Diferencia entre revisiones de «Glándula Tiroides - Anatomía & Fisiología»

Revisión del 17:57 28 dic 2011

Introduction

The thyroid gland lies in the neck, in front of the upper part of the trachea. Two types of hormones are produced, which are the iodine containing hormones; tri-iodothyronine(T3) and thyroxine (T4). Thyroid hormones regulate the basal metabolic rate and are important in the regulation of growth of tissues, particularly nervous tissue. Release stimulated by TSH from the pituitary. The second type of hormone produced from the thyroid gland is calcitonina, which regulates blood calcium levels along with parathyroid hormone and acts to reduce blood calcium by inhibiting its removal from bone.

Embryological Origin

The thyroid gland is a downgrowth from the pharyngeal endoderm of the developing lengua. The calcitonin producing cells are different and are derived from the fourth branchial pouch.

Anatomía

The thyroid gland consists of two lobes (dog, horse), one on each lateral side of the cranial trachea. In the pig the lobes are connected by an isthmus with a small, central pyramidal lobe as part of that structure. Cattle have a particularly wide isthmus.

Location

The thyroid gland is located adjacent to the cranial trachea. Close to the recurrent laryngeal nerve, carotid sheath and sternohyoid and sternothyroid muscles. The Parathyroid Glands are located dorsally to, or within the thyroid gland itself.

Supply

The thyroid gland is supplied by the cranial thyroid artery which is a branch of the common carotid artery. A subsidiary supply is provided by the caudal thyroid artery. The cranial and caudal thyroid arteries are united by substantial anastamoses along their caudal edge. Venous drainage is provided by the internal jugular vein and lymph drains into the cranial deep cervical nodes.

Ultrastructure and Histology

The gland consists of varying sized follicles, which are bounded by a single layer of cuboidal epithelial cells (follicular cells} and a basement membrane, surrounding a central lumen filled with a homogenous protein rich colloid (thyrogloblin). The apical surface of the cell membranes is covered with numerous micovilli to increase surface area. The follicular cells are connected by tight junctions, and have a dense capillary network. The colloid is a store of thyroid hormones prior to secretion. The thyroid gland is the only endocrine gland to store its hormone in large quantities. In the active gland colloid is diminished and epithelial cells are tall and columnar.

Within the connective tissue close to the follicles are C-cells alternatively known as parafollicular cells. They are found in clusters in the interfollicular space and are also known as clear cells as their cytoplasm doesn't stain with H and E. They secrete calcitonin, a hormone which acts to lower plasma Ca2+ levels.

Thyroid Gland Low Power 1
^{©RVC 2008}
Thyroid Gland Low Power 2
^{©RVC 2008}
Thyroid Gland Medium Power
^{©RVC 2008}
Thyroid Gland High Power
^{©RVC 2008}
Normal Thyroid
^{Courtesy of A. Jefferies}
Thyroid Gland High Power with C-Cells labelled
^{©RVC 2008}

Thyroid Hormone Physiology

Follicular cells synthesize thyroglobulin in their golgi apparatus. This is a glycoprotein consisting of 70 linked tyrosine molecules, 10% of which are iodinated, and is stored in the colloid.

The thyroglobulin is then split to form the two amino acid derivative hormonas produced in the thyroid gland which are triiodothyronine (T3) and thyroxine (T4). Thyroxine contains 4 iodine atoms, triiodothyronine contains 3. Creation of these two hormonas is the only role of iodine in the body.

The majority (90%) of hormone produced by the follicular cells is T4. T4 can only be made in the thyroid gland. It can then be converted by other tissues into T3.

Iodine Uptake

Iodine circulates within the blood as iodide (I^-). It is actively transported into the follicular cells by an Na+/I^- symport in the basal membrane. This pump concentrates iodine in the colloid at a level up to 250x greater than the plasma level. This process is known as iodide trapping. The pump is activated by thyroid stimulating hormone (TSH) a hormone from the pituitary gland.

Any excess iodide is excreted via the kidneys.

Secretion of Thyroid Hormones

Colloid uptake into the follicular cells takes place by endocytosis. The intracellular vesicles containing the colloid then fuse with lysosomes, where enzymes split the thyroglobulin into T3 and T4. The hormones diffuse across the basal plasma membrane into the interstitium (they are lipid soluble hormones).

Transport

Thyroid hormones are lipid soluble, thus need a transporting protein in order to travel in the blood. Half-life in the blood is 1 day for T3, 6 days for T4. 99% of thyroid hormones in circulation are bound.

The primary transport protein for thyroid hormones is thyroid binding globulin (TBG). Synthesized in the liver, this protein binds 70-80% of the circulating thyroid hormones.

The remainder are carried by thyroxine-binding prealbumin or albumin.

Degradation

Only free T3 and free T4 can enter cells to exert their actions. T4 is deiodinated to T3 in many cells of the body, particularly the liver and kidneys.

The thyroid secretes 90% T4, with 50% of this being deiodinated to T3. The remainder is converted to reverse T3 (rT3). This is an inactive form of T3, and so creation of it is a regulatory mechanism. More rT3 is created when the body needs to reduce the action of T3 and T4.

The hormones are further deiodinated to diiodothyronine and monoiodothyronine in the liver and kidneys. Iodine is recycled or excreted in the urine.

Regulation

Schematic Diagram of the Hypothalamic - Pituitary - Thyroid Axis

The hypothalamus releases thyrotropin releasing hormone (TRH) which stimulates the adenohypophysis (anterior pituitary gland) to release thyroid stimulating hormone (TSH). This water soluble hormone travels in the blood to activate the thyroid gland by 5 actions:

Increased endocytosis and proteolysis of thyroglobulin from colloid
Increased activity of the Na⁺/I^- symport
Increased iodination of tyrosine
Increased size and secretory activity of thyroid follicular cells
Increased number of follicular cells

Thyroid Hormone Actions

T3 and T4 have effects on all body systems and at all stages of life. These include: :Development where thyroid hormones are vital during the fetal period and the first few months after birth. T3 and T4 are the hormones for metamorphosis in frogs.

Thyroid hormones also promote growth as they enhance amino acid uptake by tissues and enzymatic systems involved in protein synthesis thus promoting bone growth.

They also help with metabolic actions such as carbohydrate metabolism, as thyroid hormones stimulate glucose uptake, glycogenolysis, gluconeogenesis.

In fat metabolism they mobilise lipids from adipose stores and accelerate oxidation of lipids to produce energy (occurs within mitochondria), as well as increasing the size and number of mitochondria.

Thyroid hormones also increase basal metabolic rate (BMR) in all tissues except brain, spleen and gonads. The results in increased heat production, increased oxygen consumption. This increased metabolic rate also results in increased utilisation of energy substrates causing weight loss.

Some of thyroid hormones cardiovascular actions are to increase cardiac output, heart rate and contractility. They affect the respiratory system indirectly through increased BMR causing increased demand for oxygen and increased excretion of carbon dioxide.

In the nervous system thyroid hormones are required for myelination of neurons during the development. They also enhance the sympathetic nervous system (by increasing epinephrine receptors).

Reproductive system is affected by reduced levels of thyroid hormone causing irregular cycling and decreased libido.

Finally, in the alimentary system, thyroid hormone increases appetite and feed intake, increases secretion of pancreatic enzymes and increases motility.

Influence of External Factors

Euthyroid sick syndrome: concurrent disease such as starvation, sepsis, trauma or stress can cause a depression in basal thyroid levels as a normal response, to minimise the catabolic effects of thyroid hormones.

This occurs in many species and may lead to false diagnoses of hypothyroidism or a missed diagnosis of hyperthyroidism.

In horses, many factors influence the level of T3 and T4:

In foals: thyroid hormone concentrations are up to 14 times higher than in horses over the age of 2.

During normal feeding, T3 and T4 levels increase within two hours of feeding. Undernutrition results in an increase in T4 but T3 levels are unchanged. Excess protein and energy result in a decreased T4 and an increased T3.

In adult horses: undernutrition results in a decrease in both T3 and T4. Phenylbutazone is also known to decrease T4 levels.

Thyroid hormone levels increase with age, and are higher during pregnancy and times of low temperature.

Problems associated with the Thyroid Gland

Problems with the thyroid gland include enlargement, or Goitre and also the effects of increased level of hormones in Hyperthyroidism or decreased levels of hormones in Hypothyroidism.

Glándula Tiroides - Anatomía & Fisiología Entorno de Enseñanza Virtual
Flashcards Comprobar tus conocimientos utilizando preguntas de tipo Flashcard	Thyroid Gland Equine Internal Medicine Q&A 21
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@@ Línea 1: / Línea 1: @@
-==Introducción==
+==Introduction==
-El tiroides se encuentra en el cuello, por delante de la parte más craneal de la traquea. Produce dos tipos de hormonas, las hormonas que contienen Yodo: '''Tri-yodotironina''' (T3) y '''Tiroxina''' (T4). Las hormonas tiroideas regulan el ritmo metabólico y son importantes en la regulación del crecimiento de los tejidos, especialmente del nervioso. Su liberación se ve estimulada por la TSH de la pituitaria. El segundo tipo de hormona producida en el tiroides es la '''[[calcitonina]]''', que regula los niveles sanguíneos de calcio junto con la hormona paratiroidea, reduciendo el calcio inhibiendo su extracción del tejido óseo
+The thyroid gland lies in the neck, in front of the upper part of the trachea.  Two types of hormones are produced, which are the iodine containing hormones; '''tri-iodothyronine'''(T3) and '''thyroxine''' (T4). Thyroid hormones regulate the basal metabolic rate and are important in the regulation of growth of tissues, particularly nervous tissue. Release stimulated by TSH from the pituitary. The second type of hormone produced from the thyroid gland is '''[[calcitonina]]''', which regulates blood calcium levels along with parathyroid hormone and acts to reduce blood calcium by inhibiting its removal from bone.
-== Origen Embrionario ==
+== Embryological Origin ==
-La glándula tiroides es un crecimiento del endodermo faríngeo de la [[Lengua - Anatomía & Fisiología|lengua]] en desarrollo. Las células productoras de calcitonina son diferentes y derivan del cuarto cuarto saco branquial.
+The thyroid gland is a downgrowth from the pharyngeal endoderm of the developing [[Lengua - Anatomía & Fisiología|lengua]]. The calcitonin producing cells are different and are derived from the fourth branchial pouch.
 ==Anatomía==
-Consiste en dos lóbulos (perro, caballo) uno a cada lado de la parte craneal de la [[Tráquea - Anatomía & Fisiología|tráquea]]. En el cerdo, los lóbulos están conectados por un ''istmo'' con un pequeño y central ''lóbulo piramidal'', que forma parte de esta estructura. El vacuno tiene un istmo particularmente ancho.
+The thyroid gland consists of two lobes (dog, horse), one on each lateral side of the cranial [[Trachea - Anatomía & Fisiología|trachea]]. In the pig the lobes are connected by an ''isthmus'' with a small, central ''pyramidal lobe'' as part of that structure. Cattle have a particularly wide isthmus.
-===Localización===
+===Location===
-El tiroides se localiza adyacente a la [[Tráquea - Anatomía & Fisiología|tráquea]]. Cerca del ''nervio laríngeo recurrente'', la arteria carótida y los músculos esternohioideo y esternotirioideo. La [[Glándula Paratiroides - Anatomía & Fisiología|'''glándula paratiroides''']] se sitúa dorsalmente a la glándula tiroides o entre ella.
+The thyroid gland is located adjacent to the cranial [[Trachea - Anatomía & Fisiología|trachea]]. Close to the ''recurrent laryngeal nerve'', carotid sheath and sternohyoid and sternothyroid muscles. The [[Parathyroid Glands - Anatomía & Fisiología|'''Parathyroid Glands''']] are located dorsally to, or within the thyroid gland itself.
-===Riego Sanguineo===
+===Supply===
-La glándula tiroides está irrigada por la '''arteria tiroidea craneal''', que es una rama de la arteria carótida común. Secundariamente está irrigada también por la '''arteria tiroidea caudal'''. Las arterias tiroideas craneal y caudal están unidas por varias anastomosis a lo largo de su borde caudal. El drenaje venoso corre a cergo de la vena yugular interna, y la [[Linfa - Anatomía & Fisiología|linfa]] drena a los nódulos craneales cervicales profundos.
+The thyroid  gland is supplied by the '''cranial thyroid artery''' which is a branch of the common carotid artery. A subsidiary supply is provided by the '''caudal thyroid artery'''. The cranial and caudal thyroid arteries are united by substantial anastamoses along their caudal edge. Venous drainage is provided by the internal jugular vein and [[Linfa - Anatomía & Fisiología|lymph]] drains into the cranial deep cervical nodes.
-===Ultraestructura e Histología ===
+===Ultrastructure and Histology===
- La glándula consiste en folículos de tamaño variable, limitados por una capa simple de células epiteliales cúbicas ('''células foliculares''') y una membrana basal, rodeando un lumen central lleno de un coloide homogéneo rico en proteínas (tiroglobina) La superficie apical de las células de la membrana está cubierta por numerosas microvellosidades para incrementar la superficie. Las células foliculares están unidas íntimamente y tienen una densa red capilar. El coloide es un almacén de hormonas previas a su secreción. La glándula tiroides es la única glándula endocrina que almacena su producto en grandes cantidades. En la glándula activa, el coloide está disminuido y las células epiteliales son más altas y de forma columnar.
+The gland consists of varying sized follicles, which are bounded by a single layer of cuboidal epithelial cells ('''follicular cells'''} and a basement membrane, surrounding a central lumen filled with a homogenous protein rich colloid (thyrogloblin). The apical surface of the cell membranes is covered with numerous micovilli to increase surface area. The follicular cells are connected by tight junctions, and have a dense capillary network. The colloid is a store of thyroid hormones prior to secretion.  The thyroid gland is the only endocrine gland to store its hormone in large quantities. In the active gland colloid is diminished and epithelial cells are tall and columnar.
-Entre el tejido conectivo, cerca de los folículos, se situúan las '''Células C''', también conocidas como '''células parafoliculares'''. Se disponen en racimos en el espacio interfolicular y se conocen como células '''claras''' porque su citoplasma no se tiñe con H-E. Su secreción es la ''[[calcitonina]]'', una hormona que disminuye los nivels plasmáticos de Ca 2+
+Within the connective tissue close to the follicles are '''C-cells''' alternatively known as '''parafollicular cells'''. They are found in clusters in the interfollicular space and are also known as '''clear''' cells as their cytoplasm doesn't stain with H and E. They secrete ''[[calcitonin]]'', a hormone which acts to lower plasma Ca2+ levels.
 <center><gallery>
-Image:Thyroid Gland Low Power.jpg|<p>'''Tiroides producción baja 1'''</P><sup>©RVC 2008</sup>
+Image:Thyroid Gland Low Power.jpg|<p>''' Thyroid Gland Low Power 1'''</P><sup>©RVC 2008</sup>
-Image:Thyroid Gland Low Power 2.jpg|<p>'''Tiroides producción baja 2'''</P><sup>©RVC 2008</sup>
+Image:Thyroid Gland Low Power 2.jpg|<p>'''Thyroid Gland Low Power 2'''</P><sup>©RVC 2008</sup>
-Image:Thyroid Gland Medium Power.jpg|<p>'''Tiroides producción media'''</P><sup>©RVC 2008</sup>
+Image:Thyroid Gland Medium Power.jpg|<p>'''Thyroid Gland Medium Power'''</P><sup>©RVC 2008</sup>
-Image:Thyroid Gland High Power.jpg|<p>'''Tiroides alta producción'''</P> <sup>©RVC 2008</sup>
+Image:Thyroid Gland High Power.jpg|<p>'''Thyroid Gland High Power'''</P> <sup>©RVC 2008</sup>
-Image:Normal thyroid.jpg|<p>'''Tiroides normal'''</P> <sup>Courtesy of A. Jefferies</sup>
+Image:Normal thyroid.jpg|<p>'''Normal Thyroid'''</P> <sup>Courtesy of A. Jefferies</sup>
-Image:Thyroid Gland High Power showing C Cells.jpg|<p>'''Tiroides en alta producción con células C marcadas'''</P> <sup>©RVC 2008</sup>
+Image:Thyroid Gland High Power showing C Cells.jpg|<p>'''Thyroid Gland High Power with C-Cells labelled'''</P> <sup>©RVC 2008</sup>
 </gallery></center>
-==Fisiología de las Hormonas Tiroideas==
+==Thyroid Hormone Physiology==
- Las células foliculares sintetizan '''tiroglobulina''' en su aparato de Golgi, que es una glicoproteína consistente en 70 moléculas de tirosina unidas, de las cuales un 10% están ''yodadas'' y se almacena en el coloide.
+Follicular cells synthesize '''thyroglobulin''' in their golgi apparatus. This is a glycoprotein consisting of 70 linked tyrosine molecules, 10% of which are ''iodinated'', and is stored in the colloid.
-La tiroglobulina se separa para formar las dos [[Hormonas - Anatomía & Fisiología|hormonas]] derivadas de aminoácidos que se producen en el tiroides, que son la '''triyodotironina (T3)''' y la '''Tiroxina (T4)''' La tiroxina contiene 4 átomos de yodo, y la triyodotironina contiene 3. La síntesis de estas [[Hormonas - Anatomía & Fisiología|hormonas]] es la única función del yodo en el cuerpo
+The thyroglobulin is then split  to form the two amino acid derivative [[Hormonas - Anatomía & Fisiología|hormonas]] produced in the thyroid gland which are '''triiodothyronine (T3)''' and '''thyroxine (T4)'''. Thyroxine contains 4 iodine atoms, triiodothyronine contains 3. Creation of these two [[Hormonas - Anatomía & Fisiología|hormonas]] is the only role of iodine in the body.
-La mayoría (90%) de hormona producida por las células foliculares es T4. La T4 sólo la puede producir el tiroides, aunque puede ser convertida en T3 en otros tejidos
+The majority (90%) of hormone produced by the follicular cells is T4. T4 can only be made in the thyroid gland. It can then be converted by other tissues into T3.
-===Captación del Yodo===
+===Iodine Uptake===
-El exceso de Yodo es excretado por los [[Sistema Urinario - Resumen - Anatomía & Fisiología#Tracto Urinario Superior|riñones]].
+Iodine circulates within the blood as iodide (I<sup>-</sup>). It is actively transported into the follicular cells by an Na+/I<sup>-</sup> symport in the basal membrane. This pump concentrates iodine in the colloid at a level up to 250x greater than the plasma level. This process is known as ''iodide trapping.'' The pump is activated by '''thyroid stimulating hormone (TSH)''' a hormone from the [[Pituitary Gland - Anatomía & Fisiología|pituitary gland]].
-El yodo circula por la sangre como yoduro (I<sup>-</sup>). Es transportado activamente a las células foliculares por una bomba Na+/I<sup>-</sup> en la membrana basal. Esta bomba concentra el yodo en el coloide a un nivel 250 veces por encima del nivel plasmático. Este proceso, conocido como ''secuestro del yoduro''. La bomba es activda por la '''hormona tiroidea estimulante (TSH)''', que procede de la [[Glándula Pituitaria - Anatomía & Fisiología|glándula pituitaria]].
-El exceso de Yodo es excretado por los riñones.
+Any excess iodide is excreted via the [[Sistema Urinario - Resumen - Anatomía & Fisiología#Upper Urinary Tract|kidneys]].
-===Secreción de las Hormonas Tiroideas ===
+===Secretion of Thyroid Hormones===
-El coloide es captado por las células foliculares mediante endocitosis. Las vesículas intracelulares que contienen en coloide se fusionan con los lisosomas, donde las enzimas separan la tiroglobulina en T3 y T4. Las hormonas difunden a lo largo de la membrana basal al intersticio (son hormonas liposolubles).
+Colloid uptake into the follicular cells takes place by endocytosis. The intracellular vesicles containing the colloid then fuse with lysosomes, where enzymes split the thyroglobulin into T3 and T4. The hormones diffuse across the basal plasma membrane into the interstitium (they are lipid soluble hormones).
-===Transporte===
+===Transport===
-Las hormonas tiroideas son liposolubles, así que necesitan una proteína de transporte para poder ser transportadas por la sangre. La vida media en sangre es de 1 día para la T3 y 6 días para la 4. El 99% de las hormonas tiroideas en sangre están ligadas a proteínas.
+Thyroid hormones are lipid soluble, thus need a transporting protein in order to travel in the blood. Half-life in the blood is 1 day for T3, 6 days for T4. 99% of thyroid hormones in circulation are bound.
-La proteína de transporte más importante para las hormonas tiroideas es la '''globulina fijadora de tiroxina''' (TBG) sintetizada en el [[Hígado - Anatomía & Fisiología|hígado]], esta proteína se une al 70-80% de las hormonas tiroideas en sangre.
+The primary transport protein for thyroid hormones is '''thyroid binding globulin''' (TBG). Synthesized in the [[Liver - Anatomía & Fisiología|liver]], this protein binds 70-80% of the circulating thyroid hormones.
-El resto son transpotadas por la '''prealbúmina fijadora de tiroxina''' o '''albúmina'''.
+The remainder are carried by '''thyroxine-binding prealbumin''' or '''albumin'''.
-===Degradación ===
+===Degradation===
-Sólo la T3 y la T4 libres pueden entrar en las células para ejercer su función. La T4 pierde un átomo de yodo para pasar a T3 en muchas células del cuerpo, sobre todo en hígado y riñones.
+Only free T3 and free T4 can enter cells to exert their actions. T4 is deiodinated to T3 in many cells of the body, particularly the liver and kidneys.
-El tiroides secreta un 90% de T4, aunque un 50% de esta hormona pierde un yodo para pasar a T3. La restante se covierte en '''T3 inversa (rT3)''', una forma inactiva de la T3 que se crea como mecanismo regulador. Cuando el cuerpo necesita reducir la acción de T3 y T4, se sintetiza más rT3
-Las hormonas pierden más yodo para pasar a diyodotironina y monoyodotironina en el hígado y riñones. El yodo es recilado o excretado en la orina.
+The thyroid secretes 90% T4, with 50% of this being deiodinated to T3. The remainder is converted to '''reverse T3 (rT3)'''. This is an inactive form of T3, and so creation of it is a regulatory mechanism. More rT3 is created when the body needs to reduce the action of T3 and T4.
+The hormones are further deiodinated to diiodothyronine and monoiodothyronine in the liver and kidneys. Iodine is recycled or excreted in the urine.
-===Regulación===
+===Regulation===
-[[Image:HypothalamicPituitaryThyroidAxis.jpg|thumb|240px|center|'''Esquema del funcionamiento del eje hipotálamo-pituitaria-tiroides]]
+[[Image:HypothalamicPituitaryThyroidAxis.jpg|thumb|240px|center|'''Schematic Diagram of the Hypothalamic - Pituitary - Thyroid Axis]]
-El [[Hipotálamo - Anatomía & Fisiología|hipotálamo]] sintetiza la '''hormona liberadora de tirotropina''' (TRH), que estimula la adenohipófisis ([[Glánula Pituitaria - Anatomía & Fisiología|glánula pituitaria]] anterior) para sintetizar '''hormona estimulante tiroidea''' (TSH) Esta hormona hidrosoluble viaja en la sangre para activar la tiroides mediante 5 mecanismos:
+The [[Hypothalamus - Anatomía & Fisiología|hypothalamus]] releases '''thyrotropin releasing hormone''' (TRH) which stimulates the adenohypophysis (anterior [[Pituitary Gland - Anatomía & Fisiología|pituitary gland]]) to release '''thyroid stimulating hormone''' (TSH). This water soluble hormone travels in the blood to activate the thyroid gland by 5 actions:
-#Incrementa la endocitosis y proteólisis de la tiroglobulina del coloide
+#Increased endocytosis and proteolysis of thyroglobulin from colloid
-#Incrementa la actividadde la bomba NA+/I-
+#Increased activity of the Na<sup>+</sup>/I<sup>-</sup> symport
-#Incrementa la yodación de la tirosina
+#Increased iodination of tyrosine
-#Incrementa el tamaño y la actividad secretora de las células foliculares del tiroides
+#Increased size and secretory activity of thyroid follicular cells
-#Incrementa el número de células foliculares
+#Increased number of follicular cells
-===Acción de las Hormonas Tiroideas===
-La T3 y T4 tienen efectos en todos los sistemas coroporales y todas las etapas vitales. Esto incluye: '''Desarrollo''', donde las hormonas tiroideas son vitales en el período fetal y los primeros meses después del nacimiento. T3 y T4 son las hormonas de la metamorfosis en la rana.
-:Las hormonas tiroideas promueven el '''crecimiento''' ya que mejoran la captación de aminoácidos por los tejidos y sistemas enzimáticos relacionados con la  síntesis proteíca aumentando la síntesis de hueso.
-:También ayudan en procesos metabólicos como el '''metabolismo de hidratos de carbono''', estimulando la captación de glucosa, gliconeólisis y gluconeogénesis
-:En el '''metabolismo de las grasas''', movilizan los lípidos de los depósitos grasos y aceleran la oxidación de los lípidos para producir energía (en el interior de las mitocondrias) e incrementan el tamaño y número de las mitocondrias.
-:Las hormonas tiroideas también '''aumentan el metabolismo basal''' (BMR) en todos los tejidos excepto el cerebro, bazo y gónadas. El resultado es una mayor producción de calor y consumo de oxígeno. Este ritmo metabólico acelerado resulta en una mayor utilización de energía, causando pérdida de peso.
-:Algunas de las [[Sistema Cardiorespiratorio - Resumen - Anatomía & Fisiología#Sistema Cardiovascular|'''acciones cardiovasculares''']] de las hormonas tiroideas son el incremento de ritmo cardíaco, volumen de eyección y contractilidad. Afectan también al [[Sistema Cardiorespiratorio - Resumen - Anatomía & Fisiología#Tracto Respiratorio Superior|'''sistema respiratorio''']] indirectamente al aumentar el metabolismo basal causando un incremento de la demanda de oxígeno y de la excreción de dióxido de carbono.
-:En el [[Nervous and Special Senses - Anatomía & Fisiología#Sistema Nervioso|'''sistema nervioso''']], las hormonas tiroideas son necesarias para la mielinización de las [[Estructura SNP - Anatomía & Fisiología#Neuronas|neuronas]] durante el desarrollo. También mejoran el sistema nervioso simpático (Incrementando los receptores de epinefrina)
-:El [[Sistema Reproductivo - Resumen - Anatomía & Fisiología|'''sistema reproductor''']] se ve afectado por bajos niveles de hormonas tiroideas alterando el celo y disminuyendo la líbido.
-:Finalmente, en el [[Sistema Digestivo - Resumen - Anatomía & Fisiología|'''sistema digestivo''']], la hormona tiroidea aumenta el apetito, la secreción de enzimas [[Páncreas - Anatomía & Fisiología|pancreáticas]] y estimula la motilidad intestinal.
+===Thyroid Hormone Actions===
+T3 and T4 have effects on all body systems and at all stages of life. These include: :'''Development''' where thyroid hormones are vital during the fetal period and the first few months after birth. T3 and T4 are the hormones for metamorphosis in frogs.
+:Thyroid hormones also promote '''growth''' as they enhance amino acid uptake by tissues and enzymatic systems involved in protein synthesis thus promoting bone growth.
+:They also help with metabolic actions such as '''carbohydrate metabolism''', as thyroid hormones stimulate glucose uptake, glycogenolysis, gluconeogenesis.
+:In '''fat metabolism''' they mobilise lipids from adipose stores and accelerate oxidation of lipids to produce energy (occurs within mitochondria), as well as increasing the size and number of mitochondria.
+:Thyroid hormones also '''increase basal metabolic rate''' (BMR) in all tissues except brain, spleen and gonads. The results in increased heat production, increased oxygen consumption. This increased metabolic rate also results in increased utilisation of energy substrates causing weight loss.
+:Some of thyroid hormones [[Cardiorespiratory System Overview - Anatomía & Fisiología#Cardiovascular System|'''cardiovascular actions''']] are to increase cardiac output, heart rate and contractility. They affect the [[Cardiorespiratory System Overview - Anatomía & Fisiología#Upper Respiratory Tract|'''respiratory system''']] indirectly through increased BMR causing increased demand for oxygen and increased excretion of carbon dioxide.
+:In the [[Nervous and Special Senses - Anatomía & Fisiología#Nervous System|'''nervous system''']] thyroid hormones are required for myelination of [[PNS Structure - Anatomía & Fisiología#Neurons|neurons]] during the development. They also enhance the sympathetic nervous system (by increasing epinephrine receptors).
+:[[Sistema Reproductivo - Resumen - Anatomía & Fisiología|'''Reproductive system''']] is affected by  reduced levels of thyroid hormone causing irregular cycling and decreased libido.
+:Finally, in the [[Sistema Digestivo - Resumen - Anatomía & Fisiología|'''alimentary system''']], thyroid hormone increases appetite and feed intake, increases secretion of [[Pancreas - Anatomía & Fisiología|pancreatic]] enzymes and increases motility.
 ===Influence of External Factors===
@@ Línea 97: / Línea 93: @@
 Thyroid hormone levels increase with age, and are higher during pregnancy and times of low temperature.
-==Problemas Asociados con el Tiroides==
+==Problems associated with the Thyroid Gland==
-Los problemas del tiroides incluyen sobrecrecimiento de la glándula o Bocio, y los efectos de un nivel incrementado de hormonas en el [[Hipertiroidismo|Hipertiroidismo]], y disminución de los niveles de hormonas en el [[Hipotiroidismo|Hipotiroidismo]].
+Problems with the thyroid gland include enlargement, or [[Goitre|Goitre]] and also the effects of increased level of hormones in [[Hyperthyroidism|Hyperthyroidism]] or decreased levels of hormones in [[Hypothyroidism|Hypothyroidism]].
+{{Template:Learning
+|flashcards = [[Thyroid_Gland_Flash_Cards_- Anatomy & Physiology|Thyroid Gland]]<br>[[Equine Internal Medicine Q&A 21]]
+|powerpoints = [[Endocrine Histology resource|Histology of the Endocrine system]]
+}}
 {{review}}
-[[Categoría:Sistema Endocrino - Anatomía & Fisiología]]
+[[Category:Sistema Endocrino - Anatomía & Fisiología]]