{"id":2542,"date":"2017-02-06T21:26:48","date_gmt":"2017-02-06T21:26:48","guid":{"rendered":"https:\/\/courses.lumenlearning.com\/wm-biology2\/?post_type=chapter&#038;p=2542"},"modified":"2024-04-26T00:46:54","modified_gmt":"2024-04-26T00:46:54","slug":"amniotic-animals","status":"publish","type":"chapter","link":"https:\/\/courses.lumenlearning.com\/wm-biology2\/chapter\/amniotic-animals\/","title":{"raw":"Amniotic Animals","rendered":"Amniotic Animals"},"content":{"raw":"<div class=\"textbox learning-objectives\">\r\n<h3>Learning Outcomes<\/h3>\r\n<ul>\r\n \t<li>Identify the classes of animals that are amniotes<\/li>\r\n \t<li>Describe the main characteristics of amniotes<\/li>\r\n<\/ul>\r\n<\/div>\r\n<p id=\"fs-idm17519296\">The reptiles (including dinosaurs and birds) are distinguished from amphibians by their terrestrially adapted egg, which is supported by four\u00a0<em data-effect=\"italics\">extraembryonic membranes<\/em>: the yolk sac, the amnion, the chorion, and the allantois (Figure 1). The chorion and amnion develop from folds in the body wall, and the yolk sac and allantois are extensions of the midgut and hindgut respectively. The amnion forms a fluid-filled cavity that provides the embryo with its own internal aquatic environment. The evolution of the extraembryonic membranes led to less dependence on water for development and thus allowed the amniotes to branch out into drier environments.<\/p>\r\n<p id=\"fs-idm17516299\">In addition to these membranes, the eggs of birds, reptiles, and a few mammals have shells. An\u00a0<strong><span id=\"term1186\" data-type=\"term\">amniote embryo<\/span><\/strong>\u00a0was then enclosed in the amnion, which was in turn encased in an extra-embryonic coelom contained within the chorion. Between the shell and the chorion was the albumin of the egg, which provided additional fluid and cushioning. This was a significant development that further distinguishes the amniotes from amphibians, which were and continue to be restricted to moist environments due their shell-less eggs. Although the shells of various reptilian amniotic species vary significantly, they all permit the retention of water and nutrients for the developing embryo. The egg shells of bird (avian reptiles) are hardened with calcium carbonate, making them rigid, but fragile. The shells of most nonavian reptile eggs, such as turtles, are leathery and require a moist environment. Most mammals do not lay eggs (except for monotremes such as the echindnas and platypuses). Instead, the embryo grows within the mother\u2019s body, with the placenta derived from two of the extraembryonic membranes.<\/p>\r\n\r\n<section id=\"fs-idp230325376\" data-depth=\"1\"><\/section>\r\n<h2>Characteristics of Amniotes<\/h2>\r\n[caption id=\"attachment_2547\" align=\"alignright\" width=\"400\"]<img class=\" wp-image-2547\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/1223\/2017\/02\/06212753\/Figure_29_04_01.png\" alt=\"The illustration shows an egg with the shell, embryo, yolk, yolk sac, and the extra-embryonic membranes\" width=\"400\" height=\"331\" \/> Figure 1.\u00a0The key features of an amniotic egg are shown.[\/caption]\r\n<p id=\"fs-idp97601536\">The\u00a0<span id=\"term1187\" data-type=\"term\">amniotic egg<\/span>\u00a0is the key characteristic of amniotes. In amniotes that lay eggs, the shell of the egg provides protection for the developing embryo while being permeable enough to allow for the exchange of carbon dioxide and oxygen. The\u00a0<em data-effect=\"italics\">albumin<\/em>, or egg white, outside of the chorion provides the embryo with water and protein, whereas the fattier egg yolk contained in the yolk sac provides nutrients for the embryo, as is the case with the eggs of many other animals, such as amphibians. Here are the functions of the extraembryonic membranes:<\/p>\r\n\r\n<ol id=\"fs-idl270896\" type=\"1\">\r\n \t<li>Blood vessels in the\u00a0<span id=\"term1188\" data-type=\"term\">yolk sac<\/span>\u00a0transport yolk nutrients to the circulatory system of the embryo.<\/li>\r\n \t<li>The\u00a0<span id=\"term1189\" data-type=\"term\">chorion<\/span>\u00a0facilitates exchange of oxygen and carbon dioxide between the embryo and the egg\u2019s external environment.<\/li>\r\n \t<li>The\u00a0<span id=\"term1190\" data-type=\"term\">allantois<\/span>\u00a0stores nitrogenous wastes produced by the embryo and also facilitates respiration.<\/li>\r\n \t<li>The\u00a0<span id=\"term1191\" data-type=\"term\">amnion<\/span>\u00a0protects the embryo from mechanical shock and supports hydration.<\/li>\r\n<\/ol>\r\n<ol id=\"fs-idl270896\" type=\"1\"><\/ol>\r\n<p id=\"fs-idp97615036\">In mammals, the yolk sac is very reduced, but the embryo is still cushioned and enclosed within the amnion. The\u00a0<em data-effect=\"italics\">placenta,<\/em>\u00a0which transports nutrients and functions in gas exchange and waste management, is derived from the chorion and allantois.<\/p>\r\n\r\n<div id=\"fs-idp235496192\" class=\"visual-connection ui-has-child-title\" data-type=\"note\" data-has-label=\"true\" data-label=\"\"><section id=\"fs-idp230325376\" data-depth=\"1\">\r\n<p id=\"fs-idp181595248\">Additional derived characteristics of amniotes include a waterproof skin, accessory keratinized structures, and costal (rib) ventilation of the lungs.<\/p>\r\n\r\n<\/section><\/div>\r\n<div class=\"textbox exercises\">\r\n<h3>Practice Question<\/h3>\r\nWhich of the following statements about the parts of an egg are false?\r\n<ol style=\"list-style-type: lower-alpha;\">\r\n \t<li>The allantois stores nitrogenous waste and facilitates respiration.<\/li>\r\n \t<li>The chorion facilitates gas exchange.<\/li>\r\n \t<li>The yolk provides food for the growing embryo.<\/li>\r\n \t<li>The amniotic cavity is filled with albumen.<\/li>\r\n<\/ol>\r\n[reveal-answer q=\"428004\"]Show Answer[\/reveal-answer]\r\n[hidden-answer a=\"428004\"]Statement d is false.[\/hidden-answer]\r\n\r\n<\/div>\r\n<div class=\"textbox tryit\">\r\n<h3>Try It<\/h3>\r\nhttps:\/\/assess.lumenlearning.com\/practice\/9e9fc387-2a95-4f5f-8e31-147decd115c7\r\nhttps:\/\/assess.lumenlearning.com\/practice\/2719af69-c361-4fbf-b7d7-2dc1bcd59eba\r\n<\/div>","rendered":"<div class=\"textbox learning-objectives\">\n<h3>Learning Outcomes<\/h3>\n<ul>\n<li>Identify the classes of animals that are amniotes<\/li>\n<li>Describe the main characteristics of amniotes<\/li>\n<\/ul>\n<\/div>\n<p id=\"fs-idm17519296\">The reptiles (including dinosaurs and birds) are distinguished from amphibians by their terrestrially adapted egg, which is supported by four\u00a0<em data-effect=\"italics\">extraembryonic membranes<\/em>: the yolk sac, the amnion, the chorion, and the allantois (Figure 1). The chorion and amnion develop from folds in the body wall, and the yolk sac and allantois are extensions of the midgut and hindgut respectively. The amnion forms a fluid-filled cavity that provides the embryo with its own internal aquatic environment. The evolution of the extraembryonic membranes led to less dependence on water for development and thus allowed the amniotes to branch out into drier environments.<\/p>\n<p id=\"fs-idm17516299\">In addition to these membranes, the eggs of birds, reptiles, and a few mammals have shells. An\u00a0<strong><span id=\"term1186\" data-type=\"term\">amniote embryo<\/span><\/strong>\u00a0was then enclosed in the amnion, which was in turn encased in an extra-embryonic coelom contained within the chorion. Between the shell and the chorion was the albumin of the egg, which provided additional fluid and cushioning. This was a significant development that further distinguishes the amniotes from amphibians, which were and continue to be restricted to moist environments due their shell-less eggs. Although the shells of various reptilian amniotic species vary significantly, they all permit the retention of water and nutrients for the developing embryo. The egg shells of bird (avian reptiles) are hardened with calcium carbonate, making them rigid, but fragile. The shells of most nonavian reptile eggs, such as turtles, are leathery and require a moist environment. Most mammals do not lay eggs (except for monotremes such as the echindnas and platypuses). Instead, the embryo grows within the mother\u2019s body, with the placenta derived from two of the extraembryonic membranes.<\/p>\n<section id=\"fs-idp230325376\" data-depth=\"1\"><\/section>\n<h2>Characteristics of Amniotes<\/h2>\n<div id=\"attachment_2547\" style=\"width: 410px\" class=\"wp-caption alignright\"><img loading=\"lazy\" decoding=\"async\" aria-describedby=\"caption-attachment-2547\" class=\"wp-image-2547\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/1223\/2017\/02\/06212753\/Figure_29_04_01.png\" alt=\"The illustration shows an egg with the shell, embryo, yolk, yolk sac, and the extra-embryonic membranes\" width=\"400\" height=\"331\" \/><\/p>\n<p id=\"caption-attachment-2547\" class=\"wp-caption-text\">Figure 1.\u00a0The key features of an amniotic egg are shown.<\/p>\n<\/div>\n<p id=\"fs-idp97601536\">The\u00a0<span id=\"term1187\" data-type=\"term\">amniotic egg<\/span>\u00a0is the key characteristic of amniotes. In amniotes that lay eggs, the shell of the egg provides protection for the developing embryo while being permeable enough to allow for the exchange of carbon dioxide and oxygen. The\u00a0<em data-effect=\"italics\">albumin<\/em>, or egg white, outside of the chorion provides the embryo with water and protein, whereas the fattier egg yolk contained in the yolk sac provides nutrients for the embryo, as is the case with the eggs of many other animals, such as amphibians. Here are the functions of the extraembryonic membranes:<\/p>\n<ol id=\"fs-idl270896\" type=\"1\">\n<li>Blood vessels in the\u00a0<span id=\"term1188\" data-type=\"term\">yolk sac<\/span>\u00a0transport yolk nutrients to the circulatory system of the embryo.<\/li>\n<li>The\u00a0<span id=\"term1189\" data-type=\"term\">chorion<\/span>\u00a0facilitates exchange of oxygen and carbon dioxide between the embryo and the egg\u2019s external environment.<\/li>\n<li>The\u00a0<span id=\"term1190\" data-type=\"term\">allantois<\/span>\u00a0stores nitrogenous wastes produced by the embryo and also facilitates respiration.<\/li>\n<li>The\u00a0<span id=\"term1191\" data-type=\"term\">amnion<\/span>\u00a0protects the embryo from mechanical shock and supports hydration.<\/li>\n<\/ol>\n<ol id=\"fs-idl270896\" type=\"1\"><\/ol>\n<p id=\"fs-idp97615036\">In mammals, the yolk sac is very reduced, but the embryo is still cushioned and enclosed within the amnion. The\u00a0<em data-effect=\"italics\">placenta,<\/em>\u00a0which transports nutrients and functions in gas exchange and waste management, is derived from the chorion and allantois.<\/p>\n<div id=\"fs-idp235496192\" class=\"visual-connection ui-has-child-title\" data-type=\"note\" data-has-label=\"true\" data-label=\"\">\n<section id=\"fs-idp230325376\" data-depth=\"1\">\n<p id=\"fs-idp181595248\">Additional derived characteristics of amniotes include a waterproof skin, accessory keratinized structures, and costal (rib) ventilation of the lungs.<\/p>\n<\/section>\n<\/div>\n<div class=\"textbox exercises\">\n<h3>Practice Question<\/h3>\n<p>Which of the following statements about the parts of an egg are false?<\/p>\n<ol style=\"list-style-type: lower-alpha;\">\n<li>The allantois stores nitrogenous waste and facilitates respiration.<\/li>\n<li>The chorion facilitates gas exchange.<\/li>\n<li>The yolk provides food for the growing embryo.<\/li>\n<li>The amniotic cavity is filled with albumen.<\/li>\n<\/ol>\n<div class=\"qa-wrapper\" style=\"display: block\"><span class=\"show-answer collapsed\" style=\"cursor: pointer\" data-target=\"q428004\">Show Answer<\/span><\/p>\n<div id=\"q428004\" class=\"hidden-answer\" style=\"display: none\">Statement d is false.<\/div>\n<\/div>\n<\/div>\n<div class=\"textbox tryit\">\n<h3>Try It<\/h3>\n<p>\t<iframe id=\"assessment_practice_9e9fc387-2a95-4f5f-8e31-147decd115c7\" class=\"resizable\" src=\"https:\/\/assess.lumenlearning.com\/practice\/9e9fc387-2a95-4f5f-8e31-147decd115c7?iframe_resize_id=assessment_practice_id_9e9fc387-2a95-4f5f-8e31-147decd115c7\" frameborder=\"0\" style=\"border:none;width:100%;height:100%;min-height:300px;\"><br \/>\n\t<\/iframe><br \/>\n\t<iframe id=\"assessment_practice_2719af69-c361-4fbf-b7d7-2dc1bcd59eba\" class=\"resizable\" src=\"https:\/\/assess.lumenlearning.com\/practice\/2719af69-c361-4fbf-b7d7-2dc1bcd59eba?iframe_resize_id=assessment_practice_id_2719af69-c361-4fbf-b7d7-2dc1bcd59eba\" 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-2542\">\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":14,"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":"107c3237-6b9d-4628-a412-ab2cce78b501, 3db1e5ab-0e44-41c5-87a6-9b4302e2ca9c, 2a892967-a484-4a9f-a35e-176f6450e5b8","pb_show_title":"on","pb_short_title":"","pb_subtitle":"","pb_authors":[],"pb_section_license":""},"chapter-type":[],"contributor":[],"license":[],"class_list":["post-2542","chapter","type-chapter","status-publish","hentry"],"part":148,"_links":{"self":[{"href":"https:\/\/courses.lumenlearning.com\/wm-biology2\/wp-json\/pressbooks\/v2\/chapters\/2542","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":11,"href":"https:\/\/courses.lumenlearning.com\/wm-biology2\/wp-json\/pressbooks\/v2\/chapters\/2542\/revisions"}],"predecessor-version":[{"id":8469,"href":"https:\/\/courses.lumenlearning.com\/wm-biology2\/wp-json\/pressbooks\/v2\/chapters\/2542\/revisions\/8469"}],"part":[{"href":"https:\/\/courses.lumenlearning.com\/wm-biology2\/wp-json\/pressbooks\/v2\/parts\/148"}],"metadata":[{"href":"https:\/\/courses.lumenlearning.com\/wm-biology2\/wp-json\/pressbooks\/v2\/chapters\/2542\/metadata\/"}],"wp:attachment":[{"href":"https:\/\/courses.lumenlearning.com\/wm-biology2\/wp-json\/wp\/v2\/media?parent=2542"}],"wp:term":[{"taxonomy":"chapter-type","embeddable":true,"href":"https:\/\/courses.lumenlearning.com\/wm-biology2\/wp-json\/pressbooks\/v2\/chapter-type?post=2542"},{"taxonomy":"contributor","embeddable":true,"href":"https:\/\/courses.lumenlearning.com\/wm-biology2\/wp-json\/wp\/v2\/contributor?post=2542"},{"taxonomy":"license","embeddable":true,"href":"https:\/\/courses.lumenlearning.com\/wm-biology2\/wp-json\/wp\/v2\/license?post=2542"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}