Lecture 3: The Endocrine Pancreas Flashcards
energy (food) intake is determined by the balance of activity in which two hypothalamic centres?
- feeding centre > promotes feelings of hunger and drive to eat
- satiety centre > promotes feelings of fullness by suppressing the feeding centre (insulin sensitive)
describe the glucostatic theory
food intake is determined by blood glucose: as [blood glucose] increases, the drive to eat decreases (- feeding centre, + satiety centre)
describe the lipostatic theory
- food intake is determined by fat stores: as fat stores increase, the drive to eat decreases (- feeding centre, + satiety centre).
- leptin is a peptide hormone released by fat stores which depresses feeding activity.
what are the three categories of energy output? describe each
- cellular work > transporting molecules across membranes; growth and repair; storage of energy (e.g. fat, glycogen, ATP synthesis).
- mechanical work > movement, either on a large scale using muscle or intracellularly.
- heat loss > associated with cellular and mechanical work, accounts for half of our energy output.
define metabolism
the integration of all biochemical reactions in the body
what are the three elements of metabolism?
- extracting energy from nutrients in food
- storing that energy
- utlising that energy for work
describe anabolic pathways
- build up
- net effect is synthesis of large molecules from smaller ones, usually for storage purposes
describe catabolic pathways
- break down
- net effect is degradation of large molecules into smaller ones, releasing energy for work.
After eating we enter an absorptive state. Is this an anabolic or catabolic phase?
anabolic phase
Between meals and overnight the pool of nutrients in plasma decreases and we enter a post-absorptive state (aka fasted state) where we rely on body stores to produce energy. Is this an anabolic or catabolic phase?
catabolic
how is [blood glucose] maintained during a fasted state?
- maintained by synthesising glucose from glycogen (glycogenolysis) or amino acids (gluconeogenesis).
what is the normal range of [BG]?
4.2-6.3mM (80-120mg/dl)
what [BG] is considered hypoglycaemia?
[BG] < 3mM
what % of the pancreas had endocrine function?
1%
what are the four types of islet cells and what do they produce?
4 types of islet cells: alpha, beta, delta & F.
- alpha cells produce GLUCAGON
- beta cells produce INSULIN
- delta cells produce SOMATOSTATIN
- F cells produce pancreatic polypeptide (function not really known, may help control of nutrient absorption from GIT.)
does insulin dominate in the fed state or the fasted state?
fed state
does glucagon dominate in the fed or fasted state?
fasted state
what processes does insulin stimulate?
- glucose oxidation
- glycogen synthesis
- fat synthesis
- protein synthesis
what processes does glucagon stimulate?
- glycogenolysis
- gluconeogenesis
- ketogenesis
describe the synthesis and storage of insulin
- synthesised as a large preprohormone, preproinsulin, which is then converted to proinsulin in the endoplasmic reticulum.
- proinsulin is then packaged as granules in secretory vesicles.
- within the granules, the proinsulin is cleaved again to give insulin and C-peptide.
- insulin is stored in this form until the beta cell is activated and secretion occurs.
how does glucose activate beta islet cells?
- when glucose is abundant it enters cells through GLUT proteins and metabolism increases.
- this increases the [ATP] within the cell causing the [ATP] sensitive K+ ion channel on the surface of the beta cell to close.
- intracellular [K+] rises, depolarising the cell.
- voltage-dependent Ca2+ channels open and trigger insulin sensitive vesicle exocytosis into the circulation.
how does insulin stimulate glucose uptake?
- insulin binds to tyroskine kinase recptors on the cell membrane of insulin-dependent tissues.
- in muscle and adipose tissue, insulin stimulates the mobilisation of GLUT-4 which then migrates from the cytoplasm to the cell membrane and is then able to transport glucose into the cell.
how does insulin indirectly alter glucose transport in hepatocytes?
- in fed state, liver takes up glucose because insulin activates hexokinase which lowers [intracellular glucose] creating a gradient favouring glucose movement into cells.
