W1 Glucose Metabolism Flashcards
pancreatic hormones are produced by which combination of glands?
endocrine and exocrine glands
a small cluster of cells called the islets of langerhans make up approximately what percentage of the gland?
2%
which type of cells stimulates the release of insulin?
beta cells
which type of cells stimulate the secretion of glucagon?
alpha cells
which type of cells secrete somatostatin?
delta cells
what are PP cells?
pancreatic polypeptide 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?
formation of pancreatic juice
what is the body’s most important anabolic signal?
insulin
what is insulin first produced as?
a prohormone typical of a peptide hormone in the pancreas
proinsulin consists of what 3 domains?
amino-terminal beta-chains
carboxyterminal alpha-chains
and connecting inactive C-peptide
what is the principle action of insulin?
transporting glucose into certain tissues
what is the half life of insulin in plasma?
5-8 minutes
where is insulin metabolised?
the kidney and liver
what is secretion of insulin mainly stimulated by?
the elevation of glucose and amino acid levels in plasma
what happens to allow the increased secretion of insulin?
voltage gated calcium channels allow and influx of calcium causing a secretion of insulin into the extracellular fluid by exocytosis
what is GLUT?
a glucose transport protein
glucose stimulated secretion of insulin follows a biphasic response, briefly describe stage 1 and 2:
1 - a spike due to the release of pre-formed insulin (from 5-15 mins)
2 - a gentle curve which is more prolonged due to synthesis of new insulin
insulin is also secreted by hormones produced in the GIT particularly GIP, what does GIP stand for?
gastric inhibitory peptide
what effects does food in the intestines have on insulin?
it causes GIP release which travels to the pancreas where beta-cells are stimulated to secrete insulin
insulin response is much greater when glucose is administered orally or systematically?
orally (anticipatory release of GIP)
how does the autonomic nervous system effect insylin secretion?
increased activity in parasympathetic nerve fibres in the vagus nerve stimulates insulin secretion
does insulin increase or decrease levels of glucose, amino acids and fatty acids in the blood?
decrease
insulin promotes intracellular conversion of glucose to storage forms, what are the target cells for this?
hepatocytes, myocytes and adipocytes
metabolic actions of insulin occur through its effects on membrane transport causing what?
- cellular glucose uptake and glycogen synthesis
- cellular amino acid uptake and protein synthesis
- metabolism of glucose, amino acids and lipids
in secretion of insulin enhanced before or after meals?
after
insulin causes gluconeogenesis inhibition, what are the reasons why?
it requires amino acids and insulin increases cell uptake of amino acids, it also inhibits enzymes required for gluconeogenesis
insulin increases synthesis of glycerol and fatty acids due to an increase of what substance?
triglycerides (when glucose entry increases)
how does insulin build up fat stores?
by inhibiting the breakdown of triglycerides
glucagon is first synthesised as what?
a precursor molecule
is glucagon a single or double chain peptide hormones?
single
what is glucagon’s primary target organ?
the liver
glucagon mobilises glucose from hepatic glycogen and what?
gluconeogenesis
what is glucagon stimulated by?
a decrease in plasma glucose (opposite of insulin)
and/or an increase in plasma amino acids (like insulin)
where is glucagon metabolised?
in the liver and kidney
what is glucagon’s half life?
5-6 mins
glucose is taken up by cells using carrier proteins know as what?
glucose transporters/GLUTs
how do GLUTs transport glucose?
allow facilitated diffusion down concentration gradients
