Feedback Control of Plasma Glucose Flashcards
What is fuel metabolism?
Reactions involving catabolism, anabolism and transformation of protein, carb (CHO) and fat
What 5 hormones influence glucose?
Insulin, Glucagon, Growth hormone, Adrenaline and Cortisol
What hormones control the absorptive and post absorptive state?
insulin and glucagon
What hormones control plasma glucose in emergencies?
adrenaline
What hormones are control plasma glucose during starvation?
cortisol (made in adrenal) and growth hormones (pituitary)
What is the role of the endocrine pancreas in the control of blood glucose?
Islets of langerhans, containing 4 secretory cells.
What are the 4 secretory cells of the islets of langerhans and what does each produce?
Alpha - glucagon
Beta - insulin, proinsulin, C peptide and amylin
Delta - somatostatin
F cells - pancreatic polypeptide
Describe the function of insulin?
Favours anabolism. Stimulates conversion of glucose to glycogen, fatty acids into triglycerides and amino acids into proteins
Describe the function of glucagon?
Favours catabolism. Stimulations the conversion of glycogen to glucose, triglycerides to fatty acids
What does insulin do during the feeding state?
B cells secrete more insulin
catabolism of endogenous fuel stores is inhibited
CHO, AA and lipid uptake is stimulated
insulin directs the tissues to replenish their fuel reserves that were used during the period of fasting
What does insulin do during fasting?
B cells secrete less insulin
lipids and amino acids are mobilised from tissues\
they provide fuel for oxidation and act as precursors for ketogenesis and gluconeogensis (production of glucose from non-carbs)
What does sympathetic and parasympathetic stimulation in the islets of langerhans do?
sympathetic stimulation - INHIBITS insulin secretion
parasympathetic stimulation - STIMULATES insulin secretion
What does exercise do to insulin
It surpasses insulin secretion to help prevent excessive glucose uptake by muscles
Which tissues are insulin sensitive?
Liver, Skeletal muscle, adipose tissue (cardiac muscle also)
What is glycogen an important storage form of?
CHO in both liver and skeletal muscle
How does insulin lower [glucose]p?
Liver - activates enzymes in liver and skeletal muscle which convert glucose into glycogen
Promotes storage of fats as triglycerides
Skeletal muscle - Stimulating uptake of glucose from the blood into skeletal muscle and fat cells (GLUT4)
increases glucose breakdown
Describe GLUT4?
insulin sensitive glucose transporter
insulin stimulates glucose uptake by adipose and skeletal muscle, leading to a reduction in blood glucose levels
insulin causes the GLUT4 to be inserted onto the plasma membrane from intracellular stores.
Describe type 1 diabetes? (IDDM)
Childhood onset
Little/no insulin secretion
Affects 10-20% diabetics Defect in -cell function Ketosis develops (if untreated) Insulin injections for treatment Symptoms develop rapidly
Describe type 2 diabetes? (NIDDM)
Adult onset (until recently) Insulin secretion may be normal (or exceed normal) Affects 80-90% diabetics Defect in insulin sensitivity Ketosis rare
Diet/exercise and oral drugs for treatment
Symptoms develop slowly
What are the effects of severe DM?
Plasma glucose will be very high after meals
Glucose appears in urine - leading to thirst, dehydration
There is an inability of cells to utilise glucose which causes compensatory increase in lipolysis to generate fatty acids as an energy source
Metabolism of fatty acids generates acetyl CoA - liver is unable to process extra acetyl CoA… ketone bodies formed
These lower the blood pH, leading to metabolic acidosis and compensatory hyperventilation
What is glucagon principle target tissue?
Liver
Explain the role of adrenaline in the release of glucose in emergencies?
Released from the adrenal gland in response to stress. Raises [glucose]p Stimulates glycogenolysis Stimulates gluconeogenesis Released during short-term emegencies
Explain the role of growth hormone in providing glucose during prolonged fasting.
From anterior lobe of pituitary gland
Decreases glucose uptake by muscle – “glucose sparing” action
Mobilises glucose from liver
also promotes lipolysis in fat cells
Explain the role of cortisol in providing glucose during prolonged fasting.
Released from adrenal gland in response to stress.
Raises [glucose]p
Stimulates protein catabolism
Stimulates gluconeogenesis
Also stimulates lipolysis
NOT important for rapid mobilisation of fuel
