ENI - Exotic Endocrinology Flashcards
Describe the hormonal control of larval metamorphosis in amphibians
- Relies on thyroid hormones
- Hypothalamus secretion TRH, stimualtes TSH from pituitary, T3 and T4 produced
- Controlled by T3 and T4
Descibe the inter-renals in amphibians
- Adrenal tissue in amphibians (and fish)
- Adrenal cells intermingled with renal tissue
Where are the islet cells in amphibians?
Singly or in clusters in teh pancreas
Describe the APUD cells in amphibians
- Amine precursor uptake and decarboxylation cells
- Scattered in many organs esp epithelium of GI tract
- Secrete variety of polypeptide hormones
Describe calcitonin in exotic species
- Decrease serum caliciu
- Stimulates osteobalsts to increase bone formation
- In birds, no active decrease of serum Ca2+, just reduction in Ca2+ resorption from bone
- Produced by ultimobranchial bodies in brids
Describe the ultimobranchial body in birds
- Paired, near paratyroid glands or thyroid dependign on species
- Small: 1.0-3.0mm diameter
- Cords/islands of C cells, parathyroid nodules in loose connective tissue stroma
- C-cells make calcitonin
Describe PTH in exotics
- Same roles as in mammals
- Calcitriol activation, phosphate excretion, retention of calcium in kidney
- Absorption of Ca2+ in gut
- Activates osteoclasts to resorb bone and release Ca2+
- But birds more sensitive to PTH than mammals
What are the 3 forms of serum calcium in birds?
- Same as mammals
- Ionised, protein bound and complexed
- Ionised active
- Ionised calcium is measured as total cahnges based on protein bound amount and pH (pH affects protein binding)
What is the role of vitamin D?
- Regulates Ca2+ absorption across intestinal wall
- Induces formation of carrier protein calbindin
- Stimulates bone formation by osteoblasts
Describe vitmain D in birds and reptiles
- D3 form required, cannot use D2 easily (unlike mammals)
- Sources include diet, supplements and conversion using UV-B
- Plants have D2, poor source for reptiles and birds
- Supplement is contain D3, if for mammals may be D2 and unsiotable
- Can convert D2 to D3 with sufficient UV-B light exposure
Describe calcium homeostasis in amphibians
- Across skin or GI tract
- Excretion via urine, faeces and skin
- Storage in bone, endolymphatic sacs, skin
Describe calcium homeostasis in rabbits
- Plasma Ca2+ 30-50% higher than other animals
- Passive absorption across gut wall, vit D not required but more efficient if present
- No feedback, absorb as much as is in diet
- Excretion via kidneys (can excrete up to 60%)
- Facilitated by high plasma calcium
- High tolerance for high levls of dietary Ca+
Compare glucose homeostatic mechanisms in birds to mammals
- Higher glucagon, lower insulin
- Glucagon more important in carbohydrate metabolism
- Blood glucose poor indicator of energy balance
Why is blood glucose a poor indicator of energy balance in birds?
- Many species hae small declines in glucose during polonged fasts
- Generally maintain glucose levels well
- Limited fluctuation
Outline hyperglycaemia in reptiles
- Unlikely to be due to diabetes mellitus
- Can be affected by physiological and environmental variables
- Housing, lighting, heating, diet, vitamin and mineral supplementation
- Changes to environmenta, previous medical history, treatment with drugs
- Seasonal cycles: hibernation, reproduction (high glucose in breeding season, low in sutum, high after emerge from hibernation)
- Stress-related hyperglycaemia
Describe the process of ecdysis
- Shedding of skin
- Cells in intermediate layer of epidermis replicate, form new 3 layer epidermis
- Lymph infiltrates between top and new layers, enzymes released, shed upper layer
- Controlled by thyroid hormones
Describe thyroid hormones in birds
- T3 lower than in mammals
- Bird specific assay to detect T4, specific processing
- T4 levels fluctuate over 24 hours (higher at night when fasting)
- Linked to reproduction
- Avian thyroglobulin higher percentage iodine than mammals so easily develop goitre
- To assess T4, use TSH-stimulation test
Outline the relationship between thyroid hormonnes and reproduction
Increased day length leads to increased T4 which increases reproductive activity
Outline the control of song in birds
- Song nuclei affected by photoperiod and testosterone
- Mostly males that sing
- Seasonal stimulation of song nuclei by photoperiod and testosterone
- Photoperiod has direct stimulation on photoreceptors in brain
- Testosterone (and eostrogenic and androgenic metabolites) increases in spring, stimulates singing
- Melatonin attenuates increases in song volume induced by long days
Describe the circadian system in birds
- Pineal gland (melatonin)
- Retinae of eyes (photic signal back to pineal gland)
- Self-sustained oscillatory in hypothalamus (generates own internal rhythm, affected by melatonin and light from pineal retina)
- Importance varies across species
What is the dominant glucocorticoid in reptiles, birds, amphibians and rodents vs most mammals?
Corticosterone vs cortisol in most mammals
Outline glucocorticoid release
- Stress leads to increased stimulation of corticotropin from PVN of hypothalamus
- Stimulates release of ACTH from pituitary
- Stimulates adrenal cortex (fasciculata region) to secrete glucocorticoids (corticosterone dominant in reptiles, birds, amphibians and rodents)
