control of plasma glucose Flashcards
which structures rely entirely on glucose and why?
CNS
retina
germinal epithelium
brain cannot synthesise of store more than a few minutes supply of glucose
requires a continuous supply from circulation
why do we take fasting blood glucose levels
huge variation in blood glucose spike after eating
eating different things
fasting blood glucose levels are :
70-100 mg glucose/100cm3 (dl) of blood
or
3.9 – 5.5 mmol-1
which organ is reponsible for responding to signals that indicate changes in blood glucose levels
liver is the predominant tissue
name and explain ways that glucose is used, synthesised and stored
- Glycogenesis:
- Liver causes:
- Conversion of glucose to glycogen
- Skeletal muscle & liver
- Glycogen can be used as an energy source
- Glycogenolysis:
- Breakdown of glycogen to glucose
- Liver (and kidney) can release glucose into circulation in response to low plasma glucose
- Gluconeogenesis:
- Glucose from non-carbohydrate precursors
- Proteins (amino acids) & Lipids (glycerol)
- Liver (& Kidney)
what happens when glycogen stores are fully saturated
Glucose converted to FFA and stored in adipocytes in the form of triglycerides
Glucose converted into fat
process does not usually happen in reverse
what will blood glucose levels below 3.9mmol/L lead to?
loss of consciousness (coma)
hypoglycaemia
what will blood glucose levels above 7mmol/L lead to?
glucose will appear in urine
pH of blood will fall
leads to coma - above 10mmol/L
hyperglycaemia
if there is inadequate amounts of glucose to catabolise, what is the action of the cells
what occurs during starvation
- If cells have inadequate amounts of glucose to catabolize, the cells immediately shift to the catabolism of fats for energy.
- In starvation, proteins are also used for energy after carbohydrate and fats are depleted.
short term regulators of blood glucose levels
insulin
glucagon
hormones released by gastrointestinal tract
fight or flight
long term regulators of blood glucose levels
Adrenaline,
glucocorticoids,
growth hormone
thyroid hormones
important structure of pancreas
islet of langerhans
what cells does the islet of langerhans contain and what do they secrete
alpha, beta and delta cells
secrete peptide hormones
- a cells (20%) secrete glucagon
- b cells (75%) secrete insulin
- d cells (5%) secrete somatostatin
properties of insulin
summarised role of insulin
- 5 minute half life (no carrier protein)
- Released (& stored) by the islets of Langerhans β cells in the pancreas in response to high blood sugar levels
- Blood perfuses islets
- B cells sense
- Raised plasma glucose: depolarisation of the beta cells (acts directly)
describe the events which lead to the secretion of insulin
explain actions of insulin
what is the outcome?
- Key target tissues of insulin are liver, muscle & adipose tissue
- Binds to insulin-dependent receptor and force fat and muscle cells to take up glucose from the blood through the glucose transporter (GLUT4)
- Stimulates the liver to convert glucose into glycogen (glycogenesis)
- Activates glycolysis & Inhibits gluconeogenesis
- As a result, blood glucose levels drop
how does glucose uptake in the CNS differ from the rest of the body??
glucose uptake is independant of insulin
explain the actions of insulin if the glycogen stores are fully saturated
- Stimulates excess glucose to be converted into fat: triglyceride synthesis
- Increases uptake of amino acids and promotes protein synthesis
-
Increase the number of GLUT4 receptors on the cell surface –
- increase capacity of the cell for glucose uptake
- Prevents glycogenolysis and lipolysis
- Lowers plasma glucose levels
- As a result, blood glucose levels drop
summary of insulins actions and effect on cell membrane transporters
- Insulin binds to the alpha subunits of the insulin receptor,
- which increases glucose and amino acid transport
draw graph of insulin and glucose levels after a meal
which gastrointestinal hormones have roles in lowering blood glucose levels
Glucagon-like peptide-1 (GLP-1)
gastric inhibitory peptide (GIP)
what roles do gastrointestinal hormones have in lowering blood glucose levels
- after detection of plasma glucose in lumen of the small intestine
- Increase production of incretins
- Enable cells to respond better to insulin
incretins used as diabetes medication
properties of glucagon
summarised role of glucagon :
- The most potent hyperglycaemic hormone
- Actions directly oppose insulin
- Synthesised by the alpha cells of the pancreatic islets
- 6 minute half life
- Released in response to lowered plasma glucose
- Acts to raise glucose levels
- Insulin inhibits glucagon secretion
explain the actions of glucagon
- blood glucose levels fall -> alpha cells of pancreas release glucagon
- Exerts its effects on CHO, fat and protein metabolism
- Converts glycogen into glucose (glycogenolysis)
- Inhibits glycogen synthesis (glycogenesis)
- Activates amino acid uptake and gluconeogenesis
- Lipolytic effect (triglycerides broken down to fatty acids)
- Provides a ready supply of metabolic substrates
- Enables glucose to be spared for CNS
