Thyroid Physiology Flashcards by raniya robb

Describe the general anatomical appearance of the thyroid gland

2 lobes usually joined by an isthmus

- sits in front of the trachea

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What hormones does the thyroid secrete?

T3
T4
Calcitonin

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What do the parathyroid glands secrete?

Parathyroid hormone

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What vertebrae does the thyroid sit in front of?

C5-T1

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What tracheal cartilage rings does the thyroid sit in front of?

2-4

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The thyroid decreases in size during pregnancy. TRUE/FALSE?

FALSE

It increases in size during pregnancy

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What nerve has the potential to be damaged during thyroid surgery?

Recurrent Laryngeal Nerve

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What cells are responsible for synthesising thyroid hormones?

Follicular cells

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Where can thyroid hormones be stored if the do not need released immediately/

Large Colloid in centre of follicles

Enclosed by follicular cells

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What cells are responsible for the synthesis of Calcitonin

Parafollicular C cells

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What ion is required from the bloodstream in order to make thyroid hormones?

Iodine

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How are thyroid hormones synthesised?

Iodine in from blood
Added to tyrosine molecules
Via pinocytosis and assistance from ribosomes
Hormones then released into bloodstream

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Explain the naming process when each iodine is added to a tyrosine unit

1 iodine = Monoiodotyrosine
2 iodines = Di-iodotyrosine
3 iodines = Triiodothyronine
4 iodines = Thyroxine

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Drugs to target HYPERthyroidism (e.g. carbimazole and propyluracil) target what stage of thyroid hormone production?

Creation of mono/di-iodotyrosines

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What percentage of hormone secreted by the thyroid is T3 and what percentage is T4?

T3  = 10% 
T4  = 90%

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T4 is a more potent thyroid hormone than T3. TRUE/FALSE?

FALSE

T3 = more potent

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Which of the thyroid hormones is the most biologically active?

If thyroid hormones are hydroPHOBIC, what plasma proteins are required for their transport?

thyroxine binding globulin (70%)
thyroxine binding prealbumin (20%)
Albumin (5%)

Unbound thyroid hormones are considered to be biologically active. TRUE/FALSE?

TRUE

Give examples of cases where a patient would have increased TBG and therefore increased bound T4?

Pregnancy/Oral Contraceptive
Newborn
Hepatitis
Biliary Cirrhosis
Drug related e.g. clofibrate/heroin

Give examples of cases where a patient may have decreased TBG and therefore less bound T4?

Large glucocorticoid dose
Active acromegaly
Chronic Liver Disease
Nephrotic syndrome
Drug related e.g. Phenytoin/Carbamazepine

What processes are thyroid hormones known to increase?

Basal metabolic rate
Thermogenesis
Carbohydrate/Lipid/Protein Metabolism

What aspects of growth require thyroid hormone?

Growth hormone releasing hormone (GHRH) production and secretion requires thyroid hormones
Myelinogenesis and axonal growth in foetus requires thyroid hormones

What effect can an under or overactive thyroid have on the CNS?

Hypothyroidism - slow intellectual functions

Hyperthyroidism – nervousness, hyperkinesis and emotional lability

What medication can be used to decrease the symptoms of hyperthyroidism?

beta-blocker e.g. PROPRANOLOL

Explain the process of thyroid hormone release starting from the hypothalamus

Thyrotrophin releasing hormone (TRH) from hypothalamus **STIMULATES** Thyroid stimulating hormone (TSH) release from anterior pituitary **STIMULATES** T3 and T4 release from thyroid gland

What part of the thyroid hormone pathway can T3 and T4 negatively feedback on?

Both TRH and TSH

What are the role of de-Iodinases in thyroid hormone activation?

Converts T4 -> T3 or rT3 (reverse T3)

What de-iodinases are most important in converting T4 -> T3?

De-iodinase 1 and 2

What de-iodinase converts T4 to revers T3 (rT3)?

De-iodinase 3

Where is de-iodinase 1 usually found?

liver and kidney

Where can de-iodinase 2 be found?

``` Heart Skeletal muscle CNS Fat Thyroid Pituitary ```

Where is de-iodinase 3 found?

fetal tissue placenta brain (except pituitary)

Why may a patient be deficient in thyroid hormones?

Primary (gland) failure – may be associated with goitre Secondary to TRH or TSH (no goitre) Lack of iodine in diet (may be associated with goitre)

What are the symptoms of hypothyroidism?

``` Reduced BMR Slow pulse rate Fatigue, lethargy, slow response times and mental sluggishness Cold-intolerance Tendency to put on weight easily ```

What symptom of hypothyroidism in adults is characterised by a puffy face, hands and feet?

Myxoedema

What do babies with hypothyroidism sometimes present with?

Cretinism: | - dwarfism and limited mental functioning due to deficiency of thyroid hormones present at birth

What is Grave's disease?

Autoimmune disease Causes HYPERthyroidism Thyroid stimulating immunoglobulin (TSI) acts like TSH but unchecked by T3 and T4

What can Grave's disease cause?

Goitre | Exopthalmus - bulging eyes due to water retaining carbohydrate build up behind eyes

What are the symptoms of HYPERthyroidism?

- Increased BMR - Very fast pulse rate - Increased nervousness and excessively emotional - insomnia - Sweating / heat intolerance - Tendency to lose weight easily