General Endocrine Health Flashcards
Describe the HPT axis
Hypothalamus-Pituitary-Thyroid
TRH (Thyrotropin-Releasing Hormone) stimulates TSH (Thyroid-stimulating hormone). TSH stimulates thyroid hormone release of T4 and T3
What are Iodothyronine Deiodinases?
Selenoproteins that remove iodine, contain selenium and that regulate hormone homeostatis
Name the proteins that are dependant on selenium and needed for T4-T3 conversion
D1, D2 = T3
D3=RT3
Which Thyroid homrone is the ‘inactive’ or ‘weak’ form with aprrox. 90% secreted?
T4 (Thyroxine)
What nutrients are needed for thyroid hormone synthesis?
Tyrosine Iodine Fe Selenium Vitamin D Zn Vitamins A, C, E, B2, B3, B6, B12 Cu
What can cause an iodine deficency?
Dietary deficines
High goitrogen intake - soya, millet, peanuts, pine nuts, raw brassicas
Low/no dairy/Fish, pregnancy, vegans
What can cause iodine excess?
Consumption of over-idoised salt, animal milk,
iodine-containing supplements
Radiocontrast dyes
Medications
Name some HPT disruptors
Pesticides Glyphosphate PCBs Bisphenols (BPA) Phthalates Perchlorates Halogens - fluoride - chlorine - bromine
List ways in which thyroid disruptors can be avoided
Filtered water fluoriode-free toothpaste organic avoid farmed fish avoid procesed foods and beverages limit time in chlorinated pools avoid plastic packaging organic textiles natural cleaning products
List the classifications of Hypothyroidism
Primary Secondary Tertiary Peripheral Subclinical
What are the 2 levels of Hyperthyroidism?
Thyrotoxicosis
Thyroiditis
Describe the GLUT (glucose transporter) proteins:
GLUT1
GLut4
Glut2
Glut 1- basal glucose uptake without insulin
Glut 4 - insulin regulated - increases glucose up-take 20-30
Glut 2 - mediated glycolosis and gluconeogensis
List the different types of Diabetes Mellitus
T1DM T2DM Prediabetes Gestational diabetes Secondary diabetes
What range on a HbA1c test determines diabetes?
48mmol/mol or over
6.5%
What range on a HbA1c test indicates prediabetes?
42-47mmol/mol
6.0-6.4%
What is indicated as normal on a HbA1c test?
Anything less than 42
6.0%
What kind of proteins are iodothyronine deiodinases?
Selenoproteins
What enzymes are involved in the removal of iodine?
Iodothyronine deiodonases
Which deiodinases convert T4 to T3?
D1 and D2
What is TRH and what does it do?
Thyrotropin-releasing hormone, released from the hypothalamus stimulating the release of TSH
What is TSH and what does it do?
Thyroid-stimulating hormone. Stimulates the release of T4 and T3. activates iodide uptake via the Sodium/Iodide symporter (SIS)
What is SIS? What does it do?
Sodium/Iodide Symporter. A transmembrane glycoprotein needed for active transport of iodine into thyroid follicular cells
What is T3? What does it do?
Triiodothyronine. 4 x the strength of T4.
- Increases growth, bone and CNS development
- Increases basal metabolic rate (BMR)
- Activates metaolism
- Increases heart rate
What is T4? What does it do?
Thyroxine or Tetraiodothyonine. 90% secreted, weak and inactive form.
What is RT3? What does it do?
Reverse T3. Biologically inactive. Protects tissues from excess thyroid hormones.
What nutrient do D1, D2 and D3 depend on?
Selenium
Over time hyperthyroid medication can induce hypothyroidism. What do the following medications do to the thyroid?
- Dopamine
- Lithium
- Glucocorticoids
Reduce TSH
Over time hyperthyroid medication can induce hypothyroidism. What do the following medications do to the thyroid?
- Phenytoin
- Rifampicin
Affect T4 and T3
Over time hyperthyroid medication can induce hypothyroidism. What do the following medications do to the thyroid?
- Beta-blockers
- Amiodarone
Reduce T4 and T3
Over time hyperthyroid medication can induce hypothyroidism. What do the following medications do to the thyroid?
- NSAIDs
- Diuretics
Reduce T4 and T3 binding
Over time hyperthyroid medication can induce hypothyroidism. What do the following medications do to the thyroid?
- Oestrogen
- Tamoxifen
Increase thyroglobulin
List some iodine-rich foods
Seaweed and algae (sea vegetables) Ocean fish Shellfish Cod Scallops Eggs Dairy
List some Goitrogens
Soya Millet Peanuts Pine nuts Raw Brassicas
Do goitrogens increase or decrease iodine?
decrease
What is TPO? And what does it do?
Thyroid Peroxidase. Catalyase iodination of Tyrosine to form T4 and T3
Why is Fe important for thyroid health?
Thyroid Peroxidase is haem-dependant. TPO is needed to convert tyrosine to T4 and T3.
Name 2 enzyme co-factors needed for thyroid receptor function
Selenium and Zinc
Which nutrient is a cofactor in deiodinase enzymes?
Copper
How will high goitrogen intake cause iodine deficiency?
Blocks iodine uptake
What is the Wolff-Chairkoff Effect?
A cause of excess iodine in the body. A large amount of dietary iodine inhibits thyroid hormone synthesis
What is the base material for thyroid hormones produced in the thyroid gland?
thyroglobulin
Where is T3 made?
Peripheral tissue
What is Peripheral Conversion?
When T4 is converted to T3 or RT3 in the liver and kidneys (peripheral tissues)
How are thryoid hormones metabolised?
deoidination, glucoronidation, sulphation
__ is highly bound (99.98%), 0.02% circulates freely.
__ is slightly less protein bound (99.8%), 0.2% as free fraction.
T4 is highly bound and circulates freely
T3 is slightly less protein bound
How much of T4 and T3 does the thyroid secrete on a daily basis?
T4-80-100mcg
T3-10mcg
What is RT3?
Biologically inactive thryoid hormone that binds to T3 receptors, reducing T3
Increase RT3 can present as
Hypothyroidism
Increase T4 converting to RT3 increases in what circumatances?
Chronic illness
High stress
