SNC2P1/PL: BiologyE. Wong (Updated Feb 2016)

NAME: ______Date: ______

DISSECTION INSTRUCTIONS:

  1. Put on yourgloves and safety goggles.
  2. Lay the frog in the dissecting panwith its ventral (belly) side up and the head pointed away from you.
  3. Study the diagram below which shows thecutyou will make in the frog.
  4. With forceps, lift the skin on the ventral surface of the frog near the hind legs.
  5. Insert the tip of yourscissorsthrough the skin where the hind legs meet.
  6. Cut through the skin up the midlineof the frog to the tip of the jaw.(a)
  7. Cut the skinto the side, just below the legs (b & c) and just above the hind legs(d & e)

  1. With your fingers, gently separate the skin from the muscle tissue underneath it.
  2. Pull the flaps of skin to the sides of the frog.
  3. With forceps,lift the muscle layer of the ventral surface of the frog near the hind leg.
  4. With scissors, cut through the muscle layer, following the same cut pattern you used for the skin.
  5. When you reach the point between the front legs, you will becutting through a bone that protects the heart. Be sure to keep the tips of your scissorstiltedupward to prevent damaging the organs below.
  6. When you have finished your cutting, carefully pull the flaps of muscle to the sides.
  7. If your specimen is afemale, the body may be filled with eggs and an enlarged ovary.
  8. With forceps,remove these eggs and place them in a corner of your dissecting tray.
  9. Observe the organs, as they are position in the body cavity.

LOCATE the organs below. Check () the box to indicate that you found the organs.

Fat Bodies:Spaghetti shaped structures that have a bright orange/yellow colour. You may need to remove these to see the other structures.

Peritoneum:Aspider web-like membrane that covers many of the organs, carefully pick it off to get a clearer view.

Liver: The largest structure of the body cavity; on both sides of the heart.This brown coloured organ is composed of three lobes: right lobe, left anterior and left posterior.Liver secretes a digestive juice,bile, which is needed for the digestion of fats.

Heart: A triangular structure at the top of the liver. The heart is composed of three chambers – left and right atrium (top – red brown) and single ventricle (bottom - white). The large vessels extending out from the heart is the conusarteriosis.

Lungs: Look underneath and behind the heart and liver. They are two deflated, spongy organs.

Gall bladder: A small green sac under the liver. It stores bile.

Stomach: Curving from underneath the liver; very muscular; white. It is the first major site of chemical digestion. Frogs swallow their meals whole.

The pyloric sphincter valve regulates the exit of the digested food from the stomach to the small intestine.

Small intestine: Leading from stomach.

The first straight portion of the small intestine is called the duodenum.

The curledportion is called theileum.The ileum is held together by a membrane called mesentery, where the blood vessels running through it and carry absorbed nutrients away from the intestine.

Absorption of digested nutrients occurs in the smallintestine.

Large intestine: From small intestine to cloaca; large diameter than small intestine

Cloaca: Means sewer in the frog; the last stop before wastes, sperm, or urine exit the frog’s body.

Spleen: Find this in the folds of the mesentery. This is adark red spherical object serve as holding area for blood.

Esophagus: Follow the stomach upward, where it gets smaller is the beginning of the esophagus. The esophagus is the tube that leads from the frog’s mouth to the stomach.

Open the frog’s mouth and find the esophagus, poke your probe into it and see where it leads.

STOP! DO NOT CONTINUE if you have not located each organ above.

REMOVAL OF THE STOMACH:

  1. Cut the stomach out of the frog and open it up with a scissors.
  2. Find the remains of frog’s last meal in there.
  3. Look at thetextureof the stomach on the inside.

MEASURING THE SMALL INTESTINE:

  1. Remove small intestine from the body cavity and carefully separate the mesentery from it.
  2. Stretch the small intestine out and measure it.
  3. Now measure your frog. Use a ruler to measure your frog, measure from the tip of the head to the end of the frog's backbone (do not include the legs in your measurement).

UROGENITAL SYSTEM:

The frog’sreproductive and excretory system is combined into one system – the urogenital system.

You will need to know the structures for both the male and female frog.

Kidneys:

Flattened bean shaped organslocated at the lower back of the frog, near the spine. They aredark colour. The kidneys (left and right) filter wastes from the blood.

Testes:

Located at the top of the kidney in male frogs; pale coloured and round

Oviduct:

Curled structure around outside of kidney – this is the place where eggs are produced.

Males can have structures that look similar, but serve no actual purpose.

In males, they are called vestigial oviducts.

Bladder:

An empty sac located at the lowest part of the body cavity. It stores urine.

Cloaca: Part of the urogenital system – urine, sperm and eggs exit here.

POST LAB QUESTIONS:

  1. Label the following diagrams.

conusarteriosiscloaca duodenum esophagusgall bladder left atrium liver large intestine lung pancreas right atrium spleen small intestine stomach ventricle

A / I
B / J
C / K
D / L
E / M
F / N
G / P
H
  1. Answer the questions below using the vocabulary provided. The vocabulary may be used more than once.

cloacaduodenum fat gall bladder

large intestineleft anterior left posterior liver

mesenteryperitoneum right lobesmall intestine

spleenstomach pyloric sphincter valve

a)The membrane holds the coils of the small intestine together: ______

b)This organ is found under the liver, it stores bile: ______

c) Name the 3 lobes of the liver: ______, ______, ______

d)The organ that is the first major site of chemical digestion: ______

e) Eggs, sperm, urine and wastes all empty into this structure: ______

f)The small intestine leads to the______

g)The esophagus leads to the______

h)Yellowish structures that serve as an energy reserve: ______

i)The first part of the small intestine (straight part): ______

j)After food passes through the stomach it enters the: ______

k)A spider-web like membrane that covers the organs: ______

l)Regulates the exit of partially digested food from the stomach: ______

m)The large intestine leads to the______

n)Organ found within the mesentery that stores blood: ______

o)The largest organ in the body cavity:______

Turn to next page……

  1. Label the diagram for the urogenital system for a male frog and a female frog.

testeskidneysoviductovary

bladderuretercloacafat bodies

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