Invertebrate Endocrine System

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Invertebrate Endocrinology

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 their endocrine systems is considerably more variable than in vertebrates, which comprise only part of a single phylum, the Chordata.

The 1st Endocrine System
* As you know Crustacean comprise: Crabs, Lobster, Shrimp, Amphipods (freshwater), Isopods (terrestrial) etc. have the first true endocrine system

Hormones in the Lives of Crustaceans: An Overview
Ernest S. Chang, Sharon A. Chang and Eva P. Mulder
American Zoologist 2001 41(5):1090-1097

* The crustaceans have a particularly complex physiology due to the multiple processes that may overlap and influence each other. * These processes may include dramatically different life stages (from embryo to larva to juvenile to adult), a cyclical molt cycle that can occur many times during the life of the crustacean, and a reproductive cycle that may alter much of the adult physiology.

Growth in Crustaceans
Occurs through molting = ecdysis
Stages of molting
* Proecdysis - preparation for molting
* epidermal cells separate from the old cuticle (apolysis) and divide forming the new exoskeleton * Calcium removed from old exoskeleton
* hepatopancreas - release of energy reserves from storage (animal stops feeding) * Ecdysis
* shedding of the old exoskeleton
* cuticle is soft - rapid uptake of water
* Metecdysis
* Mineral deposition into the new cuticle
* Endocuticle formation
* Feeding begins again
* New tissue formation follows
* Increased DNA and protein synthesis
* tissue replaces water
* Intermolt
* As skeleton and tissue growth nears completion metabolism is shifted to storage of energy reserves into the hepatopancreas Regulation of many processes is involved
* Metabolism
* Water /mineral balance
* Molting process

Crustacean Hormones have multifunctional nature:
1. Ecdysteroids may serve:
1. During embryonic development as morphogens or promote protective membranes 2. From larval to adult life...
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