Serosa

Definition

The outermost extraembryonic membrane in developing amniotes and many arthropods, derived from mesoderm and ectoderm, that encloses the yolk and embryo and secretes serous fluid to reduce friction during growth and movement. In insect embryology, the serosa forms from the blastoderm and surrounds the amnion, degenerating after dorsal closure as the larval cuticle is secreted. The term also denotes the serous membrane (mesothelium) lining body cavities and covering visceral organs in vertebrates.

Etymology

New Latin, from Medieval Latin serosus 'watery, serous', from Latin serum 'whey, watery fluid'

Example

In the grasshopper embryo, the serosa spreads over the yolk surface and fuses with the amnion at the serosal knot before breaking down to allow the embryo to expand during katatrepsis.

Synonyms

• serous membrane

Related Terms

• amnion
• extraembryonic membrane
• mesothelium
• peritoneum
• pleura
• pericardium
• Blastoderm
• katatrepsis
• dorsal closure

Usage Notes

In arthropod literature, 'serosa' specifically refers to the outer extraembryonic membrane; contrast with 'amnion' (inner membrane). In vertebrate anatomy, the same word refers to any serous membrane lining body cavities. The adjective 'serosal' describes features of or pertaining to this membrane. Not to be confused with 'serose' (a taxonomic epithet in several insect families).