Homeostasis and Gas exchange explained

Homeostasis, what is it?

The human bodyís ability to maintain stable internal condition when the person is threatened by the environment can be described as Homeostasis. Homeostasis monitors factors such as blood pressure, respiration. It produces hormones such as adrenaline. Every single organism the body plays a role in the process of homeostasis.

Negative feedback

Negative feedback works in order to help us maintain homeostasis. For example to maintain the average body temperature of 37 degrees Celsius, we use effectors like sweating or shivering. If itís cold outside and the body can not keep the temperature of 37 we start to shiver in order to warm up. However if it very hot outside and the body is too hot we sweat to cool down. This creates homeostasis in the body, so the system of negative feedback worked correctly.


The skin tests the air temperature outside.

Control center:

Hypothalamus of the brain, Processes the information it received from the Receptor and decides upon the next move.


Shivering or sweating


Body temperature rises or falls.


Controls the amount of response

This process can be presented on a diagram

Mechanism in gas exchange

The process of gas exchange between an organism and the environment is called respiration. That is when we breathe in air and breathe out carbon dioxide. Cellular respiration occurs when cells use oxygen in metabolic reactions and generate carbon dioxide, water, and energy. Single celled organisms can exchange gases directly with the environment by diffusion. Complex multicultural organisms have respiratory and circulatory systems designed to interface with the environment and efficiently deliver gases to distant cells, respectively. Gas exchange then must occur between the environment and the circulatory system and between the circulatory system and the tissues.

We use lungs to consume the oxygen. When we inhale, the muscles between the ribs contract and expand the chest cavity. This expansion lowers the pressure in the chest cavity below the outside air pressure. Air then flows in through the airways and inflates the lungs. The oxygen is absorbed by the blood and carried to every cell in the body, and then the blood carries the waste carbon dioxide back. When we exhale, the rib muscles relax and the chest cavity gets smaller. The decrease in volume of the cavity increases the pressure in the chest cavity above the outside air pressure. Carbon dioxide from the lungs then flows out of the airways in to the outside air.






Mr. Neilís handouts

AS Level Biology textbook