IB Biology Homeostasis of blood glucose

Blood glucose levels would rise after a meal if the body didn’t contain the hormone insulin.  

Insulin is produced in the ß -cells of the Islets in the pancreas.  It travels in the blood and causes muscle and liver cells to absorb glucose from the blood.  This lowers the blood glucose level.  

The Pancreatic Islets are part of the Endocrine system.  They are glands which release hormones that are transported in the blood.  The hormones bind to the plasma membranes of  "target cells", in this case muscle and liver cells.

There are also a-cells in these Islets which produce another hormone called, glucagon. This hormone causes liver & muscle cells to break down glycogen stores into glucose.  This raises the blood glucose level.

Blood glucose concentration are kept within normal limits by these hormones using negative feedback.  So after you eat some food blood glucose levels start to rise but this causes insulin levels to also rise, and lowers the blood glucose level.  This is an example of negative feedback. 

The cause (blood glucose level rising) produces a negative effect on itself (the production of insulin, and lowering of blood glucose level).   http://health.howstuffworks.com/diabetes.htm

Diabetes and blood glucose levels

Diabetes has two forms:

  • insulin-dependent diabetes (Type 1)
    results from the destruction of pancreatic B cells in the islets of Langerhans with the consequent loss of insulin production
  • non-insulin-dependent diabetes (Type 2)
    has many possible causes leading either to lowered insulin secretion or increased resistance to the action of insulin— mostly due to a loss of insulin receptors in muscles and liver cells.

Diagnosis is important for the proper treatment and management of the disease.  In all cases, however, hyperglycaemia is present and an elevated glucose concentration can be detected in both blood and urine due to the inability of the liver & muscle tissues to take up glucose (an insulin-dependent process). 

Symptoms of Diabetes

Regardless of the type of diabetes, diabetics exhibit several (but not necessarily all) of the following symptoms:

  • Excessive thirst (polydipsia)
  • Frequent urination (polyuria)
  • Extreme hunger or constant eating (polyphagia)
  • Unexplained weight loss
  • Presence of glucose in the urine (glycosuria)
  • Tiredness or fatigue
  • Changes in vision
  • Numbness or tingling in the extremities (hands, feet)

Diagnosis of diabetes is done by measurement of blood glucose in a glucose tolerance test.  However, measurement of urinary glucose is also a good indication of diabetes.