BIO 311D 1st Edition Lecture 27 Outline of Last Lecture I Neurons communicate with other cells at synapses II Generation of postsynaptic potentials III Summation of postsynaptic potentials IV Generation of postsynaptic potentials V Modulating signals at synapses VI Neurotransmitters Outline of Current Lecture I Hormones and the Endocrine System II Intracellular Communication III Endocrine Signaling IV Paracrine and Autocrine signaling V Synaptic signaling VI Endocrine Tissues and Organs VII Cellular Response Pathways Current Lecture Hormones and the Endocrine System Hormones and other signaling molecules bind to target receptors triggering specific response pathways Endocrine signaling is just one of several ways that information is transmitted between animal cells All hormones A are lipid soluble molecules B are protein molecules C elicit the same biological response from all of their target cells D are carried to target cells in the blood E Are produced by endocrine glands Intercellular Communication The ways that signals are transmitted between animal cells are classified by two criteria The type of secreting cell The route taken by the signal in reaching its target Endocrine Signaling Hormones secreted into extracellular fluids by endocrine cells reach their targets via the bloodstream Endocrine signaling maintains homeostasis mediates responses to stimuli regulates growth and development Paracrine and Autocrine Signaling Local regulators are molecules that act over short distances reaching target cells solely by diffusion In paracrine signaling the target cells lie near the secreting cells In autocrine signaling the target cell is also the secreting cell Synaptic and Neuroendocrine Signaling In synaptic signaling neurons form specialized junctions with target cells called synapses At synapses neurons secrete molecules called neurotransmitters that diffuse short distances and bind to receptors on target cells In neuroendocrine signaling specialized neurosecretory cells secrete molecules called neurohormones that travel to target cells via the bloodstream Signaling by Pheromones Members of the same animal species sometimes communicate with pheromones chemicals that are released into the environment Pheromones serve many functions including marking trails leading to food defining territories warning of predators and attracting potential mates Endocrine Tissues and Organs In some tissues endocrine cells are grouped together in ductless organs called endocrine glands Endocrine glands secrete hormones directly into surrounding fluid These contrast with exocrine glands which have ducts and which secrete substances onto body surfaces or into cavities Chemical Classes of Hormones Three major classes of molecules function as hormones in vertebrates Polypeptides proteins and peptides Amines derived from amino acids Steroid hormones Lipid soluble hormones steroid hormones pass easily through cell membranes while water soluble hormones polypeptides and amines do not The solubility of a hormone correlates with the location of receptors inside or on the surface of target cells Cellular Response Pathways Water and lipid soluble hormones differ in their paths through a body Water soluble hormones are secreted by exocytosis travel freely in the bloodstream and bind to cell surface receptors Lipid soluble hormones diffuse across cell membranes travel in the bloodstream bound to transport proteins and diffuse through the membrane of target cells Pathway for Water Soluble Hormones Binding of a hormone to its receptor initiates a signal transduction pathway leading to responses in the cytoplasm enzyme activation or a change in gene expression The hormone epinephrine has multiple effects in mediating the body s response to short term stress Epinephrine binds to receptors on the plasma membrane of liver cells This triggers the release of messenger molecules that activate enzymes and result in the release of glucose into the bloodstream Pathway for Lipid Soluble Hormones The response to a lipid soluble hormone is usually a change in gene expression Steroids thyroid hormones and the hormonal form of vitamin D enter target cells and bind to protein receptors in the cytoplasm or nucleus Protein receptor complexes then act as transcription factors in the nucleus regulating transcription of specific genes Multiple Effects of Hormones The same hormone may have different effects on target cells that have Different receptors for the hormone Different signal transduction pathways Signaling by Local Regulators Local regulators are secreted molecules that link neighboring cells or directly regulate the secreting cell Types of local regulators Cytokines and growth factors Nitric oxide NO Prostaglandins In the immune system prostaglandins promote fever and inflammation and intensify the sensation of pain Prostaglandins help regulate aggregation of platelets an early step in formation of blood clots Coordination of Neuroendocrine and Endocrine Signaling The endocrine and nervous systems generally act coordinately to control reproduction and development For example in larvae of butterflies and moths the signals that direct molting originate in the brain In insects molting and development are controlled by a combination of hormones A brain hormone PTTH stimulates release of ecdysteroid from the prothoracic glands Juvenile hormone promotes retention of larval characteristics Ecdysone promotes molting in the presence of juvenile hormone and development in the absence of juvenile hormone of adult characteristics
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