Pig Dissection

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Pig Dissection
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• http//faculty.clintoncc.suny.edu/faculty/Michael.
  Gregory/files/Bio20102/Bio2010220Laboratory/Fet
  al20Pig/Fetal20Pig.htm

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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.

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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.

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1. Anterior - near or toward the head
2. Posterior - near or toward the tail
3. Dorsal - referring to the back
4. Ventral - referring to the belly
5. Lateral - referring to the side
6. Median - referring to the midline
7. Cranial - referring to the head
8. Caudal - referring to the tail
9. Proximal - toward the attached end of a structure
   
10. Distal - toward the free end of a structure
11. Longitudinal - in the axis from head to tail
12. Transverse - across the longitudinal axis
13. Pectoral - chest or shoulder area
14. Pelvic - hip region
15. Inferior- toward or closer to the tail (caudal
    region)
16. Superior- toward or closer to the head region

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• Page Pig Book Use color on every page!
  Points
• 1 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
• 3 External anatomy Diagram of head, neck,
  trunk, tail. 29 LabelThorax, Abdomen, Sacral
  What is inside and out of these sections? How
  can you tell male from female?
  color5pts
• 4 Internal Anatomy Diagram with parts labeled
  and umbilical cord drawing
• 5 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
•  6 Respiratory System Purpose, flow of air,
  structures and functions. Diagram of inspiration
  and expiration
•  7 Digestive System Purpose, path of food,
  structures and functions
•  8 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 pigs body
• 9 Reproductive System Purpose, structures and
  functions Female structures and how do they
  work. Male and how do they work
• 10 Nervous System Purpose, How is it broken
  into parts?
•  
•  

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Anterior - near or toward the head
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Posterior - near or toward the tail or back
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Dorsal - referring to the back
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Ventral - referring to the belly
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Lateral - referring to the side
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Median - referring to the midline
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Cranial - referring to the head Caudal -
referring to the tail
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Proximal - toward the attached end of a structure
Distal - toward the free end of a structure
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Longitudinal - in the axis from head to tail
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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.

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Pectoral - chest or shoulder area
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Pelvic - hip region
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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.

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sagittal section

• The sagittal section, or plane, divides the
  subject into left and right portions.

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Mid-sagittal

• The mid-sagittal section splits the subject
  exactly into left and right sides.

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transverse

• A transverse plane, also known as an axial plane
  or cross-section, divides the body into cranial
  and caudal (head and tail) portions.

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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.

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left and right

• stated relative to the subject, not relative to
  the people viewing it

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anterior (cranial)

• towards the front (head) of the animal

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posterior (caudal)

• towards the back (tail) of the animal

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superior

• higher on the subject- typically used on bipeds
  such humans

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inferior

• lower on subject- also used on subjects such as
  humans

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dorsal

• towards the back

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Ventral

• towards the belly

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medial

• towards the mid-sagittal section

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lateral

• away from the mid-sagittal section

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proximal

• towards the mid-sagittal section along a limb

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distal

• away from the mid-sagittal section along a limb

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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.

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Pig Book
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• 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?

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• 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 pigs 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?

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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.

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• 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.

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• 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.

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• 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.

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Page 2

1. Anterior - near or toward the head
2. Posterior - near or toward the tail
3. Dorsal - referring to the back
4. Ventral - referring to the belly
5. Lateral - referring to the side
6. Median - referring to the midline
7. Cranial - referring to the head
8. Caudal - referring to the tail
9. Proximal - toward the attached end of a structure
   
10. Distal - toward the free end of a structure
11. Longitudinal - in the axis from head to tail
12. Transverse - across the longitudinal axis
13. Pectoral - chest or shoulder area
14. Pelvic - hip region
15. Inferior- toward or closer to the tail (caudal
    region)
16. Superior- toward or closer to the head region

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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.

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• 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 well-developed neck muscles that
  will eventually be used for rooting.

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• 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.

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• 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.

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• 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.

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Page 3
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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.

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• 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.

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1. 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.
2. 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.

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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.

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1. 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.

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1. 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.
2. Make a drawing of a cross-section of the
   umbilical cord showing the 4 vessels - label your
   drawing.

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• 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.

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• 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.

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mesentery
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• 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?

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• 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.

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Pancreas
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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.

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1. Cut the diaphragm away from the body wall on both
   sides of the pig.
2. 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.
3. 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.
4. 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.
5. 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.

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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.

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Circulatory System Page 5

• The flow of blood in the circulatory system is as
  follows
• heart--gtarteries--gtarterioles--gtcapillaries--gtvenu
  les--gtveins--gt heart

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• 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, thin- walled capillaries are
  the functional units of the circulatory system.
  The exchange of materials between blood and the
  cells takes place at the capillaries.

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• 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.

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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.

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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.

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• 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.

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• Hidden partially behind the pulmonary artery, the
  aorta is a large vessel that branches into the
  brachiocephalic(3) and the left subclavian artery
  (7)

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1. Pulmonary Artery
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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.

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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.

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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

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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.

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• 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.

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• 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.

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• 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.

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• 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.

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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.

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• 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.

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• 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.

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93
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.

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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.

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• 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.

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• 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.

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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.

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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.

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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.

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• 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.

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• 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.

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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.

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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.

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• 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.

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• 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.

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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.

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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.

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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.

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• Each student will be responsible for knowing both
  the male and female reproductive systems.

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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.

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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.

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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.

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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.

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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?

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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.

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Female reproductive organs
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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.

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• 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.

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• 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 jelly-like substance.

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• 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.

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• 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.

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• 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.
  

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