5.1 Homeostasis Flashcards
Homeostasis
Homeostasis is the regulation of the internal conditions of a cell or organism to maintain optimum conditions for function in response to internal and external changes.
Homeostasis maintains optimal conditions for enzyme action and all cell functions.
In the human body, these include control of:
Blood glucose concentration
Body temperature
Water levels
Enzyme functioning
Because humans are organisms that live in a changing environment, we must regulate our body’s internal conditions to make sure our enzymes and cells function well.
If conditions are not optimal, then our enzymes can denature (change shape).
This reduces their ability to catalyse (speed-up) metabolic reactions (chemical reactions in organisms).
Regulating internal conditions
Humans must regulate their body’s internal conditions to make sure that enzymes and cells function well. The conditions that need to be regulated are:
Internal body temperature
Urea concentration in urine
Water levels
Blood sugar levels
Carbon dioxide levels
Control system
Maintaining controlled conditions within the body is under involuntary (automatic) control.
This means that the brain stem (or non-conscious part of the brain) and the spinal cord are involved in maintaining homeostasis – you don’t consciously maintain your body temperature or blood glucose level.
These automatic control systems may involve nervous responses or chemical responses.
All control systems include:
Cells called receptors, which detect stimuli (changes in the environment).
Coordination centres (such as the brain, spinal cord and pancreas) that receive and process information from receptors.
Effectors (muscles or glands) which bring about responses which restore optimum levels.
Positive feedback
Positive feedback is the opposite of negative feedback. It makes a small change even bigger. An example of positive feedback in the body is the release of oxytocin (hormone), which increases the number of contractions during childbirth.
Negative feedback
Negative feedback mechanisms in homeostasis help to maintain conditions in the body within an optimal narrow range; any movement away from ideal conditions results in changes occurring which bring them back.
This involves detecting that the level of a substance or a condition has gone above or below normal levels, which triggers a response to bring the level back to normal again.
Blood glucose level and core body temperature control are examples of negative feedback.
Monitoring body temperature.
The human body needs to maintain a temperature at which enzymes work best, around 37°C.
Processes such as respiration release energy as heat; and the body loses heat energy to its surroundings – the energy gained and lost must be regulated to maintain a constant core body temperature.
Body temperature is monitored and controlled by the thermoregulatory centre in the brain.
The thermoregulatory centre contains receptors sensitive to the temperature of the blood.
The skin contains temperature receptors and sends nervous impulses to the thermoregulatory centre.
Increasing body temperature
If the body temperature is too low, blood vessels constrict (vasoconstriction), sweating stops and skeletal muscles contract (shiver).
These mechanisms reduce heat loss to the surroundings (with skeletal muscle contraction increasing heat released in the body).
Thermoreceptors in the hypothalamus and skin detect change. The body starts to shiver, vasconstriction occurs and skin hairs. are erected which trap air (an excellent insulator) which increases body temperature.
Decreasing body temperature
If the body temperature is too high, blood vessels dilate (vasodilation) and sweat is produced from the sweat glands.
Both these mechanisms cause a transfer of energy from the skin to the environment, cooling the body down.
Thermoreceptors in the hypothalamus and skin detect change. This increases sweating, vasodilation occurs and hairs lie flat against the skin. This decreases the temperature when the sweat evaporates.
