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Invertebrate Endocrine System Essay

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 they then function as molting hormones. 3. In adults, they may act as gonadotropins.

2. Members of the CHH (Crustacean Hyperglycemic Hormone) family of neuropeptides appear to be present from embryos to adults and a single peptide can have multiple functions (acting as a molt-inhibiting hormone and as a hyperglycemic hormone). 3. MF (Methyl farnesoate) may also function as a developmental hormone in larvae and as a gonadotropin in adults.

Molt Inhibiting Hormone
* Produced in the eyestalks  * Removal of eyestalks results in initiation of the processes seen during proecdysis * epidermal cells – cells divide form new cuticle * Calcium is removed from old exoskeleton – becomes soft – able to be broken * Hepatopancreas (storage organ) – mobilizaton of reserves * Inhibiting effect on the Y-organ (endocrine gland)

* If you remove the Y-organ – you remove the source of the molting hormone = ecdysone. * Removal only has an effect when it is done during the intermolt period, not during proecdysis. * During proecdysis the ecdysone is already there – it has already been produced. Therefore removal will have no effect. * Implanting Y-organs will during the intermolt period will induce the processes seen during proecdysis

Mandibular Glands
* Secrete JH-like compounds – morphogens
* methyl farnesoate
* farnesoic acid
* Responsible for juvenile characteristics
* Presence results in retention of juvenile characterisitcs
* However actions are not totally clear

Methyl farnesoate (MF)
* It is related to the insect juvenile hormone.
* MF is secreted by the mandibular organ
* There is some evidence that MF may have a role in larval development by acting as a hormone that retards development (a juvenilizing factor) * In adults, MF may function in a reproductive capacity.

Juvenile Hormone

Crustacean Cardioactive Peptide (CCAP)
* Hormone that causes acceleration of heartbeat
* amplitude and frequency increase
* Production site – The neurosecretory cells (NSC) in thoracic ganglion * Release site – pericardial organ = neurohemal organ – near heart * Target – neurons that innervate the heart (large cardiac ganglion cells) * No structural homology to any known peptide

Androgenic hormone
* Androgenic glands – endocrine glands in male crustaceans * Responsible for masculine characteristics – act on:
* Gonads – spermatogenesis in the testes
* Epidermis – secondary male characteristics
* specialized appendages
* i.e. large claws

Vitellogenesis Inhibiting Hormone (VIH)
* Vitellogenesis – production of yolk proteins
* VIH inhibits egg development

Mollusks
* Mollusks are the most diverse of the invertebrate phyla, being second to the insects in number of identified species.
* They comprise:
1. Bivalvia – clams, oysters, mussels
2. Cephalopoda – octopus, squid
3. Gastropoda – snails, slugs
* Prosobranchs – Crepidula
* Opisthobranchs – Sea Hare Aplysia
* Pulmonates – Snails
* Stylommatophora – terrestrial – land snails – Helix
* Basommatophora – aquatic snails – Lymnea

Notes:

* The endocrine systems of the various classes of mollusks and even of major groups of gastropods – prosobranchs, opisthobranchs, and pulmonates – differ considerably, reflecting extreme differences in morphology and life histories. * This can be exemplified by the use of vertebrate-type steroids, which do occur and play a functional role in prosobranchs. In contrast, there is no indication for pulmonates using steroids. * Recently, the first estrogen receptor sequence for an opisthobranch mollusk, the sea hare Aplysia californica, was published. * Estrogen and androgen receptors occur in a number of marine and freshwater prosobranchs * The prosobranch mollusks and the echinoderms use at least partially or even totally comparable hormones as vertebrates so that vertebrate-type sex steroids are produced in these groups and play a functional role. * Nevertheless, firm evidence of the role of these steroids in the endocrine system of invertebrates is still lacking for most phyla.

Reference
Chanco, Christine R. (2005). Endocrine System. General Zoology Lecture Manual. ACNN Printing Press. pp137 Barnes, Robert D. (1980). Invertebrate Zoology. Philadelphia: W. B. Sauders Co., 1089 pp. Storer, Tracy I., et al. (1979) . General Zoology. New York: McGraw-Hill Book Co., Inc., 902 pp. downloaded December 7, 2012. <kgaafar.com/uploads/UG-04-11.ppt>


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