ESSAY ANSWER: Describe the negative feedback mechanism involving TSH and thyroxin and describe the consequences if this mechanism does NOT function well. Content: Synthesis: (17) (3) The pituitaryis sensitive to the concentration of the hormone, thyroxinin the blood When the thyroxin concentration in the blood decreasesbelow the normal level: • The pituitary is stimulated to secrete more TSH TSH stimulates the thyroid gland • to secrete more thyroxin Thus increasing the level of thyroxin When the thyroxin concentration in the blood increasesabove the normal level: • The pituitary is not stimulated to secrete TSH There is less stimulation of the thyroid gland to secrete thyroxin Thus decreasing the level of thyroxinin the blood to normal levels Max Consequences of mechanism not working The concentration of thyroxin will not be regulated When the thyroxin level increases beyond normal limitsit causes Hyperthyroidism Hyperthyroidism causes an increase in rate of metabolismresulting in: • Weight loss Irritable/anxiety • Hyperactive Increase in heart rate Tiredness Thyroid gland swells/goitre Eyeballs protrudeMax When the thyroxin level decreases beyond normal limitsit causes Hypothyroidism Hypothyroidism causes an decrease in rate of metabolismresulting in: • Weight gain Decrease in heart rate Slow growth of hair and fingernailsMax (10) (1) (3) (3)
Posted on: Sun, 18 Aug 2013 17:08:53 +0000
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