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Wk15 Chemical Coordination Endocrine Glands - hormones A hormone from an endocrine cell is secreted into the blood, which carries it to its target cell. [Exocrine glands secrete products into a duct e.g. saliva, sweat] Hormones Vs Nerves Hormonal system Nervous system Chemical communication Nervous communication Transmission by blood Transmission by neurones Transmission relatively slow Transmission very rapid Hormones travel throughout body but only target responds Nerve impulse specifically targeted Response is widespread Response is localised Response slow Response rapid Response longer lasting Response short lived Effect may be permanent & irreversible Effect is temporary Chemical mediators Chemicals released and active in their immediate vicinity Histamine Chemical released by: Basophil white cells; Mast cells (in connective and mucus tissues); Trigger for release: Antigens; Effect: Histamine receptors in smooth muscle leads to dilation of small arteries & arterioles; Increases capillary permeability to white cells and proteins; Redness, swelling and itching. [Note: histamine has a number of other roles including as a neurotransmitter] Chemical mediators Prostaglandins A number of fatty acid derived compounds with various effects Released by: most cells; Triggered by: tissue damage; Effect: In response to injury dilation of arterioles; increased capillary permeability; increased sensitivity to pain; Other roles: relaxation of smooth muscle in the gut; promotion of muscle contraction during birth. Plant Growth Factors Tropisms: A growth movement of a plant in response to a stimulus Phototropism Geotropism Hydrotropism The Evidence Control of tropisms IAA (indoleacetic acid ) [Sometimes referred to as Auxin, which refers to a group of plant growth factors including IAA] Control of tropisms by IAA (indoleacetic acid ) Positive phototropism: growth of a coleoptile towards the direction of a light source. In roots IAA decreases cell elongation Control of Tropisms Experiments Control of Growth in Plants Phototropism: Darwin noticed germinating oat seedlings grew toward light. He and his son investigated how this happened. 12 Control of Growth in Plants Phototropism: Darwin (1880): 13 Control of Growth in Plants Phototropism: Darwin (1880): 14 Control of Growth in Plants Phototropism: Darwin (1880): 15 Control of Growth in Plants Phototropism: Darwin (1880): 16 Control of Growth in Plants Phototropism: Darwin (1880): 17 Control of Growth in Plants Phototropism: Darwin (1880): Conclusion: •coleoptile tip acts as light receptor; •message sent to stem. 18 Control of Growth in Plants Phototropism: Boysen-Jensen (1913): Coleoptile tip sends messenger substance to encourage growth on darker side. Q. What sort of messenger might this be? 19 Control of Growth in Plants Phototropism: Paal (1919): Result suggested differential diffusion of hormone. 20 Control of Growth in Plants Phototropism: Went (1928): Was able to collect hormone then named AUXIN in agar. Degree of curvature directly related to auxin concentration. 21