Insect Endocrine System PDF

INSECT ENDOCRINE SYSTEM Learning outcomes To know the parts and functions of the insect endocrine system notesonzoology.com Hormones chemical messengers that are secreted directly into the blood, which carries them to organs and tissues of the body to exert their functions Inse...

INSECT ENDOCRINE SYSTEM Learning outcomes To know the parts and functions of the insect endocrine system notesonzoology.com Hormones chemical messengers that are secreted directly into the blood, which carries them to organs and tissues of the body to exert their functions Insect hormones Brain hormones Molting hormones Juvenile hormones have been used commercially to control insect populations. Concept of Hormonal Control of Molting and Metamorphosis Sir Vincent Wigglesworth Used blood-sucking bug Rhodnius prolixus A hormone that actually prevented the development of adult characteristics in R. prolixus was juvenile hormone Wikipedia.org Critical Period a time period when the brain is necessary for its hormonal influence to be exerted Endocrine Glands 1) neurosecretory cells within the central nervous system, and 2) specialized endocrine glands such as the corpora cardiaca, corpora allata, and the prothoracic glands. Neurosecretory Cells Located in the protocerebrum of the insect responsible in insects for the coordination and control of bodily functions such as feeding, metabolism, excretion, reproduction, and development Corpora Cardiaca a pair of organs often closely associated with the aorta, and often forming part of its wall cardiaca store and release hormones from the neurosecretory cells of the brain to which they are connected by 1 or 2 pairs of nerves Corpora Allata connected to the corpus cardiaca and the subesophageal ganglion hormones secreted by the corpora allata are referred to as juvenile hormones or "JH." Prothoracic Glands a pair of diffuse glands at the back of the head or in the thorax stimulated by the brain hormone to produce another hormone called molting hormone, also known as ecdysone www.cmillanhighered.com Prothoracicotropic Hormone Originally described as “brain hormone” secreted by a neurohemal organ, the corpus cardiacum (in some insects the corpus allatum secretes PTTH) released in response to environmental stimuli stimulates the production of ecdysone by the prothoracic gland Juvenile Hormone Also called Neotenin First discovered by Vincent Wigglesworth Ensures growth of larva but prevents metamorphosis thus it is called Inhibitory or Status Quo secreted by a pair of endocrine glands behind the brain called the corpora allata Juvenile Hormone The secretory cells of corpora allata are active during larval molts Inhibits the genes that promote development of adult characteristics (e.g. wings, reproductive organs and external genitalia) At the last larval stage or nymphal stage, the corpora allata become atrophied (shrink) and stops producing juvenile hormone Ecdysone/Molting hormone Prothoracic glands are activated to secrete ecdysone Insect molting hormones are generally called ecdysteroids Ecdysone and other ecdysteroids also appear in many plants mostly as a protection agent (toxins or antifeedants) against herbivorous insects Eclosion hormone triggers ecdysis behavior at the end of each molt Towards the end of apolysis, ecdysteroid concentration falls, and neurosecretory cells in the ventral ganglia begins secreting eclosion hormone Bursicon A hormone that causes hardening and darkening of the integument (tanning) due to the formation of quinone cross-linkages in the exoskeleton (sclerotization)  HORMONES INVOLVED IN INSECT DEVELOPMENT Prothoracicotropic hormone, PTTH A neuropeptide secreted by brain neurosecretory cells. the target is prothoracic gland cells; it stimulates secretion of ecdysone or related ecdysteroids. Ecdysone, ecdysteroids steroid molting hormones. the main target is epidermal cells; it has several molecular forms and promotes synthesis of new cuticle. Juvenile hormone, JH “status quo” hormone that determines the type of cuticle secreted by epidermal cells and keeps ecdysone from forcing precocious metamorphosis; it has several molecular forms. HORMONES INVOLVED IN INSECT DEVELOPMENT Eclosion hormone, ETH eH released into hemolymph; stimulates Inka cells to make massive secretion of PetH and etH, leading to preecdysis II and ecdysis. Bursicon The tanning hormone, a neuropeptide from nervous system that promotes cuticle.