[5] Thyroid Flashcards
Most important enzyme in the production of Thyroid Hormones
Thyroid Peroxidase
Usual Amount of Iodine in Diet
400ug
Daily Requirement of Iodine in Non-Pregnant and Pregnant Adults
Non: 150 mcg/d
Preg: 200mcg/d
Importance of Thyroid Hormone in Fetuses
Brain Development
Branching of Axons and Dendrites
How long can a normal human’s Iodine stores last?
2 months (7,500mg)
Where is Iodine usually trapped?
Lacrimal glands, salivary glands
How do you assess the thyroid?
Urine Iodine Levels
Thyroid Scan w/ Uptake
Is iodine uptake increased or decreased in patients with iodine deficiency?
Additional iodine uptake occurs in patients with abnormal iodine levels
Describe: Iodide Trap/NIS
2 Na per 1 I via secondary active transport
Effect of Increased TSH in NIS
Increased Expression
Prevalence of Endemic Goiters
10%
Cause: Goiters
Lack of Iodine causes the pituitary to increase secretion of TSH to trap more iodine causing enlargement of the thyroid
What helps Iodine exit the follicular lumen?
Pendrin
How does T3 or T4 enter the cell?
Through Megalin
Thyroglobulin Components
MIT 7
DIT 6
T4 2
T3 0.2
Production Values
T4: 90ug
T3: 35ug
rT3: 35ug (Reverse T3)
Storage Values of Thyroid Hormones
90% T4
10% T3
1% rT3
What Thyroid hormone is produced more in iodine deficient states?
T3, T4 is a stored inactive form
Transport Molecules of Thyroid Hormones
Thyroid Binding Globulin: 70%
Transthyretin: 15%
Albumin: 15%
Why is TBG important in Transport?
- Enables lipid soluble hormone to traverse blood stream
- Storage for considerable amount of hormone
- Prevent loss of small hormone molecules into the urine, conserving Iodine
Effect of Estrogen on TBG
Increase
Effect of Hepatitis on TBG
Liver is the main producer of TBG, as a result of the hepatitis more of it would leak out and cause the increase in TBG
In what situation would there be increased rT3 production?
High catabolic states such as in sepsis
Location: Type 1 Deiodinase
Areas of high blood flow
Thyroid
Liver
Kidney
Skeletal Muscle
