Fetal Pig Dissection Lab Guide

Fetal Pig Dissection Labs

• The exercise involves examining the organization of body systems in a fetal pig.
• Identify major organs as you explore each system.
• Discuss function/interactions of structures with lab partners.

Recommendations

• Carefully follow the dissection guide.
• Read description of each incision and understand it completely before beginning.
• Each group requires a directions reader and a dissector.
• The rest of the group follows along with textbook/lecture notes.
• Use scissors for most incisions.
• All students must wear gloves when handling the specimen.
• Use the scalpel only when absolutely necessary.

Clean-Up

• Dispose of lab discards in provided receptacles.
• Place the pig in the plastic bag provided.
  • Expel excess air and tie the bag shut.
  • Write group name and class time on the tag and attach to the bag.
  • Place bags in the storage bin.
• Return dissection instruments to their proper places.
• Clean table tops with red bottled sanitizer.
• Wash hands before leaving class.

Fetal Pig Lab One: External Anatomy

• Examine external features.
• Two rows of nipples/mammary glands are on ventral abdominal surface in both males and females.
  • Mammary glands develop later in maturing females.
• Umbilical cord: make transverse cut and examine the cut end to locate:
  • Two umbilical arteries that carry blood to the placenta
  • Single umbilical vein delivering nutrient-rich blood back to the fetus.
• Determine the sex:
  • Females have the urogenital opening ventral to the anus with a genital papilla.
  • Males have a scrotal sac ventral to the anus with a urogenital opening posterior to the umbilical cord.
• Dissection positioning: Ventral (belly) side up; use rubber bands to tie legs to dissecting tray.

Head and Neck Dissection

• Expose mouth/pharynx structures by cutting from the angle of the lips posteriorly.
• Cut through the cheek, guiding scissors along the tongue's curvature to avoid cutting the mouth’s roof.
• Hold down the epiglottis and surrounding tissue; continue the incision dorsally into the esophagus opening.
• Repeat procedure on the other side to expose mouth/pharynx structures when the lower jaw is pulled down.
• Teeth: Only canine/incisor teeth have erupted; others are forming as bulges in the gums. Incise a bulge to observe the tooth developing.
• Tongue: attached posteriorly/free anteriorly, locate papillae on its surface.
• Hard and Soft Palate: the roof of the mouth
  • The hard palate is formed anteriorly, supported by bone and cartilage.
  • The soft palate is formed posteriorly.
  • Paired nasal cavities lie dorsal to the roof of the mouth.
• Nasopharynx is the space posterior to nasal cavities/soft palate contiguous with the oropharynx (throat).
• Oropharynx (throat) is the space posterior to the mouth; posterior extension of nasopharynx. Can be difficult to see due to cuts on each side.

General Internal Anatomy

• Make small incision through abdominal skin/muscle ½ inch above the umbilical cord using a sharp scalpel.
• Use scissors to continue cutting along the midsagittal line on the ventral surface (Incision 1) upwards toward the neck, cutting through ribs.
• Turn the tray around and cut down to the caudal end of the pelvic region leaving a ½-inch border around the umbilical cord to avoid cutting the umbilical vein/arteries.
• Continue midsagittal cut down into pelvic region, cutting around other side of the umbilical cord (Incision 2) and leaving a ½-inch border, stopping 1 inch short of the anus.
• Cut two lateral incisions in front of hind legs (Incision 3); if male, cut off-center to avoid the penis.
• Make two lateral incisions (Incision 5) through muscle/ribs out from midline incision.
• Lift lateral flaps of ribs, skin, and muscle on each side, and cut the diaphragm, which is attached to inside body wall.
• Peel open left/right flaps of ventral body wall.
• Rinse cavities of pig, keeping organs in place.
• Loop rubber bands around legs as needed.

Thoracic Organs

• Lungs: thoracic cavity contains left and right pleural cavities, the inner thoracic wall forms the mediastinum.
• Heart: enclosed in the pericardial sac located within mediastinum and attached to the diaphragm; remove sac to expose the heart.

Fetal Pig Lab Two: Neck

• Larynx (voice box) composed of cartilage/vocal cords; the trachea extends posteriorly from the larynx.
• Trachea: splits dorsal to heart to form bronchi (visible after heart removed).
• Thymus gland: whitish, near anterior heart margin, extends into the neck either side of the trachea.
• Thyroid gland: on the anterior of the trachea at the base of the neck.
• Esophagus: remove connective tissue supporting trachea to expose esophagus dorsal to it.

Cardiovascular System

• Remove tissue to expose heart, major veins, and major arteries; separate tissues with blunt probe and forceps.
• Fetal Circulation: The placenta provides oxygen/nutrients and removes metabolic wastes. Lungs, digestive tract, and kidneys are nonfunctional.
• Identify:
  • Heart atria, ventricles, coronary vessels: carefully cut away the pericardial sac.
  • Anterior vena cava: returns blood from head, neck, forelegs to right atrium.
  • Posterior vena cava: returns blood from regions posterior to heart to right atrium.
  • Pulmonary artery (trunk): carries blood from the right ventricle.
  • Aorta: carries blood from the left ventricle.
  • Umbilical vein: carries blood rich in oxygen and nutrients from placenta to fetus.
  • Ductus venosus: segment of umbilical vein going to liver and to posterior vena cava, carries blood rich in placental and nutrients.
  • Ductus arteriosus: carries blood from pulmonary trunk to aorta (bypassing the non-functional lungs).
  • Umbilical arteries: carry waste-laden blood from the pelvic region to placenta for disposal.
• Cut through major vessels and remove the heart, leaving stubs to identify them.

Respiratory System

• Larynx: composed of cartilage/vocal cords.
• Trachea: characterized by C-shaped cartilaginous rings.
• Bronchi: The trachea branches to form two primary bronchi (visible after heart removal); dissect connective tissue as needed.
• Vocal cords: view each side by mid-central incision in larynx.
• Bronchioles: dissect along bronchus to find branching as it enters lung.

Fetal Pig Lab Three: Digestive System

• Liver
• Gallbladder
• Esophagus
• Stomach
• Duodenum
• Pancreas: begins in the loop between stomach and duodenum, near spleen: clump of pinhead-sized grapes.
• Jejunum and Ileum: the coiled remainder of the small intestine.
• Cecum: thumb-like blind pouch at the junction of the ileum and colon.
• Colon (large intestine): darker, thicker, coiled.
• Rectum: the last 1-2 inches of large intestine leading to the anus.

Fetal Pig Lab Four: Urinary System

• Adrenal glands are on the anterior surface of each kidney.
• Kidneys are against the dorsal body wall:
  • Find the ureter, renal vein, and renal artery
  • Make a frontal section and observe: kidney cortex, kidney medulla, renal pyramids, renal columns, calyces, and renal pelvis.
• Ureters originate on the medial surface of the kidney, near renal vessels.
• Urinary bladder: follow ureters posteriorly into urinary bladder.
• Urethra: begins where the urinary bladder narrows.

Fetal Pig Lab Five: Reproductive System - Male / Female

• Testes in the scrotum (external pouch): cut open to expose a testis.

• Epididymis extends to form vas deferens.

• Vas deferens extends from the scrotum and loops over ureter to enter urethra.

• The urogenital opening is just posterior to the umbilical cord in reflected flap of body wall containing the urinary bladder.

• The penis extends posteriorly from urogenital opening.

• Incise alongside the penis and free it from the body wall; push to one side and use a scalpel to make a midline incision through the pelvic muscle and bones

• Urethra is at the end of the urinary bladder

• Rectum is located dorsal to the urethra; carefully separate it from the urethra.

• The seminal vesicles are small paired glands on each side of the urethra.

• Prostate gland: very small gland between seminal vesicles on dorsal surface of urethra

• Bulbourethral glands are paired glands on each side of the urethra where it enters the penis.

• Uterus and uterine tubes (horns) are dorsal to the bladder and ventral to the descending colon.

• Ovaries are just posterior to kidneys.

• Vagina is just dorsal to urethra.

• Rectum is the terminal portion of the large intestine.

• The vagina extends posteriorly from body of uterus.

Finishing Up

• Dissect the specimen.
• Properly dispose of the waste.
• Sanitize table tops.
• Wash hands