Tuesday, March 22, 2011


Animals regulate their internal environment within relatively narrow limits • The internal environment of vertebrates is called the interstitial fluid and is very different from the external environment • Homeostasis is a balance between external changes and the animal’s internal control mechanisms that oppose the changes

Regulating and Conforming • Regulating and conforming are two extremes in how animals cope with environmental fluctuations • A regulator uses internal control mechanisms to moderate internal change in the face of external, environmental fluctuation • A conformer allows its internal condition to vary with certain external changes

Mechanisms of Homeostasis • Mechanisms of homeostasis moderate changes in the internal environment • A homeostatic control system has three functional components: a receptor, a control center, and an effector • Most homeostatic control systems function by negative feedback, where buildup of the end product shuts the system off • In positive feedback, a change in a variable triggers mechanisms that amplify rather than reverse the change

Feedback Mechanisms in Thermoregulation • Mammals regulate body temperature by negative feedback involving several organ systems • In humans, the hypothalamus (a part of the brain) contains nerve cells that function as a thermostat

1 comment:

  1. Group De Sheng

    Organisms can be classified into 2 categories, ectotherms and endotherms.
    Endotherms are organisms that their body temperature change according to their surrounding while endotherms are organisms that their body temperature have to be maintained. We humans are classified as endotherms, which mean warm blooded animals.
    As we are endotherm, thermoregulation is important in regulating our body temperature without regarding the change of the surrounding temperature. Thermoregulation is a type of negative feedback mechanism. The stimulus will be the temperature change, receptor organ is the skin and the control centre is hypothalamus.
    When we feel hot, our body temperature increases. Our body hair will be lowered down to trap less air. Vasodilation of our blood vessels will occur to allow more blood to flow through the skin and increase heat loss. We will sweat more to cool down our body. Body temperature is then lowered and back to normal.
    When we feel cold, the opposite will occur. During cold weather, our body temperature decreases. First, our body hair is erected to capture more air which acts as an insulator, to reduce heat loss, vasoconstriction occur so that less blood flow under the skin thus prevent heat loss. We will also shiver to generate heat. Then, our body temperature increases and back to normal.