Chapter 45.docx

Chapter 45 Hormones and the Endocrine System Hormone: molecule that is secreted into the extracellular fluid, it circulates in the blood or hemolymph, and communicates regulatory messages throughout the body Endocrine system is in charge of chemical signaling by hormones Nervous system is a network of specialized cells (neurons) that transmit signals along a dedicated pathway Types of Signaling Molecules Hormones maintain homeostasis mediate responses to environmental stimuli and regulate growth, development, and reproduction Hormones secreted by endocrine cells into the extracellular fluid by endocrine cells reach target cells by bloodstream or hemolymphd Endocrine glands: groups of endocrine cells in ?ductless organs? that also secrete hormones Local Regulators function in paracrine and autocrine signaling, regulate blood pressure, nervous system function, reproduction Secreted molecules that act over short distances and reach their target cells by diffusion Paracrine signaling: target cells lie near the secreting cell Autocrine signaling: molecules act on the secreting cell itself Neurotransmitters and Neurohormones Neurons secrete molecules (neurotransmitters) that diffuse directly to receptors on the target cells Neurosecretory cells specialized neurons found in the brain; secrete molecules that diffuse from nerve cell endings into the blood stream These molecules are a class of hormones called neurohormones (ex. ADH) Pheromones mark trails leading to food, define territory, warn predators, attract mates Chemicals that are released into the external environment Chemical Classes of Hormones Polypeptides Formed by cleavage of a longer polypeptide chain Amines Synthesized from a single amino acid (tyrosine or tryptophan) Steroids Derived from cholesterol (steroid) Cellular Response Pathways Water soluble hormones are secreted via exocytosis travel freely through blood stream bind to surface signal receptors change in cytoplasmic molecules or alter gene transcription Lipid soluble hormones diffuse across membrane of endocrine cells travel through bloodstream bound to transport proteins diffuse into target cell bind to intracellular signal receptors change in gene transcription