{"id":4383,"date":"2017-03-28T22:25:31","date_gmt":"2017-03-28T22:25:31","guid":{"rendered":"https:\/\/courses.lumenlearning.com\/wm-biology2\/?post_type=chapter&#038;p=4383"},"modified":"2024-04-26T01:39:35","modified_gmt":"2024-04-26T01:39:35","slug":"thyroids","status":"publish","type":"chapter","link":"https:\/\/courses.lumenlearning.com\/wm-biology2\/chapter\/thyroids\/","title":{"raw":"Thyroids","rendered":"Thyroids"},"content":{"raw":"<div class=\"textbox learning-objectives\">\r\n<h3>Learning Outcomes<\/h3>\r\n<ul>\r\n \t<li>Describe the role of the thyroid and parathyroid glands in the endocrine system<\/li>\r\n<\/ul>\r\n<\/div>\r\n<h2>Thyroid Gland<\/h2>\r\n[caption id=\"attachment_4983\" align=\"alignright\" width=\"400\"]<img class=\" wp-image-4983\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/1223\/2017\/04\/12160626\/Figure_37_05_02.jpg\" alt=\"The thyroid is located in the neck beneath the larynx and in front of the trachea. It consists of right and left lobes and a narrow central region called the isthmus of thyroid. Above the isthmus of thyroid is the pyramidal lobe.\" width=\"400\" height=\"361\" \/> Figure 1.\u00a0This illustration shows the location of the thyroid gland.[\/caption]\r\n\r\nThe <b>thyroid gland<\/b> is located in the neck, just below the larynx and in front of the trachea, as shown in Figure 1. It is a butterfly-shaped gland with two lobes that are connected by the <b>isthmus<\/b>. It has a dark red color due to its extensive vascular system. When the thyroid swells due to dysfunction, it can be felt under the skin of the neck.\r\n\r\nThe thyroid gland is made up of many spherical thyroid follicles, which are lined with a simple cuboidal epithelium. These follicles contain a viscous fluid, called <b>colloid<\/b>, which stores the glycoprotein thyroglobulin, the precursor to the thyroid hormones. The follicles produce hormones that can be stored in the colloid or released into the surrounding capillary network for transport to the rest of the body via the circulatory system.\r\n\r\nThyroid follicle cells synthesize the hormone thyroxine, which is also known as T<sub>4<\/sub> because it contains four atoms of iodine, and triiodothyronine, also known as T<sub>3<\/sub> because it contains three atoms of iodine. Follicle cells are stimulated to release stored T<sub>3 <\/sub>and T<sub>4 <\/sub>by thyroid stimulating hormone (TSH), which is produced by the anterior pituitary. These thyroid hormones increase the rates of mitochondrial ATP production.\r\n\r\n<section id=\"fs-idp155960672\" data-depth=\"1\">\r\n<p id=\"fs-idp122150528\">A third hormone, calcitonin, is produced by\u00a0<strong><span id=\"term1751\" data-type=\"term\">parafollicular cells<\/span><\/strong>\u00a0of the thyroid either releasing hormones or inhibiting hormones. Calcitonin release is not controlled by TSH, but instead is released when calcium ion concentrations in the blood rise. Calcitonin functions to help regulate calcium concentrations in body fluids. It acts in the bones to inhibit osteoclast activity and in the kidneys to stimulate excretion of calcium. The combination of these two events lowers body fluid levels of calcium.<\/p>\r\n\r\n<\/section><section id=\"fs-idp47040048\" data-depth=\"1\"><\/section>\r\n<h2>Parathyroid Glands<\/h2>\r\n[caption id=\"attachment_2751\" align=\"alignright\" width=\"400\"]<img class=\"wp-image-2751\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/1223\/2017\/02\/07232109\/Figure_37_05_03.jpg\" alt=\"The parathyroid glands are round structures located on the surface of the right and left lobes of the thyroid gland. In the illustration shown, there are two parathyroid glands on each side, and one is located above the other.\" width=\"400\" height=\"377\" \/> Figure 2.\u00a0The parathyroid glands are located on the posterior of the thyroid gland. (credit: modification of work by NCI)[\/caption]\r\n\r\nMost people have four <b>parathyroid glands<\/b>; however, the number can vary from two to six. These glands are located on the posterior surface of the thyroid gland, as shown in Figure 2. Normally, there is a superior gland and an inferior gland associated with each of the thyroid\u2019s two lobes. Each parathyroid gland is covered by connective tissue and contains many secretory cells that are associated with a capillary network.\r\n\r\nThe parathyroid glands produce parathyroid hormone (PTH). PTH increases blood calcium concentrations when calcium ion levels fall below normal.\u00a0PTH and calcitonin work in opposition to one another to maintain homeostatic Ca<sup>2+<\/sup>levels in body fluids. These hormones encourage bone growth, muscle mass, and blood cell formation in children and women.\u00a0PTH is produced by chief cells of the parathyroid.\u00a0\u00a0Another type of cells, oxyphil cells, exist in the parathyroid but their function is not known.\r\n<div class=\"textbox tryit\">\r\n<h3>Try It<\/h3>\r\nhttps:\/\/assess.lumenlearning.com\/practice\/d292ab9d-2049-42d2-a83a-a6128fbebd7c\r\n<\/div>","rendered":"<div class=\"textbox learning-objectives\">\n<h3>Learning Outcomes<\/h3>\n<ul>\n<li>Describe the role of the thyroid and parathyroid glands in the endocrine system<\/li>\n<\/ul>\n<\/div>\n<h2>Thyroid Gland<\/h2>\n<div id=\"attachment_4983\" style=\"width: 410px\" class=\"wp-caption alignright\"><img loading=\"lazy\" decoding=\"async\" aria-describedby=\"caption-attachment-4983\" class=\"wp-image-4983\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/1223\/2017\/04\/12160626\/Figure_37_05_02.jpg\" alt=\"The thyroid is located in the neck beneath the larynx and in front of the trachea. It consists of right and left lobes and a narrow central region called the isthmus of thyroid. Above the isthmus of thyroid is the pyramidal lobe.\" width=\"400\" height=\"361\" \/><\/p>\n<p id=\"caption-attachment-4983\" class=\"wp-caption-text\">Figure 1.\u00a0This illustration shows the location of the thyroid gland.<\/p>\n<\/div>\n<p>The <b>thyroid gland<\/b> is located in the neck, just below the larynx and in front of the trachea, as shown in Figure 1. It is a butterfly-shaped gland with two lobes that are connected by the <b>isthmus<\/b>. It has a dark red color due to its extensive vascular system. When the thyroid swells due to dysfunction, it can be felt under the skin of the neck.<\/p>\n<p>The thyroid gland is made up of many spherical thyroid follicles, which are lined with a simple cuboidal epithelium. These follicles contain a viscous fluid, called <b>colloid<\/b>, which stores the glycoprotein thyroglobulin, the precursor to the thyroid hormones. The follicles produce hormones that can be stored in the colloid or released into the surrounding capillary network for transport to the rest of the body via the circulatory system.<\/p>\n<p>Thyroid follicle cells synthesize the hormone thyroxine, which is also known as T<sub>4<\/sub> because it contains four atoms of iodine, and triiodothyronine, also known as T<sub>3<\/sub> because it contains three atoms of iodine. Follicle cells are stimulated to release stored T<sub>3 <\/sub>and T<sub>4 <\/sub>by thyroid stimulating hormone (TSH), which is produced by the anterior pituitary. These thyroid hormones increase the rates of mitochondrial ATP production.<\/p>\n<section id=\"fs-idp155960672\" data-depth=\"1\">\n<p id=\"fs-idp122150528\">A third hormone, calcitonin, is produced by\u00a0<strong><span id=\"term1751\" data-type=\"term\">parafollicular cells<\/span><\/strong>\u00a0of the thyroid either releasing hormones or inhibiting hormones. Calcitonin release is not controlled by TSH, but instead is released when calcium ion concentrations in the blood rise. Calcitonin functions to help regulate calcium concentrations in body fluids. It acts in the bones to inhibit osteoclast activity and in the kidneys to stimulate excretion of calcium. The combination of these two events lowers body fluid levels of calcium.<\/p>\n<\/section>\n<section id=\"fs-idp47040048\" data-depth=\"1\"><\/section>\n<h2>Parathyroid Glands<\/h2>\n<div id=\"attachment_2751\" style=\"width: 410px\" class=\"wp-caption alignright\"><img loading=\"lazy\" decoding=\"async\" aria-describedby=\"caption-attachment-2751\" class=\"wp-image-2751\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/1223\/2017\/02\/07232109\/Figure_37_05_03.jpg\" alt=\"The parathyroid glands are round structures located on the surface of the right and left lobes of the thyroid gland. In the illustration shown, there are two parathyroid glands on each side, and one is located above the other.\" width=\"400\" height=\"377\" \/><\/p>\n<p id=\"caption-attachment-2751\" class=\"wp-caption-text\">Figure 2.\u00a0The parathyroid glands are located on the posterior of the thyroid gland. (credit: modification of work by NCI)<\/p>\n<\/div>\n<p>Most people have four <b>parathyroid glands<\/b>; however, the number can vary from two to six. These glands are located on the posterior surface of the thyroid gland, as shown in Figure 2. Normally, there is a superior gland and an inferior gland associated with each of the thyroid\u2019s two lobes. Each parathyroid gland is covered by connective tissue and contains many secretory cells that are associated with a capillary network.<\/p>\n<p>The parathyroid glands produce parathyroid hormone (PTH). PTH increases blood calcium concentrations when calcium ion levels fall below normal.\u00a0PTH and calcitonin work in opposition to one another to maintain homeostatic Ca<sup>2+<\/sup>levels in body fluids. These hormones encourage bone growth, muscle mass, and blood cell formation in children and women.\u00a0PTH is produced by chief cells of the parathyroid.\u00a0\u00a0Another type of cells, oxyphil cells, exist in the parathyroid but their function is not known.<\/p>\n<div class=\"textbox tryit\">\n<h3>Try It<\/h3>\n<p>\t<iframe id=\"assessment_practice_d292ab9d-2049-42d2-a83a-a6128fbebd7c\" class=\"resizable\" src=\"https:\/\/assess.lumenlearning.com\/practice\/d292ab9d-2049-42d2-a83a-a6128fbebd7c?iframe_resize_id=assessment_practice_id_d292ab9d-2049-42d2-a83a-a6128fbebd7c\" frameborder=\"0\" style=\"border:none;width:100%;height:100%;min-height:300px;\"><br \/>\n\t<\/iframe>\n<\/div>\n\n\t\t\t <section class=\"citations-section\" role=\"contentinfo\">\n\t\t\t <h3>Candela Citations<\/h3>\n\t\t\t\t\t <div>\n\t\t\t\t\t\t <div id=\"citation-list-4383\">\n\t\t\t\t\t\t\t <div class=\"licensing\"><div class=\"license-attribution-dropdown-subheading\">CC licensed content, Shared previously<\/div><ul class=\"citation-list\"><li>Biology 2e. <strong>Provided by<\/strong>: OpenStax. <strong>Located at<\/strong>: <a target=\"_blank\" href=\"http:\/\/cnx.org\/contents\/185cbf87-c72e-48f5-b51e-f14f21b5eabd@10.8\">http:\/\/cnx.org\/contents\/185cbf87-c72e-48f5-b51e-f14f21b5eabd@10.8<\/a>. <strong>License<\/strong>: <em><a target=\"_blank\" rel=\"license\" href=\"https:\/\/creativecommons.org\/licenses\/by\/4.0\/\">CC BY: Attribution<\/a><\/em>. <strong>License Terms<\/strong>: Access for free at https:\/\/openstax.org\/books\/biology-2e\/pages\/1-introduction<\/li><\/ul><\/div>\n\t\t\t\t\t\t <\/div>\n\t\t\t\t\t <\/div>\n\t\t\t <\/section>","protected":false},"author":17,"menu_order":19,"template":"","meta":{"_candela_citation":"[{\"type\":\"cc\",\"description\":\"Biology 2e\",\"author\":\"\",\"organization\":\"OpenStax\",\"url\":\"http:\/\/cnx.org\/contents\/185cbf87-c72e-48f5-b51e-f14f21b5eabd@10.8\",\"project\":\"\",\"license\":\"cc-by\",\"license_terms\":\"Access for free at https:\/\/openstax.org\/books\/biology-2e\/pages\/1-introduction\"}]","CANDELA_OUTCOMES_GUID":"7ad6521d-96e6-4cf0-bc5d-6b814653aae2, 07871f4a-42aa-4701-8812-67352cd04b47","pb_show_title":"on","pb_short_title":"","pb_subtitle":"","pb_authors":[],"pb_section_license":""},"chapter-type":[],"contributor":[],"license":[],"class_list":["post-4383","chapter","type-chapter","status-publish","hentry"],"part":3800,"_links":{"self":[{"href":"https:\/\/courses.lumenlearning.com\/wm-biology2\/wp-json\/pressbooks\/v2\/chapters\/4383","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/courses.lumenlearning.com\/wm-biology2\/wp-json\/pressbooks\/v2\/chapters"}],"about":[{"href":"https:\/\/courses.lumenlearning.com\/wm-biology2\/wp-json\/wp\/v2\/types\/chapter"}],"author":[{"embeddable":true,"href":"https:\/\/courses.lumenlearning.com\/wm-biology2\/wp-json\/wp\/v2\/users\/17"}],"version-history":[{"count":13,"href":"https:\/\/courses.lumenlearning.com\/wm-biology2\/wp-json\/pressbooks\/v2\/chapters\/4383\/revisions"}],"predecessor-version":[{"id":8543,"href":"https:\/\/courses.lumenlearning.com\/wm-biology2\/wp-json\/pressbooks\/v2\/chapters\/4383\/revisions\/8543"}],"part":[{"href":"https:\/\/courses.lumenlearning.com\/wm-biology2\/wp-json\/pressbooks\/v2\/parts\/3800"}],"metadata":[{"href":"https:\/\/courses.lumenlearning.com\/wm-biology2\/wp-json\/pressbooks\/v2\/chapters\/4383\/metadata\/"}],"wp:attachment":[{"href":"https:\/\/courses.lumenlearning.com\/wm-biology2\/wp-json\/wp\/v2\/media?parent=4383"}],"wp:term":[{"taxonomy":"chapter-type","embeddable":true,"href":"https:\/\/courses.lumenlearning.com\/wm-biology2\/wp-json\/pressbooks\/v2\/chapter-type?post=4383"},{"taxonomy":"contributor","embeddable":true,"href":"https:\/\/courses.lumenlearning.com\/wm-biology2\/wp-json\/wp\/v2\/contributor?post=4383"},{"taxonomy":"license","embeddable":true,"href":"https:\/\/courses.lumenlearning.com\/wm-biology2\/wp-json\/wp\/v2\/license?post=4383"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}