Thyroid Diseases Flashcards
What are the main thyroid hormones?
T3 (triiodo-thyronine) and T4 (tetraiodo-thyronine/thyroxine)
T4 is 93% of thyroid hormones, while T3 is 7%.
What is the primary function of thyroid hormones?
Regulation of metabolic rate, growth, development, neurologic function, reproduction, cardiovascular system, skeletal muscle, and bone remodeling
Thyroid hormones affect body heat and oxygen consumption.
What is the T4/T3 ratio released in blood?
Approximately 13:1
T4 is converted to T3 mostly in peripheral tissues.
What is the role of the Sodium-Iodide Symporter (NIS)?
Iodine trapping in the thyroid gland
It concentrates iodide from the blood by 30 times.
What is organification in the thyroid gland?
The incorporation of I2 (inorganic iodine) into thyroglobulin (TG)
It involves iodination and coupling catalyzed by Thyroid Peroxidase (TPO).
What is the dietary iodine requirement?
1 mg I-/week (50 mg/year)
Needs increase with body mass, pregnancy, and lactation.
What is the half-life of free T4 and T3 in serum?
Free T4 ~1 week, Free T3 ~1 day
Only free T4 and T3 are considered biologically active.
What is the function of peripheral deiodinases?
Regulation of thyroid hormone bioavailability
D1, D2, and D3 are the main types, converting T4 to T3 and rT3.
What are the two mechanisms of thyroid hormone action?
Genomic and non-genomic mechanisms
Genomic involves binding to nuclear receptors; non-genomic effects occur rapidly.
What are the physiological effects of elevated thyroid hormones?
Increased heart rate, weight loss, heat intolerance, anxiety, and tremors
Symptoms include exophthalmos in Graves’ disease.
What is the hypothalamus-pituitary-thyroid axis?
TRH → TSH → T3/T4 with negative feedback inhibition
TRH is produced in the hypothalamus and stimulates TSH release from the anterior pituitary.
What are stimulatory factors for thyroid hormone secretion?
- TSH
- Thyroid-stimulating antibodies
- Increased thyroid-binding globulins
- Pregnancy
These factors promote hormone synthesis and secretion.
What are inhibitory factors for thyroid hormone secretion?
- Iodine deficiency
- Excessive iodine intake
- Perchlorate
- Thiocyanate
- Propylthiouracil
- Methimazole
- Decreased TBG
- Liver disease
These factors can suppress thyroid function.
What are the common causes of hyperthyroidism?
- Graves’ disease
- Thyroid adenoma
- Excessive TRH/TSH secretion
- Exogenous thyroid hormone
Graves’ disease is the most common cause.
What are the symptoms of hypothyroidism?
- Decreased heart rate
- Cold intolerance
- Goiter
- Myxedema
- Fatigue
- Digestive issues
- Reduced brain function
- Unexplained weight gain
- Depression
- Hair loss
- Muscle weakness
- Dry itchy skin
Hashimoto’s thyroiditis is a common cause.
What is cretinism?
Congenital hypothyroidism often due to iodide deficiency
Symptoms include pot-bellied appearance, pale skin, puffy face, protruding umbilicus, and protruberant tongue.
What is Non-thyroidal Illness Syndrome (NTIS)?
Low T3 levels with normal TSH in severe illness
It complicates treatment decisions due to overlapping symptoms.
What is the main treatment for hypothyroidism?
T4 (Synthroid), T3 (Cytomel), Armour (T3/T4 extracted from pig thyroid glands)
These treatments help restore normal hormone levels.
What is the primary treatment for hyperthyroidism?
Propylthiouracil (PTU) and Methimazole
These medications block thyroid hormone production and peripheral conversion.
What are the main treatments for hypothyroidism?
T4 (Synthroid), T3 (Cytomel), Armour (T3/T4 extracted from pig thyroid glands)
These treatments aim to replace or supplement the deficient thyroid hormones.
What are the main treatments for hyperthyroidism?
propylthiouracil (PTU), Methimazole, radioactive iodine, thyroid gland surgery
PTU and Methimazole block thyroid hormone production.
What is a notable concern regarding patients treated with Synthroid?
About 1/5 of patients remain symptomatic and are not happy
This indicates a growing concern in the treatment of hypothyroidism.
What is the structure of thyroid hormones?
Two linked tyrosines with attached iodine molecules
This structure is essential for their function in regulating metabolism.
How are thyroid hormones transported in the blood?
Bound to proteins
This binding is crucial for their stability and transport in the circulation.