Homeostasis

Joanna George-Johnson, Contributor

ONE OF the most important jobs of multicellular organisms is that of maintaining a stable internal environment. This is called homeostasis.

The internal environment that needs to be kept stable is the intracellular fluid or tissue fluid as it is commonly called.

Tissue fluid is basically drained plasma. As blood passes by the cells in the body through the capillaries, substances are exchanged between the contents of the capillaries and the outside.

During this exchange, a significant amount of fluid is drained out of the capillaries. This fluid constantly bathes the cells of the body, thus forming their external environment.

The nature of the tissue fluid can then affect the functioning of the cells. Actually, if homeostasis is disrupted, cells could suffer or even die.

Among other things, the body needs to keep the following at a steady state:

• pH
• Water concentration
• Salt concentration
• Glucose concentration
• Temperature

Terms to Know

• Set point: Is the 'ideal' or 'normal' value of the specific condition or state. For example, 80mg/100ml of blood is the normal setting for blood glucose levels in the body.
• Receptors: Receives or detects the change in the condition and sends this information to a control centre.
• Effector: The mechanism that has an 'effect' on the condition that has deviated from the norm.
• Negative feedback: The mechanism that the body uses to maintain homeostasis. It occurs when feedback (from sensor to integrator) results in a reversal of the direction of change. Negative feedback tends to stabilise a system, correcting deviations from the set point.

Control of blood glucose levels

The following outlines what takes place when the level of glucose in the body goes above normal:

• You eat a meal.
• Glucose is absorbed into the bloodstream by the small intestines.
• This increase in glucose levels (above 80mg/100ml blood) is detected.
• The pancreas release insulin into the blood.
• Glucose is converted to glycogen and stored for future use.
• Blood sugar levels return to normal.
• The pancreas stops releasing insulin.
• You eat again to keep your blood sugar levels from falling.

In the event that the levels fall below normal, a similar mechanism is initiated. However, in this case, the hormone that is secreted by the pancreas is glucagon. This hormone causes the glycogen that is stored in the liver to be broken down into glucose.

Diabetes is a disease where the body is unable to keep the level of glucose in the blood from getting too high. Thus, it may be considered a disease that happens when homeostasis is not maintained.

Questions

1. Define homeostasis and explain why it is important.

2. Outline what would happen if the level of glucose in the blood gets too low.

• These students give praise to God during Kingston College's Inter-Schools Christian Fellowship gospel concert dubbed: 'Power in the Blood: Freedom Stems from the Root', at the school's Melbourne campus, Upper Elletson Road, on Friday, January 18. -Anthony Minott/Freelance Photographer

Joanna George-Johnson teaches at Ardenne High School.