L27 Regulation Of Glucose Flashcards
(32 cards)
What are the 3 main islet secretory cells?
- β (65%)
- α (20%)
- Delta (10%)
What does the beta and alpha cells of endocrine pancreas secrete?
β cells – insulin (peptide hormone), proinsulin, C peptide, amylin (IAPP)
α cells – glucagon
What does δ and f cells in endocrine tissue secrete?
δ cells – somatostatin
F (PP) cells – pancreatic polypeptide
What do ε cells produce?
Ghrelin protein
Give me examples of endocrine cells (5
ε cells
δ cells (delta)
β cells (beta)
α (cells (alpha
F (PP) cells
How are islets of langerhans perfused?
- Small arteries enter islet core and distribute blood through the fenestrated capillaries.
- Through vascular arrangement - venous blood of one cell type bathes the others.
- Richly perfused blood metabollically activate, releases hormone and sense nutrients.
How do the endocrine cells communicate to each other?
- Via gap junctions between the beta and alpha
Delta cells send dendrite-like processes to beta cells
The islets of Langerhans receive nerve signals from which types of neurones?
Adrenergic
Cholinergic
(Peptidergic neurons)
Describe how insulin secretion is regulated
1) High blood glucose stimulates insulin syntehsis + secretion, low levels inhibit
2) Neural control - Parasympathetic nervous system stimulates insulin secretion, sympathetic inhibits insulin
3) Humoral factors - GIP, Amylin, Somatostatin
4) Drugs
What is the mechanism of secretion in the beta cells of pancreas?
- Glucose enters beta cell through GLUT2 and is metabolized through glycosis and oxidative phosphorylation which increases ATP levels
- Increased ATP levels results the closing of KATP channels preventing outflow of K+
- Reduced outflow of K+ = buildup of positive charge inside the cell, causing membrane potential to depolarise
- Depolarisation opens voltage-gated calcium channels
- Calcium ions enter and secrete out insulin through exocytosis.
Receptor activation initiates a cascade of phoshporylation events that may activate or inhibit what? (4)
- PKC
- Phosphatases
- Phospholipases
- G proteins
Range of downstream effects - cell grwoth, proliferation, gene expression
What does down regulated mean?
The cell becomes less responsive to insulin which can happen when receptors become less sensitive to insulin
What are the two brief effects of insulin action?
- Decreases blood glucose concentration
- Increased glucose transport into target cells by insertion of GLUT4
Which body cells are mainly targeted by endocrine hormones?
Liver + muscle tissues are targeted to store glucose as glycogen
What is glycogenesis?
Conversion of glucose to glycogen
What is lipogenesis?
Excess glucose converted into fat
Do insulin have a stimulatory and an inhibitory effect?
Stimulates formation of glycogen from glucose (glycogenesis)
Inhibits glycogenolysis
Inhibits gluconeogensis
What are the 4 major muscle effects that the actions of insulin have?
1) Increased glucose uptake
2) Promotes glycogen synthesis
3) Promotes glycolysis and carbohydrate oxidation
4) Promotes protein synthesis
What are adipocytes?
Fat cells that store energy in the form of triglycerides (fats)
What does Lipoprotein lipase (LPL) do?
It’s an enzyme that breaks down triglycerides and releases FA
What do insulin do to adipocytes?
Insulin generally inhibits lipolysis in adipocytes
What is lipolysis?
Metabolic process by which triglycerides (fats) are broken down into glycerol and free fatty acids
What effects do insulin have on Na+/K+ pumps?
Promotes K+ uptake into cells through increased activity of N+/K+ ATPase
Direct effect on hypothalamic satiety centre
What is diabetes mellitus?
A group of metabolic disorder characterised by high blood sugar levels over a prolonged period
