Transcript Slide 1

Fetal Pig Dissection
Virtual Pig Dissection
• http://www.whitman.edu/offices_departme
nts/biology/vpd/main.html
• Go through each of the study guides and
take the quizzes.
The heart (1) lies in the middle of the thoracic cavity,
surrounded by a membrane called the pericardium. If you
have damaged the pericardium beyond recognition, look at
someone else's pig. By the time you are done the
dissection, all the pericardia will have been removed.
The top of the heart will be covered with the thymus gland,
which extends up into the throat. Much of the thymus has
been removed from the pig pictured here.
On either side of the heart are the lungs (2). Note that the left
lung is smaller. You will have cut the diaphragm (3), but it
can still be seen, as can its attachment to the body wall.
The large liver (4) may vary from reddish brown to blue. The
former is its natural color, but blue latex often fills its
numerous blood spaces. Just behind the liver on the left
side, the stomach (5) can be seen, and the spleen (6) raps
around the left side of the liver. The spleen is very delicate
and may break when you try to separate it. It is not
surprising that ruptured spleens are one of the most
common types of internal injury.
The large umbilical vein (7) can be seen entering the liver. You
had to cut this vein during the initial incisions. Its other end
can be seen on the flap carrying the umbilical cord.
The intestines of a pig are arranged somewhat differently from
those of a human. The pinkish colored jejunum (8) is seen
on the top right, the greener ileum (9) at the lower centre,
and the coiled up colon (10) at the top left.
The urinary bladder (11) folds back with the umbilical cord, and
is surrounded by the two large umbilical arteries (12). These
arteries take blood from the fetus to the placenta, where it
picks up nutrients and oxygen from the mother's blood, and
loses waste products of the fetus's metabolism.
•
By pushing the liver (1) up toward
the head, you will be able to view
many of the organs of the digestive
system.
•
The gall bladder (2) is usually quite
evident as a sort of blister on the
third lobe of the liver. The next page
looks at it more closely.
•
The stomach (3) is easily identified
as a large floppy pouch under the
left lobe of the liver. The duodenum
(4) arches away from the stomach
to the pig's right. A deep crease
indicates the location of the pyloric
sphincter (5). If you probe this area,
you will be able to detect the strong
muscular nature of this sphincter.
The spleen (6) lies just below the
stomach, and is attached to it by a
thin membrane. You may have to
break this membrane to see deeper
structures.
•
The three major parts of the
intestine, the jejunum (7), the ileum
(8) and the colon (9) are still visible
.
The gall bladder (1) is a soft
sack embedded in the liver. In
this view, with the liver turned
back, you can just make out
the attached ducts, the cystic
duct (2) which drains the gall
bladder, the hepatic duct (3)
which carries bile from the
liver to the gall bladder, and
the common bile duct (4)
which carries the bile from
both organs to the duodenum
(5). A person can live without
the gall bladder, because the
liver can drain bile directly into
the duodenum, but a special
restricted diet is required,
since bile cannot be stored up
for a large fatty meal.
•
The pancreas can be
viewed by pulling the
bottom of the stomach
up toward the head. It
will be necessary to
break some of the
membranes holding the
stomach and spleen in
place. Use a blunt
probe for this.
•
The pancreas (P) is a
long, loosely organized
gland, that has often
been described as
looking like a "bunch of
grapes". If you look
carefully, you may be
able to find the
pancreatic duct, which
goes behind the
duodenum (D) and joins
the common bile duct
before it enters the
duodenum.
The jejunum (1) appears pinky
in most fetal pigs. Remember
that the fetus is not swallowing
anything except a bit of
amniotic fluid, so there is little
in the intestine. The liver is
secreting some bile. By the
time the intestinal juices get to
the ileum (2) some of the water
has been absorbed and the
bile is more concentrated. This
makes the ileum look greenish.
The ileum ends where the
small intestine meets the colon
(3) a a "T" junction. The other
end of the "T" (4) is the
caecum. Note that the caecum
is large compared to the
human appendix, but small
compared to the pig's horselike relatives. The pig is
descended from herbivores
whose caecum was
undoubtedly vital for digesting
cellulose, but, like ourselves, it
has become an omnivore and
gets little if any nutrition from
cellulose.
•
The intestines are held in place by
a pair of membranes called the
mesenteries (1). The mesenteric
arteries run between these parallel
membranes, and give rise to a
vast number of tiny arteries (2)
that take blood to the jejunum and
ileum. These in turn break up into
the thousands of arterioles that
supply the villi and help to absorb
food.
•
Near the base of the mesenteries
is a row of white, fatty-looking
bumps. These are lymph nodes
on the lymph ducts that drain the
lacteals. Since you take so much
foreign material into your gut, it
makes sense that you should
have a strong line of defense
against any invading
microorganisms that might escape
the digestive processes.
• Close up…
•
•
•
•
•
•
To open the thoracic (chest) cavity, you will have to
cut through the cartilage of the breast bone, and the
collar bones. Try not to damage the underlying
blood vessels as you do.
When you first open the chest cavity, your view will
be dominated by the heart (1) and lungs (2,3).
Usually, the right lung (2) will be larger than the left
(3), though that is not obvious in the view shown
here. Each lung consists of several lobes.
The heart may be covered (or partly covered) by a
transparent membrane, the pericardium, seen here
almost intact. The chances are, you will have
destroyed much of it while opening the chest.
Feel the inside of the rib cage and the surface of the
lungs with a gloved finger. They are very smooth
and slippery, due to the presence of thin, moist
membranes, the pleura. The pleura allow the lungs
to slide across the walls of the thoracic cavity with
almost no friction during inhalation and exhalation.
Note the diaphragm (5) between the lungs and the
liver. Remember that you cut the attachments of the
diaphragm to the body wall during the initial cuts. If
you have a small pig, the diaphragm may look like a
translucent membrane with muscle fibers just
beginning to grow into it from the edges. If your pig
is older, it will be a definite layer of muscle, as
shown here.
Covering the top of the heart is part of the thymus
(6), an important component of the fetal immune
system. thymus tissue extends well up into the
throat, and must be carefully picked away to see
other features of the cervical region. The prominent
thyroid, an endocrine gland, is visible as a brick red
or slightly purplish round mass.
•
•
•
The view shown here is one that you
will not have, since it required
removal of the heart. You will need
the heart in place for the next part of
the dissection. By moving it around
and looking behind it, however, you
should be able to see many of the
features shown here, and perhaps to
understand them in context a bit
better.
The cavity in which the heart sat is
seen between the two lungs (1). The
muscles, glands and membranes
have been peeled away from the
front of the trachea (2) which clearly
shows the rings of cartilage that
keep it open. The trachea branches
into several main bronchi (3), of
which three are visible here.
The stumps of pulmonary arteries
and veins are also visible (4). Note
that the color of these vessels is not
a reliable guide to their identity; you
would be better to note whether they
attach to the left atrium (veins) or the
right ventricle (arteries).
•
•
•
•
By cutting through the sides of the
jaw, you can open the mouth wide
enough to view the structures at
the back. The ridged hard palate
(1) is one of the most obvious
features, grading into the soft
palate (3) of the pharynx. Small
"milk teeth" (2) are already
erupted in the mouth.
The large and muscular tongue (4)
has been pulled forward and down
in this picture. Papillae, which
contain the taste buds, are visible,
especially along the edge.
At the back of the tongue is the
epiglottis (5) which fits into an
opening from the nasopharynx (6),
allowing direct passage of air from
the nose to the trachea. During
swallowing, the epiglottis is pulled
down to cover the entrance to the
trachea, allowing food to pass
over it to the esophagus.
Depending on the position of your
cut, you may be able to see the
maxillary salivary glands (7).
• In this view, the tongue has
been pulled far forward and
down, causing the epiglottis (1)
to pull out of the nasophrynx
(4). The opening to the larynx
and trachea is clearly visible,
as is one of the cartilaginous
vocal cords (2) that stretch
across it. Vibrating vocal cords
and the resonance of the
larynx beneath them create
sounds. Just behind the
opening of the larynx is the
opening of the esophagus (3)
•
Externally, the differences between male and
female fetal pigs are small. There is no external
penis in the male, and the scrotum is not well
developed until sexual maturity. In females, the
entrance to the vagina is hidden beneath the
tail.
•
The two specimens in this view show the small
abdominal differences. The male (bottom)
clearly shows the genital pore just behind the
umbilical
cord. This is the opening through which the
erect penis will be everted for mating.
•
Running back from the genital pore along the
midline of the abdomen, a faint white line is
visible. This is the internal penis.
•
Slight development of the scrotum is visible
between the legs. This is much clearer in the
rear view, accessible by clicking at the end of
this text.
•
In the female (top) there is a lack of the above
features. The main external feature is the
genital papilla, a triangular flap of tissue that
covers the opening of the urogenital tract. It is
found just ventral to the anus, beneath the tail.
• Back views
•
This close up view shows the primary
reproductive organs of the female. The
ovaries (1) are small kidney-shaped
organs. They usually cover the fallopian
tubes (2) which just show below the right
ovary (left side!) in this view.
•
In this view, showing the top end of the
ovary (1), one can see the fallopian tube
(2) terminating in the funnel-shaped
funiculum (3). Note that the funiculum lies
right next to the ovary, but is not attached.
It must capture eggs released directly into
the body cavity. Both the ovary and the
fallopian tube are attached to the back
wall of the abdomen by a strong ligament
(4).
The fallopian tubes bring ova to the
uterine horns (3) which join in the midline
to form the uterine body (4). The uterus is
thus "Y-shaped". This allows for the
attachment of placentas for a whole litter
of young pigs along the uterine horns. The
ovary and uterus are held in place by the
broad ligament (5), which later in life will
have to bear most of the weight during
pregnancy
•
The bladder (1), lies between
the two umbilical arteries (2).
In this view it is pulled over to
the pig's right side. The left
ureter (3), which drains urine
from the kidney, can be seen
entering the bladder
•
The ovary (4) lies just
posterior to the kidney (not
visible in this view). The
uterine horns (5) pass over
the umbilical arteries and the
ureters, and join to form the
uterine body (or common
uterus)(6)
•
In this view, the pelvic canal
has been dissected. The
birth canal consists of the
uterine body and the vagina
(7). Urine leaves the body via
the urethra (8). Note that,
unlike in humans, the vagina
and urethra join to form a
short urogenital sinus (9)
before reaching the outside.
•
Close up…
The testis (1) is clearly visible as
a smooth oval body inside the
scrotum. The top end of the
epididymis (2) is visible. The
epididymis consists of thousands
of tiny tubes that collect mature
sperm from the tiny cavities in the
testis and store them until
ejaculation.
The left vas deferens (3) can be
seen ascending through the
inguinal canal and passing over
the umbilical artery. it will carry
sperm to the urethra. The gonadal
artery and vein run parallel to it, as
do very sensitive nerves (not
visible). Any blockage of the
inguinal canal can cause sterility,
pain, and varicose veins in the
scrotum. The most common
blockage is due to an inguinal
hernia, in which a small bulge of
the intestine is forced into the
canal.
Also visible in this view is the
penis (4)
•
This view of the male abdomen, with the
intestines held out of the way, shows some
features common to both sexes. A tough
membrane, still intact on the pig's left side,
separates the urinary organs from the
digestive ones. This membrane has been
removed on the pig's right side (your left) to
show the kidney (1), which extracts
nitrogen and other waste from the blood.
The kidneys are drained by the ureters (2)
which carry urine to the urinary bladder (3)
for storage.
•
In this view, the bladder has been pulled
back. In the intact animal, it would lie in
front of the rectum. Note the umbilical
arteries on either side of the bladder. After
birth, these will atrophy and become
ligaments connecting the aorta and the
front wall of the abdomen.
•
Little of the reproductive system can be
seen in the abdomen. The testes, which
originated in the abdomen, have been
pulled down into the scrotum through the
inguinal canal (5). All that can be seen are
the vasa deferentia (sing. vas deferns),
which emerge from the inguinal canal, pass
over the ureters and umbilical arteries, and
enter the urethra (not clearly visible) just
after it leaves the bladder.
•
By dissecting through the pelvic
bones, one can see the deeper
structures of the male tract. The
urethra (2) drains the urinary bladder
(1) and enters the penis (3), allowing
urine to be moved out of the body.
The urethra appears very thick at "2"
because it is surrounded by strong
muscles which control urinary flow
and also contract during ejaculation.
•
The left testis and epididymis are
dissected out of the scrotum (6). The
gubernaculum (7) has contracted to
pull the testis into the scrotum.
•
Sperm travel from the testis to the
epididymis, which loops beneath the
testis an meets the vas deferens (8).
The vas runs through the inguinal
canal, over the umbilical artery and
ureter, and joins the urethra just
below the bladder.
•
Two sets of seminal glands can be
seen attached to the urethra, the
seminal vesicles (9) and the
bulbourethral gland (10). These add
nutritive and protective fluids to the
semen as it passes on its way to the
penis
Quiz….
• Identify the labeled parts and also identify
the system each view represents.
Answers
•
•
•
•
•
•
•
•
•
•
•
•
•
•
Set 1
A - stomach
B - pancreas
C - large intestine
D - small intestine
E - digestive
Set 2
A - Uterine Horn (Fallopian Tube)
B - Ovary
C - Vagina
D - Urogenital or Reproductive
Set 3
A - penis
B - epididymus
C - teste
Set 4
A - larynx
B - trachea
C - bronchial tube
D - lung
E - respiratory
Set 5
A - kidney
B - ureter
C - bladder
D - Urogenital (Excretory)
Set 6
A - hard palate
B - epiglottis
C - tongue
Set 7
A - carotid arteries
B - Aorta
C - circulatory
• Identify the artery labled #1 in
the picture
Your answer:
a. conus arteriosus
b. umbilical artery
c. abdominal aorta
d. femoral artery
• Identify the artery labeled #2 in
the picture.
Your answer:
a. pulmonary artery
b. abdominal aorta
c. renal artery
d. external iliac
• Identify the artery labeled #3 in
the picture.
Your answer:
a. renal artery
b. subclavian artery
c. femoral artery
d. external iliac
• Identify the arteries labeled #4 in
the picture.
Your answer:
a. coronary arteries
b. pulmonary arteries
c. carotid arteries
d. subclavian arteries
• Identify the artery labeled #5 in
the picture.
Your answer:
a. common carotid
b. left subclavian artery
c. right subclavian artery
d. ductus arteriosis
• Identify the artery labeled #6 in
the picture.
Your answer:
a. left carotid artery
b. left subclavian artery
c. right subclavian artery
d. aorta
•
Identify the organ labeled #7 in the
picture.
Your answer:
liver
spleen
pancreas
stomach
•
Identify the organ labeled #8 in the
picture.
Your answer:
liver
large intestine
small intestine
pancreas
•
Identify the organ labeled #9 in the
picture.
Your answer:
small intestine
rectum
stomach
large intestine
•
Identify the organ labeled #10 in the
picture.
Your answer:
large intestine
stomach
pancreas
heart
• Identify the artery labeled
#11 in the picture.
Your answer:
abdominal aorta
renal artery
carotid artery
femoral artery
• Identify the organ labeled
#12 in the picture.
Your answer:
rectum
pancreas
kidney
liver
• Identify the vein labeled #13
in the picture.
Your answer:
renal vein
femoral artery
internal iliac artery
abdominal aorta
• Identify the organs
labeled #14 in the
picture.
Your answer:
liver
kidneys
lungs
intestines
• Identify the organ
labeled #15 in the
picture.
Your answer:
heart
spleen
stomach
lung