Blood Glucose Regulation Flashcards
Endocrine role of pancreas.
- Islet of Langerhans -> produces alpha and beta cells.
- Alpha cells -> make glucagon hormone -> Increase blood glucose.
- Beta cells -> insulin hormone -> decrease blood glucose.
Exocrine role of pancreas.
Acinar cells -> produce mixture of digestive enzymes (“pancreatic juice”) - which passes down pancreatic duct - into small intestine to help digest food.
How is blood glucose regulated?
Normal bgc = 90 mgcm-3 blood.
If falls too low:
- Low cell resp rate - Decrease in ATP - less energy for active processes.
If raises too high:
- Glucose in blood decreases water potential -> H20 leaves cells by osmosis to blood - shrink/stop functioning -> increase BP.
Response to increased blood glucose conc.
After eating -> increase detected by B cells of IOL, which secrete insulin into bloodstream.
- Body cells have receptors to respond to insulin on cell surface membrane. Insulin binds to these receptors (made of glycoproteins).
- Liver and muscle cells respond most
How cells respond to an increase in BGC:
1- more glucose transporter proteins inserted into cell membrane, so more glucose taken up from blood by facilitated diffusion.
2- Increase in conversion of glucose to glycogen (glycogenesis).
3- Increase in cell respiration rate to use up glucose.
4- Increase conversion of glucose to lipids.
5- insulin also INHIBITS glucagon.
This all decreases BGC -> insulin is then broken down by enzymes in cells of liver.
Response to decreased BGC:
Detected by alpha cells of IOL -> secrete glucagon - can only attach to cell membrane of liver/fat storage cells.
How cells respond to decreased BGC.
1- Increase breakdown of glycogen into glucose (glycogenolysis).
2-Decrease cell resp rate so less glucose used up.
3- Glucose generated from a.an and lipids (gluconeogenesis).
4- Increase release of glucose into blood by facilitated diffusion.
5- Glucagon also INHIBITS insulin.
What messenger system do both processes use?
Both insulin and glucagon are protein based hormones so both use 2nd messenger system
resting state of insulin secretion.
1- potassium ion (k) channel opens.
2- Potassium ions diffuse out of cell.
3-So potential difference across membrane is -70 mv -> more negative on inside.
4- Low conc of glucose in blood so there is little to no uptake into cell from blood through glucose transporter.
5- ATP decrease and ADP increases. Low respiration rate, so K+ ions channels stay open as otherwise ATP joins to K+ channels (causing them to close).
6- Membrane hyperpolarised.
7- So voltage-gated Ca 2+ channels stay closed - so Ca2+ ions cannot enter.
8- So no secretory vesicles release insulin by exocytosis.
How insulin is releases at glucose stimulated state - when conc is high.
1- High glucose conc in blood so glucose enters cell by glucose transporter.
2- ATP inc ADP dec. High respiration rate as glucose used up so ATP binds to K+ channels, closing it (ATP sensitive K+ channels).
3- K+ ions can no longer diffuse out of cell so PD goes to -30mv across membrane (so membrane depolarised).
4- Membrane depolarised.
5- Causes voltage - gated Ca 2+ channels to open. Ca2+ diffuses in (facilitated).
6- Causing secretory vesicles to release insulin by exocytosis.
