BIOEE 1780 Lecture Notes - Lecture 24: Digestion, Hydrostatic Skeleton, Desmosome
31 Oct 2016
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Document Summary
Hox genes: help lay out the basic body forms of many animals, directing instruction as an embryo develops. Tight junctions: seal adjacent epithelial cells in a narrow band just beneath their apical surface. Gap junctions: narrow, intercellular channels that permit the free passage between the cells of ions and small molecules. Desmosomes: localized patches that hold 2 cells together; common in epithelia (e. g. skin) Animals are generally characterized by multicellularity, heterotrophic metabolism, internal digestion, and motility. Although none of these traits are unique to animals, their similarities in hox genes, innovative cellular connections (tight junctions and gap junctions, desmosomes), and the derivation of an extracellular matrix support the hypothesis that animals are monophyletic. Major themes in the diversification of animals: levels of organization. Tissue level (first observed in ctenophores and cnidarians) Organs and organ system level (first observed in the bilaterians) Radial symmetry - cnidarians, ctenophores, and the adult stage of many echinoderms.
