Question

Which of these statements is correct? a. All major organs are formed during embryonic development. b. The hands and feet begin as paddlelike structures. c. The heart is at first tubular. d. The placenta functions until birth occurs. e. All of these are correct statements.

Short answer

All of the statements (A, B, C, and D) are true regarding human development and pregnancy. Therefore, the correct answer is E: All of these are correct statements.

Step-by-step solution

Read the statements carefully.

First, read all of the statements and try to recall any related information about human development and the placenta.

Evaluate Statement A.

"All major organs are formed during embryonic development." This statement is true because the embryonic stage of development, which lasts from the second week after fertilization until approximately the eighth week, is when all major organs are formed.

Evaluate Statement B.

"The hands and feet begin as paddlelike structures." This statement is also true. During the early stages of limb development, both hands and feet start as paddlelike structures called limb buds. These buds later develop into fully formed hands and feet.

Evaluate Statement C.

"The heart is at first tubular." This statement is true. Early in embryonic development, the heart begins as a simple tube, called the heart tube. Over time, the tube folds and remodels to form the four chambers we recognize in a fully developed heart.

Evaluate Statement D.

"The placenta functions until birth occurs." This statement is true. The placenta is a temporary organ that provides nutrients and oxygen to the developing baby and removes waste. It is an essential part of supporting a healthy pregnancy and remains functional until birth, when it is expelled from the mother's body along with the baby.

Choose the correct answer.

Since all of the provided statements A, B, C, and D are true, the correct answer is E: All of these are correct statements.

Key concepts

Organ Formation

Organ formation is a crucial aspect of embryonic development, which typically occurs during the first eight weeks after fertilization. During this time, the embryo undergoes rapid growth and differentiation to form the major organs of the body. This process is often referred to as organogenesis.

In these early weeks, the embryo lays down the basic framework of the body. The initial step involves the differentiation of the three germ layers: the ectoderm, mesoderm, and endoderm. Each of these layers gives rise to different organs and tissues:

• Ectoderm: Develops into the nervous system, skin, and parts of the eye.
• Mesoderm: Forms the muscles, circulatory system, and bones.
• Endoderm: Creates the digestive and respiratory systems.

Organ formation is a complex and highly coordinated process, with each organ developing at specific times during this embryonic phase. Any disruptions during this period can lead to congenital anomalies. It's fascinating to realize that so much of the human body's complex structure is planned out and initiated at this early stage in development.

Limb Development

Limb development is another fascinating aspect of embryonic growth. The process begins early in the embryonic stage, often around the fourth week of gestation. This is when tiny limb buds appear on the sides of the embryo.

These limb buds initially resemble paddlelike structures and are composed of a core of mesoderm (which will develop into muscles and bones) covered by ectoderm (which forms the skin). As the embryo grows, these paddles differentiate into more distinct shapes:

• Hands and feet develop first as broad, flat paddles.
• Fingers and toes form as indentations appear between the paddle segments.
• Further growth and refinement lead to the typical hand and foot structures.

The entire process is highly regulated by a series of genetic signals. Specific genes guide the formation of structures within precise time windows, ensuring organized and symmetrical growth. It's an impressive example of biological engineering, deeply rooted in genetic instructions.

Heart Development

Heart development is a remarkable journey that begins very early in embryonic life. Initially, the heart starts as a simple tube—a crucial stage that sets the foundation for the fully developed four-chambered heart.

The development process involves complex remodeling and folding of this tubular structure:

• The heart tube forms a series of bends, creating a loop structure.
• These loops transform into the atria and ventricles of the heart.
• Subsequent cell migration and differentiation lead to the formation of septa and valves, necessary for proper function.

By the end of the embryonic period, typically around the eighth week, the heart has taken on its definitive structure. This rapid and precise development is vital because the heart is one of the earliest organs to start functioning, pumping blood to support the growing embryo.

Placenta Function

The placenta plays a vital role during pregnancy, functioning as a life-support system for the developing fetus. This temporary organ forms early in pregnancy and performs critical functions to sustain fetal development.

Key roles of the placenta include:

• Nutrition: Transfers nutrients from the mother’s blood to the fetus, supplying essential glucose, amino acids, and vitamins.
• Gas Exchange: Facilitates the exchange of oxygen and carbon dioxide between maternal and fetal blood.
• Waste Removal: Removes waste products such as urea and creatinine from fetal blood.
• Hormone Production: Secretes hormones to support pregnancy, including human chorionic gonadotropin (hCG) and progesterone.

The placenta also acts as a barrier, providing some protection against infections and harmful substances. It functions efficiently until birth, when it is expelled from the mother’s body. Understanding the placenta's role underscores its significance in fetal health and successful pregnancy outcomes.