Frog Anatomy and Dissection Notes

NERVOUS SYSTEM

• Main Organs & Structures:

  • Brain (in the skull):

    • Olfactory lobes – smell

    • Cerebrum – decision-making, memory

    • Optic lobes – vision processing

    • Cerebellum – balance & coordination

    • Medulla oblongata – involuntary functions (heartbeat, respiration)

  • Spinal Cord – transmits signals between body and brain

  • Nerves – branch out from spinal cord to all muscles and organs

CIRCULATORY SYSTEM

• Type: Closed (blood stays in vessels)

• Heart:

  • 3 Chambers:

    • 2 Atria (right receives deoxygenated blood, left receives oxygenated)

    • 1 Ventricle (mixes both blood types and pumps to body/lungs)

  • Conus arteriosus – directs blood to either lungs or body

• Blood Vessels:

  • Arteries – carry blood away from heart

  • Veins – return blood to heart

RESPIRATORY SYSTEM

• Organs:

  • Nostrils (nares) – external & internal; allow air entry

  • Glottis – opening to the lungs

  • Trachea – very short; connects glottis to lungs

  • Lungs – two sac-like structures, under liver on either side

  • Skin – also used for cutaneous respiration (breathing through skin, especially in water)

DIGESTIVE SYSTEM

• Starts at the mouth:

  • Mouth:

    • Maxillary teeth (on upper jaw) – hold prey

    • Vomerine teeth (in roof of mouth) – grip prey

    • Tongue – sticky, flips out to catch prey

• Organs & Locations:

  1. Esophagus – short tube, leads from mouth to stomach

  2. Stomach (left side, under liver) – digests food with acids

  3. Small Intestine (coiled):

     • Duodenum (first section) – chemical digestion

     • Ileum (second section) – nutrient absorption

  4. Large Intestine (colon) – absorbs water

  5. Cloaca – common exit for digestive, excretory, and reproductive systems

• Accessory Organs:

  • Liver (3 large lobes) – largest organ; makes bile, stores glycogen

  • Gallbladder (under right liver lobe) – stores bile

  • Pancreas (between stomach & small intestine) – makes digestive enzymes and insulin

EXCRETORY SYSTEM

• Main Job: Filter nitrogen waste (from protein breakdown)

• Organs:

  • Kidneys (flattened, bean-shaped, along spine near back wall) – filter blood

  • Ureters – tubes from kidneys to cloaca

  • Urinary Bladder – stores urine, opens into cloaca

  • Cloaca – where urine is expelled

REPRODUCTIVE SYSTEM

• MALE:

  • Testes (small, white, on top of kidneys) – produce sperm

  • Vasa efferentia – tubes from testes to kidneys

  • Ureters also carry sperm → cloaca

• FEMALE:

  • Ovaries (gray/black, lobed when full of eggs) – produce eggs

  • Oviducts (coiled tubes) – carry eggs to cloaca

  • Ovisacs – enlarged parts of oviducts, store mature eggs

MUSCULOSKELETAL SYSTEM

• Skeleton: made of bone & cartilage

  • Skull – lightweight, flat

  • Vertebral column – short (9 vertebrae + urostyle)

  • Urostyle – long fused tailbone

  • Hindlimbs – strong for jumping

• Muscles: striated, attached to bones via tendons

  • Dorsal = back side, Ventral = belly side

INTEGUMENTARY SYSTEM (Skin)

• Smooth, moist skin – allows for gas exchange

• Chromatophores – pigment cells for camouflage

• Mucous glands – keep skin moist

• Poison glands – secrete defensive toxins (in some species)

IMMUNE & LYMPHATIC SYSTEM

• Spleen (small, round, reddish, in body cavity) – filters blood, immune responses

• Lymph nodes & vessels – transport lymph, support immune function

ENDOCRINE SYSTEM

• Glands:

  • Pituitary – controls other glands

  • Thyroid – metabolism

  • Adrenal – on kidneys, for stress response

  • Pancreas – also endocrine (insulin, glucagon)

DISSECTION TIPS

• Cut along the midline from cloaca to jaw — avoid damaging organs.

• Liver is the first major structure you’ll see.

• To see the heart: lift or move liver.

• To view reproductive organs: look near kidneys.

• Be careful when identifying kidneys vs. testes/ovaries — they’re close together.

COMMON QUIZ QUESTIONS

• What organ is shared by 3 systems? → Cloaca

• What organ is largest in frog? → Liver

• What organ lets frogs breathe underwater? → Skin

• What are the functions of the spleen? → Filters blood & helps immunity

• Where is the gallbladder? → Under the liver’s right lobe

• Why do frogs have 3-chambered hearts? → To support both lungs and skin breathing

• What muscle action helps frogs swallow? → Eyes sink into mouth

FROG DISSECTION PRACTICE QUIZ

SECTION 1: MULTIPLE CHOICE (Choose the best answer)

1. What is the main function of the cloaca in frogs?

   • A. Digestion

   • B. Urine filtration

   • C. Common exit for waste and reproductive materials

   • D. Breathing

   • Answer: C. Common exit for waste and reproductive materials

2. Where is the gallbladder located in the frog?

   • A. Inside the heart

   • B. Under the liver’s right lobe

   • C. Next to the spleen

   • D. Beneath the lungs

   • Answer: B. Under the liver’s right lobe

3. Which organ is responsible for producing bile in the frog?

   • A. Gallbladder

   • B. Pancreas

   • C. Liver

   • D. Stomach

   • Answer: C. Liver

4. What is the function of the spleen in a frog?

   • A. Digestion

   • B. Filtering blood and supporting the immune system

   • C. Producing bile

   • D. Excreting nitrogen waste

   • Answer: B. Filtering blood and supporting the immune system

5. What structure connects the mouth to the stomach?

   • A. Duodenum

   • B. Esophagus

   • C. Glottis

   • D. Cloaca

   • Answer: B. Esophagus

6. Which part of the heart receives oxygenated blood from the lungs?

   • A. Right atrium

   • B. Left atrium

   • C. Ventricle

   • D. Conus arteriosus

   • Answer: B. Left atrium

7. Which organ stores urine before it exits the body?

   • A. Kidney

   • B. Ureter

   • C. Urinary bladder

   • D. Cloaca

   • Answer: C. Urinary bladder

8. Where are the kidneys located in the frog’s body?

   • A. Behind the lungs

   • B. Near the stomach

   • C. Along the back wall, close to the spine

   • D. Under the liver

   • Answer: C. Along the back wall, close to the spine

9. What do the fat bodies in a frog do?

   • A. Produce hormones

   • B. Store energy for hibernation and reproduction

   • C. Help digestion

   • D. Pump blood

   • Answer: B. Store energy for hibernation and reproduction

10. What is the main role of the pancreas?

    • A. Filter blood

    • B. Digest fat

    • C. Produce digestive enzymes and regulate blood sugar

    • D. Produce bile

    • Answer: C. Produce digestive enzymes and regulate blood sugar

SECTION 2: TRUE OR FALSE

11. Frogs have a four-chambered heart just like humans.

    • Answer: False – Frogs have a three-chambered heart (2 atria, 1 ventricle)

12. The liver is the largest organ in the frog’s body.

    • Answer: True

13. The cloaca is found in both male and female frogs.

    • Answer: True

14. The large intestine absorbs most of the nutrients from food.

    • Answer: False – That occurs in the small intestine

15. The lungs are the only organ frogs use to breathe.

    • Answer: False – Frogs can also breathe through their skin (cutaneous respiration)

SECTION 3: SHORT ANSWER

16. What are two major differences between frog and human anatomy?

    • Answer:

      • Frogs have a cloaca; humans have separate exits for waste and reproductive materials

      • Frogs can breathe through skin, humans cannot

      • Frogs have a three-chambered heart, humans have four

17. What is the function of the aorta in frogs?

    • Answer: It carries blood away from the heart to the rest of the body.

18. During dissection, what is the first major organ you’ll see when opening the body cavity?

    • Answer: The liver

19. What structure should be cut carefully to avoid damaging internal organs?

    • Answer: The ventral body wall, cut along the midline from cloaca to jaw

20. What part of the small intestine is responsible for most nutrient absorption?

    • Answer: The ileum

SECTION 4: MATCHING

Match the organ with its function:
* A. Stomach
* B. Lungs
* C. Kidneys
* D. Fat Bodies
* E. Large Intestine

1. Absorbs water from waste
2. Stores energy reserves
3. Begins breakdown of food
4. Filters nitrogen waste from blood
5. Exchanges gases with air

Answers:
* A - 3 (Stomach = breakdown of food)
* B - 5 (Lungs = gas exchange)
* C - 4 (Kidneys = filter blood)
* D - 2 (Fat bodies = store energy)
* E - 1 (Large intestine = absorb water)