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Saturday, 4 August 2018

What are the invertebrates hormones and their functions?




Invertebrates hormones


The survival of any group of animals depends on growth, maturation, and reproduction that consist of the most favorable seasons of the year so that climate and food supply are optimal. Thus, chemicals regulating growth, maturation, and reproduction probably were among the first hormones to appear during the course of animal evolution.
The first hormones were probably neurosecretions thus, the horomones that are present in invertebrate animals are neurosecretions called neuropseptides. In these invertebrates animal some more complex hormones are present. We are discusses following invertebrates hormones.

ANNELIDS

 Annelids contain the well developed nervous system, and circulatory system, and  also have a large coelom, their well-developed endocrine control of physiological functions is not surprising. Annelids Endocrine systems are perform following function with morphogenesis, development, growth, regeneration, and gonadal maturation. For example,
In leeches, a neuropeptide stimulates gamete development and triggers color changes. Osmoregulatory hormones have been reported in oligochaetes, and a hyperglycemic hormone that maintains a high concentration of blood glucose has been reported for the oligochaete, Lumbricus.
 Polychaetes, have juvenile hormone that inhibits the gonads and stimulates growth and regeneration. Another hormone, gonadotropin, stimulates the development of eggs.

PORIFERA
The porifera that also called sponges do not have special endocrine glands. So, sponges lack neurons, and do not have neurosecretory cells.

CNIDARIANS
The nerve cells of Hydra have a growth-promoting hormone that stimulates budding, regeneration, and growth. For example, when the hormone is present in the medium in which fragments of Hydra are incubated, “head” regeneration is accelerated. This so-called “head activator” also stimulates mitosis in Hydra.

MOLLUSCS
The ganglia have the ring that part the central nervous system of molluscs that secrete neurosecretory cells. This cells produce neuropeptides  that help to regulate heart rate, kidney
function,
and energy metabolism.
In some cephalopods, the optic gland in the eye stalk produces one or more hormones that increasse egg development, proliferation of spermatogonia, and also increase the development of secondary sexual characteristics.

Several gastropods, such as, land snail Helix, have the specific hormone stimulates spermatogenesis; one other hormone, termed egg-laying hormone, stimulates egg development; and hormones from the ovary and testis stimulate accessory sex organs. But In all snails, a growth hormone controls shell growth.

ECHINODERMS

 Echinoderms are deuterostomes, they are more closely related to the chordates and protostome invertebrates. But some endocrine systems of echinoderms provide produce hormone that are different from the chordate. However, that the radial nerves of sea stars consist of the a neuropeptide called gonad-stimulating substance. Neuropeptide hormone when inserted or injected into a adult sea star, it induces immediate shedding of the gametes, spawning behavior, and meiosis in the oocytes. The neuropeptide also release hormone  that is called maturation-inducing substance, which has various effects on the reproductive system.

NEMERTEANS
Nemerteans have a larger brain, that composed of a dorsal and ventral pair of ganglia connected by a nerve ring. The neuropeptide that these ganglia produce that control gonadal development and to regulate water balance.

NEMATODES
Nematodes do not have classical endocrine glands, they do have neurosecretory cells  that associated with the central nervous system. The neuropeptide that produces from this nervous tissue controls ecdysis of the old cuticle. But note this point neuropeptide are release only when a new cuticle is produced and stimulates the excretory gland to secrete an enzyme (leucine aminopeptidase) into the space between the old and new cuticle. The accumulation of fluid in this space causes the old cuticle to split and be shed.

PLATYHELMINTHS
Platyheminthes neurosecretory cells are identified in various flatworms over 30 years ago. Neurosecretory cells of this phylum are found in the cerebral major nerve cords and ganglion. The neuropeptides that the cells produce function in regeneration, asexual reproduction, and gonad maturation.
For example, neurosecretory cells  that are present in the scolex of some tapeworms control the shedding of the proglottids or the initiation of strobilization.

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