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Saturday, April 20, 2019

Thyroid gland

                Thyroid gland



Thyroid gland




The endocrine system is a glands control and regulate a system that produces hormones within particular organs. Hormones act as "messengers" and are transported through the bloodstream to several cells in the body, which interpret and act on these messages. It seems like a crazy idea or the idea that a small chemical can enter the bloodstream and cause an action in a distant point of the body. However, this occurs in our bodies every day of our life. The ability to maintain homeostasis and respond to stimuli is largely due to the hormones secreted within the body. Without hormones, the body cannot perform their vital functions, such as the growth, produce offspring, maintain a constant temperature

The endocrine system supplies an electrochemical connection from the brain's hypothalamus to all organs that regulate metabolism of the body, growth, development and reproduction. There are two types of hormones secreted in the endocrine system: steroid and non-steroidal (or protein-based) hormones

The endocrine system regulates its hormones through negative reaction, except in very certain conditions such as birth. The increase in hormonal activity decreases the secretion of that hormone. The immune system and other factors also contribute as control factors, keeping constant levels of hormones together


Thyroid gland


Thyroid gland




It contains two lobes on both sides of the larynx, the thyroid gland is activated by the thyroid stimulating hormone secreted by the pituitary gland. Thyroid hormones, commonly called T3 and T4, develop in small pockets, the thyroid follicles, from iodine in the blood. They serve in particular to regulate growth and metabolism

The thyroid gland is one of the major endocrine glands in the body. It is located in the neck just below the larynx and has two lobes with one on each side of the trachea.It is concerned in the production of the hormones T3 (triiodothyronine) and T4 (thyroxine). These hormones increase the activity, metabolic body's. The thyroid also produces the hormone calcitonin (thyrocalcitonin) which regulates the calcium levels in the blood. Thyrocalcitonin or calcitonin lowers the concentration of calcium in the blood. Most of the calcium extracted from the blood is stored in the bones

Thyroid hormone releases of two components, thyroxine and iodine. This hormone increases the metabolism of most cells in the body. A deficiency of iodine in the diet leads to an enlarged thyroid gland, known as a simple goiter. Hypothyroidism during early development leads to cretinism. In adults, it produces myxedema, described by obesity and lethargy. Hyperthyroidism leads to a condition called exophthalmic goiter, accompanied by weight loss and hyperactive and irritable behavior


The thyroid gland is a two-lobed gland that exhibits an extraordinarily powerful active transport mechanism for the absorption of iodide ions from the blood. As blood flows through the gland, iodide becomes an active form of iodine. This iodine is combined with an amino acid called tyrosine. Two iodized tyrosine molecules combine to form thyroxine. After its formation, thyroxine binds to a protein-polysaccharide material called thyroglobulin. The normal thyroid gland can store a supply of thyroxine for several weeks in this attached form. An enzymatic division of thyroxine from thyroglobulin occurs when a specific hormone is released into the blood. This hormone, produced by the pituitary gland, is known as the thyroid stimulating hormone (TSH)

TSH stimulates some important steps that limit the rate of thyroxine secretion and therefore alter its release rate. A variety of body defects, whether dietary, hereditary or disease-induced, can reduce the amount of thyroxine released into the blood. The most popular of these defects is the one that results from iodine deficiency in the diet. The thyroid gland widens, in the continuous presence of pituitary TSH, to form a goiter. This is a futile attempt to synthesize thyroid hormones for too low iodine levels. Normally, thyroid hormones act through a negative feedback circuit in the pituitary gland to reduce thyroid stimulation. In the goiter, the feedback circuit cannot work, therefore the continuous stimulation of the thyroid and the inevitable swelling of the neck. Previously, the main source of iodine came from shellfish. As a result, goiter prevailed between inland areas far from the sea. Today, the prevalance of goiter has been drastically reduced by adding iodine to the table salt

Thyroxine releases to stimulate oxidative metabolism in cells; Increases oxygen consumption and heat production from most body tissues, an important exception is the brain. Thyroxine is necessary for normal growth. The most likely interpretation is that thyroxine improves the effects of growth hormone on protein synthesis. The absence of thyroxine significantly reduces the ability of growth hormone to stimulate the absorption of amino acids and the synthesis of RNA. Thyroxine evolves into a crucial ruin in the related elongated area of ​​organ development, particularly in the central nervous system

There is an insufficient amount of thyroxine if a condition called hypothyroidism occurs. I have been a symptom of derivothyroidism from the fact that it has seen a ridiculous rate of oxidative energy release reactions within the body's cells. Usually the patient shows swollen, slow skin and reduced vitality. Other symptoms of hypothyroidism include weight gain, decreased libido, disability to tolerate colds, muscle pain and spasms, insomnia and brittle nails. Hypothyroidism in children, a condition known with cretinism, can lead to mental retardation, dwarfism and permanent sexual immaturity

Turning over the thyroid gland produces too much thyroxine, a condition known as hyperthyroidism. This condition produces symptoms of abnormally high body temperature, severe sweating, high pressure, weight loss, irritability, pain and muscle weakness. It causes the widest characteristic of the eyeballs that emerge from the skull called exophthalmia. This is surprising because it is not a symptom generally related to rapid metabolism. Hyperthyroidism has been treated by partial removal or partial destruction of gland radiation. More recently, various drugs have been discovered that inhibit thyroid activity and their use of this support in previous surgical procedures. Fortunately, the condition of the rich in the thyroid is not a lifelong treatment and, due to the body's need for a sensitive balance of the thyroid hormone, if it is supplemented by the suppression of the thyroid function it may take months or even years to set

Function T3 and T4 inside the body

Thyroid gland




The production of T3 and T4 is regulated by the thyroid stimulating hormone (TSH), released by the pituitary gland. TSH production increases when T3 and T4 levels are too low. The thyroid hormones are released throughout the body to manage the  metabolism of the body . They stimulate all the cells of the body to work at a better metabolic rate. Without these hormones, the body's cells don't necessarily regulate the rate at which they perform chemical actions. Its use will increase in a given situation, when the temperature rises, when it is necessary to have a high metabolism to generate heat. When I was born with a thyroid hormone deficiency, I had no physical growth and development problems. Brain development can also be seriously affected

The importance of iodine thyroid hormone cannot be considered without an abundant source of iodine. The iodine concentration inside the body, even significant, can be 1/25 of the concentration inside the thyroid. When the thyroid gland has a basal iodine content, the body tries to produce T3 and T4 more easily, which they often use for inflammation of the thyroid gland, carrying a goiter

Extrathyroidal iodine :


Iodine represents 65% of the molecular weight of T4 and 59% of T3. 15 to 20 mg of iodine are concentrated in the thyroid tissue and hormones, but 70% of the body's iodine is distributed to other tissues, including the mammary glands, eyes, gastric mucosa, cervix and salivary glands. In the cells of these tissues, iodide enters directly through the sodium iodide simulator (NIS). Its role in breast tissue is related to fetal and neonatal development, but its role in other tissues is unknown. It has been shown to act as an antioxidant in these tissues

Doctors have recommended a daily amount of iodine ranging from 150 micrograms / day for adult humans to 290 micrograms / day for breastfeeding mothers. However, the thyroid gland does not need more than 70 micrograms / day to synthesize the required daily quantities of T4 and T3. These recommended daily intake levels of iodine seem higher for the optimal function of numerous body systems, including breastfeeding, gastric mucosa, salivary glands, oral mucosa, thymus, epidermis, choroid plexus , etc. In addition, iodine can be added to the double bonds of docosahexaenoic acid and arachidonic acid in cell membranes, making them less reactive to oxygen free radicals


Calcitonin:


Calcitonin is a polypeptide chain contains hormone of 32 amino acids. It is an additional hormone produced by the thyroid and contributes to the regulation of calcium levels in the blood. Calcitonin is produced by thyroid cells in response to increase calcium levels in the blood. This hormone will stimulate the movement of calcium towards the bone structure. It can also be used therapeutically for the treatment of hypercalcaemia or osteoporosis. Without this hormone, calcium will remain in the blood instead of moving to the bones to keep them strong and growing

Characteristics of Thyroid Gland


1. Morphological description:       

● Anatomy: 2 lobes joined by an isthmus, located in the front of the neck in front of the thyroid cartilage

● Histology: vesicles with: 

Follicular cells or thyrocytes -> thyroid hormones
C cells -> calcitonin
Connective vascular tissue

● Embryology

Thyroid cells arise from the floor of the pharyngeal intestine
C cells come from neural crests
The connective tissue comes from mesoblasts


2. Embriological development :         

• The thyroid body appears in the third week of development: proliferation of the epithelial floor of the pharyngeal intestine (blind hole)
• The thyroid gland sinks into the underlying mesoblast in front of the pharyngeal intestine -> bilobed diverticulum
• During migration, persistence of a canal: a thyroglossal canal that disappears secondarily
• Migration before hyoid bone and laryngeal cartilage
• 7th week: active thyroid gland
• End of the 3rd month: start of the activity (first follicle full of colloids)


Developmental anomalies

● Quasi physiological

Foramen cecum: depression at the level of the language base
Pyramidal lobe: distal end of the thyroid tract

● Thyroglossal tract cysts at all points of the draft migration path
Thyroid-> appears in the midline of the neck

● Ectopic thyroid: thyroid islands on the same path -> most of the time at the basic level of language


Histology 


The thyroid gland is the largest organ that functions exclusively as an endocrine gland. The basic structure of the thyroid is unique for the endocrine glands, consisting of follicles of varying sizes (20-250 mm) which contain colloids produced by follicular cells. Follicular cells are cubic and columnar and their secretory polarity is directed towards the lumen of the follicles. A large network of inter and intra follicular capillaries provides an abundant supply of blood to the follicular cells. Due the structure of follicular cells, which have long and rough endoplasmic reticular profiles and a large Golgi apparatus in their cytoplasm, it serves for the synthesis and packaging of substantial quantities of proteins which are transported into the follicular lumen. The interface between the luminal side of the follicular cells and the colloid is modified by numerous microvillary projections

● Vesicular or follicular endocrine gland

● Optical microscopy:

Thyroid surrounded by a conjunctival capsule
With conjunctival vascular sections -> lobules
In the lobules, vesicles with a wall formed by a single layer of cells full of colloids separated from each other by fine connective tissue, rich in reticulin fibers and highly vascularized epithelium of vesicles of varying sizes:
  • Pavorous (resting cells)
  • Cylindrical (active cells)
  • Cells are based on the basement membrane
● Electron microscopy:

Thyreocytes

● Cells with cell organelles that synthesize proteins:

  • REG at the basal pole
  • Golgi supra nuclear, secretion grains

 Numerous lysosomes at the apical pole

 Microvilli at the apical membrane level

 Union system in top mail

C cells

 At the basal pole of the tirocytes or in groups between the vesicles

 They are larger than the trainees and less stained

 Numerous dense secretion grains containing calcitonin (hormonal polypeptide)

 underdeveloped REG, abundant mitochondria and bulky golgi


Cytophysiology  

1.Function of thyreocytes:


● Secretion of hormones:

Tri-iodothyronine (T3) and tetraiodothyronine (thyroxine or T4) under the dependence of a pituitary hormone: TSH, under the dependence of the hypothalamic hormone: TRH. Synthesis of TRH stimulated by low levels of T3 and T4

a) Synthesis and conservation of hormones by vesicular cells:

• Synthesis of thyroglobulin synthesis of habitual protein synthesis in REG from tyrosine and then glycosylation in Golgi; excretion in the lumen of the gallbladder
• Capture of mineral iodine (iodides) from the blood by TSH stimulation of the iodide pump
•Transformation of mineral iodine into organic iodine thanks to a peroxidase developed by thyroid cells
• Iodification of thyroglobulin molecules in the colloid or in the apical pole by enzymatic action -> formation of monoiodine-tyrosine (MIT), diiodothyrosine (DIT), triiodothyronine (T3) and tetraiodothyronine (T4) (iodine thyrroglobulin)


b) Release of T3 and T4

• Endocytosis of colloid fragments containing iodrogroglobulin
• Fusion with lysosomes of tyrocytes
• Formation of phagolysosomes in which acid hydrolysis occurs
• Dissociation of T3 and T4 and of the thyroglobulin molecule at the cellular level and therefore release of T3 and T4 in the capillaries
• Iodothyrosines are separated from the iodine molecules by an enzyme and reused


c) roles T3 and T4

• Anabolic
• Increases the basal metabolic rate
• Role during fetal life ++ (body growth and nervous system development


● Regulations of hormones: 

T3 and T4 stimulated by the pituitary hormone: 

• TSH is administered by the blood; is installed in the receptors of the laterobasal membranes of the thyrocytes that respond by capturing a greater amount of iodine and causing an increase in synthesis and a greater release of thyroid hormones
• TSH -> Increases all thyrocyte functions:

  • Greater synthesis of thyroglobulin and its degradation so to increase the release of T3 and T4

● Increase in T3 and T4 in the blood -> decrease in TRH and TSH

T3 and T4 regulate the synthesis of the hypothalamic hormone: 

• TRH -> reduces the synthesis of TSH

2. Function of C cells:

● Secretion

• Calcitonin excreted at the basal pole of cells in the capillaries
Hypocalcemic because:
  • Prevents calcium reabsorption: prevents bone resorption by osteoclasts
  • Increases the mineralization of the osteoid edge
 Parathyroid hormone antagonist synthesized by the parathyroid that is hypercalcemic


● Regulations

• Independent of the pituitary gland
• Ca ++ level directly in the plasma membrane of C cells

Female thyroid gland

The female thyroid gland has 3 lobes and the male thyroid gland has 2 lobes. The reason why the female thyroid has three lobes is because it tries to store thyroxine through the storage of iodine and always craves badly. The closest substitute for sodium iodine is iron. The only place to get sodium iodine is in algae or aquatic plants. Iodine helps control growth, repairs damaged cells and supports healthy metabolism. Iodine is even more important when breastfeeding

Synthesis of thyroid hormone

Thyroid gland



The biosynthesis of thyroid hormones is also unique among the endocrine glands because the final assembly of the hormones takes place extracellularly within the follicular lumen. Essential raw materials, such as iodide, are effectively trapped by plasma follicle cells, rapidly transported against a gradient of light concentration and oxidized by a thyroid peroxidase in the microvillar and colloidal iodine membranes (I2). The assembly of thyroid hormones inside the follicular lumen is possible thanks to a unique protein (thyroglobulin) synthesized by follicular cells

Thyroglobulin is a high molecular weight glycoprotein (600,000-750,000) synthesized in successive subunits in the ribosomes of the endoplasmic reticulum in follicular cells. The constituent amino acids (tyrosine and others) and carbohydrates (i.e. mannose, fructose, galactose) come from the circulation. The newly synthesized thyroglobulin (17S) exiting the Golgi apparatus is packed in apical vesicles and extruded into the follicular lumen. The amino acid tyrosine, an essential component of thyroid hormones, is incorporated into the molecular structure of thyroglobulin. Iodine binds to tyrosyl residues in thyroglobulin on the apical surface of follicular cells to subsequently form monoiodothyrosine (MIT) and diiodothyrosine (DIT). The resulting MIT and DIT combine to form the two biologically active iodothyronines: thyroxine, T4 and triiodothyronine, T3, secreted by the thyroid gland

The active iodide transport mechanism is associated with a sodium iodide simulator (NaþI) (NIS). The transport of iodide ions across the thyroid cell membrane is related to the transport of Naþ. The ionic gradient generated by Naþ / Kþ-ATPase appears to be the driving force for the transport of active iodide. The transporter protein is present in the basolateral membrane of thyroid follicle cells (thyrocytes) and is a large protein that contains 643 amino acids with 12 transmembrane domains. Other tissues, such as the salivary gland, the gastric mucosa and the lactating mammary gland, also have the ability to actively transport iodide, albeit at a much lower level than the thyroid. The NIS gene is complex (16 exons, 14 introns) and its expression in the thyroid gland is regulated by TSH. The functionally active iodine transport system in the thyroid gland has important clinical applications in the evaluation, diagnosis and treatment of various thyroid disorders, including cancer. Radioiodine is used to remove residual tumor tissues, as well as recurrent and metastatic thyroid cancer. Chemical substances such as perchlorate and thiocyanate can selectively inhibit NIS and active transport of iodide, effectively blocking the gland's ability to synthesize thyroid hormones

Factors that affect Thyroid function


• Factors that contribute to the adequate production of thyroid hormones:
• Factors that increase the conversion from T4 to RT3: 
  • Stress
  • Trauma
  • Low calorie diet
  • Inflammation (cytokines, etc.)
  • Toxins
  • Infections
  • liver / kidney dysfunction
  • Certain medications
• Factors that inhibit adequate production of thyroid hormones: 
  • Stress
  • Infection, trauma, radiation, medications
  • Fluoride (iodine antagonist)
  • Toxins: pesticides, mercury, cadmium, lead
  • Autoimmune diseases: celiac
• Factors that increase the conversion from T4 to T3: 
  • Selenium
  • Zinc
• Factors that improve the sensitivity of cells to thyroid hormones: 
  • Vitamin A
  • Exercise
  • Zinc

How to recognize Thyroid issues


The thyroid gland has a butterfly-shaped, located in the neck. It is known as the main metabolic gland, when it does not work it can affect almost all aspects of your health

• Changes in hair and skin: Hair often becomes fragile, thick and dry, which it peels off and falls out easily

• Intestinal problems: Prolonged or severe constipation and diarrhea or irritable bowel syndrome

• Muscle and non-muscle pain: weakness of the arms and tendency to develop carpal tunnel in the arms / hands

• Cholesterol problems: High cholesterol, when not responding to diet, exercise or cholesterol-lowering drugs

• Menstrual irregularities and fertility problems: They can also be associated with heavier, more frequent and more painful periods or shorter, lighter and less frequent infertility

• Depression and anxiety: And even the sudden onset of panic disorder can be symptoms of thyroid disease

• Weight changes: Unexplained changes and weight problems can be signs of hypothyroidism and hyperthyroidism

• Discomfort or enlarged neck: A feeling of swelling in the neck, discomfort with turtlenecks or ties

• Family history: If you have a family history of thyroid problems, you have a greater risk of having a thyroid condition

Fatigue: Feeling exhausted when you make peace or can't work all day without a nap can be a sign of thyroid problems



Types of Thyroid Diseases


 Hypothyroidism: Condition in which the thyroid gland does not produce enough thyroid hormone

 Hashimoto's thyroiditis: The thyroid gland is attacked by the immune system in response to antibodies produced by exposure to an allergen

 hyperthyroidism: Overproduction of thyroid hormones

 Graves': The thyroid gland is attacked by the immune system, confusing the thyroid cells, causing inflammation and overproduction of T3 / T4

 Goiter: Abnormal enlargement of the gland 

• Thyroiditis: Thyroid inflammation

Thyroid Nodules: A thyroid lump

• Thyroid Cancer: A cancer of the thyroid 


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