The thyroid, or thyroid gland, is an endocrine gland in the neck consisting of two connected lobes. The thyroid gland is subdivided by capsular septa into lobules containing follicles. An endodermal thickening in the floor of the primordial pharynx between the 1 st and 2 nd pharyngeal pouches. The goal of this article is to discuss the embryology, anatomy, brief histology, and neurovascular supply of the thyroid gland. The reason for this association is unclear, but thyroid gland anatomy and embryology may provide a possible clue 21.
Start studying path parathyroid gland embryology, histology, and pathology. Thyroid gland sec thyroxine has effects on all organs of body and its secretion is regulated by pituitary. This soft tissue mass descends over the ensuing weeks anterior to airway structures. Epithelial cells lining each follicle may be cuboidal or. A branching morphogenesis program governs embryonic growth of the thyroid gland here, we show that branchinglike morphogenesis is a driving force to attain final size of the embryonic thyroid gland in mice. Thyroid gland normal in a male b6c3f1 mouse from a chronic study. Thyroid gland historical aspects, embryology, anatomy. The fully developed thyroid gland is composed of 2 lateral lobes and a central isthmus with or without a pyramidal lobe 4050%. General considerations1 histologically, the endocrine cells are epithelial cells performing special functions. The primitive pharynx is responsible for the origin of medial thyroid anlage, whereas the lateral thyroid anlage originates from neural crest, the source of parafollicular cells or c cells that secrete calcitonin. This organ is located between the c 5t 1 vertebrae of columna vertebralis, in front of the trachea and below the larynx. It develops as a proliferation of endodermal epithelial cells in the floor of the pharynx between the tuberculum impar and the copula. By 7 weeks, the thyroid gland has assumed its definitive shape and is usually located in its final site in the neck. There are about three million follicles in the adult human thyroid gland.
Around the fourth week of development, an endodermal thickening appears in the midline floor of the primitive pharynx between the first and second pharyngeal pouches, dorsal to the aortic sac. Present article throws light on some historical aspects, embryology, anatomy and physiology of thyroid gland based on relevant articles and textbooks key words. Of the neck muscles, the thyroid is covered anteriorly by the strap or infrahyoid muscles and by the sternocleidomastoid muscles. This is first seen as the ultimobranchial body, which joins the primordial thyroid gland during its descent to its final location in the anterior neck. It produces thyroid hormones, the principal ones being triiodothyronine t3 and thyroxine which can sometimes be referred to as tetraiodothyronine t4. Elucidating how the thyroid gland the only source of thyroid hormones in the body develops is thus key for understanding and treating thyroid dysgenesis, and for generating thyroid cells in vitro that might be used for cellbased therapies.
It is not allowed to publish this proof online or in. The infrahyoid muscles strap muscles are the sternohyoid, sternothyroid, thyrohyoid and omohyoid. Feb 14, 2012 a video describes embryology of thyroid gland. They also contribute to protein synthesis and the normal growth and development of body tissues, including maturation of the nervous. Medial thyroid anlage originates from endoderm in the. Imaging of ectopic thyroid tissue and thyroglossal duct cysts. Their surgical techniques, knowledge of thyroid anatomy, embryology, histology, physiology, and antisepsis practices transitioned a lifethreatening operation to one with acceptable morbidity. During embryonic development, the thyroid gland first forms at the base of the tongue and then descends into the neck. Thyroid tissue that remains entrapped in the tissue of the tongue may result in this developmental abnormality. The thyroid gland is a butterflyshaped organ composed of two lobes, left and right, connected by a narrow isthmus. Discussion of disorders of the thyroid gland can be found in a subsequent article. By this time, the thyroglossal duct has normally degenerated and disappeared. Embryology and histology of thyroid and parathyroid glands. Different morphogenetic processes across species leads to various thyroid.
The structural and functional unit of the thyroid gland. Rarely, in less than 1% of cases, the superior glands may be located above the upper thyroid pole. In the fetus, at 34 weeks of gestation, the thyroid gland appears as an epithelial proliferation in the floor of the pharynx at the base of the tongue between the tuberculum impar and the copula linguae at a point later indicated by the foramen cecum. The thyroid gland is composed of two elongated lobes on either side of the trachea that are joined by a thin isthmus of thyroid tissue located at or below the level of the thyroid cartilage 1 figure 181. Unicellular dnes apud multicellular thyroid, adrenal each endocrine gland has two different embryological origins. The superior parathyroid glands invaginate and attach themselves to the caudally migrating thyroid gland figs. Anatomy and embryology of the thyroid and parathyroid glands. To secrete the hormone, the colloid is reabsorbed from the cavity of. The thyroid gland initially arises caudal to the tuberculum figure 1. The thyroid lies in the middle layer of the deep cervical fascia. The gland may enlarge in some normal conditions like menstruation and pregnancy. The thyroid gland is a relatively small butterflyshaped organ.
When the parathyroid gland loses contact with the wall of the pharynx, it attaches itself to the dorsal surface of the caudally migrating. Elucidating how the thyroid gland the only source of thyroid hormones in the body develops is thus key for. Thyroid embryology the thyroid gland was the first gland to appear in the evolution of the species and is the first to appear in a developing human 1. What is the embryology and anatomy of the thyroid gland. In humans, untreated congenital hypothyroidism due to thyroid agenesis inevitably leads to cretinism, which comprises irreversible brain dysfunction and dwarfism. Embryonic origin and development of thyroid progenitor cells 10 kpvtqfwevkqp this thesis is focused mainly on the embryonic development of the mouse thyroid gland. The gland has two lobes, each pear shaped hugging anterolateral aspects of cervical trachea from oblique line of thyroid cartilage to 5 th or 6 th tracheal ring. Apr 30, 2020 the goal of this article is to discuss the embryology, anatomy, brief histology, and neurovascular supply of the thyroid gland.
Anatomy, physiology and pathology of the thyroid gland. Follicular cells synthesize thyroglobulin in their golgi apparatus. These cells secrete calcitonin, a hormone involved in regulation of the calcium level in the blood. Embryology and anatomy of the parathyroid glands ento key. In this location, an aberrant or ectopic thyroid gland is known as a lingual thyroid and represents a failure of the thyroid to descend. Consists of a group of cells resting on the same basal lamina surrounding a lumen filled with colloid. It is surrounded by a dense irregular collagenous connective tissue capsule, in which posteriorly the parathyroid glands are embedded. The thyroid is one of the most vascular organs in the body. It starts to form around 24 days after fertilization, from a thickening in the primordial pharynx figure 1a. Head and neck embryology and anatomy 243 finally, clefts may occur in a combination of both anterior and posterior fusion defects. The thyroid gland produces and secretes three hormones that are vital in the regulation of the level of biochemical activity of most of the.
Embryology exam 3 1the thyroid gland is connected to the tongue by a narrow tube, the thyroglossal duct. Embryology exam 3 embryology exam 3 1the thyroid gland. If this descent does not occur appropriately, an ectopic thyroid gland can develop at any point along this tract. The reason is, much is yet unknown of the molecular mechanisms that determines its formation, from. Pdf embryology and surgical anatomy of the thyroid and. The thyroid gland weighs 10 to 20 grams in normal adults. The thyroid gland is an endocrine organ found in the neck, it is responsible for regulating the bodys metabolic rate via hormones it produces. Further details regarding thyroid hormone synthesis and the key functions of the gland will also be addressed. These septa also serve as conduits for blood vessels. The primordial thyroid gland is first identifiable during the fourth week of gestation, beginning as an endodermal invagination of the tongue at the site of the foramen cecum fig. In this article, we will be looking at its anatomy, its cellular structure, its endocrine physiology and its clinical relevance. Thyroid embryologythyroid embryology stephanie johnsonstephanie johnson pgy 2pgy 2 2.
In the second section, a concise survey of the anatomy of the head and neck is provided with an attempt to simplify the description of this complex anatomical region. Normally, the thyroid gland cannot be seen and can barely be felt. The thyroid gland is a butterflyshaped organ located in the neck anterior to the trachea. Thyroid gland and parathyroid glands knowledge for. 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 hormones produced in the thyroid gland which are triiodothyronine t3 and. The thyroid gland originates from a diverticulum located in the median ventral wall of the pharynx. The modern thyroid or endocrine surgeon should have a complete understanding of the embryonic development of the thyroid and parathyroid glands. This thickening becomes the thyroid diverticulum see below.
Thyroid gland anatomy embryology, blood supply, venous drainage, innervation, histology. Jan 04, 2014 embryology of thyroid gland 1 aim mds. Derived from endoderm, the adult thyroid gland consists of two distinct cell types, thyroid follicular cells and parafollicular cells c cells. Each follicle is surrounded by variable amount of connective tissue. Anatomy and embryology of the thyroid gland springerlink. Human embryology and developmental biology, fifth edition, 20 local mesodermal inductive signals render specification of a small number of endodermal cells as few as 60 in mouse to be destined to. Thyroid gland historical aspects, embryology, anatomy and. Variation in follicle size is a normal feature of thyroid glands in mice and rats. This occurs under the influence of fibroblast growth factor signaling pathways. Background embryology, surgical anatomy and physiology embryology the thyroid gland originates from the first pharyngeal arch and begins as an outpouching of endodermal tissue from the base of the tongue, called the foramen caecum, as early as the fourth week of gestation. Thyroid gland thyroid gland stores its hormones in the form of colloid which is iodine bounded to thyroglobulin glycoprotein in cavities, surrounded by secretory cells, making up follicles. Friedman 593 the thyroid gland secretes thyroxine t 4 and triiodothyronine t 3, both of which modulate energy utilization and heat production and facilitate growth. Expertise in the gross anatomy of the thyroid gland is essential for any head and neck surgeon, whether they are excising a benign thyroglossal duct cyst or a thyroid malignancy. Elucidating how the thyroid gland the only source of thyroid hormones in the bodydevelops is thus key for understanding and treating thyroid dysgenesis, and for generating thyroid cells in vitro.
The thyroid gland is the first endocrine gland to develop in an embryo. Grossly, the gland appears brownishred and the left and right lobes are connected by an isthmus. Chapter 2 applied embryology of the thyroid and parathyroid glands amit agarwal, anand k. May 04, 2020 a branching morphogenesis program governs embryonic growth of the thyroid gland here, we show that branchinglike morphogenesis is a driving force to attain final size of the embryonic thyroid gland in mice. Detailed knowledge of thyroid gland anatomy and physiology is extremely important for any physician that manages thyroid disorders, including thyroid malignancies. Embryology also explains the diversity of certain thyroidal conditions, ranging from the lingual thyroid to the superior vena cava syndrome due to a mediastinal goiter. Emil theodor kocher and theodor billroth pioneered the surgical management of thyroid disease. Thyroid volume measured by ultrasonography us is slightly greater in men than women, increases with age and body weight, and decreases with increasing iodine intake. The thyroid gland is the first of the bodys endocrine glands to develop, on approximately the 24th day of gestation. Embryology and development first endocrine gland to appear in embryonic development begins to develop 24 days in the thyroid diverticulum descends into the neck and passes.
The developing thyroid then descends ventral to the pharyngeal gut. The functional unit of the thyroid gland is the follicle, which is composed of epithelial cells arranged as hollow vesicles of various shapes ranging in size from 0. Ultimately, the bilateral superior parathyroid glands usually locate symmetrically, either in close association with the superior pole of the thyroid gland or occasionally within the thyroid gland itself. The modern head and neck surgeon should have a meticulous surgical technique, combined with a thorough. Chapter 7 the thyroid gland introduction the thyroid gland is the endocrine gland responsible for producing thyroid hormone, a regulator of growth, development, and basal metabolic rate, and calcitonin, a regulator of calcium homeostasis described in chapter 8.
Thyroid gland is found in the neck, below the thyroid cartilage which forms the laryngeal prominence, or adams apple. The gland has two lobes, each pear shaped hugging anterolateral aspects of cervical trachea from oblique line of thyroid cartilage to 5 th or. The thyroid is located at the front of the neck, below the adams apple. Development of the thyroid gland the thyroid gland is the first of the bodys endocrine glands to develop, on approximately the 24th day of gestation. The gland consists of two lateral lobes joined by an isthmus. Lombardi, marco raffaelli this chapter contains additional onlineonly content, available on. The portion of the thyroid containing the parafollicular c cells, those responsible for the production of calcitonin, are derived from the. Applied embryology of the thyroid and parathyroid glands.
Thyroid development starts from the late 3rd to early 4th weeks of gestation, then the fetal thyroid gland develops rapidly until the 4th month of intrauterine growth thyroid development is complete with the onset of thyroid hormone synthesis thyroid is the first endocrine organ to develop in embryo, which points to its importance. The thyroid gland is composed of 2 lobes connected by an isthmus. Learn vocabulary, terms, and more with flashcards, games, and other study tools. The region is discussed under two subsections, the hard tissue framework and the soft tissue. The most prevalent disease, congenital hypothyroidism, is frequently caused by genetic defects of transcription factors involved in the development of the thyroid or pituitary gland. The thyroid is a small gland, measuring about 2 inches 5 centimeters across, that lies just under the skin below the adams apple in the neck. Oblique facial cleft the maxillary prominence does not merge with its corresponding lateral prominence, leading to exposure of the nasolacrimal duct to the surface. The thyroid gland is a single midline endocrine organ in the anterior neck responsible for thyroid hormone production which lies in the visceral space completely enveloped by pretracheal fascia middlelayer of the deep cervical fascia. The thyroid gland is among the most significant organs of the endocrine system and has a weight of 1520g. Nov 12, 2019 an aberrant or ectopic thyroid gland may occur anywhere along the path of initial descent of the thyroid, although it is most common at the base of the tongue, just posterior to the foramen cecum.
Anatomy of the thyroid gland lecturio online medical library. It weighs 25 grams in adults, with each lobe being about 5 cm long, 3 cm wide, and 2 cm thick, and the isthmus about 1. The two halves lobes of the gland are connected in the middle called the isthmus, giving the thyroid gland the shape of a bow tie. Disorders of thyroid gland development andor function are relatively common, affecting approximately one newborn infant in 20004000. Thyroid hormones are crucial for organismal development and homeostasis. The structures of the two thyroid hormones, triiodothyronine t3 and thyroxine. The thyroid gland develops in the first trimester of pregnancy from the fusion of the median thyroid anlage with the two lateral thyroid anlages derived from the pharyngeal pouches.
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