Anatomy and Physiology of the Thyroid (Unit 2A) Flashcards
What type of gland is the thyroid gland?
Endocrine gland
What does the thyroid do?
Synthesizes, stores, and secretes thyroid hormones
What does the thyroid gland function to control?
The basal metabolic rate
What is the average size of the thyroid gland?
Length: 4-6cm
AP: 1.3-1.8 cm
Isthmus: 4-6cm
Is the thyroid gland larger in males or females?
Males
What are the 4 main arteries that supply blood to the thyroid?
Superior Thyroid Arteries (2 - paired) : arise from external carotid artery
Inferior Thyroid Arteries (2 - paired) : arise from right subclavian artery
What artery can sometimes feed the thyroid?
Thyroid ima artery
What are the 3 veins that drain the thyroid plexus?
Superior thyroid veins, middle thyroid veins, inferior thyroid veins
Where do the superior and middle thyroid veins arise from?
The IJV
Where do the inferior thyroid veins arise from?
Brachiocephalic Vein
What are the 3 hormones that the thyroid secrete?
T3, T4 (thyroxine), Calcitonin (thyrocalcitonin)
What secretes Calcitonin?
Parafollicular cells (c-cells)
What does Calcitonin do?
Lowers blood calcium levels
What do T3 and T4 cells do?
Process iodine to secrete T3 and T4
What does the regulatory system involve? (3)
The hypothalamus, anterior pituitary, and thyroid gland
What does Iodine bind with within a colloid to form thyroid hormones?
Thyroglobulin (protein)
What do follicular cells reabsorb to process T3 and T4?
Thyroglobulin (protein)
Follicular cells reabsorb thyroglobulin to process which thyroid hormones?
T3 and T4
Where does TRH release from?
The hypothalamus
Does TRH stand for?
Thyrotropin-releasing Hormone
What does TSH stand for?
Thyroid Stimulating Hormone (aka Thyrotropin)
What is regulated by T3, T4 and TRH?
TSH (Thyrotropin)
Describe the Negative Feedback Loop for Thyroid hormones.
- Decrease in thyroid hormone decreases the BMR
- Decreasing BMR stimulates the release of TRH
- TRH induces the release of TSH
- Thyroid releases T3 and T4
- BMR returns to normal
What is the earliest endocrine gland to form in the human embryo?
Thyroid
At what level does development begin for the thyroid?
Level of the primitive pharynx
What is the thyroglossal tract (duct)?
A canal that usually disappears once the thyroid reaches its final position in the neck after the cells have migrated downwards in the neck
By which trimester does the thyroid fully develop?
First trimester
What is Athyrosis?
The most severe anomaly - associated with Cretinism or congenital hypothyroidism
What is the most common variation of the thyroid?
Pyramidal lobe
What is Pyramidal lobe?
An additional lobe that extends upwards from the isthmus. (can also arise from either lobe, left is more common than right)
