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Endocrine Pancreas

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Question	Answer
Regulation of blood glucose levels	Utilised by all body tissues Brain especially sensitive to low glucose Stress response hormones increase blood glucose e.g. fight or flight, cortisol Insulin is the only hormone which decreases blood glucose
Anatomy of the pancreas	Derived from the developing endoderm of the foregut Islets make up 1% of pancreatic mass Islets distinguishable in human embryo from 12th week Surrounded by lots of vessels so is hard to operate on Behind the stomach
Innervation	Innervated by both sympathetic and parasympathetic nerves Via myenteric plexus
Islets of Langerhans	Clusters of 1000 endocrine cells 1 million islets in a human Different islet endocrine types; alpha (glucagon), beta (insulin), delta (somatostatin), PP-cells (pancreatic polypeptide) and epsilon (Ghrelin)
Insulin	Gene located on chromosome 11 Expressed as preproinsulin and processed to make mature insulin Cleavage of C-peptide occurs in the golgi Mature insulin stored in secretory vesicles - 8fg per granule 10000 granules per beta cell
Glucose sensing in beta cells	Increase in glucose moving in through GLUT1/2 Converted to ATP through oxidative metabolism ATP blocks potassium ATP channels Cell depolarises opening CVGGs Leads to exocytosis of vesicles
Biphasic secretion of insulin	Initial rapid rise in insulin conc following glucose consumption Continues to increase over the next 2 hours as glucose moves into cells
Insulin action	Stimulated by increased blood glucose Inhibits release of glucose from the liver Promotes uptake of glucose into muscle and fat
Factors affecting insulin secretion	Increased blood glucose PSNS Amino acids Fatty acids Glucagon Gastrointestinal hormones SNS and Somatostatin inhibit
Insulin receptor	Tyrosine kinase Dimerises on activation and auto phosphorylates Inserts GLUT4 into membrane Enzymes involved in metabolic pathways are activated or inactivated
Main actions of insulin	Carbohydrate metabolism - GLUT4, glycolysis, glycogenesis, inhibits gluconeogenesis and glycogenolysis Protein metabolism - stimulates AA uptake and protein synthesis Lipid metabolism - Stimulates lipogenesis and inhibits lioplysis
Action of insulin on K	Insulin shifts potassium into cells by activating the sodium hydrogen transporter Promotes sodium entry Activates NA K pump Causes electrogenic influx of K
Glucose transporters	GLUT1 - plasma membrane of all cells - glucose, galactose and mannose GLUT2 - intestine, kidney etc - glucose and fructose GLUT3 - everywhere - glucose GLUT4 - muscle - glucose GLUT5 - gut - fructose
Sodium coupled glucose transporters	SGLT1 - intestine and kidneys = (2 NA for 1 glucose) SGLT2 kidney - (1 Na for 1 glucose)
Incretin hormones	GLP-1 and GIP Enhance insulin secretion - more insulin when glucose given orally than IV Appetite regulation Peripheral insulin sensitivity Secreted from small intestine
Healthy vs diseased beta cells	Healthy - incretin hormones are responsible for glucose secretion Diseased - K atp channels responsible for glucose secretion GIP pathway not active in diabetics - explains why metformin has no effect on healthy cells
Release of incretin hormones	Stimulated by glucose, AAs and FAs K cells are glucose dependant and secrete GIP L cells are nutrient regulated and secrete GLP1, peptide YY and oxyntomodulin
How does GLP1 lower glucose	Inhibits glucagon secretion Stimulates insulin secretion Decreases appetite Inhibits gastric emptying
Production and degradation of GLP1	Glucagon - pro-glucagon - GLP1 by prohormone convertase 1/3 secreted GLP1 - small peptides - amino acids by dipeptidyl peptidase IV
Alpha cells and glucagon	Highly redundant Preproglucagon processed into a large number of active proteins Converted to hormone, glucagon etc Cam mobilise glucose or promote glucose uptake Different processing gives different role
Factors affecting glucagon synthesis	Decreased blood glucose SNS AAs GI hormones inhibited by somatostatin and insulin
Glucagon receptors	Gas coupled GPCRs Mostly expressed on hepatocytes and adipocytes Mechanism of action involves adenylate cyclase activity and increase in cAMP Affects both gene expression and post translational modifications
Somatostatin	Inhibitory polypeptide found in brain, GI tract and islets Cleaved from prosomatostatin - 14aas in brain and 28 aa in islets Pancreatic inhibitor of insulin and glucagon secretion - brake on islet cell activity Inhibitory Gas GPCR
Diabetes mellitus	Urine output increases Urine contains raised amounts of glucose Caused by lack of glucose Type 1 - lack of insulin Type 2 - resistance to insulin and collapsing b cell function More than one cause of type 2
Normal blood glucose	Normal fasting plasma glucose - 3.5-5.5 mM Considered hypoglycaemic if <4 mM Diagnosis of diabetes if > 7 mM Normal individuals clear glucose in 2 hours diabetic >11.1 mM after 2 hours
Causes of diabetes mellitus	Type 1 - immune destruction of B cells Neonatal - mutations in K atp channels Type 2 - impaired b cell function and defective insulin signalling in metabolic syndrome Gestational diabetes Maturity onset diabetes of young people - mutations in 6 genes
Type 1 Diabetes	Insulin dependent Immune destruction of beta cells Complete lack of insulin signals starvation increasing gluconeogenesis and glycolysis Ketogenesis is upregulated Peak incidence 12-14 Genetic and environment play a role
Type 2 diabetes	Non-insulin dependent Adult onset and associated with diabetes Combo of insulin resistance and b cell failure No ketogenesis but hyperglycaemia seen Presents as polyuria and polydipsia Can be non-symptomatic at <11.1 mM
Complications of diabetes	Gangrenous foot - poor blood and nerve supply Neuropathy in retina leading to blindness Kidney damage - primary cause of death Albumin detected in urine due to podocyte damage Results from glycosylation of proteins in high plasma glucose
Glycosylated haemoglobin	A form of haemoglobin measured to identify the average plasma glucose concentration over prolonged periods of time HbA1c formed in non-enzymatic glycosylation on exposure to plasma glucose Marker of high glucose over a long period
Glycation	A result of covalent bonding of a protein or lipid with sugars like fructose and glucose A haphazard process that impairs function of targets