Endocrine: Glucose and its importance

What are the limits that blood glucose is regulated between?

blood glucose is regulated within very tight limits (4.0-7.0mmol/l in health)

What regulates blood glucose?

• hormones

Why is Glucose regulation so important?

• cells get energy through glycolysis:

• glucose is broken down to CO2 and H2O and ATP is formed

• cells harvest the energy in the form of ATP of those reactions.

In what two conditions can glycolysis occur?

• Glycolysis can occur under anaerobic conditions where lactic acid will be formed as well as ATP

• or under aerobic conditions where pyruvate is transported into the mitochondria and undergoes the Krebs/Citric Acid cycle.

What is the Krebs Cycle/ Citric Acid cycle?

• the citric acid cycle is a series of chemical reactions used by all aerobic organisms to generate energy through the oxidation of acetal CoA

• it occurs in the mitochondrial matrix

• we generate NADH and FADH2 and ATP

• NADH and FADH relay electrons extracted from food to the Electron Transport Chain

What is Acetal CoA derived from?

Derived from the breaking down of carbohydrates, fats and proteins via Pyruvate

What is the ETC?

• electron transport chain

• occurs in cristae of mitochondrion

• chain is made from proteins

• carries alternate reduced and oxidised states as they accept or donate electrons

• electrons drop in free energy as they go down the chain and are finally passed to O2, forming H2O

• the reactions are exergonic and thus releases free energy

• this free energy is used to translocate protons across the inner mitochondrial membrane, this will generate ATP.

How does glucose enter our cells?

• through glucose transporters

• different cells need different glucose transporters

What cells use GLUT1 glucose transporters?

• epithelial cells of the blood-brain barrier

• erythrocytes

• placenta cells

• fetal tissue cells

What cells use GLUT2 glucose transporters?

• liver cells

• kidney cells

• intestine cells

• pancreatic B cells

What cells use GLUT3 glucose transporters?

• neurones

• sperm

• white blood cells

• placental/embryonic cells

What cells use GLUT4 glucose transporters?

• skeletal muscle

• cardiac muscle

• adipose tissue

• some kidney tissue

How is glucose taken up by the gut and glomerular filtrate?

• it is important to note that glucose uptake from the gut and from the glomerular filtrate is completely achieved by Na dependent glucose transporters (SGLT1 and 2), not the GLUT family transporters.

What does exocrine mean?

• the secretion of a substance out through a duct

What does endocrine mean?

• secretion and synthesis of hormones from cells/glands (islets of Langerhans) that travel through blood

List the endocrine function of the pancreas

• there are two major hormones, insulin and glucagon

• minor ones include somatostatin and pancreatic polypeptide

What is somatostatin and its effect on the body?

• a hormone that many different tissues produce, but it is primarily found in the nervous and digestive systems and affects several areas of the body.

• In the pancreas, somatostatin inhibits the secretion of pancreatic hormones, including glucagon and insulin

What is Pancreatic Polypeptide and its effect on the body?

Pancreatic polypeptide (PP) is a hormone released from the pancreas after eating that helps regulate digestion and appetite,

• primarily by slowing gastric emptying, inhibiting gallbladder contractions, and reducing pancreatic secretions.

What is the importance of insulin?

• insulin is vitally important for achieving the movement of glucose from our bloodstream into tissues and organs, where it is needed as an energy source

How does insulin trigger the uptake of glucose into cells?

• glucose is transported into pancreatic beta cells through facilitated diffusion by GLUT2 glucose transporters 

• intracellular glucose metabolism increases ATP levels.

• A high ATP/ADP ratio induces closure of K+ channels, leading to cell membrane depolarisation

• this promotes the opening of Ca2+ channels, extracellular Ca2+ enters the beta cell, and triggers insulin exocytosis (release)

What hormone increases glucose uptake by cells?

• GLP-1 amplifies this response