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level: 16.3 Hormones and the regulation of blood glucose concentration

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level questions: 16.3 Hormones and the regulation of blood glucose concentration

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Characteristics of hormones- Glands secrete hormone directly into the blood - Carried in the blood plasma to target cells, which have specific receptors on the cell-surface membranes that are complementary to a specific hormone
Second messenger model- One mechanism of hormone action - This mechanism is used by 2 hormones involved in the regulation of blood glucose conc., namely adrenaline + glucagon
Mechanism involving adrenaline (1)- Adrenaline binds to receptor on cell-surface membrane of a liver cell - Causes the protein to change shape
Mechanism involving adrenaline (3)- Leads to the activation of an enzyme called adenyl cyclase - Converts ATP to cAMP
Mechanism involving adrenaline (4)- cAMP acts as a second messenger that binds to protein kinase enzyme, changing its shape + therefore activating it
Mechanism involving adrenaline (5)- Protein kinase enzyme catalyses the conversion of glycogen to glucose - Moves out of the liver cell by facilitated diffusion and into the blood, through channel proteins
Role of the pancreas in regulating blood glucose- Gland behind stomach - Produces enzymes (protease, amaylase, lipase) for digestion - Hormones (insulin, glucagon) for regulating blood glucose conc. - Groups of hormone-producing cells known as islets of Langerhans
What do the cells of islets of Langerhans include- alpha cells, which are larger, produce glucagon hormone - beta cells, which are smaller, produce insulin hormone
The role of the liver in regulating blood sugar- Made up of cells called hepatocytes - Regulates blood glucose conc. - While the pancreas produces hormones insulin and glucagon, it is in the liver where they have their effects
3 important processes associated with regulating blood sugar in the liver- Glycogenesis - Glycogenolysis - Gluconeogenesis
Glycogenesis- Conversion of glucose into glycogen - When blood glucose conc. is higher than normal the liver removes glucose form the blood, converts it to glycogen
Glycogenolysis- Breakdown of glycogen to glucose - When blood glucose conc. is lower than normal, the liver can convert stored glycogen back into glucose which diffuses into the blood to restore the normal blood glucose conc.
Gluconeogenesis- Production of glucose from sources other than carbs - When its supply of glycogen is exhausted, the liver can produce glucose from non-carb sources such as glycerol + amino acids
Regulation of blood glucose concentration- If conc. too low, cells will be deprived of energy + die - Brain cells are especially sensitive as can only respire glucose - If conc.too high, lowers water potential of blood, dehydration
Factors that influence blood glucose concentration, the 3 sources of glucose- Diet - food - Glycogenolysis - Gluconeogenesis
How does glucagon work?- Binds to complementary receptors on target cells - Activates cAMP (secondary messenger) - This activates phosphorylase - Hydrolyses glycogen to glucose (glycogenolysis)
How does insulin work?- Insulin increases muscle and liver cells permeability to glucose - Increases rate of diffusion into cells
Adrenaline- Similar effect to glucagon - Released in times of stress - Glycogen to glucose - Prevents glycogen formation
Diabetes- A disease signified by high blood sugar - The symptoms can include, excessive urination, thirst and tiredness
Type 1- Due to an autoimmune response - Beta cells are destoryed, therefore body cannot produce insulin - Controlled by injecting insulin
Type 2- Due to age or obesity - Insiulin is prevened from binding to receptors on cell membrane - Protein receptor changes shape - Controlled with diet or/and exercise
Negative feedback- Only when the blood glucose concentration falls below the set point is insulin secretion reduced (negative feedback), leading to a rise in blood glucose concentration - In the same way, only when the concentration exceeds the set point is glucagon secretion reduced (negative feedback), causing a fall in the blood glucose concentration
Example - after a meal- Increases blood glucose Negative feedback - back to here - B cells detect + secrete insulin - Increase cells permability to glucose - Glucose diffuses into muscle cells + liver cells - Used in respiration, converted into glyocgen, converted into lipid synthesis - Decreases blood glucose to norm
Example - fasting- Decreases blood glucose - Sensed by alpha cells Negative feedback - back to here - Glucagon - Hydrolyse glycogen - glucose - Lipids/amino acids - glucose - Increases blood glucose to norm