03-19-07, Respiratory system

The main job of the respiratory system is to get oxygen into the body and waste gases out of the body. We were talking about gas exchange and how blood allows for the exchange of gas and the carbon dioxide and oxygen that we were mentioning. Air specifically travels to and from the lungs through contractions of the lungs. If you understood the circulatory system, this particularly unit should not be difficult until we get to Boyle's law - which you should have learned when you took chemistry.

Boyle's law is the following: when the temperature is kept constant, the volume of a given mass of an ideal gas varies inversely with the pressure to which the gas is subjected. In mathematical terms, the product pressure times the volume of a given amount of gas remains constant. Thus, in comparison with the properties of a given amount of an ideal gas under two conditions, which we may call the initial and final states, we may write the following equation, applicable at constant temperature: pressure times the volume is the same at the initial state as it is at the final statement. This law furnishes the most direct test of how well a real gas corresponds to ideal behavior.

The function of the respiratory system is to transport gases to and from the circulatory system. This is all basic knowledge. The respiratory system takes gases and moves them around to provide the requirements to metabolism.

Respiration occurs at two different levels: the cellular level and another. Cellular respiration is where mitochondria require oxygen to break down glucose. They release carbon dioxide and produce 34 ATP molecules. This occurs in the crestae of the membrane of the mitochondria in the cells. There are thousands of these mitochondria. To get the structures into the mitochondria, you have to convert it to the two molecules of pyruvate acids, which pass into the mitochondrial membrane after some ten-step process to convert the glucose to those structures. This is also called internal or cellular respiration.

You can also have respiration on an organism level where an organism must get oxygen in and carbon dioxide out. The organism-level respiration takes place with the external environment, so it's just the exchange of carbon dioxide with oxygen and other stuff in the air. Respiration in terms of an organism is just air going in and out of the body, nothing really complex. There are specific steps to get the air in and out of the body, so you are going to have to know these steps.

The only reason we breath is to get oxygen to our cells. If we absorbed oxygen through our skin, we probably wouldn't have to breathe at all. You'd have to wear breathable fabrics. No spandex. That'd be outlawed. I guess you could wear it, but it would be difficult to walk around. Frogs do not really use their lungs that much. That's why you see most frogs sitting in a puddle of water. They sit there because that's where they can get their oxygen, it's where they breath and breed. So if you're sitting around water, good things might happen if you're a frog. Let's move on from this awkward aside. Isn't that what Spring break is in Florida, bunch of people sitting around water? Magical things happen around water. And bad things.

The respiratory system is a group of organs working together to bring an exchange of gases with environment. Atmosphere of the planet Earth is ~78% nitrogen and 21% oxygen. The lower levels of the atmosphere is the nitrogen gas there, because it is light enough to be that low. Everything else in the atmosphere makes up the other 1%. This is all about the gas composition of the atmosphere that surrounds the planet. Even carbon dioxide is just in that 1%. Even though it may be contributing to global warming, it's a minute fraction of the atmospheric composition. The nitrogen is coming from much of the bacteria on the surface of the planet. The one percent is going to have carbon dioxide, water vapor, and other trace gases which are such an incredibly small percentage. That 21% oxygen is what keeps our cells doing metabolism and breaking down the sugar molecules that the autotrophs are producing with the light that does get through the atmosphere full of oxygen and so on.

If the amount of oxygen fell much below 15%, our respiratory systems would be unable to extract enough oxygen molecules to support cellular respiration. This was probably found out from the Nazi concentration camps. There are also experiments at colleges where you just show up and get 30 or 50 bucks for participating in an experiment or something, it's really informal.

Air enters the respiratory system through the mouth or nose. Air entering the nose passes into the nasal cavity. This cavity is richly supplied with arteries, veins and capillaries, which bring nutrients and water to its cells. The nasal cavity has to be kept moist because it helps attract stuff and hold it there rather than at another part of the body.

After it reaches the mouth or nose, then to the nasal cavity, and then it goes to the pharynx. As air pushes back from the nasal cavity, it enters the pharynx. The pharynx is located in the back of the mouth and serves as a passageway for both air and food. This is the first space that the mouth and the digestive system and the respiratory system are going to have in common.

From the pharynx, food is swallowed, and when it is swallowed, a flap of cartilage, called the epiglottis, presses down and covers the opening of the windpipe (the air passage way). When you eat food and it goes the wrong way, it goes to the trachea, and it will be eventually forced out to the pharynx and the epiglottis will close and hopefully you can get it out, but if you choke and it is in the trachea then somebody (you or somebody else) has to force in tons of air to get the foreign object on the wrong path out of the system.

All of these passageways together have the responsibility to filter out dust, dirt, smoke, bacteria, and a variety of other contaminants found in the air. The respiratory system filters the stuff out before it gets to the lungs. The immune system and mucus help to filter this junk out.

The nose is responsible for filtering as a first stage of defense. The nose will do three things in the air we breath in: it will filter the air with moisture and mucus and hairs, move it to the nasal cavity, and it will warm the air. It will filter the air, warm the air, and provide a moist (water vapor or humidity) environment to the air. There are many capillaries going through the nose and naval cavities. Blood vessels in general help regulate heat, and heat will be lost. So since the capillaries are near the surface of the body, capillaries get bigger and smaller based on how much heat they are going to be losing, so the heat loss lets the air in the nose be warmed.

As air passes through the nasal cavities, it is warmed and humidified, so that air that reaches the lungs is warmed and moist. Nasal airways are lined with cilia and kept moist by mucous secretions. The combination of cilia and mucous helps to filter out solid particles from the air and warm and moisten the air, which prevents damage to the delicate tissues that form the respiratory system.

The moisture in the nose helps to heat and humidify the air. Increases the amount of water vapor the air entering the lungs contains. This helps to keep the air entering the nose from drying out the lungs and other parts of the respiratory system, which must be kept moist.

Larynx - located at the top of the trachea. The larynx is what is known as the Adam's apple or the voice box. The way that the voice box works is that there are muscle linings that can be stretched and pulled which force air through specific passageways. Stretched across the larynx are two highly elastic folds of tissue (ligaments) called the vocal chords. These ligaments are crossed over the larynx.

It is kind of like the guitar, where you have the “strings” crossed over the hollow portion of the guitar. In the voice box, you're passing air over that ligaments. Pushing air through your lungs does not change the pitch, but it does make it louder. What if we wanted to change the inflection of somebody's voice? The fatter the chords, the deeper the voice.

How would we change the inflection? Think back to the guitar, the way to change the sound is to tighten or loosen the strings … same thing with vocal chords. As the muscles are pulled tighter or looser, that will change the pitch that is going to come out.

Air rushing through the voice box causes the vocal chords to vibrate producing sound waves. Air moves in to the thoracic cavity through the trachea. The trachea is made up of c-shaped rings of cartilage so that it always stays open. You do not want the trachea collapsing on itself, you need that clear airway or that clear passageway through which air can be passed in and out of the body. There are gaps between the cartilage rings. This protects the trachea. This makes the trachea flexible, and keeps it from collapsing or over expanding. Cells that line the trachea produce mucus. The mucus helps to capture things still in the air.

The trachea divides into two branches. These two main branches are the bronchus. There's the left and right bronchi. There's the pathway: trachea->branch->right or left lung based off of whether it goes down the right or left bronchi.

The right lung has three lobes which are slightly large. The right lung is slightly larger because the left lung has the heart to deal with. So the left lung only has two lobes, and they're roughly the same size, but the right lung is going to have more space to work with because the heart isn't there.

The lungs are contained inside the thoracic cavity, bounded by the rib cage and diaphragm. The rib cages are on the side. The diaphragm is the boundary across the bottom. Lining the entire cavity and encasing the lungs are pleura membranes that secrete a mucus that decreases friction from the movement of the lungs during breathing.

Those membranes are very important, they secrete mucus so that the lungs will slide over the ribs. You may have experienced a lack of mucus in your pleura membrane. It is an extremely, sharp pain in your ribs when you breath. It's not when you work out hard, that's something different, but this is when you are walking along and you get a chest pain on some one side, or on the back. The lungs start to stick to the ribs when there's not enough mucus there.

Muscle pain is the build up of lactic acid, which is something different. Now, don't go around drinking mucus because you think your pleura membrane is out of mucus. They're very important; they decrease friction associated with breathing and the movement of lungs over the rib cage.

Bronchi branch to bronchioles. Both bronchi and bronchioles contain smooth muscle tissue in their walls. You do not have control over your breathing in those ways. You can sort of override the smooth muscle actions here, but you really don't have that much control over it, it's not like you can completely stop your entire respiratory system.

Bronchioles continue to subdivide until they finally end in clusters of hollow air sacs called alveoli. The reason why they are clustered like that is to increase surface area to maximize gas exchange. Form follows function.

Every single time you take a breath, or move air in and out of your lungs, two major actions take place. Air is pulled into the lungs (called inspiration). And there is expiration, where air is pushed out of the lungs. The diaphragm assists in expiration. The diaphragm is going to be running the entire show. The thoracic cavity has its volume changed. As you breath in, the volume of the cavity increases, and as the diaphragm comes up, the volume decreases.

Based on those changes in volume, the pressure of the air inside the lungs is going to change, and that's going to make air do different things with relation to the lungs, and this is going to include Boyle's law (the initial pressure-by-volume number is the same as the final pressure-by-volume number).

When you breath in, that muscle called the diaphragm comes down. And when you breath out, it pushes up. The diaphragm is kind of curved and rests below the lungs. So the breathing is facilitated by the neuromuscular expansion of the muscular tissue formed in the structure known as the diaphragm.

The action of the diaphragm delivers oxygen to the alveoli and removes carbon dioxide from the system. We're going to pass around a fake thoracic cavity to play with. There is some space around the actual lungs that also contributes to pushing the lungs to the original position and exhaling all of the gases left over. Most of us breathe 10 to 15 times per minute.

The lungs are not directly attached to any muscle, so they cannot be expanded or contracted. It's a common misperception to think that muscles are actually attached to the lungs. That's not how it works. It's based off of the gas pressure around and within the lungs.

Inhalation and exhalation are actually produced by movements of the diaphragm and the intercostals muscles. The diaphragm is located along the bottom of the rib cage.