together behind the retina due to their photoreceptors facing forward instead ofbackwards as in vertebrates.The most advanced mollusks are the cephalopods… ex. octopus and squids with some of the best vision on the planetHormones-the signals of the endocrine system are transmitted to the appropriate target organ via bloodTypes of chemical messengersoNeurotransmitters- jump synapses; localoHormones affect cells at a distance; involve blood. “Endocrine”oExocrine refers to secretion to the outside of the body. Pheromomes signal between organismsoParacrine refers to localized effects. Ex: organ growth and repair, cell positioningLipophilic hormones:
oNon-polar; and fat solubleoNeed to use transport proteins to travel through bloodoEnter cells and bind to transcription factors to effect DNA transcription; and are slow-acting (hours to days)Hydrophilic hormones:oOften polar; and blood plasma (water) solubleoDo not need transport proteins to travel through bloodoBind to cell receptors and activate protein kinases/induce signal transduction; and are fast-acting (minutes to hours)Lipophillic hormone exampesoSteroids, thyroid hormones, retinoids, vitamin D, and vitamin AoWork more slowly over a longer time period for changes that need to be gradual such as steroids/menstrual cycleHydrophilic hormone examplesoPeptide, protein, glycoprotein hormones, and catecholaminesWork much faster but for a short period of timeExample: sugar homeostasis (insulin and glucagon) or in an emergency system (adrenalin)Type I diabetes is due to the pancreas’ inability to produce the hydrophilic hormone, insulin, and is treated by insulin injections. What is true?oInsulin binds to cell receptors and signal transduction occurs so that glucose can either be moved out the blood and into cells for energy needs or stored as glycogen for later use.Lipophilic: binds to intracellular receptors thus regulating gene expressionHydrophilic: binds to cell membrane receptors to stimulate signal transduction pathwaysHow could blocking hormone production or binding decrease cancerous tumor growth?oBy blocking estrogen binding to that disuse it can slow the growth rate and or decrease the cancerous growth.oBy blocking estrogen production, one may be able to slow the growth of tumors.How does tamoxifen work to help reduce growth of breast cancer?oBlocks the action of estrogen thereby slowing the growth rate of the cancerous cellsADH- Antidiuretic HormoneoInvolved in osmotic balance.oSynthesized in the hypothalamusoReleased by posterior pituitary (neurohypophysis)oIncreased blood solute concentration (dehydration) cases the release of ADHoIn the PRESENCE of ADH, the kidneys reabsord water before forming urine.