Chemical mediators & receptors

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  • Created by: syaqub18
  • Created on: 23-04-15 12:52
what is a chemical mediator?
a chemical messenger which acts locally i.e. nearby cells
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what are the similarities between hormones and chemical mediators?
they bind to specific receptors to cause a response
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how are chemical mediators different from hormones?
theyre secreted from cells all over body and not just from glands, target cells right next to where they are produced localised effect and not widespread, short distance to travel so quicker response than hormones
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what is histamine?
chemical mediator stored in mast cells nad basophils (cell in immune system), released in response to injury or infection, increases permiability of capillaries nearby to allow more immune system cells to move from blood to area
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what is prostaglandins?
group of chemical mediators produced by most of the cells of the body, involved in inflammation,fever, blood pressure regulation and blood clotting, one type is release from blood vessle epithelium cells to relax muscles around them
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what is the resting potential?
nervous system is in resting state (not stimulated), inside is negatively charged and outside is positively charged to cause a voltage/p.d across membrane, this potenital difference is known as resting potential, generated by ion pumps and channels
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what is the generator potential?
stimulus dectected, cell membrane excited and becomes permeable to allow ions in and out of cell which alters p.d, change in p.d due to stimulus is known as generator potenial, bigger stimulus causes bigger movement of ions for a bigger p.d
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what is an action potential?
if generator potenial is big enough it will cause an action potential (electrical impluse along neurone), only achieved if generator potenital reaches threshold, if threshold not reached there is no action potential
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what is a pacinian corpucle?
mechanoreceptors which detect pressure and vibrations, found in skin, contain end of sensory neurone (sensory nerve ending) and is wrapped in lamellae
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what happens when a pacinian corpuscle is stimulated (e.g tap on the arm)?
lamellae deform and press on sensory nerve ending, this causes deformation of strech-mediated sodium channels in sensory neurones cell membrane, sodium ions diffuse in to cell via sodium channel, creates generator potenial or action potenial
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what are photoreceptors?
receptors in eye which detect light, light enters through pupil and amount of light entering is controlled by the iris, light rays focused on to retina by lens, fovea is area with many photorecptors, impulses carried by optic nerve to brain
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how do photoreceptors detect light?
light enters eye, hits photorecptors and is absorbed by light sensitive pigments, light bleaches pigments, causes chemcial change and alters permiability of membrane to sodium, impluse is sent to bipolar nerve if generator potenial reaches threshold
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what are the two types of photorecptors in the human eye?
rods and cones
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what information do rods give?
only in black and white
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what information do cones give?
in colour
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what are the three types of cones?
red sensitive, green sensitive and blue sensitive
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how does the distrubution of rods and cones affect sensitivity to light?
(in dim light) rods are sensitive as many rods join to one neurone and generator potenials combine to reach threshold to fire action potenial, cones are less sensitive as one cone joins to one neurone
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what is visual acuity?
ability to tell apart two points
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how does the distrubution of rods and cones affect visual acuity?
rods have low visual acuity as many rods join to one neurone so light coming from two objects cant be told apart, cones have high visual acuity as one cone joins to one neurone light from two objects hits two cones sends two action potenials
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where are sodium-potassium pumps and potasssium ion channels located?
on the membrane of the neurone
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how does the sodium-potassium pump work?
uses ATP for active transport to move 3 sodium ions (Na+) for every 2 potassium ions (K+) moved in
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how does the potassium ion channel work?
they allow the facilitated diffusion of potassium ions (K+) out of neurone down the concentration gradient
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how is the resting potenial maintained?
sodium-potassium pumps move out Na+ ions out of neurone but membrane is not permable to let them diffuse back, creates electrochemical gradient of Na+, sodium-potassium pumps also move K+ in to the neurone, some K+ move back out by potassium channels
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why is the inside of the neurone more negative?
because more positive ions move out than enter in, this makes the outside more postive than the inside
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Card 2

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what are the similarities between hormones and chemical mediators?

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they bind to specific receptors to cause a response

Card 3

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how are chemical mediators different from hormones?

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Card 4

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what is histamine?

Back

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Card 5

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what is prostaglandins?

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