57 Questions
Which condition is characterized by an excess of thyroid hormones in the bloodstream?
Thyrotoxicosis
Which of the following is a cause of thyrotoxicosis?
Toxic multinodular goiter
Which of the following is a clinical feature of hyperthyroidism?
Heat intolerance
Which medication could contribute to the development of thyrotoxicosis?
Amiodarone
Which symptom is commonly associated with hyperthyroidism?
Lid retraction
Which biological process is significantly affected by thyroid hormones?
Metabolism of carbohydrates, proteins, and lipids
What function do thyroid hormones have on the nervous system?
Increase the effect of catecholamines
Which statement is true regarding the conversion of T4 to T3?
25% of T4 is converted to T3 in peripheral tissues
Where does the conversion of T4 to T3 primarily take place?
Liver and kidneys
Which of the following is a non-biologically active form of T3?
Reverse T3
Which of the following treatments is rarely indicated for hyperthyroidism?
Surgery
Which of these is not a treatment option for hyperthyroidism?
Levothyroxine
Which hormone levels are greatly increased in primary hypothyroidism?
TSH
Which disease results in the destruction of the thyroid gland in primary hypothyroidism?
Hashimoto's disease
Which of the following is a cause of secondary hypothyroidism?
Pituitary disease
In severe cases of primary hypothyroidism, which treatment is generally used?
Thyroid hormone replacement
What initiates the release of TSH from the anterior pituitary gland?
TRH
What is the primary inhibitory effect of T4 and T3 in the feedback loop?
Inhibition of TSH release by the anterior pituitary gland
Which gland directly releases T4 and T3 into the bloodstream?
Thyroid gland
In the feedback loop, what role does the circulatory system play?
Transporting hormones
What is the primary method for assessing thyroid function?
Determination of free T4 and TSH levels
Where are T4 and T3 conjugated before being removed from the body?
Liver
What hormone is secreted by the hypothalamus to regulate the thyroid gland?
TRH
Which of the following is NOT part of the thyroid hormone regulation feedback loop?
Liver
What is a common finding in thyroid function tests after surgery?
Abnormal thyroid function tests
Which condition is characterized by reduced T4 and T3 levels and normal TSH levels?
Chronic renal failure
In hyperthyroidism, which of the following is typically decreased?
TSH
What is a primary cause of Grave's disease?
High levels of thyroid antibodies binding to TSH receptors
What causes thyrotoxicosis in Grave's disease?
Stimulation of thyroid hormones by thyroid antibodies
What percentage of T4 and T3 in plasma are bound to thyroxine binding globulin (TBG)?
More than 95%
Which drugs can displace T4 and T3 from their binding proteins?
Salicylate and phenytoin
The total concentration of T4 in plasma is:
60 - 150 nmol/L
The concentration of T3 in plasma ranges from:
1.0 - 2.9 nmol/L
Which factors determine the total concentration of thyroid hormones in plasma?
Thyroid gland activity and TBG concentration
What is the minimum daily requirement of iodine for normal thyroid hormone production?
75 micrograms
Which food is a major source of iodine?
Iodized salt
Why is iodine essential for thyroid hormones?
It forms part of their structure
Which of the following is NOT a source of dietary iodine?
Cereals
Thyroid hormones incorporate which element in their structure?
Iodine
Which hormone is more active in the body?
Tri-iodothyronine (T3)
What is the common characteristic between T3 and T4?
Both consist of two tyrosine molecules
Which organ is primarily responsible for converting T4 to T3?
Kidney
What is the concentration range of T4 secreted by the thyroid gland?
60 to 150 nmol/L
What is the role of tyrosine in thyroid hormone synthesis?
It is the precursor for T3 and T4
Which thyroid function test is more sensitive in primary hypothyroidism?
TSH
What does uniformly increased uptake of radioactive iodine in the thyroid gland indicate?
Grave's disease
Which measurement has become an indicator of thyroid function because it regulates the release of thyroid hormones?
TSH
In the case of hyperthyroidism, what is typically observed regarding TSH levels?
Suppressed TSH
Which test is used to diagnose Grave's disease alongside radioactive iodine uptake?
Anti-thyroglobulin antibodies
What does a single hot spot in radioactive iodine uptake indicate?
Adenoma
What does patchy uptake of radioactive iodine in multinodules indicate?
Goiter
What would be the TSH levels if the thyroid gland is suspected to be diseased but TSH is normal?
Normal
Which of the following correctly describes a key difference between primary and secondary hypothyroidism?
Plasma TSH is high in primary and low in secondary hypothyroidism.
Which of the following is NOT a clinical feature of hypothyroidism?
Tachycardia
What is the primary treatment method for hypothyroidism?
Oral administration of thyroxine
Infertility, oligomenorrhoea, and menorrhagia in hypothyroidism primarily affect which system of the body?
Reproductive system
Which of these symptoms is a direct result of the body's low metabolic rate due to hypothyroidism?
General weakness
Study Notes
Thyroid Gland and Thyrotoxicosis
- Thyrotoxicosis is an excess of thyroid hormones in the bloodstream, caused by:
- Toxic multinodular goiter
- Thyroid adenoma
- Thyroiditis
- Exogenous iodine-containing drugs (e.g., amiodarone)
- Excessive T4 and T3 injection
- Pituitary tumors
Clinical Features of Hyperthyroidism
- Loss of weight
- Sweating and heat intolerance
- Angina and heart failure
- Palpitation
- Oligomenorrhea (irregularities in menstrual cycle)
- Infertility
- Lid retraction
Regulation of Thyroid Hormones
- Hypothalamus stimulates the anterior pituitary gland to release TSH
- TSH stimulates the thyroid gland to release T4 and T3
- T4 and T3 inhibit the hypothalamus, preventing excess TSH release (negative feedback loop)
Tests of Thyroid Function (Role of TSH)
- Measuring T4 and TSH levels in the blood
- Determination of free T4 and TSH
- TSH measurement is an indicator of thyroid function
Thyroid Gland and Thyroid Disorders
- Thyroid function tests are abnormal in:
- Thyroiditis (infection of the thyroid gland)
- Malignancy
- Myocardial infarction
- Post-surgery cases
- Chronic renal failure
Disorders of Thyroid Gland
- Hyperthyroidism: excessive thyroid hormone production
- Hypothyroidism: insufficient thyroid hormone production
- Grave's disease: an autoimmune disease with high thyroid-stimulating antibodies
Thyroid Hormones
- T4 (thyroxine) and T3 (triiodothyronine) are the two main thyroid hormones
- T4 is converted to T3 in peripheral tissues (mainly liver and kidneys)
- T3 has greater biological activity than T4
- A small amount of "reverse T3" is formed, with no biological activity
Functions of Thyroid Hormones
- Normal growth and development
- Metabolic processes (carbohydrate, protein, and lipid metabolism)
- Stimulate synthesis of mRNA to participate in metabolism
- Increase the effect of catecholamines on cardiac and nervous systems
Conversion of T4 to T3
- 25% of T4 is converted to T3 in peripheral tissues
- Mainly occurs in the liver and kidneys
- T3 is released into the bloodstream
Treatment of Hyperthyroidism
- β-adrenergic blocker drugs
- Radioactive iodine
- Propylthiouracil and carbimazole
- Surgery (rarely indicated)
Treatment of Hypothyroidism
- Oral administration of thyroxine-containing drugs (replacement therapy)
- Monitoring of TSH levels
Iodine Importance in Thyroid Hormone Production
- Iodine is essential for thyroid hormone production
- Sources of iodine:
- Iodized salt
- Iodated bread
- Dairy products
- Shellfish
- Minimum requirement: 75 micrograms/day
Test your knowledge on the causes and clinical features of thyrotoxicosis, including thyroid hormones, hyperthyroidism symptoms, and related diseases.
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