Physiology 6 - Feedback control of glucose Flashcards
Why is the feedback control of plasma glucose so critical?
The brain is a “glucose obligate” tissue and stores little glycogenThe blood brain barrier makes the brain inaccessible to plasma fatty acids
When does hypoglycaemia occur?
When blood sugar levels fall below 4 mmol/L (if below 2.5 can cause confusion and coma)
What effect does chronic hyperglycaemia have on blood vessels?
Damages them
What hormones control [glucose]p in the absorptive and post-absorptive state (fed and between meals)? (2)
Insulin and glucagon (pancreas)
What hormones control [glucose]p in emergencies?
Glucagon (pancreas)
What hormones control [glucose]p during starvation? (2)
Cortisol (adrenal)Growth hormones (pituitary)
What type of cells make up the pancreatic islets of langerhans and what does each secrete?
A cells - glucagonB cells - insulinD cells - somatostatin
What ensues if the islets of langerhans are removed or destroyed?
Diabetes mellitus - lack of insulin or impaired cellular responses to insulin
Changes in glucose, insulin and glucagon levels during the absorptive state?
[Glucose]p rises[insulin]p rises[glucagon]p falls
What type of meal causes an increase in the amount of insulin released compared to there types of meals?
Carbohydrate rich meals
What does insulin do?Is insulin the hormone of the fed or hungry state?
Favours anabolismTherefore stimulates conversion of glucose into glycogen, fatty acids into triglycerides and amino acids into proteinFed-state
What does glucagon do?Is glucagon the hormones of the fed or hungry state?
Favours catabolismStimulates conversion of glycogen into glucose and triglycerides into fatty cardsHungry-state
How does insulin lower the plasma concentration of glucose? (2)
By stimulating the uptake of glucose from the blood into fat and muscle cellsActivating the enzyme in the liver and muscle which converts glucose into glycogen(insulin also promotes the incorporation of amino acids into protein in muscle and promotes lipogenesis in adipose tissue)
How does insulin promote glucose uptake into muscle and fat?
insulin causes glucose transporter proteins (GLUT4) to be inserted into the plasma membrane of muscle and dat cells from intracellular stores (when insulin levels drop off the transporters become internalised again)
What promotes the secretion of insulin? (5)
Increased glucoseIncreased amino acidsincreased parasympathetic activityIncreased glucagon (causes it to be produced and stored ready for release, not release)GIP (glucose-dependent insulinotropic peptide - hormone produced in small intestine)
What 2 factors inhibit insulin secretion?
Decreased glucose concentrationIncreased sympathetic activity (e.g. exercise or stress)
How is diabetes mellitus detected?
Oral glucose tolerance test - patient fasts overnight and is given an oral glucose load, glucose levels measured at regular intervalsIf diabetes, fasting glucose level is higher and glucose concentration is high after oral dose)
Why are patients with diabetes excessively thirsty?
Glucose appears in urine (as can’t all be converted) causing an increased urinary volume due to osmotic effects, leading to dehydration and consequently thirst
Why do patients with diabetes form ketone bodies?
Inability of cells to utilise glucose causes a compensatory increase in lipolysis to generate fatty acids as an energy sourceMetabolism of fatty acids generates acetly CoALiver unable to process extra acetyl CoA through citric acid cycle = ketone bodies formedThese lower blood pH (metabolic acidosis) initiating compensatory hyperventilation (acid drop breath)
Difference between type 1 and type 2 diabetes?
Type 1 diabetes has a childhood onset and is caused by little or no insulin secretion due to a defect in B-cell function, if untreated ketosis develops and it is treated with insulin injections (develops rapidly)Type 2 diabetes is usually an adult onset and insulin secretion mat be normal (or exceed normal), caused by defect in insulin sensitivity, ketosis rare, diet/ exercise and oral drugs for treatment (Symptoms develop slowly)
What stimulates glucagon release?
Decreased blood glucose levels (direct effect on alpha-cells)Amino acids (raises plasma glucose concentration after protein meal)Sympathetic nerve activity
What inhibits glucagon release? (2)
Raised blood glucoseInsulin
How does glucagon raise [glucose]p?
Increased liver glycogenolysisInhibiting liver glycogen synthesisPromoting liver gluconeogensisAlso promotes lipolysis in liver and adipose tissue
How long is the store of glycogen in the liver and muscle sufficient to provide glucose for in the typical adult?
Approx. 8 hours
What if we go without food for longer than our supply of glucose is?
Fats are metabolisedProtein is catabolised - serious consequences such as muscle wastingAim is to ensure brain and heart maintain energy supply
What 2 hormones raise blood glucose levels in response to stress?
Adrenaline and cortisol
Where is growth hormone released?
From anterior lobe of pituitary
What does growth hormone do during starvation?
Decreases glucose uptake by muscle - “glucose sparing” actionMobilised glucose from liverAlso promotes lipolysis
