Thyroid Flashcards
What does the thyroid regulate?
Rate of metabolism of the body: Oxygen utilization
Essential for growth and development, particularly of the CNS. Regulate lipid and carb metabolism, and thus body weight
Thyroid anatomy:
- _____, comes through _______duct- a duct cyst will ____ when swallowing
- 12 weeks, independent at 20-26. No descent no function
- _____ ______ nerves
- ____ ____ artery (EC) and ___ ____ artery ( SUB)
- Endoderm, comes through thyroglossal duct- a duct cyst will move when swallowing
- 12 weeks, independent at 20-26. No descent no function
- Recurrent laryngeal nerves
- Superior thyroid artery (EC) and inf thyroid artery ( SUB)
Histology
Single layer of ______ epithelial cells. Go _____ on hormone release
Forming a circle around lumen filled with ____.
Colloid contains ______
Also parafollicular/ C cells that secrete _____
Single layer of cuboidal epithelial cells. Go columnar on hormone release
Forming a circle around lumen filled with colloid.
Colloid contains thyroglobulin
Also parafollicular/ C cells that secrete calcitonin
Histology of thyroid and clinical relations
- Medullary thyroid cancer secretes a lot of calcitonin, and is used as the tumour marker
- Differentiated thryoid cancer cells produce a lot of thyroglobulin, used as a measure in blood.
Thyroglobulin levels thyroiditis vs factitous thyrotoxicosis
In thyroiditis, high levels. If factitous so excess intake, low-normal level thyroglobulin
What are our daily iodine needs and iodine deficiency
150ug a day, in ____ and ___
If deficient, compensatory enlargement of the thyroid, _____
If a pregnant woman has low iodine, low fetal thyroid leading to abnormal CNS development (_____)
150ug a day, in salt, fish.
If deficient, compensatory enlargement of the thyroid, GOITRE
If a pregnant woman has low iodine, low fetal thyroid leading to abnormal CNS development (cretinism)
What is iodide trapping?
Low serum iodide
Iodide is trapped by sodium-iodide symporter, NIS
Active transport of 2 Na+ and one I-. (Iodine oxidised to iodide)
Thyroid has 8000ug of iodide, storage time of 50 days for acute deficiency
1st step in thyroid hormone synthesis
Drugs?
___ brings in iodide by active transport with 2 Na+
______ inhibits ____ ____, so reduces iodine uptake (hyperthyroidism treatment)
_____ can cause hyperthyroidism due to high iodine content
NIS brings in iodide by active transport with 2Na+
Carbimazole inhibits thyroid peroxidase, so reduces iodine uptake (hyperthyroidism treatment)
Amiodarone can cause hyperthyroidism due to high iodine content
2nd Step in thyroid hormone synthesis
-Iodide transported into colloid by pendrin
-Oxidation of I- to __ is catalysed by____ _____ (TPO)
-In the presence of ____, TPO iodinates
____ residues in thyroglobulin (Tg)
This forms MIT and DIT (lumen interface?)
-Iodide transported into colloid by pendrin
-Oxidation of I- to I0 is catalysed by thyroid
peroxidase (TPO)
-In the presence of H2O2, TPO iodinates
tyrosine residues in thyroglobulin (Tg)
This forms MIT and DIT (lumen interface?)
3rd Step
Still on Tg, ___ and DIT combine to form T4 and T3
90% of what is formed is T4. T3 is the active form.
Release of T4 and T3 is stimulated by ___
Still on Tg, MIT and DIT combine to form T4 and T3
90% of what is formed is T4. T3 is the active form.
Release of T4 and T3 is stimulated by TSH
Action of TSH
Action of TSH, ____ in colloid droplets.
__ degraded from T4/3 (protease)
Unused MIT and DIT ______ and recycled
Action of TSH, endocytosis in colloid droplets.
Tg degraded from T4/3 (protease)
Unused MIT and DIT deiodonated and recycled
How is T3 converted peripherally?
By Peripheral deiodination of T4 (80% of T3 comes from this)
Thyroiditis:
- Thyroiditis: Thyroid hormones dumped into the bloodstream, as well as __. Will be thyrotoxic, then hypothyroid, then recover. Differentiate _____ ingestion of thyroxine
- Acute illness: Conversion to __ will be lower, often in liver, “sick” euthyroid state with low T3 but normal TSH
- Graves diagnosis with anti- ___ antibodies ??
- Thyroiditis: Thyroid hormones dumped into the bloodstream, as well as Tg. Will be thyrotoxic, then hypothyroid, then recover. Differentiate surreptitous ingestion of thyroxine
- Acute illness: Conversion to T3 will be lower, often in liver, “sick” euthyroid state with low T3 but normal TSH
- Graves diagnosis with anti- TPO antibodies ??
Thyroid feedback mechansims
TSH structure: Pregnancy
T4 and T3 have negative feedback on the pituitary and HT. High T4, low TSH, low T4, high TSH
TSH has the same alpha subunit as FSH, LH. Different B subunit, so determines specificity.
Pregnancy: hCG can stimulate TSH receptors thyrotoxicosis, morning sickness
Pituitary abnormality
high T4 high TSH
a low T4 but normal TSH (no response)
