digestive phys and glucose metabolism Flashcards
Pathway of digestion
- ingestion
- mechanical digestion: chewing, churning of stomach and segmentation in stomach
- propulsion: swallowing, peristalsis (esophagus, stomach, small intestine, and large intestine)
- absorption in small intestine and large intestine (mostly water)
- defecation
The pancreas (location, function, anatomy)
- gland with both exocrine and endocrine fxns
- 6-10 inches in length
- 60-100 g in weight
- location: retro-peritoneum, 2nd lumbar vertebral level
- extends in oblique, and transvere position
- parts of the pancreas: head, neck, body and tail
Embryology of pancreas?
- endodermal origin
- develops from ventral and dorsal pancreatic buds (develop independently)
- ventral bud becomes the uncinate process and inferior head of pancreas
- dorsal bud becomes superior head, neck, body, and tail
- ventral bud duct fuses with dorsal bud duct to brecome main pancreatic duct (wirsung)
- pancreas divisum when fails to fuse
What is the definition of exocrine?
- secreeting outwardly via a duct
What is the definition of endocrine?
- secreting inwardly, applied to organs and structures whose functions is to secrete into the blood or lymph a hormone that has a specific effect on another organ or part
Where is there a large capillary network in the pancreas?
- in the islet of langerhans (endocrine part of pancreas)
- islets of langerhan cells are not part of duct system
What cells make up the exocrine part of pancreas?
- acinar cells: secrete pancreatic enzymes into pancreatic duct
What is function of islet of langerhan cells?
- secrete endocrine hormones into blood vessels
Anatomy of islet of langerhans?
- insulin producing B cells are in the center closest to the blood supply and are surrounded by glucagon producing alpha cells. On outside are the delta cells which make somatostatin (produces GH), and the PP cells (gamma cells) that make pancreatic polypeptide
histology of endocrine part of pancreas?
- accounts for only 2% of pancreatic mass
- nest of cells: islet of langerhans
Four major cell types of the endocrine pancreas?
- alpha cells: secrete glucagon
- beta cells: secrete insulin
- delta cells: secrete somatostatin
- F cells (gamma cells) secrete pancreatic polypeptide
Organization of acinar cells and iselt of langerhans?
- islet of langerhans is surrounded by pancreatic acinar cells. The islet cells form cords separated by blood capillaries. The islet is surrounded by reticular fibers separating it from acinar cells
What is function of alpha cells?
- release glucagon; main action is to produce an increase in blood glucose: they do this by -
breakdown of glycogen, stimulates gluconeogenesis (inhibits glycogenesis), increases transport of AA into the liver and stimulates their conversion to glucose - high levels activate adipose cell lipase making fatty acids available for use as energy
What stimulates the release of glucagon?
- released into portal circulation in response to low glucose levels in blood, stimulated by high concentrations of AA and by strenuous exercise
Metabolic effects of glucagon?
- increase glucose, increase ketoacids,
and decrease amino acids
What factors stimulate glucagon secretion?
- hypoglycemia
- amino acids: aginine and alanine
- GI hormones: CCK, gastrin
- fasting
- exercise
- neural influences: vagal activity acetylcholine, sympathetic stim (NE, E)
What factors inhibit glucagon secretion?
- glucose
- somatostatin
- insulin (direct effect)
- GI hormones: secretin, GLP-1
- free fatty acids
- ketoacids
- neural influences: alpha-adrenergic stim
Effect of DPP-4 inhibitors
- block DPP-4 and decrease glucose
- DPP-4 enzyme inactivates GLP-1, and incretin this stimulates insulin release (stim. beta cell production) and inhibits glucagon release which lowers the blood glucose
(DPP-4 is essential in formation of glucose) - impt impact in DM II, won’t work on DM I because there are no beta cells to stimulate
Fuel metabolism during the anabolic state (building up)
- hormones: increased insulin and decreased glucagon
- fuel source is diet
- process: glycogen synthesis, triglyceride synthesis, and protein synthesis
Fuel metabolism in catabolic state?
- catabolism: decreased insulin, increased glucagon
- fuel source: storage depots, process: glycogenolysis, lipolysis, proteolysis, ketogenesis (formation of ketones)
Metabolic effects of Epi?
- increased glucose, free fatty acids from triglycerides, and increased ketoacids from free fatty acids
What hormones promote glucose production (liver)?
- Glucocorticoids, GH, glucagon, Epi
- insulin will inhibit glucose production
What hormone promotes glucose consumption in muscle and adipose tissue?
- insulin
- glucocorticoids, and GH have inhibitory effect on glucose consumption
Function of Beta cells?
- produce insulin: lowers blood glucose by: promoting uptake of glucose by target cells, provides for glucose storage as glycogen, prevents fat and glycogen breakdown
- inhibits gluconeogenesis and increases protein synthesis
- promotes fat storage by increasing transport of glucose by increasing transport of glucose into fat cells
- increases triglycerides synthesis
- Beta cells produce pro-insulin formed by an A and B cahin separated by inactive C-peptide chain which is cleaved by enzymes in the beta cells and packaged in secretory granules, insulin enters protal circulation where 50% used or degraded, 1/2 life is 15 minutes
Where do the main steps of insulin synthesis and secretion by a B cell take place?
- islets of Langerhands
- RER: synthesis of proinsulin
- small transfer vesicle - transport of proinsulin to Golgi
- golgi secretes secretory granules and conversion of proinsulin to insulin occurs
Insulin and glucose relationship in circulation?
- insulin directly enters protal venous circulation before peripheral cirulation: 2/3 of glucose is stored as glycogen in the liver, and other glucose is released back into blood to keep blood glucose at steady state after intake
What is a major regulator of insulin?
- glucose
- in pancreatic beta cell glucose transporters - allow influx of glucose: glucokinase
- results in closure of K+ channels and opening of Ca channels allowing secretion of insulin by exocytosis
What factors stimulate insulin secretion?
- glucose: mannose and galactose
- amino acids
- free fatty acids, keto acids
- glucagon (direct and indirect effects)
- GI hormones: GLP-1 and GIP
- neural influences: vagal activity (acetylcholine), B-adrenergic stimulation
- sulfonylurea drugs
What factors inhibit insulin secretion?
- somatostatin (inhibits both glucagon and insulin)
- fasting
- exercise
- neural influences: sympathetic activity: alpha-adrenergic stimulation (NE and E)
- Leptin: released from fat
What is the effect of insulin on carbohydrates?
- carbs from a meal release glucose:
- stimulates secretion of insulin
- causes uptake and storage of glucose in all tissues
- in muscle if not used glycogen is stored
- in liver stored as glycogen, once liver has stored all the glycogen it can, insulin promotes conversion of glucose to fatty acids
Metabolic effects of insulin
- decrease glucose, free fatty acids, ketoacids (fatty acids aren’t being broken down), and amino acids (proteins being stored in muscles)
Insulin effect on muscle?
- increase GLUT4 transporters
- increase glycogen
- increase glycolysis (glucose to pyruvate)
- increased protein synthesis, decreased protein degradation
- increas in triglycerides (FAs from circulation)
Effect of insulin on liver?
- GLUT2 transporter: increase glucokinase
- increase glycogen
- decrease glucose release: decrease G6Pase
- increase glycolysis: increases acetyl CoA, increases FA synthesis
- increases TG storage and export (VLDLs)
- increase protein synthesis, and decreases protein degradation
Insulin on fat metabolism?
first insulin increased the utilization of glucose (uptake) by most of the body’s tissues, which decreases utilization of fat
- once liver glycogen is maxed all add. glucose forms fatty acids
- fatty acids in the liver form TGs which are released into blood stream and are transported to adipose tissue
- once there insulin activates LPL which splits TGs into fatty acids again for them to be absorbed into adipose cells
What promotes break down of TGs to fatty acids?
- Epi, T3, Cortisol, GH
What promotes TG production from fatty acids?
- insulin
Insulin impact on adipocytes?
- increase GLUT4 transporters
- increase glycolysis: increase alpha-glycerol phosphate, increase acetyl CoA, and increase FA synthesis
- increase TGs: decrease hormone sensitive lipase and increase LPL
Insulin effects on AAs?
- stimulates transport of many AA into the cells
- inhibits the catabolism of proteins especially in muscles cells
- in the liver depresses rate of gluconeogenesis
- What will respond to low plasma glucose
- what will respond to high plasma glucose?
- low glucose: glucagon response
- high glucose: insulin response
Hormonal responses to specific glucose concentrations?
- 80-85 mg/dl: decreased insulin
- 65-70: increased glucagon, increased Epi, and increased cortisol and GH
CNS responses to specific glucose concentrations?
65-70: decreasd glucose uptake 50-55 (60): sympotoms 50: decreased cognition 40: coma 30: convulsion 20: permanent brain damage