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Homeostasis is the physiological control process by which the internal conditions of living organisms are maintained at equilibrium. Homeostasis is derived from the Greek words ‘homeo’ (which means ‘similar to’), and ‘stasis’ (which means standing still, or steady).In reality, the internal conditions within the human body are never exactly static. Instead, they are always striving to reach the optimal equilibrium…
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Jetzt kostenlos anmeldenHomeostasis is the physiological control process by which the internal conditions of living organisms are maintained at equilibrium. Homeostasis is derived from the Greek words ‘homeo’ (which means ‘similar to’), and ‘stasis’ (which means standing still, or steady).
In reality, the internal conditions within the human body are never exactly static. Instead, they are always striving to reach the optimal equilibrium state. In other words, homeostasis is a state of dynamic equilibrium characterised by different responses to changes within the external and internal environments. These changes can be inside or outside the cell, tissue, organ, or organism.
Homeostasis is essential for the functioning and survival of organisms. Homeostasis is important for maintaining proteins' structures, water potential in the body, and successfully adapting the body's temperature to changing external conditions.
Proteins are abundant macromolecules that are essential for cells to function effectively. However, proteins are very sensitive to changes in pH and temperature. Any change in these factors causes the proteins to denature and lose their native structure. When the native structure of a protein is lost, it will likely become inefficient or obsolete in its function.
Enzymes are proteins that speed up biological reactions. The enzyme’s structure is very important for its function. Enzymes have an active site that is complementary in structure to their substrate and allows the binding of the two molecules. Even a small change in pH or temperature alters the structure of the active site and can impair the enzyme's efficacy.
Denatured proteins are less soluble and are more likely to form insoluble aggregates. These aggregates can build up inside or outside of the cell and cause complications. For example, irreversable cell death.
Water potential is important for both plant and animal cells. As we know, water always moves from a system of high water potential to a system of low water potential.
In plants, the cells have a cellulose cell wall protecting them. Hence, the cells only become turgid when water diffuses in, and shrivel as water leaves them (Figure 1).
In contrast, animal cells have no cell wall, so there is a risk of cellular damage when too much water diffuses in or out (Figure 2). Maintaining blood glucose levels at a dynamic equilibrium is essential to ensure a constant water potential for the cells. It also ensures that the cells receive a sufficient amount of glucose to use for respiration.
Plasmolysis and deplasmolysis is irreversible in animal cells, while plasmolysis in plant cells is reversible.
The ability to maintain the body’s internal temperature at a constant level allows animals to be more independent of their external environment. Therefore, they will be able to survive in a wider variety of geographical ranges and in different climates. This feature has allowed mammals to inhabit most habitats, ranging from hot deserts to freezing polar regions.
In order for any homeostatic mechanism to work effectively, five components are necessary (Figure 3):
Negative feedback is the most common type of feedback in living organisms. In negative feedback, the receptor detects the need for the re-establishment of the optimum point. It conveys the signal to the control centre which then turns off the effector.
An example of negative feedback is how body temperature is regulated in endotherms like mammals. They need to maintain their body temperature at a relatively constant level, despite fluctuations in the temperature of their environment.
The optimum temperature in the human body ranges between 36°C and 38°C. There are two different sensors in humans that detect changes in temperature:
These sensors are connected to the hypothalamus, which is the control centre for body temperature. When sensory cells detect a slight deviation of the body temperature from its optimum value, they send signals to the hypothalamus which then activates various mechanisms to restore the core body temperature. These mechanisms include:
In response to cold external environments:
In response to hot external environments
Blood calcium levels are also regulated by a negative feedback mechanism which requires the action of the different hormones. One important hormone involved is the parathyroid hormone (PTH). This hormone is released from the parathyroid gland in response to low blood calcium levels.
PTH increases blood calcium levels by:
Another example of negative feedback is osmoregulation. ADH (antidiuretic hormone) is secreted in response to dehydration. ADH acts on kidneys and stimulates the retention of water. However, as the body hydrates, ADH release is inhibited (Figure 3).
Positive feedback is quite rare in biological systems. It involves causing an even further deviation from the optimum point after a small deviation is detected. One example of positive feedback is during childbirth. Uterine contraction stimulates the release of oxytocin which then stimulates more contractions. Therefore, this results in an increase in both intensity and frequency of contractions during labour (Figure 5).
It is a state of dynamic equilibrium characterised by different responses to changes within the external and internal environments.
By control mechanisms that need an optimum point, a sensor, a coordinator, an effector, and a feedback loop.
Osmoregulation, thermoregulation, and regulation of blood calcium levels.
It maintains optimal conditions for enzymes to work efficiently throughout the body, as well as all cell functions.
It acts to stop the stimulus or cue that triggered it after the optimum point is re-established.
Osmoregulation, thermoregulation, regulation of blood calcium levels.
When the condition returns to normal, and the optimum point is re-established.
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