Download THYROID OXIDASE THYROID OXIDASE DEFICIENCY – 2A

12/26/200
THYROID OXIDASE
DEFICIENCY – 2A
Marc E. Tischler, PhD;
University of Arizona
THYROID OXIDASE DEFICIENCY – 2A
•
thyroid hormones (T4,T3) are made by the follicular cells of the thyroid gland (Figure 1)
•
the key enzyme in the processing (oxidation) of iodine and formation of thyroid hormones
is peroxidase
•
lack
ac of
o peroxidase
pe o dase in thee ddisease
sease means
ea s that
a iodine
od e cannot
ca o be oxidized
o d ed nor
o attached
a ac ed for
o
making thyroid hormone
•
lack of thyroid hormone in the blood causes the brain to send out unabated signals for the
gland to make more thyroid hormone, which of course is not possible (Figure 2)
•
lack of thyroid hormone production in the disease requires hormone replacement therapy
•
thyroid hormone functions:
o
growth
o
maintaining body’s basal metabolic rate (BMR)
o
heat production
o
promoting sweating
•
consequences of hypothyroidism (low blood thyroid concentration)
o
low BMR weight gain
o
sluggishness, decreased heart rate
o
intolerance to cold
o
dry skin
12/26/200
THYROID FOLLICULAR CELL
COLLOID SPACE
IT IT
T3
IT
IT
T4
Tgb IT T3
IT
Tgb
IT
+
T4
I Tgb
T4
IT IT
Iodination
Hormone
T4
Oxidation
I-
I-
Formation
Peroxidase
Peroxidase
T
X
T
DISEASE
S
t d tto C
ll id
Secreted
Colloid
T
T
T3
Peroxidase
In Golgi
T
T4
Thyroglobulin (Tgb)
I-
T3
Tgb
T4
T
Golgi
T4
T4
Thyroglobulin (Tgb)
Hormone
release
I-
NORMAL
I-
I-
Thyroid
hormones
T4, T3 BLOOD
NORMAL
Figure 1. Iodine from the blood is oxidized and then attached to tyrosine (T)
on Tgb in the colloid. Thyroid hormones are then formed on the modified Tgb.
These events all are regulated by peroxidase. Thyroid hormone is then released
from Tgb inside the cell and from there moves to the blood. In thyroid oxidase
deficiency the peroxidase is lacking (X) and none of these events can occur.
Patients require hormone replacement therapy.
Hypothalamus
Inhibitory
signals by
thyroid
hormone
Hypothalamus
Thyrotropin releasing hormone (TRH)
Anterior pituitary gland
X
DISEASE
Loss of
inhibitory
signals
Anterior pituitary gland
X
Thyroid stimulating hormone (TSH)
Thyroid
Th id
hormones
T4, T3
Thyroid gland:
hormone secretion
and cell growth
Thyroid gland:
enhanced
cell growth only
X
Figure 2. TRH from hypothalamus region of the brain signals anterior pituitary to release TSH. TSH signals thyroid gland
to make and release thyroid hormones. Abundant thyroid hormone signals the hypothalamus and anterior pituitary to stop
releasing their stimulatory factors. In thyroid oxidase deficiency, the lack of thyroid hormones causes the stimulatory
factors to be overproduced due to loss of inhibitory signals (X) and leads to growth (enlargement) of the thyroid gland.