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Homeostasis Experiment – Investigation 6
INTRODUCTION:
Homeostasis is the process in which the body is kept stable despite the changes in the
external environment. This is very important to our body’s ability to regulate a
temperature change. The human body has a normal temperature and pulse which can be
referred to as “set points.” Our body senses changes in our environment and responds by
adjusting to those changes. This keeps our internal conditions relatively stable.
There are limits in our ability to adjust to changes and conditions. Our heart rate will
change and our body will begin to sweet even to a point of dangerous levels. Our cells
will not function well if the environment is excessively hot or too cold.
In regulating this process, our body uses the hypothalamus in the brain to act as a
thermostat and help regulate the body’s temperature to keep it from overheating or from
getting cold. The hypothalamus changes blood vessels (dilation) in our skin which
changes the amount of heat loss or retention the body heat function.
PURPOSE:
To explore Homeostasis as it regulates mechanisms within the human body by analyzing
how the body maintains internal conditions and heart rate changes.
PLAN:
Design and conduct an experiment to explore how the body self regulates through
evaluation of how the body reacts to changes and then recovers back to ‘set points’ for
temperature and pulse rate.
Create Hypothesis
Collect Data
Analyze Data
Test Hypothesis
Make Conclusions
MATERIALS:
Thermometer
Stop watch
Table to collect data
Pulse Monitor
HYPOTHISIS:
The breathing rate and temperature rate will increase during jumping jacks and then will
return to the ‘set points’ after stopping the jumping jacks.
DATA:
The following table and graph present the data that was collected to test the hypothesis.
The specimen was a 15 year old female in excellent heath.
Time Doing Jumping Jacks
(min)
1
2
3
4
5
Time After Doing Jumping
Jacks (min)
1
2
3
4
5
6
Heart Rate (beats per min)
61
100
110
130
135
Heart Rate (beats per min)
115
100
93
80
68
60
Temperature (Deg F )
97
98
99
99
100
Temperature (Deg F )
100
99
99
99
98
96
HYPOTHESIS TEST:
The Hypothesis proved positive in that the breathing rate and temperature rate increased
during jumping jacks and then returned to the ‘set points’ after stopping the jumping
jacks.
CONCLUSION:
Homeostasis regulates mechanisms within the human body and is amazingly sufficient to
maintain internal conditions and heart rate consistency after perturbations in reaction to
environmental and physical changes.
BACKUP INFORMATION:
How do the body's systems actually maintain the constancy? The most conspicuous
mechanism is generally known as ‘negative feedback’, illustrated below.
As an example, blood glucose concentration could be the ‘regulated variable’ in the
diagram. The control system for the variable is the hormone insulin, whose main action is
to accelerate the entry of glucose into many of the cells of the body, thereby lowering its
plasma concentration. Insulin is released from cells in the Islets of Langerhans of the
pancreas (the controller), the most important stimulus for its release being a rise in blood
glucose concentration, as occurs after a meal (‘disturbance’ in the diagram). The reason
for this being a ‘negative’ feedback system is that the action of insulin, by lowering the
blood sugar, tends to remove the stimulus for its own release. Negative feedback is a
ubiquitious principle in engineering and electronics.
It is clear from this example that the mechanism does not keep glucose concentration (the
regulated variable) at a fixed level. The level oscillates, because there are delays in both
arms of the system — it takes a finite time for insulin to lower blood glucose
concentrations, and also for elevated glucose concentrations to increase the production of
insulin from the pancreas.
Another regulated variable is carbon dioxide. The control of a constant partial pressure of
carbon dioxide (PCO2) in blood is a very precise feedback loop, and its control system is
the act of breathing. The body produces the gas constantly, adding it to blood. The CO2
sensor in this system consists of neurons in the medullary respiratory centre of the brain;
the control system consists of motor nerves passing from the brain to the diaphragm and
intercostal muscles. These nerves stimulate the act of breathing, which transfers carbon
dioxide from blood into the lungs, lowers the blood PCO2, and temporarily removes the
stimulus to the medullary respiratory centre. Because the body is still producing carbon
dioxide, the blood PCO2 begins to rise again, the medullary receptors are stimulated, and
the cycle repeats itself. A CO2-sensitive electrode inserted into an artery shows small,
regular oscillations whose frequency corresponds precisely to the act of breathing.
The speed of response of the carbon dioxide loop is far greater than that of the glucose
loop, a difference that derives from nervous compared with hormonal mechanisms: the
PCO2 varies by only about 10% around its average level, whereas glucose varies by
about 40%. The concentration ranges of some other constituents of blood provide us with
clues about the nature of the relevant homeostatic mechanisms. Sodium ions (135-145
mmol/litre) and chloride ions (95-105 mmol/litre) have narrow ranges; this is the result of
a mixture of nervous and hormonal mechanisms; the range is wider for potassium (3.55.0 mmol/litre) which is adjusted by hormonal action in the kidneys. By contrast, the
hormones that provide the control systems regulating these variables show far wider
concentration ranges in blood, according to the changes in secretion rates stimulated by
disturbances in the variable they control. Thus ACTH (adrenocorticotrophic hormone)
has a range of 3.3-15.4 pmol/litre, aldosterone 100-500 pmol/litre, and insulin 0-15
mUnits/ml (unfed) and 15-100 Units/ml (after food).
Homeostasis can itself be reset or entrained by higher nervous centres. The diurnal
variations shown by ACTH and cortisol demonstrate high concentrations between
midnight and midday (cortisol concentration 280-700 mmol/litre) and midday and
midnight (cortisol 140-280 mmol/litre). Similarly, on a longer time-scale, the changes
seen in the female reproductive cycle represent a 28-day cycle of entrainment. On a
longer time-scale still, the growth and development of the child must represent the
ultimate homeostatic entrainment by the brain. We might envisage old age as
representing a genetically programmed deterioration of homeostasis.
Claude Bernard's intuition about ‘le milieu intérieur’ has come a very long way in a
century. The mechanisms of homeostasis are so ubiquitous, their patterns so subtly
intertwined, that we are tempted to produce a teleological question, and ask why. What is
so useful to the organism about this precision? We do not have to look far, because the
workings of every cell in the body depend on the maintenance of a negative potential
inside the cell. In turn, this negative potential depends upon the relative concentrations of
ions inside and outside the cell: a high sodium concentration in the extracellular fluid,
and a high potassium concentration inside the cell, the gradients across the cell wall being
maintained by ionic pumps within the cell membrane. But these pumps could not begin to
control this gradient if the ionic concentrations in blood (extracellular fluid) were not
kept within narrow limits in the first place. The subject comes into sharp focus when we
consider the situation in the heart, which is very dependent on a constant plasma
potassium level, within the range of 3.5-5.0 mmol/litre. The elevation of this value by 1-2
mmol/litre constitutes a medical emergency: the excitable components of the heart begin
to conduct nervous impulses spontaneously and, without treatment, death soon follows
from uncoordinated contraction of different parts of the ventricles (ventricular
fibrillation).
It soon becomes clear that the body's function involves countless homeostatic
mechanisms, both within and outside cells. Not only are the mechanisms ubiquitous, but
careful analysis often shows two or more feedback loops apparently serving the same
function; a good example is the elaborate relationship that exists between the control of
blood pressure and plasma volume. Perhaps the apparent redundancy provides the
organism with back-up systems that improve evolutionary survival value. Improvement
or not, such duplication makes the understanding of disease processes very much more
difficult to disentangle.