Anatomy
Thyroid Anatomy
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Thyroid Anatomy
, Thyroid Physiology, Thyroid, Thyroid Gland
See Also
Parathyroid Anatomy
Endocrine Anatomy
Head and Neck Anatomy
Embryology
Thyroid Gland develops from
Tongue
root (foramen cecum)
Formed by 5th-6th week of development
Anatomy
Images
Normal Adult Thyroid weighs 20-25g
Components
Two Lateral lobes
Isthmus centrally connects the lobes
Near structures
Recurrent laryngeal nerve
Parathyroid Gland
s
Physiology
Stressors stimulate increased Thyroid function
Puberty
Pregnancy
Physiologic stress
Hypothalamus
Thyrotropin
Releasing Hormone (TRH) released
TRH passes down pituitary stalk to pituitary
Anterior Pituitary
Thyroid Stimulating Hormone
(TSH) released
TSH passes into circulation to Thyroid
Thyroid
Iodine
is absorbed from circulation
Thyroxine
(T4) released into circulation
Triiodthyronine (T3) is also 20-30% produced in the Thyroid (remainder is peripheral conversion of T4)
Peripheral Tissues
Triiodothyronine
(T3) produced from T4 deiodination
Circulation
Thyroid Binding Globulin
(TBG) binds T4 and T3
T4 is 99.96% protein bound in serum (<1% is
Free T4
, the active form)
T3 is 99.7% protein bound in serum
T4 and T3 stimulate all metabolic processes
T3 is several times more potent than T4
Effects of Thyroid hormone
Peripheral tissue oxygen utilization and basal metabolic rate increased
Positive chronotropic and ionotropic cardiovascular effects, with secondary increased
Cardiac Output
Decreases systemic vascular resistance via arteriole dilation
When Thyroid hormone is in excess (e.g.
Thyroid Storm
), high output
Heart Failure
may result
Feedback Loop
Increased T4 and T3 levels suppress TRH and TSH
References
Mason, Herbert and Swadron in Herbert (2019) EM:Rap C3 3(11):1-10
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