Pancreas anatomy and physiology Flashcards
Label the canine pancreas and associated structures
what digestive enzymes are secreted from the pancreas?
Trypsin and carboxypeptidase - acts on peptides/proteins
Lipase - acts on triglycerides
Amylasae - acts on starch
Phospholipase - acts on phospholipids
Ribonuclease - acts on RNA
Deoxyribonuclease - acts on DNA
What cells are found in the Islets of Langerhans and what do they secrete?
Beta cells - insulin
Alpha cells - glucagon
Delta cells - somatostatin
What is the function of somatostatin?
Produced by hypothalamus, stomach, intestine and pancreas
Suppressed insulin and glucagon secretion
Also inhibits growth hormone
How is insulin produced?
First synthesised as preprohormone
Then converted to prohormone = proinsulin
Intracytoplasmic pool of proinsulin ready for quick release
Removal of C-peptide from proinsulin => insulin
Describe the structure and degradation of insulin
2 polypeptide chains connected by 2 disulfide bonds
Degradation by liver or kidney via cleavage of disulfide bonds within target cells
Describe the role of C-peptide in insulin secretion
Connecting peptide - removed from pro-insulin upon secretion
Released in equal amounts to insulin
Biologically inactive and removed at slower rate
Can be used to measure pancreatic function
Describe the flow of insulin
Secreted by pancreas
Enters portal vein => liver
Acts upon liver
Enters general circulation
How is insulin secretion regulated?
3 mechanisms:
- nutrients: glucose and AAs
- GI hormones (incretins) e.g., gastric inhibitory peptide (GIP and glucagon like peptide (GLP-1)
- ANS (PNS stimulates, SNS inhibits)
What is the effect of nutrients on insulin?
Increased secretion when nutrients are abundant (after feeding)
Moves energy substrates into storage
Insulin = anabolic hormone
What is the process that causes release of insulin from B-cells?
calcium-mediated exocytosis
How is insulin secretion controlled by the intestinal tract?
Increased GIP (gastric inhibitory peptide) and GLP-1 (glucagon-like-peptide) when food reaches intestine
=> insulin release from pancreas
Describe the parasympathetic control of insulin secretion
Increase in parasympathetic activity via vagus nerve => stimulates insulin secretion after feeding
Describe the sympathetic control of insulin secretion
Direct innervation (sympathetic neurones)
Indirect response via adrenaline
Stress response: hyperglycaemia
Insulin secretion and action are inhibited
What are the 2 phases of insulin secretion?
First phase: release of intracytoplasmic pool of proinsulin via calcium mediated exocytosis
Second phase: insulin secretion from new protein synthesis
Describe the process of calcium mediated exocytosis in beta cells
How do GLUT4 glucose transporters work?
Insulin stimulates translocation of GLUT4 proteins from cytoplasmic vesicles to plasma membrane in skeletal muscle and adipose tissues
Insulin-responsive glucose transporters
Fill in this table of the function and location of glucose transporter types
Describe the impact of insulin on the brain
Insulin-independent GLUT1 transporter takes glucose into cells based on conc gradient
No GLUT4 in brain except for in satiety and appetite centres so insulin required for glucose uptake here (this is how hypothalamus detects glucose levels)
Without insulin => increased appetite
Describe the effect of insulin on fat metabolism
Inhibits hormone-sensitive lipase (HSL) => decreases lipolysis
Stimulates lipogenesis (production of fatty acids from glucose)
Promotes lipoprotein lipase (LPL) => increases delivery of fatty acids in tissues
How does insulin stimulate lipogenesis?
Excess glucose increases TCA cycle intermediates (citrate)
Activates acetyl CoA carboxylase (ACC)
Forms malonyl CoA (Fat precursor)
What is the impact of insulin on protein metabolism?
Increases AA uptake by tissues
Increases rate of transcription and translation
Inhibits catabolism of proteins
Depresses rate of gluconeogenesis within liver (inhibits enzymes and lower AA supply from tissues)
What is the impact of insulin on the liver?
No GLUT4 - glucose uptake by GLUT2
Inactivates liver glycogen phosphorylase (inhibits glycogenolysis)
Increases glycogen synthase activity (stimulates glycogenesis)
Promotes conversion of glucose into fats (lipogenesis)
Inhibits gluconeogenesis
Describe the formation and metabolism of glucagon
Secreted by alpha cells of pancreas
Synthesised as preproglucagon
Rapidly converted to glucagon
Matbolised in liver and kidneys
What is the action of glucagon?
Catabolic hormone
Respond to hypoglycaemia
Active between meals to maintain glucose levels (inter-prandial period)
Activated during negative energy balance (starvation)
Stimulates glycogenolysis and gluconeogensis in the liver
Why is glucagon secreted after a protein-rich meal?
high amino acid levels - promotes gluconeogenesis
Post-prandial hypoglycaemia protection:
- increased insulin stimulated by AAs would cause low blood glucose levels
Why are both insulin and glucagon stimulated by amino acids in circulation?
Insulin => decreased amino acids and glucose levels
Glucagon => protection from hypoglycaemia due to decreased glucose
Fill in this table showing the effect of hormones on metabolism
