Frog Dissection - Cognitive Treks

Frog DissectionDissection does not mean “to cut up”, itactually means “to expose to view”

Lab Behavior Expectations You are expected to behave appropriately inthis lab setting. If at ANY time, I feel that your behavior isinappropriate you will be asked to stop thelab. You will also face disciplinary action and MYWRATH!!!!

Video Frog DissectionFrog Dissection – Part 1Frog Dissection – Part 2Frog Life

Before we proceedWhile dissecting, be respectful of yourlab partners and of the specimen youare about to explore, observe andlearn from.Take extra care with your dissectiontools. Your scissors are your mostimportant tool, but be sure to handlethem carefully and always doublecheck instructions before cutting.If you have any questions, please ask.

Purpose and TermsPurpose: Investigate the anatomy and organ systems of the frog. To observe the relationship between organ structure andfunction. To compare frog and human anatomy to betterunderstand body systems.Vocabulary: Dorsal – toward the back Ventral – toward the belly Lateral – toward the sides Median – toward the middle Anterior – toward the head Posterior – toward the tail

Working in Pairs for DissectionsPartner Roles: Every other step will be hands on. Pick oneperson to start and then alternate. If you arethe person dissecting, then the other personin the pair is assisting. After the dissection iscompleted, share your observations so thatboth people have a completed lab report.Conclusion questions will be individual work.

Getting ReadyMaterials: Gloves Forceps Hand lensDissecting trayScalpelProbePreserved frogDissecting scissorsDissecting pinsPreparation: Tie hair back, put on apron if you desire and get a pair ofgloves. Partner 1 – get tray, frog Partner 2 – get instruments and paper towel Both partners lay out supplies at their lab table, placing theinstruments on the paper towel. Decide who will start the dissection, remember to alternateturns! When you are ready to begin, look forward and be silent.

Part A – External Anatomy1. Make sure frog is right side up so that you can see the face.2. Identify the eyes, which have a nictitating membrane that servesto moisten the eye.3. Identify the tympanic membrane, or eardrum. It is locatedbehind each eye.4. Find the external nares or nostrils.

External Anatomy (cont’d)5. Find the digits, which are like fingers on boththe fore and hind limbs6. Determine if your frog is male or female bylooking at the innermost finger of the forelimb.

Mouth1. Pry open the mouth.Use the scissors to cutthe corner of the mouthwhere the maxilla(upper jaw) andmandible (lower jaw)join together.2. Find the tongue andpull it out.

Mouth3. Feel the maxillary teeththat are along the rim ofthe upper jaw. Notice thatonly the upper jaw hasteeth.4. Locate the glottis. It is aslit opening for the voicebox on the floor of themouth.5. Find the esophagus atthe rear of the mouth.

Part C - Internal Anatomy This is where the real dissection begins. Use your tools carefully and wisely. If you are unsure of the directions, ask!

Incision 1: Skin Vertical1. Place your frog on its backand pin it to the dissectingtray.2. Lift the frog’s skin withforceps between the rear legs.3. Make a small cut throughthe lifted skin with the scalpel.This is a starting place for thescissors. Take care to cut onlythe skin.4. Use the scissors to continuethe incision up to the midlineall the way through the frog’sskin.5. Stop cutting when yourscissors reach the frog’s neck.

Incision 2: Skin Horizontal6. Use the scissors to makesideways incisions in theskin.7. The first incisions aremade between the frontlegs. The next incisions aremade just above the rearlegs8. Be careful to only cutthrough the skin, not themuscle.

Incision 3: Separate Skin9. Pick up the flap of skin withthe forceps.10. Use a scalpel to help separatethe skin from the muscle layerbelow. After you've opened the flapsof skin, pin them to thedissection tray.

Incision 4: First Muscle Incision1. Repeat the incisions, this timethrough the abdominal muscle. Youwill find it easier to begin the verticalincision by lifting the muscle layer withthe forceps. Do this between the rearlegs of the frog.2. Make a small cut with the scalpel.3. Using the scissors, continue theincision up the midline to a point justbelow the front legs.4. Don't cut too deeply. The muscle isthin. It is easy to damage the organsunderneath.

Incision 5: Chest Bone5. Cut through the chest bones.When you reach the point justbelow the front legs, turn thescissors blades sideways, so thatyou only cut through the bonesin the chest. Be careful that youdon't cut too deeply. This should prevent damage tothe heart or other internalorgans.6. When the scissors reach apoint just below the frog's neck,you have cut far enough.

Incision 6: Muscle Horizontal7. Make the horizontal incisions.Just as you did with the skin,make a sideways incision in themuscle with the scalpel. Make the first incisionbetween the front legs. The next incision is just abovethe rear legs. Again, be careful that youdon't cut too deeply.

Muscle Separation8. Separate the muscle flapsfrom the organs below. Pullback and hold the muscleflaps with the forceps.9. Use the scalpel toseparate the muscle fromthe organ tissue.10. Pin the muscle flapsback far enough to alloweasy access to the internalorgans.

Interesting FactsUnlike humans, frogs don’tstore fat next to theskin. Frogs store winterfat in fat bodies foundinside the body cavity. Ifyour frog was collectedlate in the year, the bodycavity might be full ofyellow-orange fat bodies.

Internal Body Systems1. We are now ready toexplore the frog's anatomy.To make our explorationeasier, we will look at theorgans in four differentlayers, beginning with theliver and heart layer. As we get deeper into thefrog's anatomy, we willreveal new layers.

Liver When we pull back themuscles and skin, the firstorgans we can see are theliver and heart.2. The liver is a large,brownish colored organcovering most of the bodycavity.

Heart You should also be able to seethe heart in Layer 1.3. It is a small triangular shapedorgan between the front legs, justabove the liver.4. The frog’s heart has threechambers. The picture (right)shows only the lower chamber ofthe heart. Can you find all threechambers? How many chambers do youhave in your heart?

Layer 2 - Intestines5. Reveal layer two. Theheart and liver in layer onehide some of the organsbelow them.6. Use the forceps and theprobe to pick up the liverand reveal layer two.7. Layer two includes thegall bladder, the stomach,and the small intestine.

Gall Bladder8. Examine the gall bladder.Under the liver, we see asmall, greenish sac. This isthe gall bladder. You mightalso see it by separating theright and middle lobes ofthe liver. The gall bladder can behard to find.

Stomach9. Examine thestomach. Thestomach looks like asac on the frog's leftside (on your right).It is a large firmorgan.

Small Intestine10. Examine the smallintestine. The smallintestine is a long,folded, tube like organthat is posterior thestomach. It is similar in color tothe stomach, butsmaller in diameter.

Layer 311. Reveal layer three.Remove the liver to seethe organs in layerthree.12. The liver is easier toremove if you removethe gall bladder andheart at this time. Place the organs tothe side, but still inthe dissection tray.

Lungs13. Take a close look atthe lungs and pancreas.The lungs are difficult tolocate in a preservedfrog. They're at theanterior end of thebody cavity on eitherside of the heart. We may need toremove the lungsand place them onthe tray as well.

Pancreas15. You can't see thepancreas without liftingthe stomach and intestineswith the forceps. Thepancreas is a thin,yellowish ribbon.16. The intestines are heldin place by thin,transparent tissue calledthe mesentery.

Female Frogs17. If you have afemale frog, you willneed to remove theovaries before youcan see layer four. Place the organs inthe tray.

Layer 418. To see layer four,you need to removethe stomach, smallintestine, largeintestine, andpancreas. Place the on thetray.

Spleen19. Examine the spleen.Locate the spleen in themale frog. It is a small,round reddish organ. It is a little moredifficult to find thespleen in a femalefrog

Male Kidneys20. The kidneys areelongated, brownishcolored organs found inthe lower part of thefrog's abdomen. The kidneys (Y) aresituated on each sideof the middle of thefrog just underneaththe testes (X).21. Female kidneys arelocated in the same placebut can only been seenafter removal of theovaries and oviducts.

Identification Use the frog to andwhat you have justlearned to identifyfrog anatomy You may do thiswith your partner

Clean Up - Tools One partner is responsible for cleaning thedissection tools Please wait patiently for your turn at the sink Follow all instructions on cleaning:1. Place your tools carefully in the sink.2. Rinse the tools well with water (watch sharpareas) and place on paper towels3. Wipe up any spills

Clean Up – Frog and Tray Second partner is responsible for cleaning thetray and disposing of the frogs Please walk the frog still in the tray to thedisposal area. Follow all instructions on cleaning:1. Place your frog and parts in the bio bag.2. Throw away closed bag3. Rinse tray and wipe down.4. Place where shown on counter.

Clean Up – Work area Both partners are responsible for cleaning thelab work area Please come get a disposable wipe Wipe off your work area thoroughly Throw away the wipes

Homework Conclusion Questions are independent work The last question has a research componentto it – make sure to read the instructions andfollow through.

Partner 1 –get tray, frog Partner 2 –get instruments and paper towel Both partners lay out supplies at their lab table, placing the instruments on the paper towel. Decide who will start the dissection, remember to alternate turns! When you are ready to begin, look forward and be silent.