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Human Biology (MindTap Course List)

11th Edition
Cecie Starr + 1 other
Publisher: Cengage Learning
ISBN: 9781305112100

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Chapter
Section
BuyFindarrow_forward

Human Biology (MindTap Course List)

11th Edition
Cecie Starr + 1 other
Publisher: Cengage Learning
ISBN: 9781305112100
Chapter 17, Problem 3RQ
Textbook Problem
168 views

Summarize the development of an embryo and a fetus. When are body parts such as the heart, nervous system, and skeleton largely formed?

Summary Introduction

To summarize: The development of an embryo and fetus and when body parts such as the heart, nervous system, and skeleton are largely formed.

Introduction: Gestation or pregnancy is the period during which an offspring develops within a woman. This involves several developmental stages of fetus. In humans, pregnancy is nearly nine months long, divided into three trimesters, involving several changes in the mother and the growing fetus.

Explanation of Solution

A zygote (single cell after fertilization) multiplies into a multicellular structure called as blastocyst and after implantation it is termed as embryo. During the embryonic developmental stage, the embryo grows, multiplies, and becomes complex.

Stages of tissue development in the embryo

  1. 1. Fertilization and zygote formation:

    Initially, the sperm cell fuses with the oocyte to form a fertilized diploid cell called as a zygote. This process of fusion and formation of a zygote cell is called as fertilization.

  2. 2. Formation of blastocyst:

    The multicellular structure called blastocyst is developed when the zygote undergoes multiple cell divisions.

  3. 3. Formation of germ layers:

    During the third week of embryonic development, three primary germ layers namely- ectoderm, mesoderm, and endoderm are developed from the embryoblast. As the embryo starts to develop, the cells from the germ layers migrate and start to form specialized cells, then to tissues, and finally to organs.

Stages of fetal development

In humans, pregnancy is nearly nine months long, divided into three trimesters, involving several changes in the mother and the growing fetus. The initial stages of embryonic development take place in the first 8 weeks. At this stage, morphogenesis initiates the development of major body system, including the skeletal system and nervous system, and also sex is determined by the end of the period as well. The embryo becomes a fetus with a beating heart at the end of the eighth week. Major growth and structural development occur toward the next two trimesters.

Tabular representation: Table 1 shows the stages (three trimesters) of fetal development.

Table 1: Stages of fetal development

Stages

Weeks of pregnancy

Events

First trimester (1 to 12 weeks)

2

  • • Beginning of fertilization
  • • The zygote (fertilized egg) starts to develop into blastocysts (hollow mass of cells)...

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