{"id":4487,"date":"2017-03-29T17:07:49","date_gmt":"2017-03-29T17:07:49","guid":{"rendered":"https:\/\/courses.lumenlearning.com\/wm-biology2\/?post_type=chapter&#038;p=4487"},"modified":"2024-04-26T01:45:32","modified_gmt":"2024-04-26T01:45:32","slug":"cleavage-and-blastula-stage","status":"publish","type":"chapter","link":"https:\/\/courses.lumenlearning.com\/wm-biology2\/chapter\/cleavage-and-blastula-stage\/","title":{"raw":"Cleavage and Blastula Stage","rendered":"Cleavage and Blastula Stage"},"content":{"raw":"<div class=\"textbox learning-objectives\">\r\n<h3>Learning Outcomes<\/h3>\r\n<ul>\r\n \t<li>Discuss the role of cleavage in animal development<\/li>\r\n<\/ul>\r\n<\/div>\r\nThe development of multi-cellular organisms begins from a single-celled zygote, which undergoes rapid cell division to form the blastula. The rapid, multiple rounds of cell division are termed cleavage. Cleavage is illustrated in (Figure 1a). After the cleavage has produced over 100 cells, the embryo is called a blastula. The blastula is usually a spherical layer of cells (the blastoderm) surrounding a fluid-filled or yolk-filled cavity (the blastocoel). Mammals at this stage form a structure called the blastocyst, characterized by an inner cell mass that is distinct from the surrounding blastula, shown in\u00a0Figure 1b. During cleavage, the cells divide without an increase in mass; that is, one large single-celled zygote divides into multiple smaller cells. Each cell within the blastula is called a blastomere.\r\n\r\n[caption id=\"\" align=\"aligncenter\" width=\"699\"]<img id=\"4\" style=\"font-size: 1em;\" src=\"https:\/\/openstax.org\/resources\/6e22e2f9cd2bfed5c08d3ffbcc8fd9049f5d48a5\" alt=\"Part A illustration shows a fertilized egg divided into two, four, eight, sixteen and thirty-two cells. Part B shows a hollow ball of cells. The cells on the surface are called the blastoderm, and the hollow center is called the blastocoel. \" width=\"699\" height=\"204\" data-media-type=\"image\/png\" \/> Figure 1 (a) During cleavage, the zygote rapidly divides into multiple cells without increasing in size. (b) The cells rearrange themselves to form a hollow ball with a fluid-filled or yolk-filled cavity called the blastula.[\/caption]\r\n<p id=\"fs-idp36763504\">Cleavage can take place in two ways:\u00a0<strong><span id=\"term2184\" data-type=\"term\">holoblastic<\/span><\/strong>\u00a0(total) cleavage or\u00a0<strong><span id=\"term2185\" data-type=\"term\">meroblastic<\/span><\/strong>\u00a0(partial) cleavage. The type of cleavage depends on the amount of yolk in the eggs. In placental mammals (including humans) where nourishment is provided by the mother\u2019s body, the eggs have a very small amount of yolk and undergo holoblastic cleavage. Other species, such as birds, with a lot of yolk in the egg to nourish the embryo during development, undergo meroblastic cleavage.<\/p>\r\nIn mammals, the blastula forms the <b>blastocyst<\/b> in the next stage of development. Here the cells in the blastula arrange themselves in two layers: the <b>inner cell mass<\/b>, and an outer layer called the <b>trophoblast<\/b>. The inner cell mass is also known as the embryoblast and this mass of cells will go on to form the embryo.\r\n\r\n[caption id=\"\" align=\"aligncenter\" width=\"449\"]<img id=\"5\" class=\"\" src=\"https:\/\/openstax.org\/resources\/85c553b960cbc6917d71b2401a5e2f3228e743ac\" alt=\"Illustration shows a hollow ball of cells with an inner cell mass clustered to one side. The exterior is called the trophoblast.\" width=\"449\" height=\"305\" data-media-type=\"image\/png\" \/> Figure 2. The rearrangement of the cells in the mammalian blastula to two layers\u2014the inner cell mass and the trophoblast\u2014results in the formation of the blastocyst.[\/caption]\r\n\r\nAt this stage of development, illustrated in Figure 2\u00a0the inner cell mass consists of embryonic stem cells that will differentiate into the different cell types needed by the organism. The trophoblast will contribute to the placenta and nourish the embryo.\r\n<div class=\"textbox\">Visit the <a href=\"http:\/\/www.ehd.org\/virtual-human-embryo\/\" target=\"_blank\" rel=\"nofollow noopener\">Virtual Human Embryo project<\/a> at the Endowment for Human Development site to step through an interactive that shows the stages of embryo development, including micrographs and rotating 3-D images.<\/div>\r\n<div class=\"textbox tryit\">\r\n<h3>Try It<\/h3>\r\nhttps:\/\/assess.lumenlearning.com\/practice\/b4571e71-3134-4642-806f-6e6eeb617e84\r\n<\/div>","rendered":"<div class=\"textbox learning-objectives\">\n<h3>Learning Outcomes<\/h3>\n<ul>\n<li>Discuss the role of cleavage in animal development<\/li>\n<\/ul>\n<\/div>\n<p>The development of multi-cellular organisms begins from a single-celled zygote, which undergoes rapid cell division to form the blastula. The rapid, multiple rounds of cell division are termed cleavage. Cleavage is illustrated in (Figure 1a). After the cleavage has produced over 100 cells, the embryo is called a blastula. The blastula is usually a spherical layer of cells (the blastoderm) surrounding a fluid-filled or yolk-filled cavity (the blastocoel). Mammals at this stage form a structure called the blastocyst, characterized by an inner cell mass that is distinct from the surrounding blastula, shown in\u00a0Figure 1b. During cleavage, the cells divide without an increase in mass; that is, one large single-celled zygote divides into multiple smaller cells. Each cell within the blastula is called a blastomere.<\/p>\n<div style=\"width: 709px\" class=\"wp-caption aligncenter\"><img loading=\"lazy\" decoding=\"async\" id=\"4\" style=\"font-size: 1em;\" src=\"https:\/\/openstax.org\/resources\/6e22e2f9cd2bfed5c08d3ffbcc8fd9049f5d48a5\" alt=\"Part A illustration shows a fertilized egg divided into two, four, eight, sixteen and thirty-two cells. Part B shows a hollow ball of cells. The cells on the surface are called the blastoderm, and the hollow center is called the blastocoel.\" width=\"699\" height=\"204\" data-media-type=\"image\/png\" \/><\/p>\n<p class=\"wp-caption-text\">Figure 1 (a) During cleavage, the zygote rapidly divides into multiple cells without increasing in size. (b) The cells rearrange themselves to form a hollow ball with a fluid-filled or yolk-filled cavity called the blastula.<\/p>\n<\/div>\n<p id=\"fs-idp36763504\">Cleavage can take place in two ways:\u00a0<strong><span id=\"term2184\" data-type=\"term\">holoblastic<\/span><\/strong>\u00a0(total) cleavage or\u00a0<strong><span id=\"term2185\" data-type=\"term\">meroblastic<\/span><\/strong>\u00a0(partial) cleavage. The type of cleavage depends on the amount of yolk in the eggs. In placental mammals (including humans) where nourishment is provided by the mother\u2019s body, the eggs have a very small amount of yolk and undergo holoblastic cleavage. Other species, such as birds, with a lot of yolk in the egg to nourish the embryo during development, undergo meroblastic cleavage.<\/p>\n<p>In mammals, the blastula forms the <b>blastocyst<\/b> in the next stage of development. Here the cells in the blastula arrange themselves in two layers: the <b>inner cell mass<\/b>, and an outer layer called the <b>trophoblast<\/b>. The inner cell mass is also known as the embryoblast and this mass of cells will go on to form the embryo.<\/p>\n<div style=\"width: 459px\" class=\"wp-caption aligncenter\"><img loading=\"lazy\" decoding=\"async\" id=\"5\" class=\"\" src=\"https:\/\/openstax.org\/resources\/85c553b960cbc6917d71b2401a5e2f3228e743ac\" alt=\"Illustration shows a hollow ball of cells with an inner cell mass clustered to one side. The exterior is called the trophoblast.\" width=\"449\" height=\"305\" data-media-type=\"image\/png\" \/><\/p>\n<p class=\"wp-caption-text\">Figure 2. The rearrangement of the cells in the mammalian blastula to two layers\u2014the inner cell mass and the trophoblast\u2014results in the formation of the blastocyst.<\/p>\n<\/div>\n<p>At this stage of development, illustrated in Figure 2\u00a0the inner cell mass consists of embryonic stem cells that will differentiate into the different cell types needed by the organism. The trophoblast will contribute to the placenta and nourish the embryo.<\/p>\n<div class=\"textbox\">Visit the <a href=\"http:\/\/www.ehd.org\/virtual-human-embryo\/\" target=\"_blank\" rel=\"nofollow noopener\">Virtual Human Embryo project<\/a> at the Endowment for Human Development site to step through an interactive that shows the stages of embryo development, including micrographs and rotating 3-D images.<\/div>\n<div class=\"textbox tryit\">\n<h3>Try It<\/h3>\n<p>\t<iframe id=\"assessment_practice_b4571e71-3134-4642-806f-6e6eeb617e84\" class=\"resizable\" src=\"https:\/\/assess.lumenlearning.com\/practice\/b4571e71-3134-4642-806f-6e6eeb617e84?iframe_resize_id=assessment_practice_id_b4571e71-3134-4642-806f-6e6eeb617e84\" 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-4487\">\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":18,"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":"2851a042-52b2-4881-ac7b-7a4c1ea7c15a, adf288cb-820d-478c-8fc7-8bc342b2d5aa","pb_show_title":"on","pb_short_title":"","pb_subtitle":"","pb_authors":[],"pb_section_license":""},"chapter-type":[],"contributor":[],"license":[],"class_list":["post-4487","chapter","type-chapter","status-publish","hentry"],"part":3801,"_links":{"self":[{"href":"https:\/\/courses.lumenlearning.com\/wm-biology2\/wp-json\/pressbooks\/v2\/chapters\/4487","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":10,"href":"https:\/\/courses.lumenlearning.com\/wm-biology2\/wp-json\/pressbooks\/v2\/chapters\/4487\/revisions"}],"predecessor-version":[{"id":8577,"href":"https:\/\/courses.lumenlearning.com\/wm-biology2\/wp-json\/pressbooks\/v2\/chapters\/4487\/revisions\/8577"}],"part":[{"href":"https:\/\/courses.lumenlearning.com\/wm-biology2\/wp-json\/pressbooks\/v2\/parts\/3801"}],"metadata":[{"href":"https:\/\/courses.lumenlearning.com\/wm-biology2\/wp-json\/pressbooks\/v2\/chapters\/4487\/metadata\/"}],"wp:attachment":[{"href":"https:\/\/courses.lumenlearning.com\/wm-biology2\/wp-json\/wp\/v2\/media?parent=4487"}],"wp:term":[{"taxonomy":"chapter-type","embeddable":true,"href":"https:\/\/courses.lumenlearning.com\/wm-biology2\/wp-json\/pressbooks\/v2\/chapter-type?post=4487"},{"taxonomy":"contributor","embeddable":true,"href":"https:\/\/courses.lumenlearning.com\/wm-biology2\/wp-json\/wp\/v2\/contributor?post=4487"},{"taxonomy":"license","embeddable":true,"href":"https:\/\/courses.lumenlearning.com\/wm-biology2\/wp-json\/wp\/v2\/license?post=4487"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}