thyroid hormone

Biological terminology

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Thyroid hormone is a hormone secreted by thyroid gland, which acts on almost all cells of human body. English name: tyroid horn Alias: Dry thyroid , abbreviation: TH thyroid molecular formula: C15H11O4I4N relative molecular mass ：776.93。 physical property : White Acicular crystal 。 Odorless. Odorless. Deteriorates when exposed to light. Melting point 231-233 ℃ (decomposition). Insoluble water and ethanol Common Organic solvent 。 Soluble in Inorganic acid Or alkali ethanol, also soluble in alkali hydroxide and carbonic acid Alkali solution. In its acidity Ethanol solution Joined in Sodium nitrite , it turns yellow when heated, and then add too much ammonia It turns pink. Chemical essence : Thyroxine is T4 , is tetraiodothyronine. Preparation: It can be extracted from the thyroid of cattle, sheep, pigs, etc. or synthesized artificially.

Chinese name: thyroid hormone
Foreign name: thyroid hormone

Alias: TH^[1]
Secretory organ: thyroid
Molecular formula: C15H11O4I4N

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twelve Metabolize

Dosage and usage

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Schematic diagram of thyroid hormone synthesis and metabolism

be used for Hypothyroidism : At the beginning, the oral dose should not exceed 15 ～ 30 mg per day, and then gradually increase to 90 ～ 180 mg per day. After the patient's condition is stable, the maintenance dose of 60~120 mg per day shall be used, and a dose suitable for long-term use shall be selected.

yes Petrification : The dosage varies with age, 8 to 15 mg per day within 1 year old, 20 to 45 mg per day within 1 to 2 years old, and 30 to 120 mg per day above 2 years old, all of which are taken three times in average.

Simple goiter ： Start with intramuscular injection To relieve symptoms. After remission, it was taken orally. The course of treatment is generally 3-6 months. It can promote general tissue metabolism, improve nerve excitability and Physical development effect. Used to treat thyroid Hypofunction , myxedema and Cretinism Etc.

Physiological function

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by Amino acid derivatives ， Promote metabolism and development, improve nervous system Of Excitability ； Breathing, Rhythm Accelerate, Thermogenesis Increase.

It is secreted when cold and tense.

When people encounter danger and Emotional tension It will stimulate first hypothalamus release Thyrotropin releasing hormone , the increase of this hormone concentration in the blood will affect Adenohypophysis Promote its release Thyrotropin That is to increase the content of thyroid stimulating hormone in the blood, which further acts on the thyroid Glandular cell The secretion is increased, that is, a large amount of thyroid hormone is secreted.

(Generally not Direct action Make blood sugar rise.)

Growth and growth hormone rise Synergy ; Thermoregulation Aspects and adrenaline Play a synergistic role.

Biological function

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The biological effects of thyroid hormone mainly include the following three aspects:

Promote growth and development	The effect of thyroid hormone on promoting growth and development is most obvious in infancy, and the greatest impact is in the first five months after birth. It mainly promotes bone, brain and genitals The growth and development of officials. Without thyroid hormone, pituitary GH It doesn't work. And thyroid Hormone deficiency The production and secretion of GH by the pituitary gland also decreased. Therefore, congenital or childhood thyroid hormone deficiency causes Petrification 。 Stupid patients Bone growth Stagnate Short stature The length ratio of upper and lower body is abnormal, and the proportion of upper body exceeds that of normal people. And because nerve cell Dendrite 、 axon 、 myelin sheath as well as Glial cell Growth disorders , Brain Hypoplasia and Mental retardation , they Sexual organ They can't grow and mature, and they don't have normal Reproductive function 。 newborn Hypothyroidism You should take an appropriate amount of thyroid hormone within one year of age central nervous system The development and recovery of brain function are also effective. Later than this period, even if a large amount of T3 or T4 is added later, the normal function cannot be recovered, so the treatment is often ineffective.
Effect on metabolism	yield heat effect Thyroid hormone can improve the Oxygen consumption rate , increase the heat generation effect. This thermogenic effect may be due to increased thyroid hormone cell membrane The synthesis of Na+- K+pump can increase its vitality, which is an energy consuming process. thyroxine send Basal metabolic rate Increase, 1mg thyroxine can increase heat production by 4000KJ. Hyperthyroidism The basal metabolic rate of patients can be increased by about 35%; The basal metabolic rate of patients with low function can be reduced by about 15%.
Effect on metabolism	The effect on the metabolism of the three major nutrients is very complex. In general, under normal circumstances, thyroid hormone mainly promotes protein synthesis , especially to make bone skeletal muscle , liver and other protein synthesis increased significantly, which is of great significance for growth and development in infancy. However, the excessive secretion of thyroid hormone causes the protein, especially the protein of skeletal muscle, to be decomposed in large quantities, resulting in emaciation and weakness. stay Carbohydrate metabolism On the other hand, thyroid hormone can promote the absorption of sugar in the small intestinal mucosa Glycogen decomposition Role of. At the same time, it can also promote the utilization of sugar in peripheral tissues. When hyperthyroidism occurs, blood sugar increases, sometimes Urine sugar 。 In short, it accelerates sugar and Fat metabolism In particular, it promotes the decomposition and oxidation of sugar, fat and protein in many tissues, thus increasing the oxygen consumption And heat generation.^[1]
Other aspects	In addition, thyroid hormone also plays an important role in the activities of some organs. It is important to maintain the excitability of the nervous system. Thyroid hormone can directly act on heart muscle to promote Sarcoplasmic reticulum Release Ca2+to Myocardial contractility The heart rate increases. yes water and electrolyte Influence of: When thyroid function is low Mucin Increase, can combine a large number of Positive ion And water molecules, K+and Na+remain in Tissue fluid Viscous edema occurs. Effects on nervous system: Hyperfunction When, Central nervous system Increased excitability.^[2]

Basic properties

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thyroxine Namely tetraiodide Thyronine 。 There are DL, L and D models. L-type It is white crystal. It decomposes at 235-236 ℃. Optical rotation -4.4 ° (3% over 0.13 mol/L NaOH At 70% ethanol )。 Type D is crystalline and decomposes at 237 ℃; DL type is acicular crystal, which decomposes at 231-233 ℃. Soluble in alkali solution, insoluble in water, ethanol and Ether 。 It is not confirmed that it is natural Free state Exists, possibly Thyroglobulin Split products. It can be extracted from animal thyroid. It can be composed of 3,5-diiodine- l-tyrosine It is made from raw materials. L-type activity is strong, D-type activity is small. Promotive Cellular metabolism , increase Oxygen consumption Stimulate tissue growth, maturation and differentiation. The product can be used as thyroid hormone Substitutes Or Biochemical reagent 。 L-thyroxine The physiological activity of- Racemate 2 times of, D-thyroxine Physiological activity is very low. Therefore, quantitative determination of FT4 pairs in human serum thyroid disease It is of great significance to study the pathology and physiology of thyroid gland. Use the solid phase material that binds T4 antibody, and use 25I-FT4 to antiserum Of Radioimmunoassay The method is simple and rapid for the determination of FT4 in plasma.

Formation process

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Formation process of thyroxine

The uniqueness of thyroid hormone lies in its biological activity trace element Iodine. Iodine is a rare ingredient in soil in most parts of the world, so there is little iodine in food. In evolution, organisms have formed a complex mechanism to obtain and retain this key element, and transform it into a form suitable for incorporation of organic ingredients. At the same time, the thyroid must synthesize thyroxine, which occurs in thyroglobulin.

Thyroxine is formed through synthesis, storage, iodization Reabsorption Six processes of decomposition and release:

one Follicular epithelial cells Take amino acids from the blood Rough endoplasmic reticulum The precursor of thyroglobulin synthesis, and then Golgi complex Sugar is added and concentrated to form secretory granules, which are then discharged to Follicles In cavity storage.

2. Follicular epithelial cells can take I -, I - from blood Peroxidase Activation.

3. The activated I enters the follicular cavity and binds with thyroglobulin to form iodized thyroglobulin.

4. Follicular epithelial cells, under the effect of thyroid stimulating hormone secreted by the adenohypophysis, Endocytosis Iodized thyroglobulin in the follicular cavity becomes colloid Vesicle 。

5. Glial vesicles and lysosome Fusion, thyroglobulin iodide coating hydrolase It decomposes to form a large amount of tetraiodothyronine (T4) and a small amount Triiodothyronine (T3), namely thyroid hormone.

The mechanism of action in thyroid cells^[3]

6. T3 and T4 are released into the blood at the cell base.

Total procedure of thyroid hormone synthesis. Iodine ingested from food and water is actively concentrated by thyroid oxidase Transformed into organic iodine and mixed with Follicular cell the basic level cell surface Of Gelatinous substance Thyroglobulin Tyrosine combination. Tyrosine iodization Is in 1 (monoiodothyrosine) or 2（ Diiodotyrosine ）And then coupling Formation of active hormone [Diiodothyrosine Diiodothyrosine → Tetraiodothyrosine (T4); Diiodothyrosine Monoiodothyrosine → triiodothyrosine (T3)], and some T3 comes from the iodine removal of the outer ring of I5 'deiodinase T4 in the thyroid gland. Thyroglobulin (glycoprotein containing T3 and T4) is absorbed from follicles by thyroid cells into colloidal droplets

Lysosomal protease send Globulin T3 and T4 were broken, resulting in the release of free T3 (FT3) and free T4 (FT4) Tyrosine Iodide (Monoiodothyrosine and Diiodothyrosine) are also released from thyroglobulin at the same time, but only a small part enters the blood stream Deiodinase Deiodization, which is reused by the thyroid gland

T4 and T3 are released from thyroid into blood stream through proteolysis, and are associated with thyroid hormone Binding protein Binding transport. The main thyroid hormone binding proteins are Thyroxine binding globulin (TBG), which has high affinity for T4 and T3, but low binding capacity TBG normally accounts for about 75% of the binding hormone. Other thyroid hormone binding proteins - mainly thyroid hormone binding proteins Prealbumin , also known as Thyrotropin (transhyretin), high for T4 Affinity , low combined capacity, and albumin It has low affinity for T4 and T3, and high binding capacity --- it accounts for the rest of thyroid hormone in bound serum. About 0.03% of total serum T4 and 0.3% of total serum T3 are free and in dynamic balance with bound hormone. Only FT4 and FT3 play the role of thyroid hormone in surrounding tissues

Pituitary thyroid stimulating hormone (TSH), also known as Thyrotropin It can excite follicular cells in thyroid gland and is necessary to affect and control the whole sequence reaction of T3 and T4 formation TSH and follicles Outer surface Upper thyroid cells Serous membrane Receptor binding, activation adenosine Acid cyclase, thus increasing adenosine 3 ': 5' - cyclic phosphorylation（ cAMP ）Formation, nucleotide It mediates the intracellular effects of TSH. Pituitary TSH secretion is controlled by the negative feedback regulation of FT3, FT4 in the circulation and T4 conversion to T3 in pituitary thyroid stimulating cells T3 is a metabolically active iodothyronine. The increase of free thyroid hormones (T4 and T3) inhibits pituitary TSH secretion, while the decrease of T4 and T3 levels leads to the increase of pituitary TSH release TSH secretion is also affected by TRH, which is a three amino acid peptide synthesized by hypothalamus TRH is released to the portal system between the hypothalamus and pituitary, and Anterior pituitary The binding of specific TRH receptors on thyroid stimulating cells causes the release of TSH series. Although thyroid hormones play a role in the synthesis and release of TRH, the precise mechanism is still unclear

About 20% of circulating T3 is produced by thyroid, and the remaining 80% is mainly from liver, which is produced by the conversion of the outer ring deiodination (5'D-I) of T4 The inner cyclic monodeiodinase [5-deiodinase (5D - Ⅲ)] of T4 can also occur in the liver and outside the liver, producing 3,3 ', 5' - T3 (anti T3 or rT3). These iodothyronine metabolic activities are small, but they exist in the serum of normal people and in a very small amount in thyroglobulin. About 99% rT3 is produced in the inner cyclic deiodination of surrounding tissue T4. In many cases, rT3 increases, At this time, the decrease of T3 level is due to the decrease of outer ring 5'D-I activity (e.g Chronic liver disease , nephropathy , acute and chronic disease , hunger and carbohydrate Lack). The increase of rT3 is mainly due to the decrease of the activity of the outer ring (5'D-I), which significantly reduces the clearance of rT3. These chronic causes lead to the decrease of the production of active hormone (T3) and the increase of rT3 due to the reduction of clearance The decrease of T3 production may be due to the disease Adaptive response .^[4]

Regulation process

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brain the pituitary The secreted thyroid stimulating hormone (TSH) promotes the whole process of thyroid hormone synthesis and secretion, and the secretion of TSH is regulated by the thyroid hormone releasing hormone (TRH) secreted by the hypothalamus. Stress state 、 ambient temperature Changes and some diseases affect thyroid function through TRH. On the other hand, the concentration of T4 and T3 in the blood has an effect on the release of TSH and TRH negative feedback regulation effect.^[4]

classification

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Thyroid hormones include thyroxine and triiodide Thyronine 。

Function: thyroid hormone is necessary for normal growth and development of human body, and its insufficient or excessive secretion can cause diseases. When thyroid function is insufficient, physical and mental development will be affected, which may cause dementia（ Cretinism ）, adult thyroid insufficiency can cause Myxedema 。

Promoting metabolism of thyroid hormone can promote the oxidation of substances and increase Oxygen consumption , improve Basal metabolic rate , which can increase heat production but can not be used well. Hyperthyroidism has symptoms such as fear of heat and sweating.

Nervous system and cardiovascular Effect on patients with mild illness central nervous system The development of P. When hyperthyroidism occurs, nervousness, impatience, tremor, heart rate acceleration Cardiac output Increase, etc. Because thyroid hormone can enhance the heart's catecholamine Of susceptibility 。

Thyroid hormone not only affects the growth and development of long bones, but also affects the development of brain Hormone deficiency , which will lead to height and mental retardation Stupidity

Under normal conditions, under the control of the central nervous system, the hypothalamus releases Thyroid Hormone release Hormones (TRH) regulate the secretion of pituitary thyroid stimulating hormone (TSH), which stimulates the thyroid Cell secretion T4 and T3; When the concentration of T4 and T3 in the blood increases Feedback , inhibit the synthesis and release of TSH in the adenohypophysis, reduce the responsiveness of the adenohypophysis to TRH, reduce the secretion of TSH, so that the secretion of thyroid hormone is not too high; When the concentration of T4 and T3 in the blood decreases, the negative feedback effect on the adenohypophysis weakens. The secretion of TSH increases, promoting the secretion of T4 and T3. In conclusion, the hypothalamus pituitary thyroid regulatory loop can maintain relatively constant thyroid hormone secretion.

Iodine is an important component of thyroid hormone. Iodine deficiency will lead to insufficient synthesis of thyroid hormone in the body Endemic goiter , commonly known as "big neck disease", patients will dyspnea Symptoms, eating Kelp and Iodized salt It can effectively prevent the occurrence of endemic goiter.

pharmacological action

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T3 acts quickly and strongly, while T4 acts weakly and slowly. Thyroid hormone nucleus It can bind to its receptor and induce the target Gene transcription And exert the effect. Its functions include maintaining normal growth and development, promoting metabolism and Thermogenesis Improve the body's sympathetic feeling- adrenal gland System reactivity, etc.

clinical application

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Physiological function and metabolism

1. Production of thyroid hormone

T4 The highest content of Tg Iodization amino acid , than T3 10-20 times more, T4 is also the most iodized amino acid in serum, accounting for Serum protein bound iodine The output of T3 and the capacity of outer pool are significantly less than T4.

Free T4 and T3 account for 0.02% and 0.2% of T4 and T3 respectively, and the serum concentration of T4 is 50-80 times higher than T3. The activity of free T3 is 3-5 times higher than that of T4, while RT3 has no activity.

2. Transport and metabolism of thyroid hormone

T3 and T4 are decomposed by enzymes and enter the blood. 99.98% of T4 and 99.8% of T3 are mixed with Binding protein Transport in combination.

T3 and T4 are metabolized in two ways:

(1) It is produced by mixing with glucuronide and sulfuric acid Conjugates In the form of bile And urine excretion, accounting for 15% - 20% of the total daily consumption.

(2) It is de iodized Enzymatic degradation Other iodamine, such as T2 is T3, rT3 Main points of Metabolites 。

3. Regulation of thyroid hormone

Secretory receptor of thyroid hormone hypothalamus ， Adenohypophysis And thyroid hormone level in plasma to maintain dynamic equilibrium This is the hypothalamus pituitary thyroid axis system.

TSH yes Anterior pituitary Secretory glycoprotein , which is affected by hypothalamic Thyrotropin releasing hormone （ TRH ）Stimulation and release. The increase of serum T4 and T3 levels can inhibit the secretion of TSH, which is called negative feedback.

The thyroid also has an autonomous regulation function. Iodide The intake of Iodine deficiency To a certain extent Self regulation Compensatory effect 。

4. Physiological function of thyroid hormone:

(1) Oxidation, heat generation and temperature control

Thyroid hormone increases the oxidation rate of cells and generates heat

（2） Material metabolism Role of

Promote sugar, fat and protein Metabolism of.

(3) Promotion Growth and development

Thyroid hormone promotes: a. The cells increase and the volume increases, so the body grows. b. Cartilage ossification and tooth development; c. Brain maturation

Clinical significance

1. Clinical significance of TSH

identify Hypothyroidism disease	from hypothalamus Hypothyroidism after functional impairment. This may be because TRH ↓→ causes TSH ↓→ causes T3, T4 ↓, which is called secondary Hypothalamic hypothyroidism. and Primary T3 and T4 in patients with hypothyroidism are too low and the secretion is strong. The location of secondary hypothyroidism is hypothalamus and pituitary. The primary hypothyroidism is located in the thyroid gland.
Hyperthyroidism	hyperthyroidism The patients' T3 and T4 are too high, Feedback suppression The secretion of TSH reduces the serum TSH level to near zero. Hypersensitive TSH (S-TSH or h-TSH) is used to diagnose hyperthyroidism (while conventional TSHRIA is an outdated test).
Goiter	Hyperthyroidism In patients with iodine deficiency, the secretion of T3 and T4 decreases, so the secretion of TSH increases. When the patients become swollen or after iodine supplementation, the TSH level can Return to normal 。 Hypothyroidism Myxedema 、 Stupidity 。
Goiter	TBG Binding force Down.
TSH Reactivity Low visibility	Hyperthyroidism.
	Autonomic function without hyperthyroidism thyroid disease 。
	Pituitary gland or Hypothalamus damage Caused by hypothyroidism.
	PRL tumor.
	Cushing's syndrome.
	Acromegaly Etc.

2. Clinical significance of T3 and T4

(1) T3 increases in the following diseases:

a. Hyperthyroidism; b. T3 type hyperthyroidism ； c.T3 Toxemia ； d. Using Thyroid preparation Overtreatment; e. TBG binding capacity increase syndrome; f. Thyroiditis Etc;

T3 decreases in the following diseases: a wrong Thyropathy Low T3 syndrome; d. Chronic thyroiditis Etc.

(2) T4 has parallel changes with T3 in the following diseases (hyperthyroidism, T3 toxemia).

3． FT3 and FT4 Clinical significance of

T4 and T3 enter the blood after hydrolysis, 99.98% of T4 and 99.8% of T3 Noncovalent bond And Plasma protein The rest are FT4 0.02% and FT3 0.2%. FT3 and FT4 are actually entered Target cell Hormones that bind to receptors and act. Therefore, the mechanism of thyroid is closely related to the level of FT3 and FT4 in circulation. It can be used to distinguish hyperthyroidism, hypothyroidism and thyroid function Subclinical state 。 Its normal value is not affected by the increase and decrease of TBG in various situations, and it is a sensitive indicator reflecting thyroid function. In 1989, Hamburger recommended that TSH, FT3 and FT4 with high sensitivity be Thyroid function test The first choice method of is widely adopted by the clinical community.

The following scheme is for reference when clinically diagnosed as hyperthyroidism or hypothyroidism:

In the diagnosis of hyperthyroidism, it was believed that TT3 had the highest coincidence rate, followed by TT4, and TSH was the lowest. Scholars at home and abroad unanimously recognized that S-TSH (hypersensitive TSH detection), FT3, and FT4 Joint testing It is obviously superior to TT3 and TT4. The former is not affected by the serum TBG content, and can make some early hyperthyroidism with normal TT3 and TT4 diagnosed. S-TSH can make the diagnosis of hyperthyroidism rise to the subclinical level.

The order of sensitivity for diagnosis of hyperthyroidism is S-TSH>FT3>TT3>FT4>TT4

Hypothyroid Diagnostic sensitivity The sequence is S-TSH>FT4>TT4>FT3>TT3

Normal reference range of TSH: 0.34-5.06uIU/ML (according to different instruments and reagents, the values are also different)

Normal reference range of TT3 and TT4: 1.34-2.73nmol/78.4-157.4nmol/l

Normal reference range of FT3 and FT4: 3.67 -10 .43pmol/11.2-20.1pmol/l

matters needing attention

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1. Long term excess may cause Hyperthyroidism Clinical manifestations, such as palpitations Tremor of hand 、 hyperhidrosis Weight loss, increased nerve excitability and insomnia. In the elderly and heart disease Can occur angina pectoris and myocardial infarction 。 available Beta blocker And immediately stop using this product.

2. Can be connected with Phenytoin sodium 、 Acetylsalicylic acid ， Dicoumarin Class and Oral hypoglycemic agents And plasma protein production competitiveness Combine to increase the free amount of these drugs in the plasma, so as to enhance their effect and aggravate Adverse reactions , even accidents, special attention should be paid.

three diabetes 、 coronary heart disease Waiting for patients contraindicated 。

thyroid hormone Secretory abnormality Disease caused

1: Cretinism

2: Hyperthyroidism

3: (Iodine deficiency) Endemic goiter , commonly known as: neck disease.

Intellectual development

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Thyroid hormone for nervous system It plays a very important role. nerve cell The normal development and maturation of thyroid gland depend on the action of thyroid hormone. Embryonic stage to Childhood It is an important period for the growth and development of the nervous system. If the thyroid hormone is insufficient during this period, the development of the nervous system can be impaired, and intelligence can be significantly affected. The children showed different degrees of stupidity. In serious cases, they could not even manage their own lives, and in light cases, they could not go to school as normal as children of the same age. Their academic performance was extremely poor.

If thyroid hormone treatment is given in time, stupidity can be avoided and intelligence can be recovered and developed. Adult patients Hypothyroidism Since the development of its nervous system has also been completed, it has little impact on intelligence, but only shows Unresponsive ， Thinking ability Decrease.

Metabolize

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⑴ Thyroid hormone is synthesized, stored and released by thyroid. The raw materials for synthesizing thyroid hormone are iodine and Tyrosine 。 Under normal diet, the human body ingests 100-200 micrograms of iodine every day. The intestinal absorption of iodine is complete. The iodine in the diet is first converted into iodide on the intestinal mucosa and then absorbed; Iodine can also be absorbed by skin, mucosa and lung, but it is much worse than intestinal absorption. Iodine absorbed by intestinal tract is mainly distributed in Extracellular fluid 。 Iodide concentration in serum is 0.5 μ g%. Thyroid has the ability to concentrate iodine. Intrathyroid Iodine concentration It is 20-40 times higher than the iodine concentration in the blood. The concentration capacity of hyperthyroidism patients can be increased by 100~200 times. The salivary glands are also derived from the thyroid gland Foregut , so salivary glands It also has the function of concentrating iodine. The ratio of normal saliva iodine to serum iodine was 20. In clinic, the iodine concentration ability of thyroid can be judged simply by measuring the iodide content in salivary gland. Except in the body salivary glands In addition, other glands also have the ability to concentrate iodine, which is similar to that of thyroid. Normally, iodine in saliva and gastric juice passes through the digestive tract Reabsorption Return to extracellular fluid.

⑵ Thyroid concentrated iodine is concentrated from low concentration to high concentration, which is an active concentration function and requires energy consumption. The thyroid's ability to concentrate iodine is mainly affected by the pituitary gland Thyrotropin (TSH) is also inhibited by the high concentration of iodide in the body. The higher the thyroid stimulating hormone, the stronger the ability of thyroid to concentrate iodine; The higher the iodine concentration in the blood, the lower the ability of thyroid to concentrate iodine.

Enter thyroid Follicular epithelial cells Iodine in Peroxidase The function of Thyroglobulin Tyrosine synthesis on Monoiodothyrosine (T1) and Diiodotyrosine （T2）。 2 DIIOTYROSINE coupling become thyroxine (T4), a diiodotyrosine and a monoiodothyrosine are coupled to form a triiodothyronine (also known as triiodothyronine - T3). Thyroid hormones synthesized on the surface of thyroglobulin are stored in Follicles In the colloid. Thyroid follicular cavity The main components in Thyroglobulin 。 The thyroid hormone stored in thyroid follicular cavity can be used by the body for 2-3 months. Thyroid hormone synthesis takes place on the surface of thyroid globules. Thyroid is the only hormone stored outside the cell in the body Endocrine organ 。 Other endocrine organs and glands store hormones in cells.

When the body needs it, Thyroid follicle adopt Pinocytosis , absorb the colloid in the follicle cavity to form colloid drops, and lysosome Syngenetic formation Phagocytosis lysosome 。 Lysosomes contain Proteolytic enzyme And Peptidase 。 T4 and T3 are hydrolyzed from thyroglobulin and released into the blood, which is transported to the whole body to play a role. Lysosomal enzyme When hydrolyzing T4 and T3 on thyroglobulin, monoiodothyrosine and diiodotyrosine are also hydrolyzed, and further Deiodinase Under the action of, free inorganic iodine is released. The latter is mostly Follicular cell And then use synthetic thyroid hormone. This is very important for the thyroid to use the limited iodine in the body economically.

⑶ Most thyroid hormones in the blood combine with proteins in the plasma, mainly Thyroid binding globulin TBG binding, plasma protein (ALB) binding, thyroid binding Prealbumin (TBPA). T4 (75%) mainly binds to TBG, and T3 (90%) mainly binds to thyroglobulin and Plasma albumin combination; Blood circulation 99.97% of T4 is bound, and 99.7% of T3 is bound. Although binding thyroid hormone accounts for the vast majority in the blood, it is still free thyroid hormone that really plays a physiological role. Thyroid binding globulin It is a single chain glycoprotein produced by the liver, half life 5-6 days. It carries 70% of T4 and T3; Thyroid binding prealbumin is generated by the liver with a half-life of 1 to 2 days Affinity Compared with thyroid binding globulin, it has a lower affinity for T4. It carries 10%~20% of T4 and almost no T3. High concentration of plasma albumin, up to 3000-4500 ml/ Deciliter However, it has the lowest affinity to thyroid hormone, and can only carry 5%~15% T4 and 30%~50% T3. Some factors affecting thyroid binding protein will affect the level of thyroid hormone, but the level of free thyroid hormone is normal, and the thyroid function is normal. In the case of true hyperthyroidism or hypothyroidism, serum total thyroid hormone and free thyroid hormone are like objects. Thyroid binding protein is like "warehouses". There are countless "warehouses" in our body. Most of the items produced by the "factory" are stored in the "warehouse" first, and a few are stored in the "store". Only those items in the "store" can be purchased, while most of the items in the "warehouse" cannot be purchased. With powerful "warehouse" items as the backing, the items in the "store" have always been kept at a very stable level. Although there are many items in the "warehouse", they are not circulating and can not function. What is really valuable and can play a physiological role are those items placed in the "store". The number of "warehouses" can affect the number of our items, but not the items in the "store". A large amount of bound thyroid hormone exists in the blood, which avoids the loss of a large amount of thyroid hormone from the urine when the blood is filtered from the kidney, and ensures that Human evolution In the process, iodine will be used more economically from the ocean rich in iodine to the land relatively deficient in iodine. Secondly, a large number of conjugated thyroid hormones exist in the body, maintaining the stability of thyroid hormones day and night, and ensuring the continuous demand of thyroid hormones for metabolism in the body.

T4 and protein binding Tight, slow clearance, half-life in plasma is 7 days; T3 is relatively loosely bound to protein, and is rapidly cleared in plasma, with a half-life of 1 day. T4100% of plasma T4100% comes from thyroid, 20% of plasma T320% comes from thyroid's direct secretion, 80% comes from plasma T4's transformation in the peripheral, and more than 95% rT3 (anti T3) comes from T4's deiodination in the peripheral. Therefore, serum T4 concentration, rather than T3 concentration, should really represent thyroid function.

⑷ The part of thyroid hormone metabolism in the body is filtered out directly from the kidney, and some is discharged after degradation in the body. Its degradation pathway in vivo: ① discharged after deiodination; ② through Side chain degradation Rear discharge; ③ The degradation of thyroid hormone mainly occurs in the liver and also around Muscle tissue Degrade and metabolize to generate inactive iodide. T4 passes 5, deiodinase acts from Outer ring One iodine is removed to generate T3; At 5, deiodinase can also remove one iodine in the inner ring to generate anti T3 (rT3). T3 biological activity Very strong, rT3 activity is very low. When suffering from serious disease, chronic hunger innutrition And taking certain drugs such as Propyl group Thiouracil 、 steroid and Peace of mind 5, Deiodization enzymatic activity Inhibited. 5. The activity of deiodinase increases, showing that serum T3 decreases and rT3 increases, which is a reaction of the body to protect itself under adverse circumstances. When the body returns to normal, 5, deiodinase activity also returns to normal, and serum T3 and rT3 also return to normal. The metabolites of thyroid hormone are mainly discharged by the kidney, and a small part is discharged into the intestinal tract through bile, and then enter the blood through the liver intestine circulation for reuse. Urinary iodine The content accounts for about 90% of our iodine intake, so we can estimate the daily iodine intake by measuring the urine iodine content.

⑸ In addition to deiodination metabolism, there are other thyroid hormones Metabolic pathway , such as T4 and T3 can be produced by oxidative deiodination Tetraiodothyroacetate and Triiodothyroacetate ； T4 and Glucuronic acid Combination, T3 and Sulfate radical Binding is discharged from the body

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