Thyroid gland Flashcards

1
Q

describe the structure and location of the thyroid glands.

A
  • lies against and around front larynx and trachea below thyroid cartilage.
  • 2 lobes joined by isthmus from 2nd to 3rd trachea ring; bow tie shaped.
    DIFFERENT TO PARATHYROID.
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2
Q

what is the arrangement of thyroid tissue?

A
  • follicular cells arranged in spheres called thyroid follicles makes thyroglobulin.
  • colloid (stores thyroglobulin extracellularly surrounding follicle) contains deposits of thyroglobulin.
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3
Q

describe the composition of thyroid hormones. Briefly mention the function of thyroglobulin in its formation.

A
  • 2 tyrosines linked together with iodine (at 3rd/ 4th position).
  • only molecules in the body that contain iodine.

*The two hormones (T3/ T4) are made though the linkage of two molecules of iodinated tyrosine on the thyroglobulin scaffold. Thyroglobulin acts as scaffold/ substrate in its formation, undergoing iodination and coupling.

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4
Q

what is the importance of thyroid peroxidase?

A
  • enzyme important in regulating 3 reactions involving iodine.
  • oxidation of iodine to iodide which needs H2O2.
  • addition of iodine to tyrosine on throglobulin.
  • coupling in generating thyroid hormones.
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5
Q

what is the significance of iodine uptake to our body?

A
  • dietary iodine reduced to iodide before absorption in small intestine.
  • thyroid hormones and precursors only molecules with iodine in body.
  • iodine taken up from blood via sodium-iodide symporter/ iodine trap.
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6
Q

why is T4 converted to T3?

A
  • T3 biological activity is 4 times that of T4, so most converted in liver & kidneys.
  • T3 & T4 both transported in blood bound to thyroxine-binding globulin.
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7
Q

describe the negative feedback regulation of the thyroid hormones.

A
  • high levels of TSH negatively feedbacks onto hypothalmus to inhibit further TRH onto anterior pituatiry.
  • T3 & T4 negatively feedbacks and inhibits both hypothalamus & TRH and also anterior pituitary & TSH release.
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8
Q

describe the structure and function of TSH.

A
  • glycoprotein hormone composed of alpha and beta subunit.
  • stimulates iodine uptake and oxidation, thyroglobulin synthesis and iodination, colloid pinocytosis to cell, proteolysis of thyroglobulin, cell metabolism and growth.

*via induced GaS (adenylyl cyclase PKA) and also GaQ (PLC, calcium) to stimulate thyroid hormone synthesis and release.

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9
Q

what are some general actions of the thyroid hormone?

A
  • increase in basal metabolic rate and heat production : increase mitochondria, enzymes synthesis.
  • stimulation of metabolic pathways : lipid, carb.
  • sympathomimetric effects : via AD, NAD.
  • CVS in response to AD, NAD increased CO, HR, peripheral vasodilation.
  • nervous system : myelination and neurone development.
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10
Q

describe the structure of the thyroid receptors.

A
  • nuclear receptors which function as hormone-activated transcription factors.
  • acts by modulating gene expression.
  • receptors bind DNA in absence of hormone leading to transcription repression.
  • hormone binding causes conformational change to activate which relieves the repression.
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11
Q

what exactly is measured to check thyroid hormone levels?

A
  • free T4 / T3 : meaning hormone not bound to plasma proteins!!!
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12
Q

what is thyroid scintigraphy?

A
  • TC used for isotope scanning of thyroid with gamma camera.
  • 1 day half life, radiation exposure low.
  • uptake suggets problems.
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13
Q

what is thyroid scintigraphy?

A
  • TC used for isotope scanning of thyroid with gamma camera.
  • 1 day half life, radiation exposure low.
  • large uptake suggests problems like graves.
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14
Q

what is the purpose of antithyroid drugs?

A
  • used to treat overactive thyroid in hyperthyroidism like graves.
  • blocks thyroid hormone formation.
    eg : carbimazole prevents thyroid peroxidase from coupling and iodinating tyrosines on thyroglobulin.

TAKES 2-3 MONTHS TO TAKE EFFECT as iodinised stores in body.

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