19 Questions
What is the main function of the thyroid gland?
Secrete hormones to regulate metabolism
Which hormone is known as the most active thyroid hormone?
T3
What is the role of calcitonin in the body?
Decrease the amount of calcium in the blood
Where is thyroglobulin synthesized within the follicular cell?
Endoplasmic reticulum (ER)
Which cells in the thyroid gland secrete calcitonin?
Parafollicular cells (C cells)
What is the function of TRH (Thyrotropin releasing hormone) in thyroid hormone synthesis?
Stimulate the release of thyroid-stimulating hormone (TSH)
How is iodide transported into the follicular cells from the blood?
Active transport
What is the main function of TSH (Thyroid stimulating hormone) in thyroid hormone synthesis?
To bind to receptors on thyroid follicular cells
Which organelle within the follicular cell is responsible for synthesizing thyroglobulin?
Endoplasmic reticulum (ER)
What is the role of parafollicular cells (C cells) in thyroid function?
Produce calcitonin
What is the basic unit of thyroid hormone T3?
3 iodine molecules attached to a tyrosine molecule
What are the two main functions of thyroid peroxidase (TPO)?
Oxidation of iodide to iodine and coupling iodine with thyroglobulin
What is the most common cause of primary hypothyroidism?
Autoimmune thyroid destruction (Hashimoto's thyroiditis)
Which of the following is NOT a characteristic of Hashimoto's thyroiditis?
Permanent hypothyroidism that resolves without treatment
What is the primary cause of Riedel's thyroiditis?
IgG4 antibody production leading to fibrous tissue formation
What is the proposed mechanism behind DeQuervain's thyroiditis?
Viral upper respiratory tract infection leading to thyroid inflammation
What is the underlying cause of the Wolff-Chaikoff effect?
Large ingestion of iodine inhibiting thyroid hormone production
What is the primary distinguishing feature between primary and secondary hypothyroidism?
The level of TSH in the blood
What is the underlying cause of Sheehan's syndrome?
Massive postpartum hemorrhage leading to pituitary necrosis
Study Notes
Thyroid Gland
- Largest endocrine gland, wraps around the front of the trachea
- Consists of two lateral lobes connected by a median tissue mass (isthmus)
- Composed of groups of thyroid follicles surrounded by connective tissue capsules
- Follicles contain a space filled with glycoprotein colloid, enclosed by a layer of follicular cells
Thyroid Hormone Synthesis
- Hypothalamus initiates synthesis of hormone, releasing TRH (Thyrotropin-releasing hormone)
- TRH travels to the pituitary gland, stimulating the release of TSH (Thyroid-stimulating hormone)
- TSH binds to receptors on thyroid follicular cells, stimulating the synthesis of thyroid hormones
Thyroid Hormones
- Triiodothyronine (T3), the most active thyroid hormone
- Thyroxine (T4), a precursor to T3
- Calcitonin, produced by parafollicular cells (C cells), decreases blood calcium levels
Hypothyroidism
- Two classifications: Primary and Secondary
- Primary Hypothyroidism: destruction of the thyroid gland or iodine deficiency
- Secondary Hypothyroidism: dysfunction of the hypothalamus and/or pituitary gland
Primary Hypothyroidism
- Three main causes of thyroid destruction:
- Autoimmune thyroid destruction (Hashimoto's, Postpartum, Riedel's)
- Infectious thyroid destruction (DeQuervain's)
- Iatrogenic thyroid destruction (Thyroidectomy, Wolff-Chaikoff Effect)
Autoimmune Thyroid Destrution
- Hashimoto's Thyroiditis: most common cause of hypothyroidism in the US
- Antibodies against thyroglobulin (anti-TG) and Thyroid Peroxidase (anti-TPO)
- Progressive depletion of thyroid epithelial cells due to autoimmune destruction
- Postpartum Thyroiditis: transient hypothyroidism occurring within a year of childbirth
- Riedel's Thyroiditis: characterized by developing fibrotic tissue at the thyroid gland
Infectious Thyroid Destrution
- DeQuervain's Theory: rare, caused by viral upper respiratory tract infection
- Painful thyroid goiter, elevated erythrocyte sedimentation rate (ESR)
Iatrogenic Thyroid Destrution
- Thyroidectomy: recent thyroid surgery
- Wolff-Chaikoff Effect: caused by large ingestion of iodine, inhibiting TPO and preventing thyroid hormone production
Secondary Hypothyroidism
- Dysfunction of the hypothalamus and/or pituitary gland
- Unable to produce TRH and/or TSH, resulting in low thyroid hormone production
- Low T3 and T4, with low TSH (important for diagnosis)
Pituitary Dysfuncion
- Pituitary adenoma: tumor on the pituitary gland
- Sheehan Syndrome: postpartum hypopituitarism due to necrosis of the pituitary gland
Test your knowledge about hypothyroidism, a condition where the thyroid gland is underactive and produces low levels of T3 and T4 hormones. Learn about the structure and function of the thyroid gland, its hormone production, and its role as an endocrine organ.
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