Thyroid Flashcards by Maddie Greaves

What is the process called that concentrates iodide in the cell?

Iodide trapping

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How does iodide get into thyroid cells?

Sodium-iodide symporter (NIS) which co-transports one iodide with two sodium ions

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What ensures there is a concentration gradient for sodium in thyroid cells so iodide can be transported in?

Na/K ATPase which pumps sodium out of cell

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Where is thyroglobulin produced and modified?

Produced in the RER and modified in the Golgi apparatus of follicular cells

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What molecule on thyroglobulins does iodine combine with to form thyroid hormones?

Tyrosine

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What needs to happen to iodide ion before it can bind to tyrosine and what promotes this?

Oxidation (removal of electrons) to iodine by peroxidase and hydrogen peroxide

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When one molecule of iodine is bound to a tyrosin on thyroglobulin what is the product called?

Monoiodotyrosine (T1)

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Where is thyroglobulin with iodine atoms attached stored?

Lumen of thyroid follicle and is called colloid

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What is the process by which colloid re-enters follicular cells?

Pinocytosis

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What cleaves T3 and T4 from thyroglobulin?

Digestive enzymes (e.g. proteases) released by lysosomes

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What is the main plasma protein that T3 and T4 bind to?

Thyroxine-binding globulin.

The biologically active hormones are unbound

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What is the long name of T3

Triiodothyronine

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What is the long name of T4

(tetraiodothyronine) Thyroxine

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Name 3 actions of TSH

1) Active uptake of iodine
2) Stimulates uptake of colloid
3) Induces growth of the thyroid gland
4) Stimulates other reactions involved in thyroid hormone synthesis

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What is the most common cause of congenital hypothyroidism?

Absence of thyroid or ectopic thyroid

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What is a treatment for hypothyroidism?

Thyroxine

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What is the commonest non-iatrogenic cause of hypothyroidism in the UK and how does it cause hypothyroidism?

Hashimoto’s Disease.

Autoantibodies against thyroid peroxidase and/or thyroglobulin

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What supplements can interfere with treatment of hypothyroidism?

Calcium and iron supplements

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What is Graves’ disease?

Autoimmune thyroid disease that causes hyperthyroidism

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What is more common in the UK hyper or hypo thyroidism and is it more common in men or women?

Hypothyroidism more common and both more common in women.

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Why does hyperthyroidism cause fatigue?

The excitable effects of the hormone on synapses make it difficult to sleep

Name 4 methods of treatment of hyperthyroidism

1) Thionamides - e.g Carbimazole, propylthiouracil
2) Beta-blockers - to alleviate some symptoms
3) Radioactive iodine
4) Surgical removal

What is a goitre?

Swelling of the neck resulting from enlargement of thyroid gland

Anatomically, what level can the thyroid be found?

C5-T1

What kind of receptor does TSH bind to on the thyroid?

GPCR

What stimulates TSH secretion from the anterior pituitary gland?

Thyrotropin-releasing hormone (TRH) from the hypothalamus

List some symptoms of hyperthyroidism

- Excitability - Intolerance to heat - increased sweating - weight loss - diarrhoea - muslce weakness - nervousness or other psychic disorders - extreme fatigue but inability to sleep - tremor of hands - exophthalmos

What is exophthalmos

protrusion of the eyeballs - symptom of hyperthyroidism

Normally, what feedback to T3 and T4 have on hypothalamus and anterior pituitary gland?

Negative feedback

List some symptoms of hypothyroidism

- fatigue and extreme somnolence - extreme muscular sluggishness - slowed HR - decreased HR and BP - sometimes increased body weight - constipation - mental sluggishness - dry, scaly skin, depressed hair growth

What is the cause of endemic goiters and what is the pathophysoilogy?

Lack of iodine. prevents production of T3 and T4 No hormone to inhibit TSH. Large amounts of thyroglobulin colloid form and gland grows larger

Other than lack of iodine, what can cause goitres?

- Deficient iodide-trapping mechanism - Deficient peroxidase system - Deficient coupling of iodinated tyrosines - Deficiency of deiodinase enzyme preventing recovery of iodine from iodinated tyrosines that are not coupled to form thyroid hormones

How does carbimazole work?

prevents thyroid peroxidase enzyme from coupling and iodinating tyrosine residues thus reducing formation of T3 and T4

What is the pathophysiology of Graves' disease

Autoantibodies to TSH receptor so it's constantly stimulated. Increased TSH produced

What is endocrinology?

the study of glands and the hormones they produce

What is the difference between exocrine and endocrine cells?

Exocrine - secrete products externally or into lumen/duct. | Endocrine - secrete in blood stream

Using the HPA axis as an example, what occurs in primary adrenal insufficiency? State how the levels of CRH, ACTH and cortisol will be affected. Name an example where this happens

Problem with adrenal gland itself. Don't get negative feedback to pituitary and hypothalamus as normal. Cortisol level = low CRH = high ACTH = high Addison's Disease - hyperpigmentation due to pituitary gland producing high levels of proopiomelanocortin which is a precursor for ACTH but also melanocyte-stimulating hormone

Using the HPA axis as an example, what occurs in secondary adrenal insufficiency? State how the levels of CRH, ACTH and cortisol will be affected.

Pathology in pituitary gland. ACTH = low Cortisol level = low CRH = high

Using the HPA axis as an example, what occurs in tertiary adrenal insufficiency? State how the levels of CRH, ACTH and cortisol will be affected.

Pathology in hypothalamus. CRH = low ACTH = low cortisol = low

What test is used to test how well a gland is functioning?

Dynamic function test

In dynamic function testing what do you do if you suspect 1) gland insufficiency 2) gland over-production

1) Stimulate gland | 2) Suppress gland

How do levels of cortisol, ACTH and CRH differ in Cushing's syndrome compared to cushing's disease?

Cushing's syndrome (tumour or adenoma in adrenal cortex) - increased cortisol, low ACTH and CRH Cushing's disease (pathology in pituitary) = High ACTH and cortisol but low CRH

If you had low levels of T4 but high levels of TSH and TRH what would be the diagnosis?

Primary hypothyroidism

Diagnose - Low levels of T4 and TSH but high TRH

Secondary hypothyroidisme

Low levels of T4, TSH adn TRH - Diagnosis?

Tertiary hypothyroidism

High levels of T4, low levels of TSH and TRH - Diagnosis?

Primary hyperthyroidism

High levels of T4 and TSH. low levels of TRH - Diagnosis?

Pituitary (secondary) hyperthyroidism

What effect does dopamine have on prolactin?

Inhibits it - hence why dopamine antagonists cause hyperprolactinemia

What is another name for vasopressin?

Anti-diuretic hormone

Name an example of a positive feedback?

Prolactin - baby sucking causes further release of prolactin | Oxytocin - stretching of neurons during childbirth produces more oxytocin which contracts uterus to aid in delivery

What two hormones are made in the hypothalamus then stored/released by the posterior pituitary?

ADH | Oxytocin