Fetal Pig Dissection Lab Notes
Fetal Pig Dissection Lab
Introduction
Examining characteristics of an unborn mammal (fetal pig).
Dissection provides a 3-dimensional understanding of how systems fit together.
Observe spatial arrangement and texture of organs.
Additional help: http://www.esu7.org/~lweb/Lakeview/science/fetal.html
Lab Components
External Anatomy
Oral Cavity
Digestive System
Circulatory System
Respiratory System
Urogenital System
Nervous System
Materials
Preserved fetal pig
Dissecting pan
Scissors
Forceps
Blunt probe
Twine/string
Safety goggles
Disposable latex gloves
Tape measure
General Directions
Locate underlined words on the pig.
Answer numbered questions.
Teacher will check questions.
Use scissors for most cuts.
Dissect carefully to avoid destroying the pig.
Keep all parts with the pig.
Pig Lab #1 - External Anatomy
Examine characteristics of an unborn mammal.
Review directional names on packet page 13.
Gestation period for the pig is 112-115 days.
Estimate fetus age by measuring body length (snout to tail attachment).
Compare length to data on fetal pig sizes at different times during gestation:
21 days: 11 mm
35 days: 17 mm
49 days: 28 mm
56 days: 40 mm
100 days: 220 mm
115 days: 300 mm
Mammals are classified by external appearance.
External features include number of digits, method of locomotion, and teeth characteristics.
Unique mammalian characteristics:
Hair at some point during development
Mammary glands with external openings for nourishing offspring with milk
Fetal pig may not have much hair due to being undeveloped.
Lips are well developed with a philtrum (groove on upper lip).
Humans also have a philtrum (indent under nose and above upper lip).
External nares (nostrils) are found on the nose.
Ears have a flexible outer flap called the pinna.
Pinna helps focus sound into the middle ear.
Many mammals have sensory facial hairs called vibrissae; our pigs do not possess these yet.
Vibrissae help organisms feel their way around in the dark.
Vibrissae of dogs and cats are commonly called whiskers.
Eyes have upper and lower lids and a nictitating membrane in the upper corner.
Nictitating membrane helps keep the eye clean.
Birds use this membrane to moisten their eyes in flight without blinking.
Pig is unguligrade because it walks on its hooves.
Humans are plantigrade because we walk on the entire soles of the foot.
Dogs and cats are digitigrade because they walk on their digits.
In pigs, the first digit of both fore and hind limb is absent, and the second and fifth are reduced in size but remain functional.
The pig's trunk is divided into two regions: thorax (chest) and abdomen (stomach).
Umbilical cord contains three blood vessels: a large vein (blue) and two smaller arteries (red).
Observe the paired row of nipples on the ventral surface of the abdomen in both sexes.
Number of nipples varies among mammals.
Animals with litters tend to have more nipples.
Pig Gender Determination Information
Male pig: penis and urethral opening located posterior to the umbilical cord on the ventral surface.
Young male pig: scrotal sacs (ventral to the tail and anus) may be empty; testes descend just before birth.
Mature male pig: testes have descended to fill the scrotum.
Female pig: a small projection is noticed just below her tail.
Anus: opening immediately ventral to her tail.
Vaginal opening: opening ventral to the anus, associated with the small projection.
Most mammals have separate urogenital and anal openings.
Female pigs: urinary and genital openings are also separated.
Urethral opening: the most ventral.
Vaginal orifice: just dorsal to the urethral opening.
Anus: located at the base of the tail dorsal to the vaginal orifice.
Urethral opening excretes urine.
Vaginal orifice is the opening of the birth canal.
Male urogenital structures: penis (opening just behind the umbilical cord) and scrotum, containing the testes.
Scrotum lies ventral to the anus.
Anus of the male is at the base of its tail.
Locate these two openings: urogenital opening of the penis and the anus; they are posterior to the umbilical cord.
Internal Anatomy - General Directions
Proceed by systems; remove organs only when directed.
Study and use diagrams.
Keep in mind the interrelationships of systems.
Use care not to damage other systems.
ALL cuts will be done with the scissors.
Dissect carefully and accurately.
Use caution when carrying and cleaning sharp dissection tools.
Pig Lab #2 - Oral Cavity
Cut deeply into both corners of the mouth with scissors.
Follow the curvature of the throat.
Examine the oral cavity containing the tongue and teeth.
Notice the ridged roof of the mouth called the hard palate.
Soft palate: fleshy portion of the roof of the mouth, lies caudal to the hard palate.
Locate the tongue with all its taste buds.
Mammals have two types of teeth: incisors (front) and cheek teeth (back).
Cut through the bone of the jaw and apply gentle pressure to force the mouth open.
Pharynx: common passage for food (esophagus) and air (lungs).
Epiglottis: flap-like structure at the top of the trachea.
Esophageal opening: entrance to the esophagus (food tube) in the nasopharynx.
Esophagus is located dorsal to the trachea.
Pig Lab #3 - Digestive System
Tie twine around wrist and ankle and attach to dissecting pan.
Open the abdominal cavity with incisions.
Cut carefully to avoid damaging organs.
Hold scissors parallel to the pig.
Lift scissors upward with every cut.
Cut through bone in the thoracic cavity.
Cut skin flaps back to the dorsal surface to expose organs.
Be careful not to injure the kidneys.
Pull back skin flaps and muscle to view organs.
Locate the umbilical vein inside the abdomen; cut it and lay back the cord and its strip of skin.
Liver: large, reddish-brown organ that occupies much of the abdominal space.
Gall bladder: located on the pig’s right side.
Diaphragm: thin brown muscular tissue separating the thoracic and abdominal cavities.
Esophagus goes through the diaphragm to the stomach.
Stomach: pouch-like, on the upper left side of the abdominal cavity, connected to the esophagus.
Slit open the stomach longitudinally.
Rugae: longitudinal ridges that line the stomach.
Duodenum: first 3-4 cms of the small intestine.
Ileum and jejunum: remaining length of the small intestine.
Small intestine is held in place by the mesentery.
Mesentery contains veins and arteries that carry absorbed nutrients to the liver through the hepatic-portal vein.
Villi: finger-like projections inside the small intestine.
Villi increase the surface area of the small intestine for absorption (microscopic).
Large intestine: compact coil, larger in diameter than the small intestine.
Caecum: small pouch-like structure at the junction of the large and small intestine (appendix in humans).
Caecum helps in the slow digestion of plant materials in other animals.
Large intestine (colon) leads to the rectum.
Rectum: straight end portion of the large intestine in the dorsal wall of the abdominal cavity.
Water is absorbed by the body in the large intestine.
Waste material stored in the rectum leaves the body through the anus.
Pancreas: large white granular organ located below the stomach.
Pancreas makes digestive enzymes that travel to the small intestine through the pancreatic duct (difficult to find).
Spleen: red elongated organ extending around the outer curvature of the stomach; resembles a tongue.
Spleen helps destroy old red blood cells.
Pig Lab #4 - Circulatory System
Consists of the heart, arteries, veins, and capillaries.
Pulmonary circulation: moves oxygen-poor blood to the lungs and returns oxygen-rich blood to the heart.
Systemic circulatory system: supplies all parts of the body with oxygen-rich blood (arteries & arterioles) and returns oxygen-poor blood to the heart (venuoles & veins).
Cut through the sternum to open the thoracic cavity.
Pericardium: thin, tough membrane covering the heart.
Thymus gland: globular structure partially covering the heart; largest in young individuals.
Thymus is part of the immune system and makes T-cells.
Heart is composed of 4 chambers: 2 atria and 2 ventricles.
Pig may have been injected with colored latex (veins - blue; arteries - red).
Anterior and posterior vena cava: carry blood from the cranial and caudal portions of the body, respectively.
Pulmonary veins: carry blood from the lungs to the left atrium (oxygenated blood).
Aorta: curves to the left and passes cranially along the dorsal side of the thoracic and abdominal wall.
Pulmonary artery: arises from the anterior portion of the right ventricle and divides into the right and left pulmonary arteries.
Other arteries are named for the body part they serve (gastric, hepatic, renal, carotid).
Locate the carotid artery, jugular vein, and descending aorta.
Remove the heart by carefully cutting the arteries and veins leading to and from the heart as far away from the heart as possible; DO NOT damage any lung tissue.
Cut the heart in half through the frontal plane using a sharp blade; ASK FOR TEACHER ASSISTANCE if unsure.
Identify the right atrium, right ventricle, left atrium, and left ventricle.
A/V valves: found between the atria and the ventricles; prevent back flow of blood.
Semilunar valves: found between the ventricles and the pulmonary artery and vein; prevent back flow of blood.
Septum: structure between the two ventricles.
Coronary arteries and veins: on the surface of the heart.
Ductus arteriosus: short vessel in the fetal mammalian heart that allows blood to bypass pulmonary circulation until birth; closes completely at birth.
Pig Lab #5 - Respiratory System
Responsible for gas exchange.
Pig takes in oxygen and rids itself of carbon dioxide.
Air enters through the external nares.
Air is drawn into the nasopharynx (nose chambers) where sensory nerve cells detect smell.
Glottis: opening of the trachea.
Trachea: tube that extends from the neck to the chest; white and lined with cartilage.
Larynx (voice box): enlargement at the anterior end of the trachea; contains vocal cords.
Trachea splits into two bronchi in the chest cavity.
Bronchi extend into the lungs and split into smaller tubes called bronchioles.
Lungs: located on either side of the heart.
Alveoli: tiny air sacs in the lungs where gas exchange occurs (microscopic).
Diaphragm: thin muscular muscle just above the liver; responsible for drawing air into the chest cavity.
Spasms of this muscle result in hiccups.
Pig Lab #6 - Urogenital System
Study of urinary (excretory) and reproductive (genital) systems.
Urinary and genital systems are structurally related.
Paired structures; what is observed on one side may be seen on the other.
Kidneys: two lumps low in the abdominal cavity, behind the peritoneum.
Remove the peritoneum to see the bean-shaped kidneys.
Ureter: originates from the concave side of the kidney; follows posteriorly to the urinary bladder; do not remove.
Renal artery and vein: come out of the kidney; artery carries blood to the kidney; vein carries blood out of the kidney.
Remove one kidney and dissect it horizontally into 2 halves; locate the cortex and medulla.
Prepare for the observation of the reproductive organs by pulling the hind legs apart.
Cut anteriorly a little to one side of the mid-ventral line to avoid cutting the penis on the male.
Press firmly on the tissue between the legs to feel the cartilaginous structure of the pubic symphysis (part of the pelvic girdle).
Continue the incision anteriorly and cut through the pubic symphysis; expose the urethra.
Urethra: tube that leads from the bladder to the outside world.
Male Reproductive System:
Scrotal sac (scrotum) at the posterior end of the male pig; open one sac and determine the presence of a testis.
Testes descend just before birth to the outside of the body proper because the ordinary temperature of the human body () would kill sperm.
The 3-4 degree lower temperature of the testes outside the body keeps the sperm viable or alive.
Advanced fetal development: testes may have already descended into the scrotal sacs.
Otherwise, they may be found in a tube like structure, the inguinal canal, small oval organs.
Locate one of the testes and note the coiled tubule making up the epididymis.
Follow this tube forward as it passes through the inguinal canal as the vas deferens.
At this point, as in humans, the urethra becomes a urogenital duct.
Female Reproductive System:
Spread the legs to separate the pubic symphysis and thereby expose the female reproductive system.
Locate the oval-shaped ovaries which are found caudal to the kidneys.
Leading from the ovaries are the twisted oviducts or Fallopian tubes.
The oviducts continue posteriorly and are soon supported by broad ligaments.
Further on, the oviducts join to form the common uterus.
Notice a slight constriction of the common uterus marking the location of the cervix.
The cervix can often be a site where cancer develops in females.
Posterior to the cervix, the remainder of the tube forms the vagina.
Locate the point where the urethra joins to form the common-urogenital sinus.
MAKE SURE YOU OBSERVE A PIG WHICH IS THE OPPOSITE SEX OF YOURS. YOU WILL BE RESPONSIBLE FOR IDENTIFYING BOTH THE MALE AND FEMALE REPRODUCTIVE PARTS!
Nervous System
May only be done AFTER labs 1-6 are completed and with teacher’s permission.
EVEN IF YOU DO NOT HAVE TIME / PERMISSION TO PERFORM THIS DISSECTION, YOU MUST ANSWER THE QUESTIONS FOR LAB 7!
Position the animal so that the dorsal side is up.
Remove the skin from the entire skull.
Central nervous system: brain and spinal cord.
Remove skull bone (cranium) to observe the brain.
Insert the point of your scissors just under the bone at the base of the skull.
Angle the tip of the scissors upward so as not to damage the soft brain tissue.
Cut forward along the midline of the brain to the eyes; cut to either side at the points where you started and stopped cutting.
Gently remove the cranium by carefully using forceps to break and peel away the pieces.
Meninges: membranes which cover the brain; mammals have three layers.
Dura mater: outermost
Pia mater: inner membrane
Arachnoid mater: lies in between.
Olfactory lobes: located at the anterior end of the brain; receive nervous stimuli from the nose and are concerned with the sense of smell.
Cerebrum: behind the olfactory lobes; divided into two cerebral hemispheres by a deep groove named the longitudinal cerebral fissure.
Cerebrum of most mammals has a folded surface.
Cerebrum controls voluntary muscle movements, thinking, memory, judgment, and the senses.
Cerebellum: behind the cerebrum; principally a motor coordinating center.
Medulla oblongata: behind the cerebellum; leads to the spinal cord.
Medulla oblongata controls respiration, heart rate, and blood pressure; also helps in regulating sensory impulses, hormonal secretions, and general awareness (consciousness).
TERMS:
Cerebellum: A part of the brain responsible for coordinating voluntary movements and maintaining posture and balance.
Medulla Oblongata: The continuation of the spinal cord within the skull, controlling autonomic functions such as breathing and heart rate.
Spinal Cord: A long bundle of nervous tissue that extends from the brain and transmits messages between the brain and the rest of the body.
Sensory Impulses: Nerve impulses that convey information from sensory receptors to the central nervous system. Thalamus: A brain structure that acts as the primary relay station for sensory information, processing and transmitting it to the appropriate areas of the cortex.
Alveoli: tiny air sacs in the lungs where gas exchange occurs (microscopic).
A/V valves: found between the atria and the ventricles; prevent back flow of blood.
Anus: located at the base of the tail dorsal to the vaginal orifice.
Anterior and posterior vena cava: carry blood from the cranial and caudal portions of the body, respectively.
Aorta: curves to the left and passes cranially along the dorsal side of the thoracic and abdominal wall.
Bronchi: extend into the lungs and split into smaller tubes called bronchioles.
Bronchioles: smaller tubes that split from the bronchi in the lungs.
Caecum: small pouch-like structure at the junction of the large and small intestine (appendix in humans).
Cerebellum: behind the cerebrum; principally a motor coordinating center.
Cerebrum: behind the olfactory lobes; divided into two cerebral hemispheres by a deep groove named the longitudinal cerebral fissure.
Cervix: a slight constriction of the common uterus marking the location of the cervix. The cervix can often be a site where cancer develops in females.
Coronary arteries and veins: on the surface of the heart.
Cortex: outer part of the kidney.
Diaphragm: thin brown muscular tissue separating the thoracic and abdominal cavities; thin muscular muscle just above the liver; responsible for drawing air into the chest cavity.
Duodenum: first 3-4 cms of the small intestine.
Ductus arteriosus: short vessel in the fetal mammalian heart that allows blood to bypass pulmonary circulation until birth; closes completely at birth.
Dura mater: outermost membrane of the meninges.
Epididymis: coiled tubule making up the epididymis.
Epiglottis: flap-like structure at the top of the trachea.
Esophageal opening: entrance to the esophagus (food tube) in the nasopharynx.
Esophagus: food tube; located dorsal to the trachea; goes through the diaphragm to the stomach.
External nares: nostrils found on the nose.
Fallopian tubes: twisted tubes leading from the ovaries.
Gall bladder: located on the pig’s right side.
Glottis: opening of the trachea.
Hard palate: ridged roof of the mouth.
Ileum: remaining length of the small intestine.
Inguinal canal: tube like structure where testes may be found, small oval organs.
Jejunum: remaining length of the small intestine.
Kidneys: two lumps low in the abdominal cavity, behind the peritoneum.
Large intestine: compact coil, larger in diameter than the small intestine.
Larynx: enlargement at the anterior end of the trachea; contains vocal cords.
Left atrium: chamber of the heart.
Left ventricle: chamber of the heart.
Liver: large, reddish-brown organ that occupies much of the abdominal space.
Lungs: located on either side of the heart.
Medulla: inner part of the kidney.
Medulla oblongata: behind the cerebellum; leads to the spinal cord.
Meninges: membranes which cover the brain.
Mesentery: holds the small intestine in place; contains veins and arteries that carry absorbed nutrients to the liver through the hepatic-portal vein.
Nictitating membrane: helps keep the eye clean.
Olfactory lobes: located at the anterior end of the brain; receive nervous stimuli from the nose and are concerned with the sense of smell.
Ovaries: oval-shaped and found caudal to the kidneys.
Oviducts: twisted tubes leading from the ovaries.
Pancreas: large white granular organ located below the stomach.
Pancreatic duct: digestive enzymes that travel to the small intestine through the pancreatic duct (difficult to find).
Penis: opening just behind the umbilical cord.
Pericardium: thin, tough membrane covering the heart.
Pharynx: common passage for food (esophagus) and air (lungs).
Philtrum: groove on upper lip.
Pia mater: inner membrane of the meninges.
Pinna: flexible outer flap of the ears.
Pulmonary artery: arises from the anterior portion of the right ventricle and divides into the right and left pulmonary arteries.
Pulmonary circulation: moves oxygen-poor blood to the lungs and returns oxygen-rich blood to the heart.
Pulmonary veins: carry blood from the lungs to the left atrium (oxygenated blood).
Rectum: straight end portion of the large intestine in the dorsal wall of the abdominal cavity.
Renal artery: comes out of the kidney; artery carries blood to the kidney.
Renal vein: comes out of the kidney; vein carries blood out of the kidney.
Right atrium: chamber of the heart.
Right ventricle: chamber of the heart.
Rugae: longitudinal ridges that line the stomach.
Scrotal sac: scrotum at the posterior end of the male pig.
Scrotum: contains the testes; lies ventral to the anus.
Semilunar valves: found between the ventricles and the pulmonary artery and vein; prevent back flow of blood.
Septum: structure between the two ventricles.
Small intestine: held in place by the mesentery.
Soft palate: fleshy portion of the roof of the mouth, lies caudal to the hard palate.
Spinal cord: part of the central nervous system.
Spleen: red elongated organ extending around the outer curvature of the stomach; resembles a tongue.
Stomach: pouch-like, on the upper left side of the abdominal cavity, connected to the esophagus.
Testes: descend just before birth to the outside of the body proper because the ordinary temperature of the human body () would kill sperm.
Thymus gland: globular structure partially covering the heart; largest in young individuals.
Trachea: tube that extends from the neck to the chest; white and lined with cartilage.
Umbilical cord: contains three blood vessels: a large vein (blue) and two smaller arteries (red).
Umbilical vein: located inside the abdomen; cut it and lay back the cord and its strip of skin.
Ureter: originates from the concave side of the kidney; follows posteriorly to the urinary bladder; do not remove.
Urethra: tube that leads from the bladder to the outside world.
Urethral opening: the most ventral.
Urogenital opening: opening of the penis just behind the umbilical cord.
Vagina: posterior to the cervix, the remainder of the tube forms the vagina.
Vaginal orifice: opening ventral to the anus, associated with the small projection; just dorsal to the urethral opening.
Vas deferens: tube that passes through the inguinal canal.
Vibrissae: sensory facial hairs.
Villi: finger-like projections inside the small intestine.