5.4.4 regulating blood glucose
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normal blood concentration of glucose
between 4-6 mmmol dm-3
hypoglycaemia
blood glucose concentration drops below 4mmol dm-3 & remain low for long periods
main problem caused by hypoglycaemia
inadequate delivery of glucose to body tissues & brain
symptoms of mild hypoglycaemia
include: - tiredness - irritability
symptoms of severe hypoglycaemia
include: - impairment of brain function & confusion - lead to seizures, unconsciousness & even death
hyperglycaemia
blood glucose concentration allowed to rise too high for too long
what can permanently high blood glucose lead to (hyperglycaemia)
significant organ damage
diagnosis of diabetes mellitus
consistently higher blood glucose conc. exceeding 7 mmol dm-3
which cells monitor concentration of glucose in blood
cells in islets of Langerhans
what hormone is released if blood glucose too high/low
too high = insulin too low = glucagon
what cells do insulin/glucagon act upon
hepatocytes (liver cells) - which store glucose in form of glycogen
describe the process if blood glucose raises too high
• detected by beta cells in islets of Langerhans • secrete insulin into blood • insulin travels via circulatory system • target cells are liver cells, muscle cells & some other body cells (eg. brain)
describe human insulin
• small protein of 51 amino acids = unable to pass through cell surface membrane
what do the target cells possess
specific membrane-bound receptors for insulin
what happens when insulin binds to the insulin receptors on target cells
• activates enzyme tyrosine kinase which is associated with receptor on inside of membrane • tyrosine kinase causes phosphorylation of inactive enzymes in cell • this activates enzymes leading to cascade of enzyme-controlled reactions inside cell
effects of insulin on cell
• more transporter proteins specific to glucose placed into cell surface membrane = achieved by causing vesicles containing transporter proteins to fuse with membrane • more glucose enters cell • glucose in cell converted to glycogen for storage (glycogenesis) • more glucose converted to fats • more glucose used in respiration
glycogenesis
glucose in cell converted to glycogen for storage
what is a low blood glucose concentration detected by
alpha cells in islets of Langerhans
what do the alpha cells secrete
glucagon into blood
describe glucagon
small protein containing 29 animo acids
target cell of glucagon
hepatocytes (liver cells) = possess receptor for glucagon
what happens when glucagon reaches hepatocytes
• glucagon binds to receptors • stimulates G protein inside membrane • activates adenyl cyclase inside cell • adenyl cyclase converts ATP to cAMP • activates series of enzme-controlled reactions in cells
effects of glucagon on cells
• glycogen converted to glucose by phosphorylase A (one of enzymes activated) = glycogenolysis • more fatty acids used in respiration • amino acids & fats converted into additonal glucose = gluconeogenesis
glycogenolysis
glycogen converted to glucose by phosphorylase A