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Biol 1106 Lesson 11: Endocrine SystemThe signals of the endocrine system are transmitted to the appropriate target organ via blood.Types of chem. Messengers:Neurotransmitters: jump synapses; local. Paracrine refers to localized effects ex. Organ growth and repair, cell positioning. Hormones affect cells at a distance; involve blood. “Endocrine”. Exocrine refers to secretion to the outside of the body. Pheromones signal between organisms.Major human endocrine organs:Adrenal glands and pancreas are not under the control of the nervous system; instead they respond to chemicals in the bloodHormone types:Polar: Peptides/ Proteins Ex. Insulin. Nonpolar lipophilic hormone: Slow-acting with longer duration. Bindto hormone-activated transcription factors to affect DNA transcription. Polar Hydrophilic hormones: Fast-acting with shorter duration. Activate protein kinases to phosphorylate proteins.Why both? Some hormones work really fast but for a short period of time, for example in sugar homeostasis or in an emergency system. Some hormones that work more slowly over a long time period,for changes that need to be gradual such as steroids/menstrual cycle, etc.