Welcome back to one more of our series of physiology concepts and today we will be discussing
the process of homeostasis. So what is homeostasis?
Let's look at the definition. Homeostasis is a self-regulating process by which biological
systems in the body tend to maintain stability by adjusting to conditions that are optimal
to survival.
We need to understand the meaning of maintain stability.
It means that the body is always going to change.
There's always going to be external or internal variables that will change within the body
and homeostasis will help to adjust these variables back to the optimal levels for survival.
If this does not work disease or even death can ensue. So what are the wrong definitions
of homeostasis? Homeostasis does not mean that the body remains static. The body is always
changing and the function of homeostasis is to adjust back to normal physiological limits. Let's look let's look at some examples of those limits or those variables as we call
them. An example is heart rate. Everybody has an average heart rate and if it goes too much
fast or too much slower than the norm this person has some disease. The same for blood
pressure. We have accept average of blood pressure, body temperature, some blood levels of substances
as glucose or calcium. So these are some variables that we're going to discuss in a minute. Now
who controls homeostasis? Two main systems in the body are responsible for regulating
the homeostasis. First, a nervous system. Second, the endocrine system. Let's look at this. Let's
compare them. How fast is the response of the nervous system? Very, very fast. So anytime there
is disturbance in the homeostasis, the nervous system is going to be the one that will respond
first. The response is for very fast. The endocrine system takes just a little bit longer. How
about the effect of the nervous system? The effect is very short-lived. The effect of the
endocrine response is a little longer in the body. How do these work? So the nervous system
is going to produce a response using electrical nerve impulses. These are going to travel down
the nerve fibers. At the end of the nerve is going to be the release of certain chemical
substances called neurotransmitters. The endocrine system responds by producing again chemical
substances called hormones. So the endocrine system consists of glands and these glands
will secrete the hormones. These hormones are carried by the blood and they will produce
the homeostatic effect. What are the components of homeostatic control? How does all of this
actually work? There are three main components we need to remember. First, a receptor. Second
a control center. And then the effector. Let's start with the receptor. What is a receptor?
A receptor is a group of sensors in the body. And these sensors will always monitor the
normal physiological levels. if at any time there is disturbance in the level of this
variable this is going to be detected by the receptor and the receptor is going to send
a message to the control center. How does it do that? By means of efferent pathways. Now
the control center is going to take this information that it received. It's going to process it and
make a decision. How do I reverse those changes? And accordingly, the control center is going
to send a message to the effector organs to make the changes in order to restore the balance.
So the pathway again is this is homeostasis. If there is an imbalance in the homeostasis
this is going to be detected by the receptors. Receptors will send a message via efferent
pathways to the control center. The control center will decide what needs to be done and
accordingly is going to send a message to the effector organs via the efferent pathway.
And now the affected organ is going to produce a certain response and the response will bring
back the imbalance to normal. It will correct it and homeostasis will be regained. So we're
going to look here at what actually happens in this area. How does the effector organ make
the response to the change. The mechanism for restoring homeostasis is by using either a
negative feedback loop or a positive feedback loop. Let's look at the differences and then
we're going to look at examples. In a negative feedback loop, the response is opposite the
direction of the initial state change. In the positive, the response is in the same direction
as the initial change. The response here in the negative it will counteract or negate
the initial change and this is where the word negative comes into focus. The response here
will in reinforce the initial change. Examples of negative feedback that occur in the body
is how we controlled by the temperature, blood sugar levels, and blood pressure. There are
much fewer examples of positive feedback. Labor contractions during child and blood clotting.
Let's look at this example of negative feedback. So this is the normal homeostatic level of
blood temperature. If there are outside conditions that tend to decrease this norm below 98.6
which is a normal body temperature, there are going to be receptors-- and remember receptors
are sensors-- they will detect the change, the deviation from the norm, and these receptors
will send afferent pathways to the control center. The control center for body temperature
is the hypothalamus. It's an area in the brain. And the hypothalamus will want to regain the
normal body temperature. So what does it do? It's going to do two things. Number one it's going
to cause a person to shiver and this shivering is very rapid muscle contractions. These will
produce heat . At the same time, certain stimuli are going to go to the layers of the skin
where there are blood vessels and there's going to be vasal constriction of the blood
vessels of the skin and this will retain the heat in and prevent loss of heat from the
surface of the body. And these two functions will increase the body temperature back to
its norm. Again, remember, why do we call this negative feedback? Because the initial change
was lowering of the temperature. The homeostatic mechanism is going to result in increasing
the temperature back to normal. So these two are is opposite directions. Let's look at the positive
feedback loop. And this is the example of what happens during childbirth. So when a mother
goes into labor the baby's head is pushing against the cervix. This will stimulate some
nerve impulses that are going to travel all the way up to the brain and in the brain there
is a very important gland called the pituitary gland. It will secrete a very important hormone
called oxytocin. Oxytocin is carried in the blood and comes back to the uterus. What is
the effect of oxytocin? It's going to stimulate uterine contractions. It's going to increase
the contractions of the uterus. This will result in pushing the baby's head a little further
down. This will push some more on the cervix. We have more impulses, more oxytocin and so
forth until the baby is delivered. And then this positive feedback loop is going to stop. Again, why do we call it positive because the initial change is increased and the homeostatic
loop is in the same direction. It will keep increasing until the final effect is reached.
We're going to conclude by looking at one of the important outcomes if there is imbalance
in the homeostatic mechanism. And this is a very famous example. We are looking at the
normal blood level of glucose and we're going to see if the homeostatic mechanism does not
function what can happen. So this is the normal blood glucose level. It usually increases a
little after we eat anything that is high in sugar or carbohydrates. And accordingly,
the normal homeostatic mechanism is this is going to be detected and the pancreas is a
very important endocrine gland. Because of the high blood glucose level it will secrete
insulin. Insulin is going to go to the body cells or the liver. In the liver, insulin is
going to pick up the glucose and store it so it will lower the blood sugar level and
this else is going to allow the cells to pick up the glucose and remain inside. So by those
two mechanisms these two effector organs blood glucose level will go back down to normal.
If this mechanism fails somebody has high blood glucose level after a meal if the pancreas
does not function to produce enough insulin or if the insulin receptors in the cells are
not working they're not receiving the insulin and they're not doing what they're supposed
to do this system will fail and accordingly a person might have the famous condition of
diabetes and they might have to take treatment, medication, insulin and watch their diet and
so forth. Thank you for joining us. This concludes the presentation and thank you for tuning
in.