Biol 118 1st Edition Lecture 30Outline of Last Lecture I. How Do Sensory Organs Convey Information to the Brain?II. Mechanoreception: Sensing Pressure ChangesIII. Photoreception: Sensing LightIV. Chemoreception: Sensing ChemicalsV. Other Sensory SystemsOutline of Current Lecture I. Introduction to Chemical Signals in AnimalII. Cell-to-Cell Signaling: An OverviewIII. 3 Hormone Signaling PathwaysIV. Chemical Characteristics of HormonesV. How is the Production of Hormones Regulated?VI. The Hypothalmus-Pituitary AxisCurrent LectureIntroduction to Chemical Signals in Animal- In response to external stimuli or internal conditions, cells of CNS or endocrine system release molecule- hormoneso 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 streamCell-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 ofcells throughout the body- Autocrine signals: act on the same cell that secretes themo Cytokines: best studied autocrine signals; amplify the response of a cell to a stimulusThese 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 glandso 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 potentialo 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 cello They do not act on or at the synapseo Ex. ADH produced by neurons located in the hypothalamus of the brain, acts on kidney collecting duct cells3 Hormone Signaling Pathways- Hormones act via 3 pathways, all of which regulated by negative feedback or feedback inhibition, which regulates homeostasiso 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 stimuluso Neuroendocrine pathway: releases neuroendocrine signals that act directly on effector cellso 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 glandso Vary widely among animals Neurons that manufacture & secrete hormones are particularly importantin insects, they regulate molting, metamorphosis & other processes Salmon have an unusual gland that secretes a hormone responsible for regulating calcium ion concentrationo Pituitary gland: with distinct anterior & posterior regions, sits just below the hypothalamuso Thyroid gland: situated in the necko Parathyroid glands (4): embedded in the thyroid glando Kidneys (2): lie in the posterior part of the abdominal cavityo Adrenal glands (2): Sit atop the kidneyso Pancreas: located in the anterior part of abdominal cavityo Ovaries/testes: in or suspended below the pelvic cavity, respectively- Exocrine glands: deliver their secretions through ducts into a space other than the circulatory systemChemical Characteristics of Hormones- Most animal hormones belong to one of 3 chemical families:o Polypeptides: chains of amino acids linked by bondso Amino acid derivativeso Steroids: family of lipids distinguished by four-ring structure- The only difference between hormone families is that only steroids are lipid solubleo 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 surfaceo 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 hormoneo Remove the pituitary gland & the animal stops growingo Stimulates mitosis & growtho 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 physiologyWhat Do Hormones Do?- Hormones coordinate the activities of cells in 3 areaso Development growth & reproductiono Response to environmental changeso Maintenance of homeostasis- Growth & sex hormones are vital to growth & development in animalso Combination promotes cell division, growth & sexual differentiation- Metamorphosis: process in which an insect or amphibian will change from a larvae to anadulto 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 wayso By growing & forming new structureso They may die, as in cells that form the tadpole’s tailo They may change structure & function Can cause a tadpole’s long intestine into an
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