the jaw. Remove one of the teeth and
note that the cavity of the tooth is filled with a jellylike substance.
• The top and side of the skull must be
removed to see the brain. Start at the top of
the skull and carefully remove the bone, a
small piece at a time. In order to keep the
brain from being damaged, free the tough
covering of the brain from the skull bone
before it is completely broken away. The
coverings of the brain are called the
meninges. The tough outer layer is the
dura mater. The finer inner layer, which
closely follows the contours of the brain, is
the pia mater.
• Several bones of the skull will be identified at this
time. A pair of frontal bones are located
immediately between the orbits (a single bone in
man). Posterior to the frontal bones are the
parietals. The cerebrum of the brain is
underneath the frontal and parietal bones. The
cerebrum is composed of 2 cerebral
hemispheres. The nasal bones are anterior to
the frontal bones and cover the olfactory organs.
Parts of the sphenoid bone will be removed in
the region of the orbits as well as the temporal
bone, which is posterior to the orbits. The
occipital bones make up the posterior region of
the skull. It will be necessary to remove the neck
muscles to expose and remove the occipital
bones. The cerebellum and medulla regions of
the brain are located underneath the occipital
bones.
• Identify the skull bones listed above on the human
skeleton located in the room. Refer to the figure of a
human skull provided.
• Make a vertical cut in the olfactory organ after the nasal
bones have been removed. The numerous folds of
olfactory organ are covered with sensory epithelium. Cut
into one of the nasal cavities from above and follow the
cavity posteriorly to the olfactory organ and then to the
pharynx.
• Following exposure of the cerebrum, cerebellum and
medulla, cut the brain into 2 equal halves and remove
the left half. It is now possible to observe the relationship
of the brain stem (including the medulla) to the cerebrum
and cerebellum. The pituitary gland, which is located in
a small pit in the floor of the skull, may be observed
immediately in back of the optic nerves.