Endocrine Health Revision PDF

Summary of Key Learning Points from the Lecture on Endocrine Health: 1. Thyroid Function and Hormone Regulation Thyroid hormones: T3 (triiodothyronine) and T4 (thyroxine) are the main thyroid hormones. HPT Axis: The hypothalamus releases TRH, stimulating the pituitary to rele...

Summary of Key Learning Points from the Lecture on Endocrine Health: 1. Thyroid Function and Hormone Regulation Thyroid hormones: T3 (triiodothyronine) and T4 (thyroxine) are the main thyroid hormones. HPT Axis: The hypothalamus releases TRH, stimulating the pituitary to release TSH, which in turn prompts the thyroid to secrete T3 and T4. Conversion: T4 is converted into the active T3 by deiodinase enzymes in peripheral tissues (e.g., liver, kidneys), while some T4 is converted into inactive reverse T3 (RT3). Nutritional Factors: Iodine, selenium, iron, zinc, and vitamins A, D, and B-complex are essential for thyroid hormone synthesis and function. 2. Hypothyroidism Causes: Iodine deficiency, autoimmune diseases (e.g., Hashimoto’s thyroiditis), chronic stress, nutrient deficiencies, and environmental toxins (e.g., BPA, fluoride). Symptoms: Fatigue, weight gain, depression, cold intolerance, dry skin, hair loss, and menstrual irregularities. Subclinical Hypothyroidism: Elevated TSH but normal free T4 levels, often undetected, linked to cognitive impairment and cardiovascular risks. 3. Hyperthyroidism Causes: Grave’s disease (autoimmune), viral infections, iodine excess, and inflammation. Symptoms: Weight loss, irritability, insomnia, heat intolerance, palpitations, and menstrual irregularities. Grave’s Disease: Abnormal IgG antibodies (TRAbs) occupy TSH receptors, overstimulating thyroid hormone production. 4. Impact of Nutritional and Environmental Factors Iodine: Both deficiency and excess iodine can disrupt thyroid function. Thyroid Disruptors: Chemicals like fluoride, BPA, and pesticides can interfere with thyroid hormone synthesis and action. Gut Health and Thyroid: Gut dysbiosis can impact thyroid function due to its role in iodine metabolism and systemic inflammation. Mechanism of Action of Thyroid Hormones: 1. Production and Release: o The hypothalamus releases TRH (thyrotropin-releasing hormone), which stimulates the anterior pituitary to release TSH (thyroid-stimulating hormone).  o TSH binds to receptors on the thyroid gland, stimulating the production of T4 (thyroxine) and T3 (triiodothyronine). 2. Conversion: o T4, the primary hormone released by the thyroid, is largely inactive. It is converted into T3 (the active form) in peripheral tissues, particularly in the liver and kidneys, via deiodinase enzymes (D1 and D2). o T3 binds to nuclear receptors within cells, influencing gene expression to regulate metabolism, growth, and development. 3. Reverse T3 (RT3): o Some T4 is converted into reverse T3 (RT3), an inactive form that blocks T3 receptor binding, thus reducing thyroid hormone action during times of stress or illness (e.g., Low T3 Syndrome). Relationship with the HPA and HPO Axes: 1. HPA Axis (Hypothalamus-Pituitary-Adrenal) o Chronic stress activates the HPA axis, leading to increased cortisol production. Elevated cortisol can inhibit the conversion of T4 to T3, leading to higher RT3 levels, which decreases the overall thyroid activity. o Cortisol also reduces TSH secretion from the pituitary, thus lowering thyroid hormone production and potentially leading to hypothyroidism. 2. HPO Axis (Hypothalamus-Pituitary-Ovarian) o The thyroid hormones interact with the HPO axis by influencing estrogen and progesterone levels. Dysregulated thyroid function (especially hypothyroidism) can lead to menstrual irregularities, fertility issues, and altered ovulation due to disrupted estrogen levels. o Conversely, estrogen increases thyroid-binding globulin (TBG) levels, which can lower the availability of free thyroid hormones. Flashcards for Revision: Flashcard 1: Q: What is the primary function of the thyroid hormones T3 and T4? A: Regulate metabolism, growth, bone development, and increase heart rate. Flashcard 2: Q: How does the hypothalamus-pituitary-thyroid (HPT) axis regulate thyroid hormones? A: The hypothalamus releases TRH, stimulating the pituitary to secrete TSH, which prompts the thyroid to produce and release T3 and T4. Flashcard 3: Q: What enzyme converts T4 into active T3? A: Deiodinase enzymes (specifically D1 and D2). Flashcard 4: Q: What is reverse T3 (RT3) and its function? A: RT3 is an inactive form of T3 that blocks T3 receptor activity, reducing thyroid hormone action during stress or illness. Flashcard 5: Q: What impact does chronic stress have on thyroid function? A: Chronic stress increases cortisol, which inhibits the conversion of T4 to T3, increases RT3 levels, and reduces TSH secretion. Flashcard 6: Q: How does hypothyroidism affect the HPO axis? A: Hypothyroidism disrupts estrogen and progesterone levels, leading to menstrual irregularities, fertility problems, and altered ovulation. Flashcard 7: Q: What are common symptoms of hypothyroidism? A: Fatigue, weight gain, depression, cold intolerance, hair loss, and menstrual irregularities. Flashcard 8: Q: What is Grave’s disease, and how does it affect thyroid function? A: An autoimmune condition where TRAbs bind to TSH receptors, overstimulating the thyroid to produce excess hormones, leading to hyperthyroidism. Flashcard 9: Q: What are key nutritional factors for thyroid health? A: Iodine, selenium, zinc, iron, vitamins A, D, B-complex, and antioxidants. Flashcard 10: Q: How can gut health impact thyroid function? A: Gut dysbiosis affects iodine metabolism, promotes inflammation, and disrupts thyroid hormone conversion and action. These flashcards cover the core concepts of thyroid hormone function, regulation, and their interactions with the HPA and HPO axes. Flashcard 11 Q: What are the key hormones produced by the thyroid gland, and what are their functions? A: The thyroid produces T3 (triiodothyronine) and T4 (thyroxine). T3 is the active hormone that regulates metabolism, heart rate, and development, while T4 is mostly inactive but can be converted to T3 in peripheral tissues. Flashcard 12 Q: What is the role of the hypothalamus-pituitary-thyroid (HPT) axis in thyroid regulation? A: The HPT axis regulates thyroid function through the release of TRH from the hypothalamus, which stimulates the pituitary to release TSH. TSH prompts the thyroid to release T3 and T4. Flashcard 13 Q: What enzyme converts T4 into the active form T3, and which nutrient is critical for this process? A: Deiodinase enzymes (D1 and D2) convert T4 into T3. The nutrient selenium is crucial for the proper function of these enzymes. Supplement: Selenium (150-200 mcg/day). Flashcard 14 Q: What is reverse T3 (RT3), and when is its production increased? A: RT3 is an inactive form of T3 that can bind to T3 receptors, blocking its action. Production increases in response to stress, chronic illness, high cortisol levels, and nutrient deficiencies (e.g., zinc, selenium, iron). Flashcard 15 Q: Which key nutrients are required for thyroid hormone synthesis? A: The key nutrients include iodine, tyrosine, selenium, iron, zinc, and vitamins A, D, and B- complex. Key Marker: Ensure iodine sufficiency via urine iodine test (100-199 mcg/L). Supplement: Iodine (150–400 mcg/day, avoid in autoimmune thyroid disorders). Flashcard 16 Q: What are the common symptoms of hypothyroidism? A: Symptoms include fatigue, weight gain, cold intolerance, constipation, dry skin, hair loss, depression, and irregular periods. Flashcard 17 Q: What are the main causes of hypothyroidism? A: Causes include iodine deficiency, autoimmune conditions (e.g., Hashimoto’s thyroiditis), chronic stress, nutrient deficiencies, and environmental toxins (e.g., BPA, fluoride). Flashcard 18 Q: How does chronic stress affect thyroid function through the HPA axis? A: Chronic stress leads to increased cortisol levels, which inhibit TSH release and reduce the conversion of T4 to T3, leading to higher RT3 levels and lower thyroid activity. Flashcard 19 Q: Which supplements can support thyroid function in hypothyroidism? A: Selenium (150-200 mcg/day) – supports T3 production and reduces antibodies in autoimmune thyroiditis. Zinc (15–30 mg/day) – cofactor for deiodinases and TRH synthesis. Vitamin D (2000 IU/day or more) – supports immune modulation, especially in autoimmune conditions. Iron (10-30 mg/day) – essential for thyroid peroxidase (TPO) enzyme activity. Flashcard 20 Q: What are common diagnostic markers for hypothyroidism? A: TSH: Elevated (optimal range: 0.4–2.5 mU/L). Free T4: Low or normal (optimal range: 12.8–19.5 pmol/L). Free T3: Often low in relation to T4 (optimal range: 3.2–4.5 pmol/L). Thyroid antibodies (TPOAb and TgAb) may be present in autoimmune hypothyroidism. Flashcard 21 Q: What is subclinical hypothyroidism, and why is it important to treat? A: Subclinical hypothyroidism is characterized by elevated TSH with normal T4. It can progress to overt hypothyroidism and is associated with increased risk of heart disease and infertility. Flashcard 22 Q: How does the gut microbiome influence thyroid health? A: Gut dysbiosis can affect thyroid hormone metabolism by disrupting iodine uptake, intestinal permeability, and promoting chronic inflammation (e.g., high LPS levels). Supplement: Probiotics (e.g., Lactobacillus and Bifidobacterium). Flashcard 23 Q: What are the symptoms of hyperthyroidism? A: Symptoms include weight loss, anxiety, heat intolerance, sweating, irritability, palpitations, and menstrual irregularities. Flashcard 24 Q: What are the main causes of hyperthyroidism? A: Causes include Grave’s disease (autoimmune hyperthyroidism), multinodular goitre, iodine excess, and thyroiditis (often viral or autoimmune). Flashcard 25 Q: How does Grave’s disease affect thyroid function? A: Grave’s disease occurs when TRAbs (TSH receptor antibodies) bind to and overstimulate the thyroid, causing excessive production of thyroid hormones. Key Marker: Presence of TRAbs and TPO antibodies confirms autoimmune hyperthyroidism. Flashcard 26 Q: What supplements can help manage hyperthyroidism? A: L-carnitine (2000-4000 mg/day) – inhibits the effects of thyroid hormones on the heart and muscles. Selenium (200 mcg/day) – reduces oxidative stress and slows disease progression in Grave’s disease. Bugleweed (herbal supplement) – inhibits thyroid hormone synthesis. Flashcard 27 Q: How can iodine disrupt thyroid function when consumed in excess? A: Excess iodine can overstimulate the thyroid, leading to hyperthyroidism, or trigger the Wolff- Chaikoff effect, causing hypothyroidism in susceptible individuals. Flashcard 28 Q: What are key strategies to reduce goitrogens in food? A: Cooking (steaming, boiling) helps inactivate goitrogenic compounds present in foods like cruciferous vegetables (e.g., kale, cabbage). Flashcard 29 Q: What role do antioxidants play in thyroid health? A: Antioxidants like vitamin C, vitamin E, selenium, and glutathione reduce oxidative stress, which is essential in managing autoimmune thyroid conditions and preventing further thyroid damage. Flashcard 30 Q: What are common thyroid-disrupting chemicals (TDCs), and how can they be avoided? A: Common TDCs include BPA, phthalates, fluoride, and pesticides. Avoiding plastic packaging, drinking filtered water, and choosing organic foods can help reduce exposure.