Overview of the Endocrine System * System of ductless glands that secrete hormones * Hormones are “messenger molecules” * Circulate in the blood * Act on distant target cells * Target cells respond to the hormones for which they have receptors * The effects are dependent on the programmed response of the target cells * Hormones are just molecular triggers * Basic categories of hormones * Amino acid based: modified amino acids (or amines), peptides (short chains of amino acids), and proteins (long chains of amino acids) * Steroids: lipid molecules derived from cholesterol
As You know: * Invertebrates are animals without a backbone. * The invertebrates form all of the major divisions of the animal kingdom called phyla, with the exception of vertebrates. * Invertebrates include the sponges, coelenterates, flatworms, nematodes, annelids, arthropods, mollusks, and echinoderms.
Hormonal System of Invertebrates * Invertebrates hormonal systems are rather poorly understood in comparison with vertebrates * The endocrine systems of invertebrates generally regulate the same processes that are found in vertebrates such as development, growth, and reproduction. * The best understood endocrine systems are those of insects, followed by crustaceans, echinoderms and mollusks, although the latter are perhaps characterized by the most diverse hormonal systems of the invertebrate phyla.
Diversification of hormonal system of Invertebrates 1. Diversified life histories of invertebrates with characteristic events such as the formation of larval forms, often with a succession of different stages and/or pupation, metamorphosis, diapauses or other types of resting stages, which do not occur in vertebrates. 2. Invertebrates represent more than 30 different phyla within the animal kingdom. Consequently, it is not surprising that regulation of the above mentioned processes by