What Is Homeostasis?
Definition
Homeostasis
The regulation of internal conditions to maintain a stable environment for optimal cell function.
- Homeostasis is the regulation of internal conditions to keep them within a safe, functional range.
- Cells work efficiently only when conditions such as temperature, water balance, and blood glucose stay stable.
- Even if the external environment changes, the body keeps these internal factors tightly controlled.
Why Do Living Organisms Need Stable Internal Conditions?
- Enzymes control nearly all reactions in cells and work only within narrow temperature and pH ranges.
- If internal conditions drift too far from optimum, enzyme activity slows or stops.
- Stable conditions ensure cells receive a steady supply of materials and energy.
Example
- High temperature can denature enzymes.
- Unstable blood glucose disrupts energy supply.
- Incorrect water balance causes cells to shrink or burst.
Common Mistake
- Homeostasis doesn't keep everything constant.
- It keeps conditions within a safe, functional range.
What Factors Are Controlled by Homeostasis?
- Homeostasis regulates conditions that directly affect enzyme activity and cell function.
- Key regulated variables:
- Body temperature: ensures enzymes work at optimal rates.
- Blood glucose concentration: provides cells with a steady energy supply.
- Water content of the blood: maintains osmotic balance and blood pressure.
Note
- Breakdowns in regulation can lead to:
- Diabetes when glucose control fails
- Heatstroke when temperature regulation is lost
- Dehydration when water balance is disrupted
How Does the Homeostasis Control System Work?
Homeostasis works through a coordinated system of receptors, coordination centres, and effectors:
- Receptors
- Detect changes (stimuli) in the internal or external environment.
- Coordination centers
- Process information from receptors and send instructions.
- Includes the brain, spinal cord, and pancreas.
- Effectors
- Carry out responses to restore normal conditions.
- Includes muscles and glands.
What Is Negative Feedback and Why Is It Important?
Definition
Negative feedback
A mechanism that reverses a change to maintain stability.
- Negative feedback reverses a change to bring the body back to its normal range.
- If a condition becomes too high, effectors bring it down.
- If a condition becomes too low, effectors bring it up.
- This constant adjustment keeps internal conditions stable.
Exam technique
- In the MYP eAssessment of N21, Question 3a requires the identification of two body systems that interact to regulate body temperature.
- This question tests understanding of homeostasis as a coordinated process, where one system detects a temperature change, and another carries out the response.
- The nervous system monitors body temperature using receptors, while systems such as the muscular or integumentary system help maintain temperature through responses like shivering or reducing heat loss.
- In the MYP eAssessment of N21, Question 3b asked to describe how the two systems identified in part (a) work together when body temperature decreases.
- Correct responses explain that temperature receptors detect a drop in body temperature, signals are sent to the brain, and effectors respond by reducing heat loss and increasing heat production.
How Does the Body Regulate Blood Glucose?
- Blood glucose levels are controlled by insulin and glucagon, two hormones released by the pancreas.
- When glucose is too high:
- The pancreas releases insulin
- Cells absorb more glucose
- The liver converts glucose to glycogen for storage.
- Blood glucose returns to normal.
- When glucose is too low:
- The pancreas releases glucagon
- The liver breaks down glycogen into glucose.
- Blood glucose rises back to normal.
What Is Osmoregulation and Why Is Water Balance Important?
Definition
Osmoregulation
The control of water content in the body.
- Osmoregulation is the control of water content in the body.Water levels change constantly through sweating, breathing out, urination, and digestion.
- Cells need a stable water concentration to avoid shrinking or bursting.
How the body adjusts water balance
- The kidneys filter the blood
- Anti diuretic hormones (ADH) controls how much water is reabsorbed
- More ADH → more water saved → concentrated urine
- Less ADH → more water lost → dilute urine
Tip
- Too little water → cells shrink and become dehydrated
- Too much water → cells swell and may burst
Common Mistake
Water balance isn't about drinking “enough water,” it's about keeping the inside of cells at the correct concentration.
What Are The Key Homeostatic Processes?
| Internal Factor | Systems Involved | What Happens if Not Regulated |
|---|---|---|
| Body temperature | Brain, muscles, sweat glands | Enzymes denature; heatstroke/hypothermia |
| Blood glucose | Pancreas, liver | Diabetes; low energy availability |
| Water balance | Kidneys, ADH, brain | Dehydration; cell swelling (bursting) |
Self review
- Why must blood glucose remain within a narrow range?
- How do insulin and glucagon work together in a negative feedback loop?
- Why do cells malfunction when water balance is disrupted?
- What roles do receptors, coordination centres, and effectors play in maintaining stability?
- Why do enzymes make homeostasis necessary?
