Download THYROID HORMONE THYROID HORMONE DYSGENESIS I

12/26/200
THYROID HORMONE
DYSGENESIS I
Marc E. Tischler, PhD;
University of Arizona
THYROID HORMONE DYSGENESIS I
•
thyroid hormones (T4,T3) are made by the follicular cells of the thyroid gland (Figure 1)
•
production of thyroid hormones is signaled by thyroid stimulating hormone (TSH) from
the anterior pituitary (Figure 2)
•
thee inability
ab y too transport
a spo iodide
od de intoo thee thyroid
y o d gland
g a d results
esu s in a lack
ac of
o formation
o a o of
o
thyroid hormones as their synthesis depends on iodine (Figure 1).
•
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)
•
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
T
IT IT
T3
IT
IT
T4
Tgb IT T3
IT
Tgb
IT
+
T4
I Tgb
T4
IT IT
Iodination Hormone
T4
I-
T
Formation
T
DISEASE
T
T
T3
Thyroglobulin (Tgb)
NORMAL
T4
T3
Tgb
T4
T
T4
T4
Thyroglobulin (Tgb)
Hormone
release
I-
Iodide transport
protein
BLOOD
Thyroid hormones (T4, T3)
I-
X
I-
Figure 1. Iodine from the blood is taken into the follicular cell by an iodide transport protein. Iodine is
then attached to tyrosine (T) on thyroglobulin (Tgb) in the colloid. Thyroid hormones (T4,T3) form on
the iodinated Tgb, then are released from Tgb in the cell, and then move to the blood. In thyroid
hormone dysgenesis, the iodide transport protein is lacking (X). Without uptake of iodide the
follicular cell cannot produce thyroid hormone. Patients require hormone replacement therapy.
NORMAL
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 hormone dysgenesis, 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.