Thyroid

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Author:
ZacLyndon
ID:
244693
Filename:
Thyroid
Updated:
2013-11-03 13:05:51
Tags:
Thyroid Physiology Anatomy Clinical
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Description:
Thyroid revision for medical students
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  1. Describe the arterial blood supply of the thyroid gland.
    • - Superior Thyroid Artery (branch of external carotid)
    • - Inferior Thyroid Artery (branch of thyrocervical trunk)
    • - Ima (branch of aorta). Not seen in all patients.
  2. Describe the venous drainage of the thyroid gland.


    • - Superior Thyroid Veins (drains into internal jugular)
    • - Middle Thyroid Veins (drains into internal jugular)
    • - Inferior Thyroid Veins (drains into brachiocephalic vein)
  3. Major nerves near thyroid gland?
    • - Vagus nerves in carotid sheath
    • - Recurrent laryngeal nerves medially. Left recurrent loops around aortic arch, right loops around right subclavian.
  4. Stages of thyroid hormone synthesis and secretion?
    • 1. Iodide Trapping & Conversion
    • Iodide is actively transported into follicular cells and oxidised into iodine by H202 and thyroid peroxidase.
    • 2. Thyroglobulin Synthesis
    • Many tyrosine molecules form thyroglobulin (TGB) in ER.
    • 3. Iodinisation of Tyrosine
    • 1 iodine binding yields T1, 2 yields T2. Substance termed 'colloid'
    • 4. Coupling
    • T1 + T2 = T3
    • T2 + T2 = T4
    • 5. Endocytosis and Digestion
    • Proteases in the lysozome break down TGB and cleave off T3 & T4.
    • 6. Secretion
    • T3 and T4 are lipid-soluble and diffuse into capillaries.
    • 7. Iodine recycling
  5. List the effects of T3 on the cardiovascular system:
    • Increased:
    • - Cardiac output
    • - Tissue blood flow
    • - HR
    • - Myocardial contractility
    • - Respiratory/ventilatory rate
  6. List the effects of T3 on cellular metabolism:
    • Increased:
    • - Size and number of mitochondria
    • - Na/K ATPase
    • - Glucose absorption
    • - Gluconeogensis
    • - Lipolysis
    • - O2 consumption
    • - CO2 production
    • - Protein synthesis
    • - BMR
    • - Ryanodine receptor expression
    • - Ca2+ uptake from sarcoplasmic reticulum
  7. Clinical tests for assessment of thyroid function?
    • - Serum TSH
    • - Free T3
    • - Free T4
  8. Describe the pathology of Graves' Disease
    • IgG antibodies bind to TSH providing an agonistic effect; upregulating adenylyl cyclase and thus increasing thyroid hormone synthesis.
    • Also other antibodies can be present but are cytotoxic, including TGB, TPO and the sodium-iodide transporter.
  9. Describe the steps in thyroid hormone secretion from the hypothalamus, in addition to feedback mechanisms.
    • 1. TRH released from hypothalamus.
    • 2. TSH released from anterior pituitary.
    • 3. TSH acts on follicular cells of thyroid gland to produce T3 and Twhich are secreted into blood and act on virtually all tissues in the body.
    • 4. T3 levels sensed by both hypothalamus and ant.pituitary to provide negative feedback in order to regulate levels.

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