Homeostasis
Homeostasis is the ability of an organism to maintain a constant internal environment
External Environment:
Internal Environment:
External Environment:
- Surrounding where organism lives
- Most organisms (apart from humans) have little ability to control their external environment
Internal Environment:
- Surroundings of cells in a multi-celled organism e.g. in humans this refers to tissue fluid (intercellular fluid)
Examples of Homeostasis in Humans:
- Maintaining body temperature close to 37°C
- Keeping the pH of blood and tissue fluid close to 7.4
- Preventing the build up of toxic chemicals in the body
- Maintaining sufficient levels of oxygen in the body
- Regulating the level of glucose in blood plasma so it stays close to 0.1%
Organs and Systems Involved:
Small Organisms:
In some cases, organisms (e.g.small, single celled organisms) can exchange materials with the environment by diffusion
e.g. materials such as gases, nutrients and toxic waste
Large Organisms:
In large multi-celled organisms, diffusion is not sufficient. The problem of diffusion and exchange are overcome by different methods
- Skin: Controls body temperature
- Kidneys: Controls blood plasma and tissue fluid pH
- Liver and Kidneys: Prevents build up of toxic waste
- Defence System: Prevents infection
Small Organisms:
In some cases, organisms (e.g.small, single celled organisms) can exchange materials with the environment by diffusion
e.g. materials such as gases, nutrients and toxic waste
Large Organisms:
In large multi-celled organisms, diffusion is not sufficient. The problem of diffusion and exchange are overcome by different methods
Methods Used to Improve Diffusion and Exchange
- Organs/ Organism may be flattened (e.g. leaf) which reduces the distance between two surfaces and allows materials to be exchanged by diffusion
- Respiratory system provide increased surface area for exchange of gas by diffusion e.g. alveoli in lungs
- Respiratory and excretory systems take materials to the body surface e.g. in humans - gasses pass in and out of lungs and waste products are excreted from from the body
- Diffusion is only effective over short distances - large active animals such as humans have to develop a circulatory system. This can transport materials such as gases, nutrients and toxic waste over long distances
The Need For Homeostasis
- Homeostasis allows organisms to function efficiently
- Homeostasis controls the environment surrounding cells - this allows cells to maintain constant conditions enabling them to function, under optimal (most suitable) condition
Homeostasis Allows Slight Change
Homeostasis allows conditions in the body to be changed slightly at different times
Homeostasis allows conditions in the body to be changed slightly at different times
- Body temperature falls by about 1°C when we sleep
- Body temperature rises when we have an infection
- Blood glucose levels rise rapidly when we get a fright (caused by hormone adrenaline)
- Hormonal changes during puberty and menstrual cycle after or change the internal environment of the body
Temperature Regulation in Humans
Body Temperature
Ectotherms
Ectotherms gain or lose heat from or to their external environment
Endotherms
Endotherms generate their own heat from metabolic reactions
Body Temperature
- Temperature affects the rate of enzyme action
- High temperatures can damage enzymes, low temperatures will slow down reactions
- To control the rate of enzyme reactions it is important to control body temperature
Ectotherms
Ectotherms gain or lose heat from or to their external environment
- Ectotherms (formally called cold blooded) are animals such as frogs, snakes and lizards, that gain or lose heat from their environments
- Their temperature changes with the external temperature
Endotherms
Endotherms generate their own heat from metabolic reactions
- Endotherms (formally called warm-blooded) animals such as humans that generate their own heat by metabolic reactions.
- They maintain constant body temperature