Endocrine Health Flashcards
Describe the stages of the Hypothalamus-Pituitary-Tyroid axis?
Thyrotropin-release hormone (TRH) - Hypothalamus
stimulates
Thyroid-stimulating hormone (TSH)
stimulates
Thyroid hormone release T4 (around 90%) and T3
What enzymes are key for the tyroid?
Selenoproteins
Deiodinase - 1 & 2 convert T4 to T3
Deiodinase 3 - converse T4 to Reverse T3
What is T3
Triiodothyronine
4x the ‘strength’ of T4
Increases grow, bone and CNS development
Increases BMR, heart rate and activates the metabolism.
What is T4?
Thyroxine
Weak thyroid activity ‘inactive form
What is Reverse T3
Biologically inactive - one hypothesis is it protects tissues from excess thyroid hormones
What does Thyroid Releasing Hormone do?
Stimulates TSH release from the anterior pituitary
What does Thyroid Stimulation Hormone do?
Stimulates thyroid hormone production
Actives iodide uptake via the sodium / iodide symporter (SIS)
What nutrients are needed for thyroid hormone synthesis?
Tyrosine and Iodine
Iron
Selenium and zinc
Vitamin D
Vitamins A, C, E, B2, B3, B6 and B12
Copper
What is copper’s role?
Cofactor for deiodinase enzymes
What is Vitamins A, C, E, B2, B3, B6 and B12’s role?
Synthesis and function
What is Vitamin D’s role?
Immune modulation in autoimmune thyroid disorders (AITD and VDR polymorphisms)
What are selenium and zinc’s functions?
Co-factors and receptor function
What is iron’s role?
Thyroid peroxidase is haem-dependent
What is tyrosine and iodine’s role?
To form T4 and T3
Thyroid peroxidase (TPA) catalyses iodination of tyrosine in thyroglobulin to form T4 and T3.
What is the Wolff-Chaikoff effect?
When the body rejects excess iodine but is inhibited in some people
What can cause excess iodine?
Supplements
Over-iodised salt
Radiocontrast dyes
Medications (e.g. amiodarone used for heart arrythmias)
What are iodine-rich foods?
Sea veg
Ocean fish
shellfish
Eggs and dairy in the UK
Common causes of iodine deficiency?
Dietary deficiency
Increased risk - vegan / pregnant / low diary/fish diet
High goitrogen intake - raw brassicas, soya, peanuts
How much T3 and T4 is secreted daily?
80-100mcg of T4 - 99.9% is highly bound -0.02% free circulation
10 mcg of T3 - slightly less bound 0.2% free circulation
only 10% T3 from thyroid - rest for peripheral conversion (liver and kidney)
How are thyroid hormones metabolised?
Deiodination
Sulphation
Glucuronidation
Consider detox protocals
Which enzymes convert T4 to T3 and reverse T3?
T3 - D1 and D2
Reverse T3 - D3
Important point about Reverse T3 and what causes and increase in RT3?
Biologically inactive but can bind to T3 receptors block T3
Chronic/critical illness
High Stress
Co-factor deficiency (low zinc/selenium/iron)
Liver dysfunction
Fasting/calorie restriction
How to halogens disrupt the thyroid and where can they be found?
Interfere with the sodium iodide symporter and reduce iodine uptake
Fluoride - water / toothpaste / pesticides
Chlorine - swimming pools, PCBs
Bromine - pesticides, flame retardants, farmed fish
4 HPT disruptors apart from halogens
Pesticides - e.g. glyphosate (lowers TSH reduces D2 and D3 transporters)
PCBs and bisphenols
Phthalates
Perchlorates (food packaging / fertilisers) block NA-I symporter
5 ways to avoid HPT disruptors
Drink filtered water
Fluorie-free toothpaste
Eat organic
Avoid farmed fish
Avoid processed food
Limit time in chlorinated pools
Avoid plastic packaging
Organic textiles
Natural cleaning products
4 medications that impact thyroid function and mechanism?
Hyperthyroid medications may induce hypothyroidism
