3.6.4.2 Control of blood glucose concentration

Hormonal Transmission

Protein Hormones

Large and potentiially hydrophilic, transported in aquesous blood

Steroid (lipid) hormones

Small and hydrophobic - based on cholesterol structure, Act upon DNA in the nucleus

Diffuse across the phosophlipid bilayer of cells

Bind to complementary receptors on target cells and initiate a s response by the cell

Natural sources of blood glucose

Directly from the diet

Break down of glycogen (glycogenolysis)

gluconeogenesis - prodcution of new glucose from sources other than carbohydrates

Pancreas

Exocrine function - secretes digestive enzymes into the pancreatic duct

Endocrine function - secretes hormones directly into the blood

Islets Of Langerhans

Alpha Cells - produce and secrete glycagon

Beta Cells - produce and secrete insulin

Insulin and Beta Cells

If blood glucose becomes high, Beta cells act as a controller and detect this stimulus

Beta cells secrete insulin (a peptide hormone) into the blood

Insulin binds with a complementary cell surface receptor protein found on the surface of most body cells

Binding activates protein kinase enzymes to increase the rate of respiration (increase glucose consumption), increase glycogenesis (using many glucoses to form glycogen in liver and muscle cells), increase rate of lipogenesis (using glucose to synthesis lipid in liver cells), increase permeability of cells to glucose (more glucose transporter channels are inserted into the membrane)

Stimulus

High Blood Glucose Concentration

Receptor

Beta Cells in Pancreas

Hormone Released

Insulin

Traget Cells

Insulin binds to receptors on membrane of liver and muscle cells

Action of effector cells

Glucose transporters inserted into cell membrane. Glycogenesis, lipogenesis, increased respiration. Glucose removed from blood

Negative Feedback Lopp

Beta cells detect set point reach. stop releasing insulin

Glucagon and Alpha Cells

If blood glucose becomes lower than normal, alpha cells in the pancreas act as receptors and detect this stimulus

Alpha cells secrete glucagon (peptide hormone) into the blood

Glucagon binds to complementary cell surface receptor proteins found on the surface of liver cells only.

secondary messenger model

Glucagon binds to a specific cell surface receptor protein on liver cell membranes.

This causes the membrane to change shape, activating a membrane bound enzyme called adenyl cyclase.

This enzyme converts ATP to cyclic AMP. cAMP activates the protein kinase enzymes. These enzymes cause increased glycogenolysis and gluconeogenesis.

This results in increased glucose concentration in cells and a faster rate of diffusion of glucose into the blood.

Adrenaline

Adrenaline in another hormone that increases blood sugar levels in response to pain/shock 'fight or flight' response

Its produced in the adrenal glands and binds to complementary receptors on liver cell membranes and activates the same secondary messenger model as glucagon

It raises blood glucose by activating the enzyme that causes the breakdown of glycogen to glucose in the liver and inactivating an enzyme that synthesises glycogen

Diabetes

The partial or complete breakdown of glucose homeostasis

affects ~1.6 million people in the UK

Type 1

Caused by autoimmune condition, their immune system has destroyed the beta cells. Needs alleles, genetic risk and environmental factors, infected with virus

Insulin dependent diabetes mellitus. The beta cells don't produce insulin in response to high concentration of glucose in the blood

Onset in children, very quickly over a few weeks

Extreme symptoms: high blood glucose, glucose in urine, thirst, excessive urination

After eating a meal they measure their blood glucose, and inject a specific volume of insulin to reduce their blood glusoce. insulin pump

Type 2

Caused by cells no longer responding to insulin due to genetic factors, insulin receptors are less complementary. Environmental factors, persistent high blood glucose levels due to a diet with lots of sugars, simple carbs, obesity

Insulin resistant diabtes mellitus. Other cells of the body no longer respond to insulin

Onset in older adults (40+), very slowly over months/years

Gradual symptoms

Control with exercise, control carb intake, lose weight, lower glucose levels with specific drugs