Rodents

Question 1

What characteristic is rodent classification based on?

Answer 1

Continuously growing incisor teeth

Question 2

How are rodents classified?

Answer 2

Order = Rodentia
Suborders = myomorphs (mouse-like), hystricomorphs (porcupine- like), scuriomorphs (squirrel-like), castorimorphs (beavers ect.), anomaluromorphs (scaly-tailed squirrels)

Question 3

What is the dental formula of a myomorph?

Answer 3

I 1/1 C 0/0 P 0/0 M 3/3 = 16

Question 4

What is the dental formula of a hystricomorph?

Answer 4

I 1/1 C 0/0 P 1/1 M 3/3 = 20

Question 5

What is the lower:upper incisor crown ratio of myomorphs?

Answer 5

3:1

Question 6

Describe the growth of myomorph molars

Answer 6

Anelodont = NOT continually growing/ erupting

Question 7

Describe the growth of hystricomorph molars

Answer 7

Elodont = continually growing

Question 8

What kind of GI tracts do rodents have?

Answer 8

mono-gastric

Question 9

Describe the stomach of rodents

Answer 9

glandular part of the stomach is separated from forestomach by ridge

Question 10

Why can’t rodents vomit?

Answer 10

limiting ridge b/w oesophagus + cardia of stomach, strong oesophageal sphincter, diaphragmatic muscle too weak

Question 11

What is the advantage of caecotrophy?

Answer 11

Enhances the uptake of essential vitamins/ amino acids

Question 12

What anatomical structures make rodents obligate nasal breathers?

Answer 12

high larynx, elongated soft palette

Question 13

Describe the lungs of rodents

Answer 13

• L lung = 1 lobe

- R lung = cranial, caudal, middle, accessory

Question 14

How are rodents respiratory systems adapted for high O2 requirements?

Answer 14

• short airways + increased rr
• more alveoli + thinner diameter
• high chest wall compliance

Question 15

Explain the shift of the haemoglobin curve in rodents

Answer 15

Curve shifted to R- haemoglobin offloads O2 more readily @ tissues

Question 16

Describe what thermogenesis mechanisms rodents have?

Answer 16

• Behavioural (huddling/ tunnelling)
• Shivering
• Peripheral vasoconstriction
• Brown fat behind scapula/ neck

Question 17

What heat loss mechanisms do rodents have?

Answer 17

• Sweat glands (minimal)
• Saliva
• Arteriovenous shunts in ears/ feet/ tail

Question 18

Compare the reproductive strategies of myomorphs + hystricomorphs

Answer 18

• Myomorph = large litter, short gestation, altricial young

- Hystricomorph = small litter, long gestation, precocial young

Question 19

What type of reproductive tract does a guinea pig have?

Answer 19

bicornate (1 cervix, 2 horns)

Question 20

What type of reproductive tract do rat, mice, hamsters have?

Answer 20

Duplex (cervix associated w/ each horn)

Question 21

What is the most reliable method of sexing rodents?

Answer 21

ano-genital distance- longer in males than females

Question 22

Name the method used to determine the stage of oestrus?

Answer 22

Cytology of vaginal secretions

Question 23

What is the ‘Copulatory Plug’?

Answer 23

congealed sperm, mucus + accessory ejaculatory fluid that hardens within cervix for 8-12hrs- makes making more successful