Fetal Pig Dissection

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Fetal Pig Dissection
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Virtual Pig Dissection

• http//www.whitman.edu/offices_departments/biology
  /vpd/main.html
• Go through each of the study guides and take the
  quizzes.

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• 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.

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• 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 .

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• 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.

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• 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.

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• 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 horse-like 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.

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• 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.

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• Close up

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• 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.

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• 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).

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• 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).

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• 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)

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• 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.

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• Back views

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• 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

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• 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.

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• Close up

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• 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)

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• 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.

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• 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

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Quiz.

• Identify the labeled parts and also identify the
  system each view represents.

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Answers

• Set 1
• A - stomachB - pancreasC - large intestineD -
  small intestineE - digestive
• Set 2
• A - Uterine Horn (Fallopian Tube)B - OvaryC -
  VaginaD - Urogenital or Reproductive
• Set 3
• A - penisB - epididymusC - teste
• Set 4
• A - larynxB - tracheaC - bronchial tubeD -
  lungE - respiratory
• Set 5
• A - kidneyB - ureterC - bladderD - Urogenital
  (Excretory)
• Set 6
• A - hard palateB - epiglottisC - tongue
• Set 7
• A - carotid arteriesB - AortaC - circulatory

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• Identify the artery labled 1 in the picture
• Your answera. conus arteriosusb. umbilical
  arteryc. abdominal aortad. femoral artery
• Identify the artery labeled 2 in the picture.
• Your answera. pulmonary arteryb. abdominal
  aortac. renal arteryd. external iliac
• Identify the artery labeled 3 in the picture.
• Your answera. renal arteryb. subclavian
  arteryc. femoral arteryd. external iliac

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• Identify the arteries labeled 4 in the picture.
• Your answera. coronary arteriesb. pulmonary
  arteriesc. carotid arteriesd. subclavian
  arteries
• Identify the artery labeled 5 in the picture.
• Your answera. common carotidb. left subclavian
  arteryc. right subclavian arteryd. ductus
  arteriosis
• Identify the artery labeled 6 in the picture.
• Your answera. left carotid arteryb. left
  subclavian arteryc. right subclavian arteryd.
  aorta

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• Identify the organ labeled 7 in the picture.
• Your answerliverspleenpancreasstomach
• Identify the organ labeled 8 in the picture.
• Your answerliverlarge intestinesmall
  intestinepancreas
• Identify the organ labeled 9 in the picture.
• Your answersmall intestinerectumstomachlarge
  intestine
• Identify the organ labeled 10 in the picture.
• Your answerlarge intestinestomachpancreashear
  t

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• Identify the artery labeled 11 in the picture.
• Your answerabdominal aortarenal arterycarotid
  arteryfemoral artery
• Identify the organ labeled 12 in the picture.
• Your answerrectumpancreaskidneyliver
• Identify the vein labeled 13 in the picture.
• Your answerrenal vein
• femoral arteryinternal iliac
  arteryabdominal aorta

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• Identify the organs labeled 14 in the picture.
• Your answerliverkidneyslungsintestines
• Identify the organ labeled 15 in the picture.
• Your answerheartspleenstomachlung

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