Category Archives: Homeostasis

Homeostasis – Regulation of Blood Glucose Levels

isle of langerhans

The pancreas is an important exocrine and endocrine gland located between the stomach and small intestine. It has two important roles (1) as an exocrine gland it releases digestive enzymes into the duodenum that aid in the break down of food (2) as an endocrine gland it releases insulin and glucagon into the bloodstream.

Insulin is produced in the beta cells of the islets of Langerhans in response to the stimulus of rising blood glucose levels. Insulin travels in the bloodstream and binds with receptor sites on the cell membranes, resulting in a cascade of events dependent on the cell type. In liver cells, for example, glucose in converted to glycogen, fat and carbon dioxide.

Glucagon is produced by alpha cells in the islets of Langerhans in response to the stimulus of falling blood glucose levels. Glucagon travels in the bloodstream and binds to receptor sites on liver cell membranes, resulting in the breakdown of stored glycogen into glucose. This results in an increase in blood glucose levels.

These two hormones act to regulate the body’s blood glucose levels, maintaining an average concentration of 5.0 mmol/Litre (between 3.5 mmol/Litre after several hours without food and 7.0 mmol/Litre soon after a meal). This is a negative feedback loop, as the response results in a change in the stimulus in the opposite direction. A person with diabetes is unable to regulate their own blood glucose levels without external intervention – it may be that their body does not produce enough insulin, as in Type 1 Diabetes mellitus.

Co-ordination and Regulation – Endocrine Systems

Signal_Transduction_Pathways_Model

Image Source

In this chapter you need to become familiar with the following concepts:

  • homeostasis (maintaining a stable internal environment in terms of temperature, hydration, pH, blood pressure and volume, oxygen and carbon dioxide concentration in the blood and the concentration of various ions, including sodium and glucose).
  • stimulus-response and sensors-effectors
  • positive and negative feedback mechanisms
  • glands and hormones, including phermones
  • signal transduction and signaling molecules

it is important to understand that lipid soluble hormones (lipophilic or hydrophobic) can pass through the cell membrane directly, but water-soluble hormones (hydrophilic or lipophobic) bind to a receptor molecule embedded in the cell membrane, which results in the activation of a secondary protein or messenger. This secondary messenger causes the cell to initiate a response. Signal transduction is a series of events (sometimes called a ‘cascade’) that changes the signal received by the cell.

 

Homeostasis – maintaining a stable internal environment

brain copy 2

In Unit 3: Area of Study 2 – Detecting and Responding – a key concept is homeostasis, the process of maintaining a stable internal environment, either within a cell or inside an organism, despite changes in the external environment of that cell or organism. The changes can be temperature, pH, concentrations of various ions, hydration, blood pressure or glucose levels in the blood. Access the first two resources to find out more about homeostasis.