Embryology Exam Quiz

The placenta is a vital structure formed from the chorionic villi of the embryo and the decidua of the maternal endometrium. It functions as the exchange site for nutrients, gases, and wastes between the maternal and fetal bloodstreams. The placenta not only supports the fetus with necessary nutrients and oxygen but also removes carbon dioxide and metabolic wastes.

The embryonic period is considered complete at the end of organogenesis, which is the process where the embryonic germ layers differentiate into the internal organs of the organism. Typically, this period spans the first eight weeks post-fertilization in humans, after which the embryo is referred to as a fetus.

Hematopoiesis first occurs in the yolk sac, an extra-embryonic structure that provides nutrients to the developing embryo. Early in development, the yolk sac is responsible for generating the initial blood cells and germ cells, playing a critical role in the establishment of the embryo’s circulatory system.

Gastrulation involves significant cell movements where cells from the outer layer of the embryo move inward, forming the three germ layers each with distinct cell fates. This process, essential for establishing the basic body plan, involves complex cellular rearrangements including invagination, ingression, and migration.

The primary role of the trophoblast, the outer cell layer of the blastocyst, is implantation. The trophoblast facilitates the attachment of the blastocyst to the uterine wall and subsequently invades the endometrium, allowing the developing embryo to access maternal blood vessels for nourishment and waste removal.

The mesoderm, one of the three primary germ layers formed during embryonic development, differentiates into several key structures, including the musculoskeletal system. It gives rise to muscles, bones, and connective tissues, as well as the circulatory and lymphatic systems, ensuring structural and functional support for the organism.

The neural tube is formed from the ectoderm, the outermost germ layer. During neurulation, a portion of the ectoderm thickens and folds inward, forming a groove that eventually becomes the neural tube. This structure later develops into the central nervous system, comprising the brain and spinal cord.

Human Chorionic Gonadotropin (hCG) is crucial for maintaining the corpus luteum during early pregnancy. Produced by cells of the embryo, hCG signals the corpus luteum to continue producing progesterone and estrogen to prevent menstruation and support the uterine lining, creating a conducive environment for the embryo to grow.

HOX genes play a crucial role in the development of the anterior-posterior axis by providing cells with positional information during embryo development. These genes regulate the expression of various growth factors that influence cell differentiation and organ development along the head-to-tail axis of the body.

Gastrulation is initiated by the process of cleavage, which is the rapid, successive series of cell divisions that follow fertilization. Cleavage leads to the formation of the blastula, which then undergoes significant cellular rearrangements during gastrulation to form the three primary germ layers: ectoderm, mesoderm, and endoderm. This process lays the foundational structure for all organs and tissues in the organism.