8.2 Homeostasis

Homeostasis is the process by which organisms keep internal conditions relatively constant despite changes in the external environment. Animals have two environments in their lives: an external environment in which the organism is situated, and an internal environment in which the tissues live.

Definition

Homeostasis: Homeostasis means 'keeping things in balance'. Homeostasis is the process by which organisms keep internal conditions relatively constant despite changes in external environment.

External Environment: The external environment consists of varying conditions of atmosphere, marine and freshwater.

Internal Environment: The internal environment is formed by the interstitial fluid or tissue fluid that surrounds and bathes all the tissues and circulating fluids like lymph or plasma the liquid part of the blood.

Main Idea

• Animals have two environments in their lives.
• External environment — in which the organism is situated.
• Internal environment — in which the tissues live.
• External environment consists of varying conditions.
• Internal environment is formed by interstitial fluid or tissue fluid.
• It also includes circulating fluids like lymph or plasma.
• Homeostasis means 'keeping things in balance'.
• Homeostasis is the process by which organisms keep internal conditions relatively constant.
• The human organ systems are working constantly to maintain a controlled, stable environment.
• The digestive system takes in and digests food.
• The respiratory system adds oxygen to the blood and removes carbon dioxide.
• The liver and kidneys contribute greatly to homeostasis.
• The hormone insulin regulates glycogen storage.
• The kidneys excrete wastes and salts.

Core Concept

• Homeostasis = keeping internal conditions constant
• External environment = outside the organism
• Internal environment = interstitial fluid; lymph; plasma
• Digestive system = takes in and digests food
• Respiratory system = adds oxygen; removes carbon dioxide
• Liver = removes glucose; stores glycogen
• Kidneys = excrete wastes and salts
• Insulin = regulates glycogen storage

Detailed Explanation

Homeostasis

• Animals have two environments in their lives, an external environment in which the organism is situated and an internal environment in which the tissues live.
• The external environment consists of varying conditions of atmosphere, marine and freshwater.
• The internal environment is formed by the interstitial fluid or tissue fluid that surrounds and bathes all the tissues and circulating fluids like lymph or plasma the liquid part of the blood.
• Homeostasis means keeping things in balance'.
• Homeostasis is the process by which organisms keep internal conditions relatively constant despite changes in external environment.

Role of Organ Systems

• The human organ systems are working constantly to maintain a controlled, stable environment.
• The digestive system takes in and digests food, providing nutrient molecules that enter the blood and replace the nutrients that are constantly being used by the body cells.
• The respiratory system adds oxygen to the blood and removes carbon dioxide.
• The amount of oxygen taken in and carbon dioxide given off can be increased to meet the body needs.
• The liver and kidneys contribute greatly to homeostasis.
• For example, immediately after glucose enters the blood, it can be removed by the liver and stored as glycogen.
• Later glycogen is broken down to replace the glucose used by the blood cells.
• In this way, the glucose composition of the blood remains the same.
• The hormone insulin, secreted by the pancreas, regulates glycogen storage.
• The kidneys are also under hormonal influence as they excrete wastes and salts, substances that can affect the pH level of the blood.

Summary Table of Homeostasis

Intermediate Level

Homeostasis

Role of Organ Systems

Hormonal Regulation

Formula / Mathematical Form

Not applicable to this topic.

Solved Example

Not applicable to this topic (descriptive topic).

Important Points

• 1. Homeostasis means keeping things in balance.
• 2. Homeostasis keeps internal conditions constant.
• 3. It occurs despite changes in external environment.
• 4. Animals have two environments: external and internal.
• 5. External environment includes atmosphere, marine, freshwater.
• 6. Internal environment includes interstitial fluid, lymph, plasma.
• 7. Digestive system takes in and digests food.
• 8. Respiratory system adds oxygen and removes carbon dioxide.
• 9. Liver removes glucose and stores glycogen.
• 10. Glycogen is broken down to replace glucose.
• 11. Insulin regulates glycogen storage.
• 12. Kidneys excrete wastes and salts.
• 13. Kidneys affect pH level of blood.
• 14. Organ systems work constantly to maintain stable environment.
• 15. Homeostasis is essential for survival.

Remember

• - Homeostasis = keeping internal conditions constant
• - External environment = outside the organism
• - Internal environment = interstitial fluid; lymph; plasma
• - Digestive system = takes in and digests food
• - Respiratory system = adds oxygen; removes carbon dioxide
• - Liver = removes glucose; stores glycogen
• - Kidneys = excrete wastes and salts
• - Insulin = regulates glycogen storage

Common Mistakes

• 1. Confusing homeostasis and thermoregulation — Homeostasis is broader; thermoregulation is a part.
• 2. Mixing up external and internal environments — External = outside; internal = inside.
• 3. Forgetting the role of the liver — Stores glycogen; regulates glucose.
• 4. Mixing up the roles of organs — Digestive: food; respiratory: gases; kidneys: wastes.
• 5. Forgetting the role of insulin — Regulates glycogen storage.
• 6. Thinking homeostasis is only about temperature — It also involves glucose, pH, water, electrolytes.
• 7. Believing homeostasis is not important — It is essential for survival.
• 8. Mixing up the internal environment components — Interstitial fluid, lymph, plasma.
• 9. Forgetting the role of the kidneys — Excrete wastes and salts; affect pH.
• 10. Thinking homeostasis is static — It is a dynamic process.

Quick Revision

Animals have two environments in their lives, an external environment in which the organism is situated and an internal environment in which the tissues live. The external environment consists of varying conditions of atmosphere, marine and freshwater. The internal environment is formed by the interstitial fluid or tissue fluid that surrounds and bathes all the tissues and circulating fluids like lymph or plasma the liquid part of the blood. Homeostasis means keeping things in balance'. Homeostasis is the process by which organisms keep internal conditions relatively constant despite changes in external environment. The human organ systems are working constantly to maintain a controlled, stable environment. The digestive system takes in and digests food, providing nutrient molecules that enter the blood and replace the nutrients that are constantly being used by the body cells. The respiratory system adds oxygen to the blood and removes carbon dioxide. The amount of oxygen taken in and carbon dioxide given off can be increased to meet the body needs. The liver and kidneys contribute greatly to homeostasis. For example, immediately after glucose enters the blood, it can be removed by the liver and stored as glycogen. Later glycogen is broken down to replace the glucose used by the blood cells. In this way, the glucose composition of the blood remains the same. The hormone insulin, secreted by the pancreas, regulates glycogen storage. The kidneys are also under hormonal influence as they excrete wastes and salts, substances that can affect the pH level of the blood.

60-Second Revision

• Homeostasis = keeping internal conditions constant
• External environment = outside the organism
• Internal environment = interstitial fluid; lymph; plasma
• Digestive system = takes in and digests food
• Respiratory system = adds oxygen; removes carbon dioxide
• Liver = removes glucose; stores glycogen
• Kidneys = excrete wastes and salts
• Insulin = regulates glycogen storage
• Warning: Homeostasis maintains a stable internal environment despite changes outside

NEXT TOPIC

• Chapter:
• 8. Thermoregulation and Homeostasis

• Topic:
• 8.2.1 COMPONENTS OF HOMEOSTATIC MECHANISMS

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