Glucose Metabolism Flashcards
What cells of the islets of langerhans produce insulin?
beta cells
what type of signal is insulin?
the body’s most important anabolic signal
how is insulin first produced?
it is first produced as a prohormone typical of a peptide hormone in the pancreas
what does proinsulin consist of?
it consists of 3 domains
what is the half life of insulin?
5-8 mins in the plasma and metabolised in kidney and liver
what is secretion of insulin secreted by?
by a number of factors, mainly elevation of glucose and amino acid levels in plasma
GLUT?
glucose transport protein
Once GLUT detect the increase in glucose in blood what happens?
glucose is converted to … –> increase in ATP –> Voltage gated calcium channels –> influx of Ca –> secretion of insulin into the extracellular fluid by exocytosis
what response does a glucose-stimulated secretion of insulin follow?
it follows a biphasic response
Describe the biphasic of insulin secretion?
1st phase is release of pre-formed insulin (lasts 5-15mins elevation)
2nd phase is more prolonged due to the synthesis of new insulin
GIP?
gastric inhibitory peptide
what is insulin also secreted by?
by hormone produced in the intestinal tract - particularly GIP
after eating, what happens regarding GIP?
the food in the intestines causes GIP release which travels through the circulation to the pancreas where the B cells are stimulated to secrete insulin
What does an anticipatory release of GIP result in?
insulin response is much greater when glucose administered orally compared to systemically
what does insulin have an effect on - regarding carbs?
has an effect on metabolism of carbs proteins and fats –> lowers glucose, AA and FA in the blood
what does insulin promote?
intracellular conversion of glucose to storage forms –> target cells are hepatocytes, myocytes and adipocytes
what are the metabolic actions of insulin?
cellular glucose uptake and glycogen synthesis
cellular amino acid uptake and protein synthesis
metabolism of glucose, amino acids and lipids
when is insulin secretion enhanced?
after meals
what does insulin inhibit?
inhibits gluconeogenesis
hepatic gluconeogenesis requires?
amino acids
how does insulin inhibit gluconeogenesis?
because hepatic gluconeogenesis requires AA and insulin increases cell uptake of AA
insulin also inhibits the enzymes required for gluconeogenesis
insulin overall function
gets glucose and amino acids out of bloodstream and into cells
and creates stores of glucose
where is glucagon secreted from?
alpha cells - first synthesised as a precursor molecule
what type of hormone is glucagon?
single chain hormone
what is the primary target organ of glucagon?
the liver and mobilises glucose from hepatic glycogen and gluconeogenesis
what is glucagon release stimulated by?
by a decrease in plasma glucose (unlike insulin)
where is glucagon metabolised?
in liver and kidney
half life of glucagon?
half life of 5-6 mins
other than a decrease in plasma glucose, what else stimulates release of glucagon?
an increase in plasma amino acids (like insulin)
it needs to balance out glucose
what effect does glucagon have on adipose tissue?
stimulates hormone - sensitive lipase
increases ffa concentration in plasma
how is glucose taken up by cells?
by using carrier proteins know as GLUTS
particularly in skeletal muscle cells
facilitated diffusion down conc gradient
recruited by insulin
what transport of glucose isn not dependant on insulin?
in neurones as brain needs constant energy
where are pancreatic hormones released from?
from a small cluster of cells called the Islets of Langerhans which make up approx 2% of the gland
what cells secrete glucagon?
α-cells from the islets of langerhans
what cells secrete somatostatin?
δ-cells
what cells secrete pancreatic polypeptide?
PP cells
what are the endocrine functions of the pancreas?
produces hormones
capillaries transport secreted hormones to the portal vein
what are the exocrine functions of the pancreas?
pancreatic juice
what are the 3 domains that proinsulin consists of?
-amino-terminal β-chain, carboxyterminal α-chain and the connecting inactive C-peptide
what does the principal action of insulin involve?
it involves transport of glucose into certain tissue cells
how does the autonomic nervous system stimulate secretion of insulin?
there is increased activity in the parasympathetic nerve fibres in the vagus nerve which stimulates secretion
what insulin increase the synthesis of?
increases the synthesis of glycerol and FAs into triglycerides when entry of glucose into cells increases
what insulin inhibit the breakdown of?
inhibits the breakdown of triglycerides and builds up fat stores
