Abstract:
:The gross morphology, histology, and ultrastructure of the thyroid gland of the koala, Phascolarctos cinereus, is described. Generally, the glands were found to contain large-diameter follicles in association with an epithelium of low height. Morphometric analysis demonstrated a high relative thyroid weight (0.3 +/- 0.2 g/kg) for koalas compared with the 0.07-0.24 g/kg typical of eutherian mammals and 0.03-0.1 g/kg found in other marsupials. The relative thyroid weight of glands (0.33 +/- 0.21 g/kg) from the coastal population (less than 28 km from the coastline) was found to be significantly higher (ANOVA: P = 0.007, significant at the 1% level) than that for glands (0.21 +/- 0.11 g/kg) of noncoastal koalas (greater than 28 km from the coastline). Follicle size was positively correlated (at the 0.1% level) with relative thyroid weight in the overall koala sample. The presence of C cells, occurring singly in the epithelial layer, was demonstrated in electron micrographs. Structural features such as low epithelial height, large follicle length and width, and large intercellular spaces in association with low concentrations of free T4 (3.3 +/- 2.1 pM) and free T3 (1.4 +/- 0.9 pM) as reported previously (Lawson et al., 1996) are consistent with an unusually low level of glandular activity in the koala thyroid even though iodine concentrations in the thyroid gland [4.7 +/- 1.6 mg/g (dry weight)] as well as leaf [0.8 +/- 0.3 microg/g (dry weight)] and soil samples [3.8 microg/g (dry weight)] from the koalas' habitat appear unremarkable.
journal_name
Gen Comp Endocrinoljournal_title
General and comparative endocrinologyauthors
Lawson VJ,Carrick FNdoi
10.1006/gcen.1998.7076subject
Has Abstractpub_date
1998-06-01 00:00:00pages
295-306issue
3eissn
0016-6480issn
1095-6840pii
S0016-6480(98)97076-9journal_volume
110pub_type
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