Welcome back to BOGObiology.
This is 5 minute bio, where we discuss a key concept in 5 minutes or less.
Today's topic is homeostasis.
Homeostasis is a dynamic equilibrium or balance which is actively regulated to maintain a
variable a constant level.
In biology, homeostasis is often related to an internal balance within a cell or organism
because so many creatures have a very narrow range of conditions in which they can survive.
Two examples of homeostasis you might be familiar with are body temperature and blood glucose
level.
The human body has an ideal temperature of about 98.6 degrees Fahrenheit, or about 37
degrees Celcius.
If the human body gets too hot or too cold, the proteins and chemical reactions that are
crucial to make our bodies work will not function properly.
If the problem is not fixed, there is a distinct risk of tissue or even organism death.
Blood glucose level is also a common example of homeostasis although one that you are probably
less familiar with.
Your body needs sugar in order to run the process of cellular respiration and provide
energy for your cells.
There is an ideal amount of sugar to have in one's blood, which is about 90-120 milligrams
per deciliter.
Having the wrong amount of sugar in one's blood can have serious consequences, particularly
if your blood sugar dips too low.
While skipping a meal might cause someone to be irritable or have low energy, having
blood sugar that is severely below normal can cause coma and even death.
Before we move on, see if you can think of other examples of homeostasis and also think
about the consequences of deviating from a set point for too long.
Hopefully you figured out that prolonged deviation from an ideal set of conditions can cause
cell, tissue and organism death.
Maintaining homeostasis often requires that an organism have an internal environment that
is different from its external environment.
Barriers between internal and external environments allow the organism to maintain an internal
environment despite what's going on in the external environment.
A great example of this is the cell membrane.
Organisms, including humans, use something called a feedback loop to help maintain homeostasis.
Feedback loops are broken into three parts; the stimulus, the sensor and the response.
Let's start with this loop over here on the left.
Imagine that it's a very hot day and the individual's body temperature is rising.
The rising temperature is the stimulus.
The stimulus is then detected by the sensor located in the brain.
In humans, a temperature change would be detected by the hypothalamus, but obviously Homer Simpson's
brain is a little different (!). Because high temperatures can cause cell death, the body
then goes into action to bring its core temperature down.
Blood vessels will dilate, allowing heat to radiate outwards.
The person will also begin to sweat in order to decrease their body temperature via evaporative
cooling.
Hopefully, the overall effect of these steps will be enough to bring the individual's body
temperature back down towards normal.
This phenomenon is called a negative feedback loop, not because it is bad, but because it
helps to make the situation less extreme.
See if you can figure out what would happen on the right side of this loop when the temperature
gets too cold, rather than too hot.
Ideally, if your body temperature gets too cold, you begin to shiver after detecting
the decreased temperature in your hypothalamus.
The shivering generates heat, which should bring your body temperature back up.
Positive feedback is pretty rare in nature because it tends to make a situation more
extreme.
However, we do have two examples here; the clotting of blood and the increase in uterine
contractions during labor.
Both passive and active transport can be used to help maintain homeostasis.
In passive transport, such as osmosis and diffusion, particles flow from an are of high
concentration to an area of low concentration and can very effectively fill a space.
If deviation from a set point has been detected, ATP can also be spent in order to pump particles
against the concentration gradient and restore homeostasis.
A few key concepts to remember: First, homeostasis is a desirable state of equilibrium.
Generally, maintaining homeostasis in biology also means maintaining ideal internal survival
conditions.
Second, most organisms use negative feedback loops to maintain the state of homeostasis.
Finally, we also use passive and active transport in order to maintain this desirable state
of equilibrium.
That's it for today!
As always, make sure to cite your sources.
If you'd like to cite BOGObiology, there is an APA citation in the video description.
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