Thyroid Anatomy and Pathology I Flashcards
thyroid gland forms at the base of the __, then it descends to set at the __ __. there are still connections from where it started to where it ended up called the __ __. If this duct is compromised, the thyroid might be in the ___ ___ position, called an __ __.
A cyst can also develop on the residual duct, called (creatively) a __ ___ ___.
All in all, if there are changes in the embryonic development of the thyroid, it can cause dysfunction and lead to __ __.
thyroid gland forms at the base of the tongue, then it descends to set at the epitracheal rings. there are still connections from where it started to where it ended up called the thyroglossal duct. If this duct is compromised, the thyroid might be in the wrong anatomical position, called an ectopic thyroid.
A cyst can also develop on the residual duct, called (creatively) a thyroglossal duct cyst.
All in all, if there are changes in the embryonic development of the thyroid, it can cause dysfunction and lead to neonatal hypothyroidism.
A lingual thyroid is caused by a failure of ___. It can be seen on physical exam and by trapping of radioiodine
A lingual thyroid is caused by a failure of __. It can be seen on physical exam and by trapping of radioiodine
a thyroglossal duct cyst
Thyroid gross anatomy
Normal adult gland weighs 15-20 gm
- ___ lateral lobes, 4 cm long, 2 cm wide
- __ joins the lobes, below the cricoid cartilage.
- lobes extend up to the level of the __ cartilage
Gland is surrounded by a thin __ __ that is
posteriorly attached to the __ & __ (and is __ sensitive- the thyroid doesnt have pain but the capsule does)
– thus, the thyroid gland moves upwards with swallowing
Normal adult gland weighs 15-20 gm
• Two lateral lobes, 4 cm long, 2 cm wide
• Isthmus joins the 2 lobes, below the cricoid cartilage.
- lobes extend up to the level of the thyroid cartilage
Gland is surrounded by a thin fibrous capsule that is
posteriorly attached to the trachea & larynx (and is pain sensitive)
– thus, the thyroid gland moves upwards with swallowing
Arterial Drainage;
- Inferior thyroid artery is a branch of the __ artery
- Superior thyroid artery is a branch of the __ carotid
Venous drainage: __, __, __ thyroid veins
Arterial Drainage;
Inferior thyroid artery is a branch of the subclavian artery
Superior thyroid artery is a branch of the external carotid
Venous drainage: superior, middle, inferior thyroid veins
__ __ nerve lies adjacent to the postromedial aspect of the thyroid, near the __ between the lateral aspect of the __ & __; this nerve contains the __ __ for the abductor muscles of the true __ __.
Recurrent laryngeal nerve lies adjacent to the postromedial aspect of the thyroid, near the groove between the lateral aspect of the trachea & esophagus; this nerve contains the motor fibers for the abductor muscles of the true vocal cords.
A thyroid malignancy may not be palpable on the exam, but you might see it in the ___ ___.
lymph glands. YOU MUST DO A LYMPH EXAM WHEN DOING A THYROID EXMA
Tracheal blockage would cause what kind of sound while breathing? What would the volume curve show?
inspiratory stridor
common symptoms of large goitor
inspiratory stridor
- hoarseness because of recurrent laryngeal nerve impingement
dysphagia because of esophageal compression
microscopic anatomy of thyroid:
compartmentalized into __ composed of ___. Around these cells are _____ which contain calcitonin
compartmentalized into lobules composed fo follicles. Around the follicles are parafollicular/C cells that create calcitonin
pemberton sign
goiter blocks the thoracic inlet of the jugular veins, preventing blood flow when you raise your arms
which laryngeal nerve is affected when the thyroid is enlarged?
only the LEFT!
pituitary TSH stimualtes the follicular cells of the thyroid, which releases __
pituitary TSH stimualtes the follicular cells of the thyroid, which releases thyroxin.
In the image, the “colloid” is the stored thyroxin
thyroxin is aka
T4
Outline the hypothalamic hormonal control of the thyroid
- hypothalamus releases TRH: thyrotropin releasing hormone
- TFH stimulates pituitary to release TSH: thyroid stimulating hormone
- Pituitary TSH stimulates the follicles of the thyroid to release THYROXIN: T4, as well as T3.
Outline the how thyroid hormones influnece;
1. heart
- liver
- bone
- CNS
- heart- increase in contraction
- liver: increase release
- bone : growth
- CNS: works more– wakes up– less sluggish
- overall, thyroid hormone is a stimulator
How is the thyroid involved in negative regulation?
TSH secretion (made by th epituitar) is regulated by the T4 and T3 from the thyroid and from TRH of the hypohalamus.
- response to elevated levels of thyroid hormones shuts off the production cascade
What is the mechanism of action of TSH peptide on thyroid?
the TSH (from pituitary) have alpha and beta subunits. Beta is unique– there are different beta units in FSH, LH, and betaHCG). it binds to G protien receptor on the thyoid.
What happens inside the thyroid gland?
All in response to the stimulation by TSH:
1.Uptake of __ into the follicular cell
2.Synthesis of _ (and __) within the __ cell
(and stored)
3.Release of ready-made stored T4 (and T3) from the _ of the follicle into the circulation
All in response to the stimulation by TSH:
1.Uptake of iodine into the follicular cell
2.Synthesis of T4 (and T3) within the follicular cell
(and stored)
3.Release of ready-made stored T4 (and T3) from the colloid of the follicle into the circulation
you need __ to create T4 and T3.
you need iodine to create T4 and T3.
synthesis of T4 and T3 happen on the __ protein, which uses __ to differentiate between different thyroid hormones. It is then stored in the __.
synthesis of T4 and T3 happen on the THYROGLOBULIN protein, which uses iodine to differentiate between different thyroid hormones. It is then stored in the colloid.
ex/ Tyrosine on the TGP adds 1 Iodine to create mono-iodotyrosine (MIT). If tehrea re 3 iodines, it’s T3, and if its 4 iodines, it’s T4.
___is the main secreted form of thyroid hormone, and the main form transported in __;
__ is mainly an intracellular product of T4 in the target cells
T4 is the main secreted form, and the main form transported in blood;
T3 is mainly an intracellular product of T4 in the target cells
Which form of thyroid hormone acts on the DNA of the cell that it gets engulfed in?
T4 is the main circulator, but when it gets endocytosesd by the receiving cell, it gets de-iodinated to become T3. T3 acts inside the cell.
otuline the release of thyroxin (and some T3) into the blood from the thyroid
thyroxin is contained in the colloid (middle of the follicle). It gest endocytosed into the thyroid follicular cell, where lysosomes degrade the colloid vesible and the thyroglobulin component is cleaved by proteolysis to releas T3 and T4
Outline the peripheral metabolism of thyroxine, when it gets absorbed by the peripheral target cell
T4 goes in, where D2 cleaves it to T3. T3 enters the nucleus and affects transcription by binding to the Tr-RXR activator, causing transcription of the T3 resposnive gene.
MrnA is created which causes protein synthesis and overall T3 effects. Depending on the cell, growth, temperature incrase, oxygen consumption, increase in metabolism, cardiovascular effects
Outline the Wolff Charikoff Effect
During the first day of iodine xposure, the sodium-iodide symporter transports the excess iosine into the thyroid, resulting in transient inhibition of thyroid peroxidase (TPO) and a decrease in thyroid hormone synthesis.
- the decrease in sodium-iodide symporter expression results in decreased iodine transport and the subsequent resumption of thyroid hormone synthesis.
The Wolff–Chaikoff effect is an effective means of rejecting a large quantity of imbibed iodide, and therefore preventing the thyroid from synthesizing large quantities of thyroid hormone.
outline the general mechanism for how iodine deficinecy causes goiter
T/F when assessing T4 levels, you should measure total levels
false. only measure FREE t4, because many are protein bound which renders bound T4 inactive.
Serum ___ is the most sensitive screening test for primary hyperthyroidism and primary hypothyroidism
Serum TSH is the most sensitive screening test for primary hyperthyroidism and primary hypothyroidism
serum TSH is high in ____ ___
serum TSH is low in ____ ____
serum TSH is high in PRIMARY HYPOTHYROIDISM
serum TSH is low in PRIMARY HYPERTHYROIDISM
Serum TSH is the BEST initial test for primary thyroid disease, since it lets the pituitary tell you how the thyroid is doing.
What test should be done to confirm a THYROID disease after the serum TSH is found to be abnormal?
SERUM FREE THYROXIN (non-protein bound)
Miscellaneous Lab Measurements;
Hashimotos’ thyroiditis:
Graves disease:
A test done in the absence of the thyroid gland:
Hashimotos’ thyroiditis: Anti-thyroid antibodies
Graves disease: Antibody to TSH receptor
A test done in the absence of the thyroid gland: Serum thyroglubulin
note; outline the diagnostic approach for primary thyroid dysfunction
