L49- glucose homeostasis and the pancreas

what is the absorptive state and the fasted state

• also known as the fed state

• this is when we eat and have food

• we gain nutrients’’ which are stored in the cells

• the fasted state is when we haven’t eaten for a long time

• e.g. when we are asleep

explain the link between the food we eat and insulin

• when we have food we gain nutrients such as glucose, amino acids and fats

• insulin affects each of these

• it uses them for synthesis, and energy

what is the exocrine and the endocrine functions of the pancreas

exocrine-releases digestive enzymes into ducts

endocrine- it releases hormones into the blood

what is the cell and its cell type that is responsible for the secretion of different hormones in the pancreas

islets of Langerhans

• alpha cells- secrete glucagon

• beta cells secrete insulin ( the majority )

• delta cells-secrete somatostatin

describe glucose balance

• when we have glucose in the blood after eating insulin is produced

• the insulin will stimulate the muscles and the adipose tissue to take up the glucose (anabolic state/effect )

• when the glucose concentration is low, like during the fasted state the glucagon acts as the counter to insulin and increases the plasma glucose

• by breaking down glycogen → glucose and stimulating the production of ketones in the liver ( catabolic effect )

what is the function of insulin

it decreases plasma glucose, amino acids and fat free fatty acids

how does glucose enter the cells

through transporters

how is the liver involved in the production of glucose

• glucagon will produce free fatty acids that are transported into the liver to produce ketone

• the ketones made by the liver will then produce glucose from alternative substrates

what is the ‘process’ of forming active insulin

preprohormone→ prohormone→ active insulin

what enzyme degrades insulin

• insulinase in the liver and the kideneys

• half life of 6 minuets

describe what happens when high glucose concentration in the blood

• the blood passes through the middle of the Langerhans cells next to the beta cells

• the glucose from the plasma enters inside the beta cells through the glucose transporter 2

• the glucose is then converted into glucose- 6- phosphate by glucokinase ( this stops the glucose from leaving the cell )

• glucose 6 phosphate is then metabolized inside the mitochondria producing ATP

• the ATP closes k⁺ channels inside the cells

• this causes a depolarisation of the cell which opens calcium voltage gated channels allowing calcium to enter

• this calcium is able to release insulin vesicles inside the cells which secrete the insulin via exocytosis

how does insulin induce its effects

• insulin must bind onto specific receptors on the plasma membrane of target cells

• this receptor is a tyrosine kinase receptor and its a dimer

• when insulin binds to the tyrosine receptor it causes the dimerization

• this causes autophosphorylation which is activation of the receptor

• it then has intracellular effects on kinases and phosphatases

• and have effects on key enzymes

describe how insulin makes carbohydrate metabolism happen

• insulin facilitates glucose entry into muscle and adipose tissue

• it also stimulates the liver to store glucose as glycogen

• this leads to a decrease in plasma glucose concentration

describe how insulin makes lipid metabolism happen

• insulin promotes synthesis of fatty acids in the liver

• once glucose is inside the liver insulin converts it into glycogen but if there’s excess then it’ll convert it into fatty acids in the liver as triglycerides

• the liver then send the triglycerides ( using lipoproteins carriers ) into the adipose tissue for storage through the blood

• insulin also inhibits the breakdown of fats in the adipose tissue

• and it promotes glycerol synthesis from glucose and increases triglyceride synthesis

explain why the muscles and adipose cells tissue need/ depend on the insulin for glucose whilst liver doesn’t

• in the muscles and adipocytes the transporters are inside the cell

• when there’s a rise in extracellular glucose insulin is released and binds to the receptors to activate them and extracellular enzymes

• this causes the translocation of the transporters from the inside of the cell → to the outside of the cell allowing glucose inside the cells

• without insulin this isnt possible

describe the entry of glucose into the muscles

• when the glucose enters its converted into glucose-6-phosphate trapping it inside

• the glucose can either be stored as glycogen or used for energy or converted into lactic acid that’s transported into the liver

• the glycogen in the muscles when broken down into glucose can only be used inside the muscle

describe the entry of the glucose in the liver and insulins effect

• when the glucose enters its converted into glucose6-phosphate stopping it from leaving

• this doesn’t need input from insulin to happen

• insulin stimulates glucokinase ( the enzyme which converts glucose → glucose-6-phosphate) and it inhibits glucose-6-phosphotase which is an enzyme that makes glucose-6-phosphotase into glucose

• the glycogen inside the liver is able to be broken down into glucose and is able to regulate glucose in the blood

• the glucose can also undergo glycolysis where the glucose-6-phosphate can convert into fatty acids which are stored in lipoproteins and transported into the adipose tissue

describe glucose entry inside the adipose tissue

• the glucose enters through transported and is converted by glucokinase into glucose-6-phoshosphate

• this is then converted into triglycerides using glycerol phosphate

• the lipoproteins containing the fatty acids from the liver arrive at the adipose tissue and the liver stimulates the lipoprotein lipase to free the fatty acids and allow them to enter the cell

• insulin also stimulates the uptake of amino acids in side the adipose

what is glucagon and what does it do

• it is the counter- regulatory hormone of insulin

• its synthesised and released by the alpha cells of islets

• it is released when glucose levels fall

• it stimulates glycogenolysis ( breaks down glycogen into glucose )

• promotes gluconeogenesis ( production of glucose, through alternative substrates )

• increases breakdown of fats

explain the effects of glucagon on the blood glucose

• alpha cells will release glucagon

• the glucagon will act on the liver by increasing glycogenolysis in the liver

• and it has an effect on the muscles by increasing the protein breakdown

• and increasing fats into fatty acids int eh adipose tissue

• this causes blood glucose to rise

what is hypoglycaemia

what is hyperglycaemia