Homeostasis
Principles of homeostasis
Homeostasis is the maintenance of an internal environment within restricted limits in
organisms. It serves to ensure that a constant internal environment consisting of factors
such as temperature, water potential, pH and blood glucose level is maintained, despite
changes in the external environment of the organism. Homeostasis is especially important
in body temperature and blood pH because if these change too much then enzymes will
become denatured e.g. if body temperature rises above 37oC.
Importance of homeostasis:
- Enzymes rate of reaction is affected by even small fluctuations in temperature and
pH, they my even denature.
- The maintenance of a constant blood glucose concentration is essential in ensuring a
constant water potential and a reliable source of glucose for respiration by cells.
changes to the water potential of the blood and tissue fluid may cause cells to shrink
and expand so they cannot operate normally.
- Organisms that can maintain a constant internal environment are more independent
of changes in the external environment. For example, since mammals can maintain a
constant body temperature they are found in most habitats.
Control mechanisms
- optimum point- the point at which the system operates best. this is monitored by a…
- receptor- detects any deviation from the optimum point (i.e stimulus) and informs
the…
- coordinator- coordinates information from receptors and sends instructions to an
appropriate…
- effector- a muscle or a gland, which brings about the changes needed to return the
system to the optimum point. this return to normality creates a…
- feedback mechanism- by which a receptor responds to a stimulus created by the
change to the system brought about by the effector
Feedback mechanisms
Positive feedback
- Occurs when a deviation from an optimum causes changes that result in an even
greater deviation from the normal
- for example, when neurones detect a stimulus, this leads to a small influx of sodium
ions. This influx increases the permeability of the neuronal membrane to sodium
ions, more ions enter, causing a further increase in permeability and even more
rapid entry of ions.
- Positive feedback doesn't occur as often as negative feedback
- positive feedback increases the original change in the conditions
, When in fact it has corrected any deviation and returned the system to the optimum point,
it is important that this information is fed back to the receptor. If the information is not fed
back, the receptor will continue to stimulate the effector, leading to an over correction in
causing a deviation in the opposite direction (basically positive feedback).
Negative feedback
- negative feedback counteracts any change in internal conditions.
- This means that all changes are reversed to restore the optimum conditions.
- In order for the negative feedback pathway to work, the following elements need to
be present: sensory receptors such as temperature receptors to detect changes in
internal conditions, in a case where a change is detected, the receptors pass the
message either via the nervous or hormonal system to the effectors such as the
liver or muscles bringing about a response to restore the optimum conditions.
- An example is if blood glucose begins to fall then hormones are released to convert
glycogen to glucose to bring it back to normal levels.
Hormones and the regulation of blood glucose concentration
Hormones and how they work
- Hormones are produced in glands, which secrete the hormone directly into the
blood (endocrine glands)
- They are carried in the blood plasma to the cells on which they act, known as target
cells, which have specific receptors on their cell surface membrane that are
complementary to a specific hormone
- they are effective in very low concentrations, but often have widespread and long
lasting effects
The concentration of glucose in blood varies depending on food intake and energy
requirements. It is important to keep the blood glucose concentration in the correct range
of about 70-99mg/dl to ensure that all the essential processes such as respiration of brain
cells is maintained. However, if the concentration of blood glucose is too high, it is excreted
in urine thus meaning it is of no use to the body as it cannot be stored in the form of either
glycogen or fat.
Principles of homeostasis
Homeostasis is the maintenance of an internal environment within restricted limits in
organisms. It serves to ensure that a constant internal environment consisting of factors
such as temperature, water potential, pH and blood glucose level is maintained, despite
changes in the external environment of the organism. Homeostasis is especially important
in body temperature and blood pH because if these change too much then enzymes will
become denatured e.g. if body temperature rises above 37oC.
Importance of homeostasis:
- Enzymes rate of reaction is affected by even small fluctuations in temperature and
pH, they my even denature.
- The maintenance of a constant blood glucose concentration is essential in ensuring a
constant water potential and a reliable source of glucose for respiration by cells.
changes to the water potential of the blood and tissue fluid may cause cells to shrink
and expand so they cannot operate normally.
- Organisms that can maintain a constant internal environment are more independent
of changes in the external environment. For example, since mammals can maintain a
constant body temperature they are found in most habitats.
Control mechanisms
- optimum point- the point at which the system operates best. this is monitored by a…
- receptor- detects any deviation from the optimum point (i.e stimulus) and informs
the…
- coordinator- coordinates information from receptors and sends instructions to an
appropriate…
- effector- a muscle or a gland, which brings about the changes needed to return the
system to the optimum point. this return to normality creates a…
- feedback mechanism- by which a receptor responds to a stimulus created by the
change to the system brought about by the effector
Feedback mechanisms
Positive feedback
- Occurs when a deviation from an optimum causes changes that result in an even
greater deviation from the normal
- for example, when neurones detect a stimulus, this leads to a small influx of sodium
ions. This influx increases the permeability of the neuronal membrane to sodium
ions, more ions enter, causing a further increase in permeability and even more
rapid entry of ions.
- Positive feedback doesn't occur as often as negative feedback
- positive feedback increases the original change in the conditions
, When in fact it has corrected any deviation and returned the system to the optimum point,
it is important that this information is fed back to the receptor. If the information is not fed
back, the receptor will continue to stimulate the effector, leading to an over correction in
causing a deviation in the opposite direction (basically positive feedback).
Negative feedback
- negative feedback counteracts any change in internal conditions.
- This means that all changes are reversed to restore the optimum conditions.
- In order for the negative feedback pathway to work, the following elements need to
be present: sensory receptors such as temperature receptors to detect changes in
internal conditions, in a case where a change is detected, the receptors pass the
message either via the nervous or hormonal system to the effectors such as the
liver or muscles bringing about a response to restore the optimum conditions.
- An example is if blood glucose begins to fall then hormones are released to convert
glycogen to glucose to bring it back to normal levels.
Hormones and the regulation of blood glucose concentration
Hormones and how they work
- Hormones are produced in glands, which secrete the hormone directly into the
blood (endocrine glands)
- They are carried in the blood plasma to the cells on which they act, known as target
cells, which have specific receptors on their cell surface membrane that are
complementary to a specific hormone
- they are effective in very low concentrations, but often have widespread and long
lasting effects
The concentration of glucose in blood varies depending on food intake and energy
requirements. It is important to keep the blood glucose concentration in the correct range
of about 70-99mg/dl to ensure that all the essential processes such as respiration of brain
cells is maintained. However, if the concentration of blood glucose is too high, it is excreted
in urine thus meaning it is of no use to the body as it cannot be stored in the form of either
glycogen or fat.
