Captions are on! Take a deep breath. And let it out. Isn’t
it remarkable? The human respiratory system, I mean. The system that lets us
do that – an exchange of gases. Now don’t confuse the respiratory system with
cellular respiration. If you watched our cellular respiration video, you learned about why our cells
need oxygen. Your cells need oxygen to make ATP, an energy currency, and the gas byproduct
produced is carbon dioxide which the body must remove. This is part of the equation in
aerobic cellular respiration done by your cells. But your respiratory system which takes in the
oxygen and expels the carbon dioxide – working closely with the circulatory system and other
systems to do so – is how we get that oxygen into human body in the first place. And that
oxygen will be needed for cellular respiration. So you inhale. Air passes through your
nasal cavity. The air is warmed, humidified, and filtered. This involves mucus and hairs. Nasal
hairs that you can see and then microscopic cilia which are similar to hair-like structures. Now,
we come to the pharynx. A junction if you will of both food and air. From the pharynx, we go
through the larynx (often called the voice box). Then the trachea. By the way, food should be
traveling down the esophagus not the trachea. We mention in our digestive system video that an
epiglottis keeps food from going down the trachea. The trachea is a pretty fascinating cylinder tube
with rings of cartilage. That cartilage helps support the trachea and keep it open for that air
to travel through. The trachea goes down, down, down to the primary bronchi. One on each side
as this branches to the lungs. Just to mention a bit about the lungs. There are two. Each
lung has sections called lobes. Three lobes on the right and two on the left. There’s a
cardiac notch on the left lung side where it's a little indention to give the heart some room.
The left lung is generally smaller than the right. Now our main focus is going to be what’s happening
inside the lungs so let’s continue to go through the primary bronchi. Primary bronchi divide into
secondary bronchi then tertiary bronchi and then smaller bronchioles. And, you know, it kind of
looks like an upside down tree. I like trees. So a general recap of where we’ve gone: nasal
cavity -> pharynx -> larynx trachea primary bronchi secondary bronchi
tertiary bronchi bronchioles. Diameter is getting smaller as you
go through these different areas. Beyond the terminal bronchioles, there will
be branching into respiratory bronchioles and then on to alveolar ducts. Each alveolar
duct is surrounded by alveolar sacs. Alveolar sacs look a lot like…a bunch of grapes. I’m
not the only one to think that. Each of these alveolar sacs contain alveoli and this is
where the gas exchange will actually occur. That’s because these alveoli are made of thin
walled cells, have a lot of surface area, and they have direct contact with capillaries. We mentioned
that other body systems work closely together: the circulatory system works closely with the
respiratory system here. Red blood cells in the capillaries can pick up the oxygen that was
inhaled to deliver it throughout the body and also bring carbon dioxide -a waste gas that
needs to be removed- so that it can be exhaled. Besides the circulatory system, there are other
body systems working with this respiratory system. The skeletal system includes the ribs that
protect the lungs like a cage around them. But muscles of the muscular system are involved
too. Muscles involved in respiration includes muscles between your ribs called intercostal
muscles. It includes a major muscle under your lungs called the diaphragm. It includes
abdominal wall muscles. All of these are part of the muscular system – and they are involved with
helping to expand or contract the thoracic cavity. While you can take voluntary
control of your breathing, you’ll notice that most of the
time your breathing is involuntary: that is, you aren’t consciously controlling it.
The nervous system regulates this, and here’s something pretty cool: it uses pH to do so. The
pH scale is based on hydrogen ion concentration (H+). Acidic substances – shown here as lower
numbers on this pH scale - have a higher H+ concentration compared to bases - which have a
lower H+ concentration. Ultimately, the increase of carbon dioxide concentration in the blood
increases the concentration of H+. If you want to learn more about how that happens – fascinating
chemistry- check out our further reading links. So as the carbon dioxide concentration
increases in the blood, the blood pH falls slightly lower on the pH scale – it is becoming
more acidic. The increasing acidity is detected and sent as signals to the brain. The brain
can then control the intercostal muscles, diaphragm, and abdominal muscles in order to
increase the rate and depth of breathing. This can restore the blood to a normal blood pH and keep
the blood pH stable. Around 7.4. Great example of keeping homeostasis. Just think about when you’re
exercising and how amazing it is to have such a fine-tuned system so your breathing rate and depth
can increase as needed. And while we’re really trying to give general examples to emphasize
that body systems don’t work in isolation, keep in mind that there are other systems
involved with the respiratory system to explore. Before we go, there are 2 final notes I want
to mention. First, we want to remind you we focused on humans. But obviously it’s
not just humans that have gas exchange. Earthworms actually have gas exchange through
their skin. Fish can use gills for gases to diffuse, insects can have a tracheal system
which means they can have little openings on their body- called spiracles – that connect
to little tubes inside. It’s fascinating to learn about all these different systems for
getting oxygen in and carbon dioxide out. Second, understanding how the respiratory
system works can help us understand treatments for respiratory illnesses
or respiratory problems that may arise. There are many careers that focus specifically
on the respiratory system – two examples include pulmonologists and respiratory therapists. They
may be involved in the treatment of respiratory conditions like asthma or emphysema, and, an
example I’d like to end with: they might be involved in the treatment for premature babies
that might not have fully developed lungs. So to expand on this: remember we were talking
about the alveoli – we mentioned alveoli have a large surface area? Ideal for gases to diffuse.
But without something called surfactant inside them, alveoli can be prone to collapse due to
the surface tension of water inside the alveoli. Surface tension being a great thing to review in
our properties of water video. So, type 2 alveolar cells makes surfactant, a substance that includes
phospholipids and proteins. Surfactant interferes with the bonding of water which contributes to
lowering the surface tension, making it easier for alveoli to inflate. But sometimes, babies that
are premature may not yet have enough surfactant in their lungs. This can make it difficult
for the alveoli to inflate properly; it can cause collapse. This can result in respiratory
distress syndrome (RDS). But now…due to better understanding of this, artificial surfactants
can be used to treat premature infants and it’s saved the lives of many. Well, that’s it for the
Amoeba Sisters, and we remind you to stay curious.