Gastrulation is a turning point in development. Cells migrate and invaginate, establishing the three germ layers—ectoderm, mesoderm, and endoderm—from which all tissues and organs of the body later develop.
Basic Knowledge
Gastrulation: The process in which cells of the blastula migrate and invaginate to form three germ layers.
The point of invagination is called the blastopore, and the internal space formed is called the archenteron. Depending on whether the blastopore later becomes the anus (deuterostomes = vertebrates and echinoderms) or the mouth (protostomes = arthropods and mollusks), animals are divided into two major groups.
Germ layers and their derivatives:
・Ectoderm: Epidermis, nervous system, sense organs, lens of the eye, oral epithelium, and others.
・Mesoderm: Muscles, skeleton, circulatory system, kidneys, reproductive organs, dermis, and others.
・Endoderm: Digestive-tract epithelium, lungs, liver, pancreas, thyroid gland, and others.
Gastrulation in frogs: The blastopore forms on the vegetal-pole side, and cells on the animal-pole side invaginate inward through the blastopore (involution), forming the endoderm and mesoderm. The layer remaining on the surface becomes the ectoderm.
Answer: (a) Spinal cord = ectoderm (derived from the neural tube) (b) Skeletal muscle = mesoderm (c) Digestive-tract epithelium = endoderm (d) Kidney = mesoderm (e) Lung = endoderm
- Ectoderm → epidermis, nervous system, sense organs
- Mesoderm → muscles, bones, circulatory system, kidneys, reproductive organs
- Endoderm → digestive-tract epithelium, lungs, liver, pancreas
- Blastopore → becomes the anus in deuterostomes (vertebrates)
- In protostomes (arthropods), the blastopore becomes the mouth
- Archenteron = the precursor of the digestive tract formed inside the embryo
Practice
- Name two organs that differentiate from each of the three germ layers (ectoderm, mesoderm, and endoderm).
- Explain the difference between deuterostomes and protostomes in terms of the fate of the blastopore.
- Explain the changes in cell-cell adhesion that are important when cells invaginate during gastrulation.