CHAPTER 49 Chemical Signals in Animals PPT Notes 5 7 2014 cells of CNS endocrine system release molecules hormones in response to external stimuli internal conditions hormones have a longer lasting effect response than action potentials electrical impulses on small pops of cells both electrical chemical signals coordinate activities of cell throughout body endocrine system produces chemical signals secretes into bloodstream chemical signals hormones have concentrations but effects on target cells of animal ex growth hormone GH stimulates mitosis growth removal of pituitary gland makes animal stop growing 5 categories of chemical signals in animals autocrine signals act on same sell that secretes them cytokines are autocrine signals that amplify response of cell to stimulus ex interleukin 2 paracrine signals diffuse locally act on neighboring cells insulin glucagon somatostatin cross categories act as both paracrine signals hormones trio produced by cells known as islets of Langerhansin pancreas control blood sugar levels may act at a distance secrete into bloodstream to control blood sugar levels 3 molecules paracrine endocrine endocrine signals hormones produced secreted by specialized cells or discrete organs glands carried btwn distant cells by bodily fluid neural signals neurotransmitters diffuse a short distance from presynaptic cell to postsynaptic cell binding to membrane receptor causes in membrane potential short lived quickly removed broken down neuroendrocrine signals neurohormones released from neurons still considered hormones bc carried by bodily fluids act on distant cells unlike neural signals do not act on at synapse ex antidiuretic hormone endocrine nervous systems work together to regulate response to stimulus 3 hormone signaling pathways regulated by negative feedback feedback inhibition to regulate homeostasis endocrine pathway sends hormones directly from endocrine to effector cells 1 hormones produced by effector cells feed back to endocrine cells hormone production 2 effector hormone feeds back to neuroendrocrine neuroendrocrine to endocrine pathways 3 endocrine signals released in response to electrical signals that modulate signal from nervous system neuroendrocrine pathway releases neuroendrocrine signals that act directly on effect or cells CNS to endocrine pathway neuroendrocrine signals stimulate cells in endocrine system stimulated cells make endocrine signal that acts on effector cells endocrine system glands secrete hormones into bloodstream tissue organs that compose endocrine system vary among animals ex neurons making secreting hormones important in insects for molting metamorphosis etc ex salmon secrete hormone that regulates Ca2 ion concentration o major human endocrine system glands pituitary gland sits below hypothalamus has distinct anterior posterior regions thyroid gland in neck parathyroid glands 4 embedded in thyroid gland kidneys are in posterior part of abdominal cavity adrenal glands sit atop kidneys pancreas endocrine component in anterior part of abdominal cavity ovaries testes in below pelvic cavity some glands not a part of endocrine system some secrete hormones although not organized into glands ex exocrine glands that deliver secretions via ducts into a space that is not circulatory system 3 chemical families of animal hormones polypeptides chains of amino acids linked by peptide bonds o o o o o o o o o o o o o 5 7 2014 all not lipid soluble bind to receptors on surface of target cell amino acid derivatives most not lipid soluble bind to receptors on surface of target cell thyroxine lipid soluble amino acid derivative exception steroids family of lipids distinguished by 4 right structure o o lipid soluble diffuse through plasma membrane bind to receptors inside target cell a single hormone can have a variety of effects several different hormones may affect the same aspect of physiology o 3 areas of activity coordinated by hormones development growth reproduction environmental response homeostasis 1 development growth reproduction growth sex hormones promote cell division growth sexual differentiation ex metamorphosis process where insect amphibian goes from larvae to adult T3 thyroid hormone trioodothyronine produced bc of brain signals responsible for most changes in metamorphosis in amphibians T3 in juveniles has 3 possible effects growth formation of new structures cell death of cell structure function in insects larvae molt then form pupal stage juvenial hormone ecdysone interact JH levels ecdysone induce growth by molting JH levels ecdysone triggers metamorphosis transition from adulthood to sexual maturity in vertebrates hormones also direct anatomical physiological changes later in life of reproductive organs primary sex determination dictate whether gonads become testes or ovaries controlled by genes on sex chromosomes NOT hormones testes and ovaries produce different hormones w different effects on reproductive development testes produce testosterone mullerian inhibitory substance testosterone induces development of male reproductive system Mullerian inhibitory substance inhibits female productive system development ovaries produce steroid hormone estradiol estradiol in estrogen molecule family needed for female reproductive system development puberty occurs w surges of sex hormones developmental s that make adult phenotype reproductive capability hormones regulate seasonal preproduction in some species sperm production menstrual cycle endocrine disruptors chemicals that disrupt hormone action xenoestrogens bind to estrogen receptors cause estrogen like effects atrazine herbicide that causes reproductive abnormalities Bisphenol A BPA abnormal brain development reproductive tissue cancer risk 2 response to environmental challenges hormones regulate short term and long term responses short term rxn fight or flight response triggered by sympathetic nervous system sympathetic nerves stimulate adrenal gland to release epinephrine adrenaline some sympathetic nerves release norepinephrine directly onto target cells catecholamines molecules that are neurotransmitters hormones include adrenaline norepinephrine neurotransmitters gene expression in neurons hormones gene expression in target cells long term rxn cortisol produced in adrenal gland ensures constant supply of glucose for brain prioritizes brain needs while other tissues organs become expendable cortisol is a glucocorticoid manages 3 processes for the maintenance of
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