endocrinology of exotics

Question 1

when an animal encounters a stressor the hypothalamus responds by producing which hormone

Answer 1

corticotropin releasing hormone

Question 2

stress stimulates the release of ACTH from which gland

Answer 2

pituitary

Question 3

what is the predominant glucocorticoid in reptiles, birds, amphibians and rodents

Answer 3

corticosterone

Question 4

in mammals, what hormone is produced when calcium leves are high

Answer 4

calcitonin

Question 5

how does calcitonin work to reduce serum calcium levels in mammals

Answer 5

• inhibiting the breakdown of bone
• inhibiting the reabsorption of calcium in the kidney

Question 6

what hormone is released when calcium levels are low

Answer 6

parathyroid hormone and caltiriol (activated by PTH)

Question 7

how does parathyroid hormone help to increase blood serum concentrations of calcium

Answer 7

• stimulating bone brakedown by osteoclasts
• increasing reabsorption of calcium from the kidney (and decrease excretion)
• increasing reabsorption of calcium from the gut

Question 8

where is calcitonin secreted

Answer 8

ultimobranchial gland (thyroid)

Question 9

discuss calcium homeostasis in birds

Answer 9

• calcium is important for bone strength, biochemical reactions, egg laying
• rapid response
• inclcludes PTH, cacitonin, calcitriol
• oestrogen, androgens and prostaglandins
• calcitonin produced in high concentrations
• birds more sensitive to PTH
• 3 forms: ionised, protein bound and complex anions (must measure ionised in birds)

Question 10

discuss vitamin D in birds and reptiles

Answer 10

• D3 form required (unlike mammals, cannot easily use D2)
• get from diet (plants have D2)
• supplements
• can convert D2 to D3 if sufficient UV-B light exposure

Question 11

discuss calcium homeostasis in rabbits

Answer 11

• Plasma Ca2+ levels
• 30-50% higher in rabbits compared to other mammals
• (Ionised calcium similar to other mammals)
• Most absorbed in intestine
• Passive absorption by PTH, calcitonin
• Not vitamin D dependent
• absorption directly proportionate to amount ingested
• have HIGH tolerance for high levels of dietary Ca
• excess excreted in urine (can excrete up to 60% ingested Ca which precipitates as calcium carbonate in urine leading to cloudy/sludgy urine)

Question 12

what hormones control ecdysis

Answer 12

T3 and T4

Question 13

metamorphisis is controlled by what hormones

Answer 13

thyroid hormones

Question 14

discuss the thyroid in birds

Answer 14

• produces T3 and T4
• stimulates new feather growth
• controls metabolism
• regulates heat and growth
• regulates reproductions and egg production
• avian thyroglobulin has higher percentage iodine than mammals

Question 15

discuss issues of the thryoid in birds

Answer 15

• more susceptible to thyroid deficiency
• hypothyroidism and thryoid hyperplasia relatively common
• clinical signs: abnormalities in skin and feathers, depression and lethargy, increased susceptibility to infections, visible swelling in neck, regurgitation and weight loss, respiratory abnormalities and loss of voice

Question 16

discuss diagnosis of hypothyroidism in birds

Answer 16

• T4 much lower in birds than mammals and can be affected by illness, stress etc.
• need bird specific assays to detect T4
• T4 levels have a diurnal rhythm
• to assess T4, use TSH stim test instead of one off T4 measurement

Question 17

discuss the pineal complex in mammals

Answer 17

• pineal gland in brain does same as in mammals
• also have parietal eye (3rd eye) which is photoreceptive structure on top of head
• has lens, cornea and retina
• produces and secretes melatonin