🧬 Chapter 14.4: Homeostasis – Keeping Life Stable!

Hello Biologists! This chapter is all about how your body works hard behind the scenes to keep everything perfectly balanced, like an expert tightrope walker! If your internal conditions change too much, your enzymes won't work, and you could get very sick. This constant balancing act is called Homeostasis.

Don't worry if the words sound long. We will break down how your body controls temperature and sugar levels step-by-step.

1. Defining Homeostasis (Core Concept)

Homeostasis is defined as the maintenance of a constant internal environment.
Think of it like the air conditioning unit (AC) in your house:

  • You set the AC to 22°C. This is your set point.
  • If the temperature goes up to 25°C, the AC switches on (the body responds).
  • If the temperature drops to 19°C, the AC switches off and the heater might come on (the body responds differently).

Your body does the same thing, constantly adjusting to keep conditions perfect for cells to function.

Key Takeaway:

Homeostasis means keeping things like temperature and blood glucose exactly right, no matter what happens outside.

2. The Principle of Homeostatic Control: Negative Feedback (Supplement)

The body maintains stability primarily through a system called negative feedback.

Analogy Alert: Negative feedback is like saying "No!" when something drifts too far away from the set point.

How Negative Feedback Works:

1. Set Point: This is the ideal condition (e.g., 37°C for temperature, or a normal blood glucose level).

2. Change Occurs: A stimulus causes the internal condition to move away from the set point (e.g., you start exercising, and your temperature rises).

3. Detection: A receptor (like sensory cells in your skin or chemical detectors in your blood) detects the change.

4. Correction/Response: The brain/control centre sends instructions to an effector (like a muscle or gland) to carry out an action that reverses the change.

5. Return to Set Point: The condition returns to normal, and the response stops.

Example Flow:

Internal Temp Rises (Change) → Brain detects change (Detection) → Sweat glands produce sweat (Response) → Temperature drops back to 37°C (Reversal)

3. Control of Blood Glucose Concentration

Glucose is the main energy source for all your cells. Its concentration in the blood must be kept constant (the set point) because:

  • If glucose is too low, cells (especially the brain) won't have enough energy.
  • If glucose is too high, it can damage organs and cause problems (like in diabetes).

This control involves two key hormones produced by the pancreas: Insulin and Glucagon (Supplement 14.4.5).

The Role of the Liver (Supplement 14.4.4):

The liver is the body’s glucose warehouse. It stores excess glucose in the form of an insoluble carbohydrate called glycogen.

A) When Blood Glucose is TOO HIGH (e.g., after a meal):
  1. The pancreas detects the high glucose level.
  2. The pancreas secretes the hormone insulin into the blood (Core 14.4.2).
  3. Insulin travels to the liver and muscles.
  4. Insulin causes the liver to take up glucose from the blood and convert it into glycogen for storage.
  5. Result: Blood glucose concentration decreases back towards the set point.
B) When Blood Glucose is TOO LOW (e.g., during exercise or fasting):
  1. The pancreas detects the low glucose level.
  2. The pancreas secretes the hormone glucagon into the blood (Supplement 14.4.5).
  3. Glucagon travels to the liver.
  4. Glucagon causes the liver to break down stored glycogen back into glucose and release it into the blood.
  5. Result: Blood glucose concentration increases back towards the set point.

Quick Review:
Insulin = Moves glucose in (out of the blood).
Glucagon = Glucose is gone (released back into the blood).

4. Diabetes Mellitus (Type 1) (Supplement)

Type 1 Diabetes is a condition where the pancreas fails to produce enough insulin.

Without insulin, glucose cannot be converted into glycogen for storage, meaning blood glucose levels remain dangerously high, even after eating.

Treatment of Type 1 Diabetes:
Treatment involves regularly monitoring blood glucose levels and administering insulin injections to replace the hormone the pancreas cannot produce (Supplement 14.4.5).

5. Control of Body Temperature (Thermoregulation)

Mammals (like humans) are endotherms, meaning we maintain a constant internal body temperature, typically around 37°C.

Why 37°C?
This is the optimum temperature for the majority of metabolic reactions in the body, ensuring that enzymes work efficiently. If the temperature gets too high, enzymes start to denature.

The control center for temperature is the brain (specifically the hypothalamus) (Supplement 14.4.7).

Skin Structures and Thermoregulation (Supplement 14.4.6)

The skin plays a vital role. You must be able to identify and know the roles of the following structures in diagrams:

  • Hairs and Hair Erector Muscles (erect hairs to trap air).
  • Sweat Glands (produce sweat).
  • Blood Vessels (arterioles supplying the skin surface capillaries).
  • Fatty Tissue (insulation layer under the skin).
  • Receptors and Sensory Neurones (detect internal/external temperature changes).

6. Responses to Being TOO HOT (Supplement 14.4.7 & 14.4.8)

When the internal body temperature rises above the set point, the brain initiates cooling mechanisms:

1. Vasodilation:

  • The arterioles (small blood vessels) near the skin surface widen (dilate).
  • This allows a greater volume of blood to flow close to the skin surface capillaries.
  • More heat energy is transferred from the blood to the cooler surroundings via radiation.
  • Result: Skin looks flushed (red) and loses heat faster.

2. Sweating:

  • Sweat glands produce sweat (a watery solution).
  • The liquid sweat evaporates from the skin surface.
  • Evaporation requires heat energy, which is taken from the skin and blood.
  • Result: Cooling effect on the body.

3. Insulation and Metabolism:
The body reduces metabolism and decreases the insulating effect of trapped hair/fur (hair erector muscles relax).

7. Responses to Being TOO COLD (Supplement 14.4.7 & 14.4.8)

When the internal body temperature falls below the set point, the brain initiates warming mechanisms:

1. Vasoconstriction:

  • The arterioles near the skin surface narrow (constrict).
  • This reduces the volume of blood flowing through the surface capillaries.
  • Less heat energy is carried to the skin surface, thus reducing heat loss.
  • Result: Skin looks pale and conserves core heat.

2. Shivering:

  • Muscles contract and relax rapidly (shivering).
  • This rapid movement requires respiration, which releases heat energy as a by-product.
  • Result: Heat generation warms the body.

3. Insulation:

  • The hair erector muscles contract, pulling the hairs upright (giving you "goosebumps").
  • This traps a layer of air close to the skin. Air is a poor conductor of heat, increasing the insulating layer.

Did You Know? The reason we get "goosebumps" when cold is a leftover evolutionary response from when our ancestors had thick fur. Raising the fur trapped more air!

Memory Aid for Blood Vessels:

VasoConstriction = Conserving heat (When Cold).
VasoDilation = Discharging heat (When Dangrously hot).

📝 Quick Review of Homeostasis

Key Terms to Master:
  • Homeostasis: Constant internal environment.
  • Negative Feedback: Mechanism that reverses a change to maintain a set point.
  • Insulin: Hormone that decreases blood glucose (stores glucose as glycogen in the liver).
  • Glucagon: Hormone that increases blood glucose (breaks glycogen down in the liver).
  • Vasodilation: Arterioles widen to lose heat.
  • Vasoconstriction: Arterioles narrow to conserve heat.
  • Shivering: Muscle contractions that generate heat through respiration.

You've successfully covered how the body handles two massive challenges: balancing fuel (glucose) and managing heat (temperature). Keep practicing those diagrams, and you’ll ace this topic!