Did you know that our nervous system controls our breathing? This lesson describes the basic elements of the homeostatic system responsible for balancing oxygen supply with metabolic demand.
Regulation of Ventilation
How long can you hold your breath? I remember competing with my buddies to see who could stay under the water the longest. I think the longest I managed to pull off was about one minute before I had to come up for air. Thank goodness we don’t have to think about breathing.
Our nervous system ultimately overrides any effort we make to hold our breath. Furthermore, the nervous system regulates our breathing even if we’re not trying to hold our breath.Breathing is formally referred to as ventilation, the process of moving air into and out of our lungs.
As you know, we breathe for the purpose of taking in oxygen and getting rid of carbon dioxide. Our cells use oxygen to make ATP, while carbon dioxide is produced by the same process. In other words, oxygen is needed for cellular respiration and carbon dioxide is produced as a result.
As our metabolic needs change from moment to moment, so must ventilation. In this lesson, we will discuss how the nervous system regulates ventilation to meet our metabolic needs.
Homeostasis is the maintenance of a relatively constant internal environment.
Much like the temperature in our homes is regulated by a furnace, ventilation is regulated by our nervous system. That is, ventilation is increased or decreased to maintain a constant balance between oxygen supply and metabolic demand. Every homeostatic system has the same basic elements. Let’s consider these elements before we discuss how they apply specifically to ventilation.The basic elements of homeostasis are a stimulus, a receptor, an integration center, and an effector (or more than one effector).
All of these elements are needed for homeostasis to work. There are different types of receptors that sense different stimuli – that is, changes in the environment. An integration center determines what to do about the change – about the stimulus. Finally, the integration center sends signals to effectors, which then act to restore homeostatic balance. So, that’s how a basic homeostatic system works.
Homeostasis and Ventilation
Now, let’s identify the basic components of the homeostatic system responsible for maintaining balance between oxygen supply and metabolic demand. First, we must identify the stimulus – in other words, what changes.
The most important stimulus for regulation of ventilation in healthy persons is increased levels of carbon dioxide, which is known as hypercapnia. Hypoxia, or decreased oxygen levels, can become a powerful stimulus for ventilation in sick persons.Let’s make sense out of this. Carbon dioxide levels increase when metabolism increases; therefore, hypercapnia is a good measure of metabolic activity.
Oxygen levels, on the other hand, don’t change very much with everyday changes in metabolism for healthy persons. This is due to the large store of oxygen that’s bound to the hemoglobin in our red blood cells. Therefore, carbon dioxide levels more accurately reflect our metabolism on a regular basis. However, increased metabolism due to illness can decrease oxygen levels – that is, cause hypoxia.
In these cases, hypoxia can become a powerful stimulant for ventilation.
Have you ever heard the expression ‘if a tree falls in the forest and nobody is there to hear it fall, did it make a noise?’ Let’s apply this expression to homeostatic regulation of ventilation.
If nothing senses a change in carbon dioxide or oxygen levels, will the stimulus go undetected? The answer is yes! Therefore, we have what we call chemoreceptors, which serve to sense changes in carbon dioxide and oxygen levels in our body. These chemoreceptors are located in our brains and some large arteries that deliver blood to the brain. The central chemoreceptors are located in the medulla oblongata, and they’re sensitive to changes in carbon dioxide levels. The peripheral chemoreceptors are located in the aorta and carotid arteries, and they deliver blood to the brain. These receptors are sensitive to changes in carbon dioxide and oxygen.
|Homeostatic working properly. The strong feelings of hunger