Biol 118 1st Edition Lecture 30 Outline of Last Lecture I How Do Sensory Organs Convey Information to the Brain II Mechanoreception Sensing Pressure Changes III Photoreception Sensing Light IV Chemoreception Sensing Chemicals V Other Sensory Systems Outline of Current Lecture I Introduction to Chemical Signals in Animal II Cell to Cell Signaling An Overview III 3 Hormone Signaling Pathways IV Chemical Characteristics of Hormones V How is the Production of Hormones Regulated VI The Hypothalmus Pituitary Axis Current Lecture Introduction to Chemical Signals in Animal In response to external stimuli or internal conditions cells of CNS or endocrine system release molecule hormones o Result in a longer response than the action potential of CNS Group of organs cells that make up the endocrine system produces chemical signals secretes them in the blood stream Cell to Cell Signaling An Overview Animal chemical signals are present in extremely low concentrations but can have enormous effects on their target cells Unlike action potentials which are electrical impulses that have short term effect on a single cell or on a small population of adjacent cells the messages that chemical signals carry have a relatively long lasting effect In combination electrical chemical signals allow animals to coordinate the activities of cells throughout the body Autocrine signals act on the same cell that secretes them o Cytokines best studied autocrine signals amplify the response of a cell to a stimulus These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute o Best example is interleukin 2 secreted by t cells to fight off infections Paracrine signals diffuse locally act on neighboring target cells o Insulin glucagon somatostatin act as paracrine signals but also as hormones Produced by cells known as islets of Langerhans in the pancreas Act locally to control blood sugar levels May also act at a distance Endocrine signals hormones that are produced secreted by specialized cells or discrete organs called glands o Hormones are carried between distant cells by blood or other bodily fluids Neural signals neurotransmitters that diffuse a short distance presynaptic cell to a postsynaptic cell where it binds to a membrane receptor results in a change in the membrane potential o Short lived signals quickly removed broken down Neuroendocrine signals released from neurons but are considered hormones because they are carried by blood or other bodily fluids and act on distant cells Neurohormones o Like endocrine signals they act on distant cell o They do not act on or at the synapse o Ex ADH produced by neurons located in the hypothalamus of the brain acts on kidney collecting duct cells 3 Hormone Signaling Pathways Hormones act via 3 pathways all of which regulated by negative feedback or feedback inhibition which regulates homeostasis o Endocrine pathway sends hormones directly from endocrine cells to effector cells 3 steps lead to feedback response and shutting down hormone action Hormones produced by effector cells feed back to the endocrine cells lowering hormone production The effector hormone also feeds back to the neuroendocrine neuroendocrine to endocrine pathways Endocrine signals are released in response to electrical signals which modulate the signal from the nervous system Endocrine nervous systems work closely together to regulate the response to a stimulus o Neuroendocrine pathway releases neuroendocrine signals that act directly on effector cells o CNS to endocrine pathway neuroendocrine signals stimulate cells in the endocrine system which respond by producing an endocrine signal that acts on effector cells Organs that secrete hormones into the bloodstream are called endocrine glands o Vary widely among animals Neurons that manufacture secrete hormones are particularly important in insects they regulate molting metamorphosis other processes Salmon have an unusual gland that secretes a hormone responsible for regulating calcium ion concentration o Pituitary gland with distinct anterior posterior regions sits just below the hypothalamus o Thyroid gland situated in the neck o Parathyroid glands 4 embedded in the thyroid gland o Kidneys 2 lie in the posterior part of the abdominal cavity o Adrenal glands 2 Sit atop the kidneys o Pancreas located in the anterior part of abdominal cavity o Ovaries testes in or suspended below the pelvic cavity respectively Exocrine glands deliver their secretions through ducts into a space other than the circulatory system Chemical Characteristics of Hormones Most animal hormones belong to one of 3 chemical families o Polypeptides chains of amino acids linked by bonds o Amino acid derivatives o Steroids family of lipids distinguished by four ring structure The only difference between hormone families is that only steroids are lipid soluble o Thyroxine amino acid derivative hormone that is lipid soluble an exception to this rule To affect a target cell all polypeptides most amino acid derivatives bind to a receptor on the cell surface o Lipid soluble hormones in contrast can diffuse through the plasma membrane bind to receptors inside the cell Are generally low in concentration but have a great effect on the animal Growth hormone o Remove the pituitary gland the animal stops growing o Stimulates mitosis growth o In cows there is only 04g of GH per kg of cow pituitary a very small amount A single hormone can exert a variety of effects Several different hormones may affect the same aspect of physiology What Do Hormones Do Hormones coordinate the activities of cells in 3 areas o Development growth reproduction o Response to environmental changes o Maintenance of homeostasis Growth sex hormones are vital to growth development in animals o Combination promotes cell division growth sexual differentiation Metamorphosis process in which an insect or amphibian will change from a larvae to an adult o Thyroid hormone triiodothyronine T3 is responsible for most of the changes observed in metamorphosis In juvenile amphibians cells respond to increased levels of T3 in one of three ways o By growing forming new structures o They may die as in cells that form the tadpole s tail o They may change structure function Can cause a tadpole s long intestine into an adult s short intestine Insect metamorphosis is triggered by a hormone from the brain o Results in transition from juvenile larvae to
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