Question

At three months, the embryo has a. become a fetus. b. body systems already. c. a head, arms, and legs. d. ears and eyes, which don't function. e. All but b are correct.

Short answer

The correct answer is option e: All but b are correct. At three months, the embryo has become a fetus (option a), has a head, arms, and legs (option c), and has ears and eyes that don't yet function (option d). Option b is unclear and not considered correct.

Step-by-step solution

Option a: become a fetus

At the three-month mark, the embryo is called a fetus. This is because most of its major organs and body systems have already developed, and the baby will continue to grow and mature during the remaining months of pregnancy. So, option a is correct.

Option b: body systems already

This option is not clear and seems to be incomplete. It is not clear if it refers to the development of body systems in the embryo or their functioning. Since it's unclear, we will not consider this option as correct.

Option c: a head, arms, and legs

At three months, the fetus has a head, arms, and legs. The limbs will continue to grow and develop over the remaining months of pregnancy. So, option c is correct.

Option d: ears and eyes, which don't function

At three months, the fetus has ears and eyes, but they are not fully developed, and the baby cannot see or hear. These organs continue to develop, and their functions will be operational later on in pregnancy. So, option d is correct.

Option e: All but b are correct

Since options a, c, and d are correct but option b is unclear and not considered correct, option e is the correct answer. Therefore, the correct options for this exercise are options a, c, d, and e.

Key concepts

Embryo

An embryo is the term used to refer to the early stages of human development, right after fertilization and through the next eight weeks. During this time, a fertilized egg goes through multiple cell divisions. The embryo forms distinct layers that will later differentiate into various organs and tissues.

The embryo starts off as a small cluster of cells, but quickly grows and begins to take on a more complex structure. The initial stages focus on establishing essential body structures and the blueprint for major systems. By the end of the embryonic stage, the basic shape, including early brain and spinal structures, as well as preliminary heart and limb buds, begins to emerge.

• The embryonic period is critical for laying down the foundational structures that will support later development.
• Any interruptions or abnormalities during this stage can have significant impacts on development.

Fetus

After eight weeks, the embryo is usually referred to as a fetus. This change in terminology signifies a transition to a new stage where growth and maturation become the main focus.

From this point until birth, the fetus will continue to develop the organs and systems initiated during the embryonic stage. While the shape and form of the fetus are established, many of its internal organs are still immature and continue growing.

• The distinction between embryo and fetus is important as it highlights the developmental milestones achieved by the end of the first trimester.
• During the fetal stage, less new structures are formed, and existing ones grow and refine their functions.
• Organ systems begin to work together, setting the groundwork for post-birth adaptation.

Body Systems

Body systems begin forming during the embryonic stage and continue developing throughout the fetal stage. Each system has a unique timetable and pattern of growth, with some reaching maturity before others.

Key body systems include:

• Nervous System: The brain and spinal cord are among the first systems to develop, laying down the framework necessary for future growth and complexity.
• Cardiovascular System: The heart begins to beat during the embryonic stage, pumping blood to support organ development.
• Respiratory and Digestive Systems: These systems continue developing throughout pregnancy, preparing the fetus for breathing and feeding post-birth.

Body systems undergo significant changes during pregnancy, ensuring the fetus is equipped for the external environment after birth.

Fetal Development Stages

Human fetal development is typically broken down into key stages based on changes and milestones. Understanding these stages helps in tracking normal development and spotting potential issues.

**First Trimester (0-12 Weeks):**

• Early body systems form, and the embryo becomes a fetus.
• Critical structures, such as the heart, brain, and basic limb formation, are established.

**Second Trimester (13-26 Weeks):**

• Organ systems continue developing, and the fetus becomes more active.
• Bone structure solidifies, and facial features become more pronounced.

**Third Trimester (27-40 Weeks):**

• Final maturation of organ systems, especially lungs and brain.
• Fetus gains significant weight, preparing for birth.

Monitoring these stages helps healthcare providers ensure that development is on track and that the transition to extrauterine life is smooth.