Demonstrate understanding of how an animal maintains a stable internal environment
1 Demonstrate
understanding involves using biological ideas to describe a control system
by which an animal maintains a stable internal environment. Annotated diagrams or models may be used to
support the description.
Demonstrate
in-depth understanding involves using biological ideas to explain how or why
an animal maintains a stable internal environment. This includes explaining how a specific
disruption results in responses within a control system to re-establish a
stable internal environment.
Demonstrate
comprehensive understanding involves linking biological ideas about maintaining
a stable internal environment in an animal.
This includes at least one of:
·
a discussion of the significance of the control
system in terms of its adaptive advantage
·
an explanation of the biochemical and/or
biophysical processes underpinning the mechanism (such as equilibrium
reactions, changes in membrane permeability, metabolic pathways)
·
an analysis of a specific example of how
external and/or internal environmental influences result in a breakdown of the
control system.
2 A control system that maintains a stable
internal environment (homeostatic system) refers to those that regulate:
·
body temperature
·
level of blood glucose
3 The biological ideas related to the control system
includes the:
·
purpose of the system
·
components of the system
·
mechanism of the system (how it responds to the
normal range of environmental fluctuations, interaction and feedback mechanisms
between parts of the system)
·
potential effect of disruption to the system by
internal or external influences.
4 Environmental influences that result in a
breakdown of the control system may be external influences such as extreme
environment conditions, disease or infection, drugs or toxins, or internal
influences such as genetic conditions or metabolic disorders.
Homeostasis
Homeostasis refers to a system's ability to respond to fluctuations in order to maintain a relatively stable or constant internal environment. For human systems homeostasis involves being able to sense changes in the internal environment away from ideal conditions, process information from multiple sensors, and respond using biochemical and biophysical pathways to return to the system to its normal acceptable range to support life processes.
Examples of ideal human conditions include:
Core body temperature 37 degrees Celsius
Blood pH of 7.365
Mean normal blood glucose concentration 5.5 mmol/L
General Homeostatic systems require 3 parts.
Sensors (receptors) - Specialised cells/tissues/organs which sense fluctuations in a specific variable
Control Centre - Receives the information from sensors and processes the appropriate response
Effectors - Specialised cells/tissues/organs which take action to counteract the imbalance.
Adaptive Advantage of Homeostasis
Throughout this topic it is important to consider how being able to control one's internal environment may provide an advantage to interacting/surviving/reproducing. Alternatively, what challenges or limitations would be imposed on humans if we were unable to regulate our internal environment.
For instance...
How would our eating habits change if we could not store and retrieve energy inside our bodies?
How would humans cope with the changing seasons and extreme temperatures at high altitude or at a distance from the equator?
How do fluctuations in temperature, pH and substrate concentration affect the efficiency of enzyme catalysed metabolic reactions?
Thermoregulation
Often described as "warm-blooded" humans are in fact homeothermic. We are able to regulate the rate at which we generate and dissipate (lose) heat.
This is in contrast to "cold-blooded" or poikilothermic organisms whose internal environment fluctuates as their external conditions change.
This video provides a good summary of how humans sense, process and respond to information regarding body temperature to ensure our internal environment is optimal for enzymes produced by gene expression.
Before you begin, consider these questions:
1) How do we generate heat?
2) Why is it necessary to lose heat?
3) How can environmental conditions affect our ability to thermoregulate?
Even though humans possess an efficient thermoregulatory system which allows them to inhabit a wide range of environments, dealing with the challenge of balancing heat production with heat loss can be quite stressful.
It is important to remember that our bodies have evolved in relation to the normal fluctuation of environmental conditions and temperatures experienced by our ancestors. Brief changes to internal metabolic rate and/or external environmental conditions rely on a constant negative feedback loop to make minor adjustments to heat production and heat dissipation (loss).
From the graphic below, one can see the narrow tolerance range for internal temperature fluctuations and the responses that are initiated in an effort to restore homeostasis. Under extreme conditions, the limitations of our system may be tested.
Consequences of extreme hypothermia and hyperthermia.
Enzymes are biological catalysts which assist in nearly all metaboilic reactions. Because enzymes perform optimally across a norrow range of temperatures it is essential that the body respond quickly and skillfully to fluctuations in internal temperature. Failing to do so can result in the breakdown of cellular function and even contribute to cell death.
At temperatures below their optimal level, enzyme function may slow drastically or even result result in the inability of cells in the brain to effectively communicate with one another, or with other parts of the body. Confusion, fatigue and loss of consciousness may even result.
In the case of internal temperatures becoming too high, enzymes may become irreversabily denatured stopping cell function through the breakdown of enzyme catalysed metaboilic pathways.
Cardiovascular complications and homeostatic breakdown
When cells are unable to get enough oxygen to perform cellular respiration, or when they are unable to remove wastes at an efficient rate, they begin to die. A constant blood supply, rich in glucose, oxygen and other nutrients is necessary.
Normal responses to hypothermia including vasoconstriction and shivering are usually effective in generating additional heat energy and increasing the insulating potential of our soft tissues. Reducing the rate of heat loss through radiation and convection are the best strategies to returning body temperature to its set point. As core temperatures drop below 36 degrees, the central nervous system (hypothalamus) may signal the release of hormones such as thyroid stimulating hormone which is produced in the pituitary gland. This hormone targets the thyroid causing it to release thyroxine, a hormone that travels through the blood and stimulates brown fat cells to increase their metabolic rate in an attempt to produce additional heat.
Prolonged vasoconstriction of peripheral blood vessels in response to ongoing extreme cold environments can lead to frostbite. In the worst case scenarios, amputation may be required. Severe hypothermia results in decreased coordination of muscles and temperatures below 29 degrees can inhibit the brain's own ability to respond to cooling - the feedback loop breaks down. As brain function slows, death becomes possible. Below 25 degrees Celsius, cardiac arrest and death become likely.
On the other hand, an inability to dissipate (lose) excess heat produced during intense activity can result in serious problems. Heat exhaustion and heat stroke are potential outcomes associated with in inability of the body to effectively lose heat. The evaporation of sweat is the most effective way to lose heat, especially when exercising in very warm conditions (where radiant heat is more likely to be absorbed. Excessive sweating depletes the circulatory system of enough fluid to maintain blood pressure. As a result of reduced blood volume, the body is also unable to direct more heat into the peripheral arterioles through vasodilation.
Heat exhaustion occurs when the body temperature rises to 39 degrees. Excessive loss of sodium ions through sweating makes it difficult for the body to continue sweating and dehydration reduces the amount of blood available to be redirected to the arms and legs. Staying active also causes the body to prioritise blood flow to the working muscles. Dizziness, cramping and nausea are associated with this breakdown. Fluids (electrolytes) and assistance to increase convection and evaporation are suggested.
Above 40 degrees, maintaining the fluids necessary to transport oxygen, nutrients and wastes in a way that supports cell activities and prevents their damage becomes difficult. Sweating stops and severe symptoms are felt. Heat stroke is a serious condition requiring medical attention. External assistance in losing heat such as cold wet towels applied to the skin and moving to a cooler environment are necessary, along with the administration of electrolytes to increase critically low levels of blood plasma. Enzymes may begin to denature irreversibly, slowing cellular function. Unconsciousness could be followed by death if untreated.
Review and Other Systems
The following video revises the thermoregulatory mechanism and introduces glucose metabolism (followed by calcium homeostasis).
Glucose Metabolism
