ANATOMY - Small Mammals Flashcards
What are two of the main methods used by small mammals to thermoregulate in cold temperatures?
Burrowing
Peripheral vasoconstriction (ears and tail)
Which thermoregulatory method during cold temperatures is unique to rodents?
Rodents have brown adipose tissue which generates heat through non-shivering thermogenesis
What are two of the main methods used by small mammals to thermoregulate in hot temperatures?
Burrowing
Peripheral countercurrent heat exchange
Why is thermoregulation so important in small mammals?
Small mammals have a very hight metabolic rate and are thus prone to dehydration and hypothermia. This makes thermoregulation very important in these species
What are the main adaptations to the lagomorph (rabbit) forelimbs to allow for digging?
Lagomorph (rabbit) forelimbs are shorter and their radius and ulna are fused to facilitate the fast movements used in digging
What are the main adaptations to the lagomorph (rabbit) hindlimbs to allow for propulsion/hopping?
Lagomorph (rabbit) hindlimbs are longer and their fibula and tibia are fused to facilitate the propulsion used in hopping
What is the vertebral formula for lagomorphs (rabbits)?
C7, T12-13, L7, S4, Cd15-16
Why are rabbits prone to fractures at L6-L7 of their vertebral column?
Rabbits are prone to fractures at L6-L7 due to the hindlimbs twisting around the lumbar-sacral junction as the rabbit hops which can cause fractures if the rabbit has not been handled properly
Why do the last five to six ribs in the lagomorph (rabbit) skeleton not meet at the sternum?
The last five to six ribs do not meet at the sternum to allow for better chest wall compliance, allowing the rabbit to meet it’s high oxygen requirements
What is the vertebral formula for guinea pigs?
C7, T13-14, L6, S3-4, Cd4-7
What is one of the main unique features associated with the guinea pig rib cage?
The final two ribs (12-14) are cartilaginous in the guinea pig ribcage
How many digits do guinea pigs have on their forepaws?
Guinea pigs have four digits on their forepaws
How many digits do guinea pigs have on their hindpaws?
Guinea pigs have three digits on their hindpaws
What stance are guinea pig hindlimbs classified as?
Plantigrade
What is the vertebral formula for rats?
C7, T13, L6, S4, Cd27-31
At what age does a rat skeleton fully ossify?
A rat skeleton fully ossifies at one year of age
At what age do the growth plates at the proximal humerus and the distal radius and ulna fuse in a rat?
The growth plates at the proximal humerus and the distal radius and ulna fuse at two years of age in the rat
What are the two main functions of the rat’s tail?
Balance
Thermoregulation
Why do myomorph (rat and hamster) bones take so long to heal?
Myomorphs have a poorly developed Harversian remodelling system causing their bones to take longer to heal compared to other species
What anatomical adaptation allows for myomorphs (rats and hamsters) to have increased flexibility when gnawing?
Cartilaginous mandibular symphysis allows for myomorphs to have increased flexibility when gnawing
Why do ferrets require hindlimb support when being handled?
Ferrets require hindlimb support due to their very flexible vertebral column which can be prone to fractures if not handled properly
What does elodont mean?
Elodonts are species which have teeth which grow continuously throughout their life
What does aradicular mean?
Aradicular species have open rooted teeth
(T/F) All lagomorphs and rodents have elodont, aradicular incisors and cheek teeth
FALSE. Omnivore rodents have elodont, aradicular incisors however their cheek teeth stop growing at around four months old
What are ‘peg teeth’?
Peg teeth are the two rudimentary incisors present on the lagomorph (rabbit) upper jaw
What causes rat incisors to always appear yellow?
Rat incisors have an iron pigmentation causing the incisors to appear yellow (this is normal)
What does a loss in a rats iron pigmentation indicate?
Suboptimal diet
What are hamster cheek pouches?
Hamster cheek pouches are distensible invaginations of the lateral buccal epithelium that extend all the way back to the dorso-caudal scapula
What is the function of hamster cheek pouches?
Hamster cheek pouches are designed to carry food, bedding and neonates
Which four diseases are hamster cheek pouches susceptible to?
Abscesses
Impactions
Prolapse
Tumours
What type of stomach do small mammals have?
Monogastric stomachs
What are the three gastrointestinal anatomical structures unique to lagomorphs (rabbits)?
Sacculus rotundus
Vermiform appendix
Fusus coli
Where in the lagomorph (rabbit) gastrointestinal system is the sacculus rotundus located?
The sacculus rotundus is located at the ileocaecocolic junction
What is the function of the sacculus rotundus?
The sacculus rotundus is made up mostly of lymphoid tissue so aids in immunosurveillance while also preventing backflow from the large intestine into the small intestine
Where is the lagomorph (rabbit) gastrointestinal system is the vermiform appendix located?
The vermiform appendix is located at the terminal end of the caecum
What is the function of the vermiform appendix?
The vermiform appendix is mostly made up of lymphoid tissue so aids in immunosurveillance which also secreting bicarbonate to buffer caecal acid to allow for proper nutritional processing
What is the function of the caecum in lagomorphs (rabbits)?
Rabbits are hindgut fermenters, so the caecum is their site of fermentation. At the level of the caecum, cellulose and proteins are broken down into volatile fatty acids and absorbed into the bloodstream
What is the prominent species of bacteria found in the lagomorph (rabbit) caecum?
Bacteroides
Why must special care be taken when carrying out abdominal surgery on rabbits?
Care must be taken during abdominal surgery as the rabbit abdominal wall is very thin and it is very easy to accidentally cut into the caecum
What are the three anatomical features present on the lagomorph (rabbit) proximal colon that are involved in colon motility?
Taenial bands
Haustra
Fusus coli
What is the function of the fusus coli?
The fusus coli is thick smooth muscle which acts as a pacemaker to control colon motility for the formation of hard and soft faeces (caecotrophs)
What regulates the activity of the fusus coli?
Autonomic nervous system
Aldosterone
What is the purpose of caecotrophy?
The rabbit diet is high in fibre so needs to pass through the digestive tract twice to obtain maximum nutrition
How often are caecotrophs produced in rabbit?
Caecotrophs are produced every eight hours after feeding
How can obesity prevent rabbits from ingesting caecotrophs?
Obese rabbits cannot reach their anus to ingest caecotrophs and instead the caecotrophs will get stuck to them which can lead to miasis (fly strike) and scalding
Why is lagomorph (rabbit) urine always cloudy?
Most mammals regulate their blood calcium to maintain the levels within a particular narrow range. This is done through controlling gut absorption of dietary calcium. Rabbits however, absorb all of the dietary calcium from their gut into their bloodstream and any excess calcium is excreted via the kidneys and into the urine (causing rabbit urine to constantly be cloudy)
Where is the harderian gland located in rodents?
The harderian gland is located behind the eye in rodents
What is the function of the harderian gland?
The harderian gland produces lipids and porphyrin red pigment involved in ocular lubrication and pheromone production
How can the harderian gland be a good indicator if a rodent is under some form of stress?
The harderian gland secretion increases in response to stress leading to a red deposit around the eyes known as chromodacryorrhea which is an obvious indicator if a rodent is under stress
Why is open mouth breathing a poor prognosis in rodents and lagomorphs?
Rodents and lagomorphs are obligate nasal breathers, thus, if they are open mouth breathing they are not achieving a sufficient level of gas exchange
Why are lagomorphs and rodents obligate nasal breathers?
Their larynx is located very high up in their oropharynx
What are the three anatomical adaptations that allow for rodents and lagomorphs to achieve their high oxygen demand due to their high metabolic rate?
Low residual lung capacity
Good chest wall compliance
Larger number of alveoli
Why is it important to raise and lower a rabbit’s head every two minutes during CPR?
Lagomorphs (rabbits) do not use their intercostal muscles during respiration, instead they use they diaphragmatic muscles. Raising and lowering their head during CPR encourages diaphragmatic breathing
What causes pneumonia to spread very quickly in lagomorphs (rabbits)?
Rabbits have very poor lung lobulation, allowing pneumonia to spread very quickly
What are the two lymph nodes which are very susceptible to disease in lagomorphs and rodents?
Submandibular lymph nodes
Cervical lymphs nodes
Why are the submandibular and cervical lymph nodes so prone to disease in lagomorphs and rodents?
The submandibular and cervical lymph nodes drain the oral cavity and the top off the neck and are thus prone to disease due to the high occurrence of dental disease in lagomorphs and rodents
Which bacteria is commensal to the lagomorph and guinea pig oral cavity?
Streptococcus Zooepidermicus
Why is the guinea pig thymus so commonly used for immunological research?
The guinea pig thymus so commonly used for immunological research as it is located in the cranial mediastinum which is easily accessible
Which species of small mammal is particularly susceptible to endocrine disease?
Ferrets
What type of uterus do lagomorphs (rabbits) and most rodents have?
Duplex uterus
What type of uterus do most guinea pigs have?
Bicornate uterus
What type of uterus do ferrets have?
Bicornate uterus
Which accessory glands do male rabbits have?
Prostate
Seminal vesicles
Bulbourethral glands
Which accessory glands do most male rodents have?
Prostate
Seminal vesicles
Ampullary gland
Bulbourethral glands
Which accessory glands do guinea pigs have?
Prostate
Seminal vesicles
Bulbourethral glands
Coagulating gland
Which species’ of small mammal are induced ovulators?
Lagomorphs (rabbits)
Ferrets
Degus
How long are rabbits in oestrus?
Rabbits are in oestrus for 5-6 days
How long is a rabbit’s gestation period?
Rabbits have a gestation period of 31-32 days
(T/F) Rabbits have a low embryonic mortality rate
FALSE. Rabbits have a high embryonic mortality rate
Which species’ of small mammal are seasonally polyoestrus?
Ferrets
Hamster
Chinchillas
How long are ferrets in oestrus?
Ferrets are in oestrus for up to five months
How long is a ferret’s gestation period?
Ferrets have a gestation period of 42 days
How long are hamsters in oestrus?
Hamsters are in oestrus for 4 days
How long is a hamster’s gestation period?
Hamsters have a gestation period of 15-18 days
Which species’ of small mammal are non-seasonally polyoestrus?
Guinea pigs
Rats
How long are guinea pigs in oestrus?
Guinea pigs are in oestrus for 15-17 days
How long is a guinea pig’s gestation period?
Guinea pigs have a gestation period of 59-72 days
How long is a female guinea pig in postpartum anoestrus?
Guinea pigs are in postpartum anoestrus for 2-10 hours after parturition
How long are rats in oestrus?
Rats are in oestrus for 4-5 days
How long is a rat’s gestation period?
Rats have a gestation period of 21-23 days
At what age do male rabbit testes descend?
Male rabbit testes descend into the scrotal sac at 12 weeks old
What are the two reasons a male rabbit would retract their testes back into the body?
Stress
Temperature regulation
What is the function of the inguinal glands lateral to the lagomorph (rabbit) anus?
The inguinal glands are used for scent marking
