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Chapter 34: Problem 27

Gastrulation is the process in which the cells in the blastula rearrange themselves and form three layers of cells. Each layer will differentiate into a different organ system. At what point of development do the major organs begin to develop? a. fertilization b. first trimester c. second trimester d. third trimester

Short Answer

Expert verified
b. first trimester

Step by step solution

01

Understand the Question

The question is asking at which stage of human development do the major organs begin to develop.
02

Define Key Terms

Identify what each option represents in terms of human development: a. Fertilization: the union of sperm and egg. b. First Trimester: the first three months of pregnancy. c. Second Trimester: the fourth to the sixth months of pregnancy. d. Third Trimester: the seventh to the ninth months of pregnancy.
03

Recall Developmental Milestones

Recall that organogenesis, the process where the major organs start to form, typically occurs during the embryonic period, which is part of the first trimester.
04

Select the Correct Answer

Using the information from the previous steps, determine that major organs start to develop during the first trimester.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

blastula rearrangement
The process of gastrulation involves the transformation of a blastula, a small ball of cells, into a structure with three layered cells known as the germ layers.
During gastrulation, these cells rearrange and migrate into specific positions.
This transformation is crucial as each layer, called the ectoderm, mesoderm, and endoderm, will develop into various parts of the human body.
  • The ectoderm forms the skin and nervous system.
  • The mesoderm forms muscles, bones, and the circulatory system.
  • The endoderm forms the digestive system and internal organs.
This rearrangement not only sets the stage for complex organ development but also marks the beginning of the next stage in development: organogenesis.
organogenesis
Organogenesis is the stage where the three germ layers formed during gastrulation begin to differentiate into major organs. This process starts in the embryonic period, which is a part of the first trimester.
Several crucial developments occur during organogenesis:
  • The heart begins to beat.
  • The brain and spinal cord start forming.
  • Rudimentary organs such as kidneys, liver, and lungs start to develop.
Organogenesis is essential for creating the basic structures that will later grow and become fully functional. During this stage, the embryo is highly sensitive to external substances, so any harmful exposures can significantly affect organ development.
embryonic period
The embryonic period spans from fertilization until the end of the eighth week of pregnancy, falling within the first trimester. During this time, the basic building blocks for the baby's body are established.
This period is marked by several key events:
  • Gastrulation, where the blastula transforms into three germ layers.
  • Neurulation, where the neural tube that becomes the central nervous system forms.
  • Folding and shaping of the embryo, setting the basic body plan in place.
The embryonic period is followed by the fetal period, wherein the formed structures continue to grow and mature.
first trimester development
The first trimester is from weeks 1 to 12 of pregnancy and is a critical time for the baby鈥檚 development. During this phase, the groundwork for all major body systems is established.
Key highlights of first trimester development include:
  • From week 1-4, fertilization and gastrulation occur, leading to the formation of a foundation for major tissues and organs.
  • By weeks 4-8, organogenesis is in full swing, where the heart forms and begins to beat, and the tiny limbs start to bud.
  • By week 12, the baby starts to resemble a small human, with all major organs present and beginning to function at a rudimentary level.
This trimester is foundational, and any disruptions can have significant lifelong impacts.
human development stages
Human development is typically divided into several stages, each with distinct milestones:
  • Fertilization: The union of sperm and egg to form a zygote.
  • Blastula stage: Multiple cell divisions resulting in a blastula.
  • Gastrulation: Rearrangement of the blastula into three germ layers.
  • Embryonic period: Early organ formation including organogenesis, lasting until the first eight weeks.
  • Fetal period: From the end of the eighth week to birth, focusing on growth and maturity.

Understanding these stages helps in grasping how complex organisms like humans develop from a single cell into a full-fledged body with diverse systems.

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Most popular questions from this chapter

Explain the fate of the newly released secondary oocyte after ovulation. a. If it fuses with a sperm, the resulting zygote enters the cervix for implantation. If it is not fertilized, it will return to the oviduct. b. If it fuses with a sperm, the resulting zygote enters the uterus for implantation. If it is not fertilized, it will return to oviduct. c. If it fuses with a sperm, the resulting zygote enters the uterus for implantation. If it is not fertilized, it will degrade and exit the body. d. If it fuses with a sperm, the resulting zygote enters the cervix for implantation. If it is not fertilized, it will degrade and exit the body.

How is an oocyte released from a human ovary so it can enter the oviduct? a. the beating action of the flagellum on the oocyte b. the force of the follicular ejection directing the oocyte into the oviduct c. the wavelike beating of cilia lining the oviduct d. muscular contraction of the ovaries

A couple has been trying to conceive for some time and goes to an endocrinologist for advice. If the endocrinologist diagnoses an obstruction in the oviducts of the female, what type of treatment can she recommend? a. opting for in vivo fertilization or ligation of the fallopian tubes surgically so that the tubes are sealed b. opting for in vivofertilization or removal of the obstruction surgically and then re-ligation of the ends of the fallopian tubes c. opting for in vitro fertilization or ligation of the fallopian tubes surgically so that the tubes are sealed d. opting for in vitro fertilization or removal of the obstruction surgically and then re-ligation of the ends of the fallopian tubes

What is the nature of the oogonium and the secondary oocyte? Which process results in the formation of the secondary oocyte? a. A diploid oogonium forms a haploid oocyte by the process of mitosis. b. A haploid oogonium forms a diploid oocyte by the process of meiosis. c. A diploid oogonium forms a haploid oocyte by the process of meiosis. d. A haploid oogonium forms a haploid haploid oocyte by the process of meiosis.

Which of the following statements regarding early embryonic stages is false? a. The endoderm, mesoderm, and ectoderm are germ layers. b. The trophoblast is a germ layer. c. The inner cell mass is a source of embryonic stem cells. d. The blastula is often a hollow ball of cells.
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