Fetal Pig Dissection Notes

Determining Sex in Fetal Pigs

  • Both males and females have mammary papilla (nipples), so this is not a reliable indicator of sex.
  • Locate the umbilical cord on the underside of the pig.
  • Male:
    • The urogenital opening is located just below the umbilical cord.
    • A distinct bump (scrotum) is present near the anus.
    • The scrotum houses the testes.
  • Female:
    • No urogenital opening is present below the umbilical cord.
    • The urogenital opening is located near the anus, covered by a small bump called the genital papilla.
  • The genital papilla is a flap of tissue covering the urogenital opening.

Cheek Dissection

  • Make an initial incision in the neck, where blue dye (veins) and red dye (arteries) have been injected.
  • The thick fatty neck tissue covering the area is the parotid gland, which provides protection.
  • Use tweezers to lift the skin and scissors to cut the connective tissue just below the skin.
  • Remove large pieces of skin to get a clear view of the underlying structures.
  • Be cautious not to cut too deep, as there are fragile structures beneath the skin.
  • The first major muscle encountered is the masseter muscle, a large, round cheek muscle that controls the jaw.
  • Scrape away tissue to expose deeper structures without damaging them.
Facial Nerve & Parotid Duct
  • A thin white line crossing the top of the masseter muscle is the facial nerve, which controls facial features.
  • The parotid duct is a thin white line below the facial nerve, leading into the parotid gland. Arteries are located behind the parotid duct.
Mandibular Gland
  • Underneath the parotid gland, to the right of the masseter muscle, is the mandibular gland. It appears as a small, bean-shaped structure.
  • Glands typically appear as either fatty tissue (like the parotid gland) or small beans (like the mandibular gland).

Mouth Dissection

  • Tie up the pig to keep its legs out of the way.
  • Make incisions on each side of the mouth, cutting down into the jawbones.
  • Follow the tongue down towards the throat, avoiding cutting into the head.
  • Take pictures and videos of the cheek dissection before proceeding, as this area is delicate.
  • Cut enough to get down to the throat, separating the muscles and bones that prevent access.
  • Stop cutting once you see a small flap, the epiglottis.
  • The epiglottis flaps up and down to control breathing and swallowing.
    • Breathing: Airway goes down.
    • Swallowing: Closes off so food doesn't enter the airway.
Key Structures
  • Esophagus: The major hole leading down the throat.
  • Glottis: A smaller hole leading towards the tongue.
  • Epiglottis: The flap on top of the glottis (epi- meaning "on top").
  • Nasopharynx: A passageway leading towards the nose (naso- referring to the nose).
  • Soft Palate: The soft part of the roof of the mouth at the back.
  • Hard Palate: The hard part of the roof of the mouth at the front.

Throat Dissection

  • Continue working from the initial neck incision.
  • Cut through the fatty neck tissue to reveal a ball in the throat, the larynx (voice box).
  • Cut around the larynx and down into the trachea (bumpy tube in the throat), but don't cut the larynx itself.
Key Structures
  • Larynx: The large ball in the throat, or voice box.
  • Trachea: The bumpy tube in the throat, which is the airway.
  • Thyroid Gland: A small, bean-shaped structure sitting below the larynx and on top of the trachea

Body Cavity Dissection

  • Follow the manual for proper incision techniques based on the pig's sex.
  • Female: Cut around the umbilical cord.
  • Male: Cut above the urogenital opening and down.
  • Cut the first layer of skin to expose the diaphragm, a thick membrane covering the body cavity.
  • Pinch the skin, insert a probe, and cut around it to open the cavity.
  • The skin is not attached to the organs, allowing for large incisions without damage.
  • Remove excess fluids, disposing of them properly (not down the sink).
  • Make larger cuts to expose the liver and other organs.
  • Cut around the male's flap, or the female's umbilical cord, leaving them intact.
Umbilical Vein
  • Cut the umbilical vein, which connects the umbilical cord to the liver, to allow for better access to the organs.

Chest Cavity Dissection

  • The chest cavity is similar to the body cavity, with a membrane (pleura) surrounding it.
  • Start on the sides to avoid damaging major structures, potentially nicking the lungs (but this is not critical).
  • The outer layer membrane is the diaphragm
  • The lungs are not directly attached to the cavity walls.
  • Lift up and look in while cutting to avoid damaging underlying structures.
Sternum Caution
  • Avoid the breastbone (sternum) area in the first week due to its concentration of circulatory vessels.
  • Cut above the rib cage, separating the membrane from the ribs.
  • The lower part of the heart will become visible.
  • The pericardial membrane surrounds the heart.
Structures
  • Heart: Visible after removing ribs and connective tissues.
  • Pericardial Membrane: The thin membrane covering the heart (para- meaning "around," cardio- meaning "heart").
  • Thymus: A flat, glandular-looking structure sitting on top of the pericardium.
  • Lungs: Lobes of the lungs are visible on either side of the heart.

Heart Structures and Blood Flow

  • Cut the pericardium to expose the heart structures.
Oracles
  • Dark flaps on either side of the heart are the oracles (no need to distinguish right from left).
  • Underneath the pericardium are the oracles, while above it is the thymus.
Pulmonary Artery & Aorta
  • The pulmonary artery (large white structure) carries deoxygenated blood from the heart to the lungs. It is on the pig's left hand side.
  • Pull the heart down to reveal the aorta (large white structure) and the vena cava (large blue structure) behind the oracles.
  • The coronary artery is a thin line crossing the heart.
Vena Cava
  • Lift the heart to see the continuation of the vena cava, with the caudal vena cava (below the heart) and cranial vena cava (above the heart).
Circulation Process
  • Vena Cava: Largest vein, brings deoxygenated blood back to the heart.
    • Veins bring blood to the heart.
    • Arteries carry blood away from the heart.
  • Right Atrium: Deoxygenated blood enters from the vena cava (caudal or cranial).
    • Atriums are the top portion of the heart.
    • Ventricles are the bottom portion of the heart.
  • Tricuspid Valve: Blood flows through the tricuspid valve (an AV valve) into the right ventricle.
  • Pulmonary Valve: Blood flows out the pulmonary valve.
  • Pulmonary Artery: Blood travels to the lungs through the pulmonary artery (only artery with deoxygenated blood).
Gas Exchange in Lungs
  • Deoxygenated blood flows over capillaries in the lungs, where gas exchange occurs.

Abdominal Organs Dissection

  • Diaphragm is the thick membrane covering the whole lower body cavity.
  • The most noticeable organ is the liver, which may be blue or brownish and has several lobes.
  • Cut the umbilical vein (which was going towards the umbilical cord) and flap it down.
Key Organs
  • Gallbladder: A deflated sac located under the right side of the liver, which stores bile (produced by the liver).
  • Common Bile Duct: A tube that transports bile from the gallbladder to the duodenum.
  • Stomach: A deflated bag located under the liver.
    • Spleen: A red, tongue-looking organ attached to the stomach.
  • Duodenum: First hard part of of the stomach
  • From the stomach, the content enters the small intestine.
Mesentery
  • Jejunum: Spread small intestine out and observe the mesentery (connective tissue with mesenteric arteries and veins) attaching it. Jejunum will have the most mesentery.
  • Ileum: Observe a part of the small intestine that has very little mesentery, that falls off into its own little ball.
  • Spiral Colon: A giantic colon looking thing in a spiral.
  • Cecum: A tiny little dead end finger like projection between the ileum and the spiral colon.
Kidneys
  • Kidneys: Giant bean looking things located on either side of the pig
Rectum
  • The rectum is in between the kidneys heading from the small and spinal colon down towards the anus; function is to transfer nondigestible material passes through and then out towards the anus.

Circulatory System Diagram

Vessels to note that the arteries/veins may be cut away.
  • Umbilical Arteries: Located going up the umbilical cord
  • Umbilical vein: Has been cut down from the live
  • Iliac: Branches of the aorta, and located on either side of the body.
    • Femoral: after each iliac branches it becomes the femoral, one on either side.

Reproductive and Excretory Systems

  • Pancreas: A white, fatty-looking organ located underneath the liver and the stomach.
  • Spleen: Located right underneath the kidney.
  • Ureter: Transports urine from the kidneys to the urinary bladder.
  • Adrenal gland: A tiny little flat looking gland near/on top of the kidney
  • Renal Artery and vein: Red artery and blue vein that are going into the kidney
    *Note: ''Renal'' means kidney''

Male Reproductive System

Key Structures
  • Urogenital Opening: Located underneath the cord.
  • Penis: Rub fingers back and forth along to feel the penis tube. It is desirable to cut away all excess skin.
  • Bulbourethral Gland: A gland y looking thing right on top of the penis before getting to the Urethra
  • Urethra A small tube that connects Bulbourethral Gland to the urinary bladder. (note dig deep in the diagram)
  • Scrotal Sac: The scrotum when covered. One on each side
  • Teste: A ''Round Bean looking shape ball'' inside the Scrotal sac.
  • Epididymis: Small ''flap'' sitting on top and the side of the testes.
  • Seminal Vesicles: In that Y shape formation these comprise the base of the Y.
  • Vas Deferens: Comprise the arms of the Y.

Female Reproductive System

  • A very similar Y shape except, the legs are now