rat dissection from notes

What is the scientific name of the rat?

Rattus norvegicus

List common names for rats

Rat, sewer rat, street rat, Norway rat, wharf rat, brown rat

What kingdom does the rat belong to?

Animalia

What kingdom does the rat belong to?

Animalia

What phylum?

Chordata

What subphylum?

Vertebrata

What class?

Mammalia

What order?

Rodentia

Where did rats originate?

Asia

What does Rodentia mean?

“To gnaw”

How many species are in Order Rodentia?

Over 2,000 species

How are rodents classified into groups?

By physical appearance and genetics

Name rodents in the first group

Chipmunks, woodchucks, squirrels, prairie dogs, gophers

Name rodents in the second group

Mice, rats, gerbils, hamsters, lemmings

Name rodents in the third group

Porcupines, guinea pigs, chinchillas

What does the rat’s upper lip expose?

Large front incisors

How many pairs of incisors do rats have?

2 pairs

What is special about rodent incisors?

They grow continuously

How are incisors kept at the correct length?

Constant chewing

What covers the rat’s body?

Hairy coat

Where are sensory whiskers located?

On the face

What are whiskers called?

Vibrissae

What is the function of vibrissae?

Help rats feel through tight spaces in the dark

What is found in the inside corner of the eye?

Nictitating membrane

What is special about rat eyes?

They have large pupils

Is the nictitating membrane found in most mammals?

Yes

What are the external ears called?

Pinna

What is the pinna made of?

Cartilage covered by skin

What is the function of the pinna?

Rotates to detect sound direction

What are nostrils called?

External nares

Function of external nares?

Respiration and odor detection

Where are nipples located?

Ventral (stomach) side

Do males have nipples?

Yes (non-functional)

When do human embryos develop external sexual organs?

Between 7–12 weeks after fertilization

What is the embryo called starting week 9?

Fetus

How many nipples do rats have?

12

What is the average litter size?

8–10 young

Can rats have larger litters?

Yes, up to 15

How long is rat gestation?

21–24 days

How many litters per year (average)?

4

Vibrissae = ?

Whiskers

Nictitating membrane = ?

Eye membrane (inner corner)

Pinna = ?

Ear

External nares = ?

Nostrils

Incisors = ?

Continuously growing front teeth

What systems have exit openings in rats?

Digestive, excretory, and reproductive systems

How many exit openings do male rats have?

2

How many exit openings do female rats have?

3

What is the digestive opening called?

Anus

What is the excretory opening called?

Urinary opening (for urine)

What is the reproductive opening called?

Vagina

What is the digestive opening called in males?

Anus

What is the second opening in males called?

Urogenital opening

What passes through the urogenital opening?

Urine and sperm

Why must testes be outside the body?

To stay cooler than body temperature for sperm production

Where are testes located?

In a sac called the scrotum

What are testes outside the body called?

Testicles

Do rats have hair on their tails?

No

Which rodents DO have hairy tails?

Gerbils, squirrels, chipmunks

What type of body cavity do mammals have?

Eucoelomates

What muscle helps mammals breathe?

Diaphragm

How does the diaphragm work?

Contracts to pull in air (negative pressure breathing)

What does the diaphragm separate?

Thoracic and abdominal cavities

What is in the thoracic cavity?

Heart and lungs

What is in the abdominal cavity?

Digestive, excretory, and reproductive organs

Male openings = ?

2 (anus + urogenital)

Female openings = ?

3 (anus + urinary + vaginal)

Urogenital opening = ?

Urine + sperm

Diaphragm = ?

Muscle for breathing + separates cavities

Rats’ tails = ?

No hair

Where is the liver located?

Just under the diaphragm

What does the liver look like?

Large, dark-colored organ

How many lobes does a rat liver have?

3 lobes (humans have 4)

What are the functions of the liver?

Digests fats (via bile), stores glycogen, transforms toxins

Do rats have a gallbladder?

No

Why don’t rats have a gallbladder?

They do not eat fatty foods

Where is the stomach located?

Right side, just under the liver

What is the shape of the stomach?

Curved organ

What tube connects to the stomach?

Esophagus

What is the cardiac sphincter?

Where esophagus and stomach meet

Function of cardiac sphincter?

Prevents food from going back into the esophagus

Where is the pancreas located?

Near the duodenum (next to small intestine)

How do you find the pancreas?

Lift the stomach

What does the pancreas look like?

Thin membrane or bumpy “cottage cheese-like” tissue

What is the function of the pancreas?

Releases digestive enzymes into the small intestine

Where is the spleen located?

Attached to the greater curvature of the stomach

What color is the spleen?

Similar to liver

What shape is the spleen?

Banana-shaped

What does the spleen do?

Controls white blood cells, red blood cells, and platelets

What else does the spleen do?

Removes old/damaged red blood cells and filters blood

Where do the small intestines begin?

At the pyloric sphincter

What is the pyloric sphincter?

Opening at the bottom of the stomach

What does “small” refer to?

Diameter, NOT length

What are the 3 parts of the small intestine?

Duodenum, jejunum, ileum (DJI)

Which part is mostly straight?

Duodenum

Which parts are curly?

Jejunum and ileum

Liver = ?

Under diaphragm, 3 lobes, no gallbladder

Cardiac sphincter = ?

Prevents backflow to esophagus

Pancreas = ?

Bumpy membrane, releases enzymes

Spleen = ?

Banana-shaped, filters blood