هرمون الدرقية
هرمونات الدرقية thyroid hormones، ثيروكسين (T4) وثيرونين ثلاثي اليود (T3)، هي هرمونات مبنية على تيروسين تنتجها الغدة الدرقية وهي مسئولة أساساً عن تنظيم الأيض. اليود مكون هام في تخليق هرمونات الدرقية. الشكل الرئيسي لهرمون الدرقية في الدم هو الثيروكسين (T4)، التي لها عمر نصف أطول من T3. نسبة T4 إلى T3 المُفرزة في الدم هي تقريباً 20 إلى 1. يتحول الثيروكسين إلى T3 نشط (وهو أقوى ثلاث لأربعة أضعاف الـ T4) داخل الخلايا بواسطة الديأيودينازات deiodinase (5'-iodinase). وأولئك يخضعوا لمزيد من المعالجة بواسطة نزع الكربكسلة decarboxylation ونزع اليود لانتاج أيودوثيرونامين iodothyronamine (T1a) وثيرونامين (T0a).
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الدوران والنقل
نقل الپلازما
معظم هرمونات الدرقية الدائرة في الدم مرتبطة بنقل البروتينات. فقط نسبة طفيفة من الهرمون الدائر تكون حرة (غير مرتبطة) ونشطة حيوياً، ولذلك فقياس تركز هرمونات الدرقية الحرة له قيمة تشخيصية عظيمة.
فعندما يكون هرمون الدرقية مرتبطاً، وليس نشطاً، فإن كمية T3/T4 الحرة تكون هي المهمة. ولهذا السبب، فقياس الثيروكسين الإجمالي في الدم يمكن أن يكون مضللاً.
| النوع | النسبة المئوية |
|---|---|
| مرتبط بـthyroxine-binding globulin (TBG) | 70% |
| مرتبط بـtransthyretin أو "thyroxine-binding prealbumin" (TTR or TBPA) | 10-15% |
| پارا ألبومن | 15-20% |
| unbound T4 (fT4) | 0.03% |
| unbound T3 (fT3) | 0.3% |
T3 and T4 cross the cell membrane easily as they are lipophilic molecules, and function via a well-studied set of nuclear receptors in the nucleus of the cell, the thyroid hormone receptors.
T1a and T0a are positively charged and do not cross the membrane; they are believed to function via the trace amine-associated receptor TAAR1 (TAR1, TA1), a G-protein-coupled receptor located in the cell membrane.
وثمة أداة تشخيصية هامة أخرى هي قياس كمية الهرمون المحفز للدرقية (TSH) الموجود.
الوظيفة
الأمراض المرتبطة
Both excess and deficiency of thyroxine can cause disorders.
- Hyperthyroidism (an example is Graves Disease) is the clinical syndrome caused by an excess of circulating free thyroxine, free triiodothyronine, or both. It is a common disorder that affects approximately 2% of women and 0.2% of men.
القياس
الاستخدام الطبي لهرمونات الدرقية
الصياغات
Today most patients are treated with levothyroxine, or a similar synthetic thyroid hormone[2][3][4].
انتاج هرمونات الدرقية
المركزي
- Thyroglobulin is synthesized in the rough endoplasmic reticulum and follows the secretory pathway to enter the colloid in the lumen of the thyroid follicle by exocytosis.
- Meanwhile, a sodium-iodide (Na/I) symporter pumps iodide (I-) actively into the cell, which previously has crossed the endothelium by largely unknown mechanisms.
- This iodide enters the follicular lumen from the cytoplasm by the transporter pendrin, in a purportedly passive manner.[6]
- In the colloid, iodide (I-) is oxidized to iodine (I0) by an enzyme called thyroid peroxidase.
- Iodine (I0) is very reactive and iodinates the thyroglobulin at tyrosyl residues in its protein chain (in total containing approximately 120 tyrosyl residues).
- In conjugation, adjacent tyrosyl residues are paired together.
- The entire complex re-enters the follicular cell by endocytosis.
- Proteolysis by various proteases liberates thyroxine and triiodothyronine molecules, which enter the blood by largely unknown mechanisms.
Thyroid hormones (T4 and T3) are produced by the follicular cells of the thyroid gland and are regulated by TSH made by the thyrotrophs of the anterior pituitary gland. Because the effects of T4 in vivo are mediated via T3 (T4 is converted to T3 in target tissues), T3 is 3- to 5- fold more active than T4.
الأدوية المضادة للدرقية
Iodine uptake against a concentration gradient is mediated by a sodium-iodine symporter and is linked to a sodium-potassium ATPase. Perchlorate and thiocyanate are drugs that can compete with iodine at this point. Compounds such as goitrin can reduce thyroid hormone production by interfering with iodine oxidation.[7]
أثر الثيروكسين
- Increases cardiac output
- يرفع معدل نبض القلب
- Increases ventilation rate
- Increases basal metabolic rate
- Potentiates the effects of catecholamines (i.e. increases sympathetic activity)
- Potentiates brain development
- Thickens endometrium in females
- increase metabolism of proteins and carbohydrates
الأعشاب
There are no herbs (plant chemicals) that contain thyroid hormone[8][9]. Therefore, while there are some herbs that may provide some help for a sluggish thyroid (i.e. if the thyroid is producing a low amount of thyroid hormone, but has not stopped completely)[10], myxedema requires treatment with synthetic or desiccated natural thyroid hormones[9][11]. However, there are many edible plants that have high concentrations of iodine (e.g., seaweed and kelp). Iodine is an irreplaceable precursor to the biosynthesis of thyroid hormones.
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انظر أيضاً
- هرمون
- غدة الدرقية
- الهرمون المحفز للدرقية
- Thyronamines, metabolites of the thyroid hormones that act at the trace amine-associated receptor TAAR1 (TAR1)
- گويتر
- Graves-Basedow disease
الهامش
- ^ References used in image are found in image article in Commons:Commons:File:Thyroid_systbcvhxcxcfffgem.png#References.
- ^ Robert Lloyd Segal, MD Endocrinologist
- ^ "preferred thyroid hormone -- Levothyroxine Sodium (Synthroid, Levoxyl, Levothroid, Unithroid)", Retrieved on 2009-3-27
- ^ "Hypothyroidism Causes, Symptoms, Diagnosis, Treatment Information Produced by Medical Doctors", Retrieved on 2009-3-27
- ^ Chapter 48, "SYNTHESIS OF THYROID HORMONES" in: Walter F., PhD. Boron (2003). Medical Physiology: A Cellular And Molecular Approaoch. Elsevier/Saunders. p. 1300. ISBN 1-4160-2328-3.
- ^ How Iodide Reaches its Site of Utilisation in the Thyroid Gland – Involvement of Solute Carrier 26A4 (Pendrin) and Solute Carrier 5A8 (Apical Iodide Transporter) - a report by Bernard A Rousset. Touch Brieflings 2007
- ^ Spiegel C, Bestetti GE, Rossi GL, Blum JW (1993). "Normal circulating triiodothyronine concentrations are maintained despite severe hypothyroidism in growing pigs fed rapeseed presscake meal". J. Nutr. 123 (9): 1554–61. PMID 8360780.
{{cite journal}}: Unknown parameter|month=ignored (help)CS1 maint: multiple names: authors list (link) - ^ خطأ استشهاد: وسم
<ref>غير صحيح؛ لا نص تم توفيره للمراجع المسماةthyroid.about.com refusngmeds - ^ أ ب "Thyroid Disease: A Natural/Herbal Perspective -- Interview with Shasta Tierra-Tayam, L.Ac", Retrieved on 2009-3-27
- ^ “WikiAnswers - Is there are natural herb to take for a sluggish thyroid”, Retrieved on 2009-3-27
- ^ "Hypothyroidism Causes, Symptoms, Diagnosis, Treatment Information Produced by Medical Doctors", Retrieved on 2009-3-27
وصلات خارجية
علاج هرمون الدرقية في مرض الدرقية
- Thyroid Hormone Treatment Brochure by the American Thyroid Association
- Elaborate article about the use of thyroid drugs Written by an MD
- What is the "Best" Thyroid Drug? Is it Synthroid, Unithroid, Armour, Thyrolar, or Something Else? Article by health activist and patient advocate Mary Shomon
- Thyroid Disease Manager Collection of elaborate medical articles on thyroid disease, including information on thyroid hormones
- Stop the thyroid madness Collection of references to articles comparing different treatment methods of hypothyroidism