Respiratory Anatomy

Now that we understand why respiration is important let’s look at the structures we need to do it!

Pieces and Parts

Housing: Thoracic Cavity and Pleura

The largest portion of our respiratory system, the lungs, is housed in our thoracic cavity. There they are protected from damage by our ribs and surrounded by two layers of connective tissue called pleura. The first layer, the visceral pleura, sits directly on the lung while the second layer the parietal pleura envelops each lung and attaches to the inner wall of the thoracic cavity. Between both layers, there is a small fluid-filled space called the pleural space. The fluid helps lubricates the two pleura allowing them to slide easily against one another. Additionally, this fluid cushions the lungs against impacts and helps protect them as we go about our day.

Muscular Pump: Diaphragm and Intercostals

Laying just outside of the parietal pleura is the diaphragm and the intercostal muscles. These guys are the workhorses of respiration and are ultimately responsible for the movement of air into our lungs. By contracting they expand the rib cage and decrease the pressure in the lungs causing air to flow into our lungs. When they relax they shrink the size of our ribcage forcing air out of our lungs. We will look at this process in-depth in the next lesson to we can get a good sense of all the moving parts and the gas laws that explain it

Image: Diaphragm getting pulled down = contraction causing it to expand. Imagine it as being elastic and little people have to exert effort to pull it downwards thus inspiration takes effort. Snaps back into place without any issues though so exhalation is passive.

Hoses: Pharynx, Trachea, and Bronchial System

Our respiratory system is comprised of an elaborate series of tubes that help conduct air into our lungs where atmospheric gases can be exchanged and transported into our blood. This portion of our respiratory system comprises the upper respiratory system and is sometimes called dead space because at this level no gas exchange occurs.

Instead, the upper respiratory system acts only as a transport tube starting at the nares, more commonly known as the nostrils, or the mouth depending on how we are breathing. From there the air dumps into the oral cavity and progress into the pharynx through the larynx past the epiglottis and into the trachea. The trachea then branches into two bronchi and then into smaller hoses called bronchioles. This pattern of branching allows for air delivery to a much greater surface area. So by the time the air reaches our alveoli, it is spread out over a far greater surface area increasing gas exchange efficiency.

Exchanger: Alveoli

At this point, the air has finally reached our alveoli where gas exchange occurs. It is called exchange because different gases are moving in different directions and exchange places with one another. In this case, CO2 flows out of the pulmonary capillaries into the alveoli while O2 flows out of the alveoli and into the pulmonary capillaries through simple diffusion.

Image: Following from the previous theme I think of alveoli as a garden where oxygen is exchanged alveoli already look like trees so I think that is where that idea comes from for me. Open to ideas and suggestions since this is a bit vague and inchoate. Like the dollar signs though so maybe we can weave that in somehow. Since oxygen is like the currency for energy creation.

Here diffusion is driven by a difference in the partial pressures of gases between the alveoli and the pulmonary capillaries. It works in nearly the same way as a regular old concentration gradient except here pressure replaces concentration. We will take a deeper look at this process in the next section so we can get a good sense of how this works.

Air Purifiers: Hairs, Mucus, and Cilia

Unfortunately, when we inhale we aren’t just getting air. We are also taking in all of the pathogens, microscopic dust particles, or not so microscopic bugs suspended in the air. This is a big problem for our lungs because pathogens can cause infection and dust and bugs can damage the delicate alveoli that allow us to exchange air.

Thankfully, we have a series of air purifiers that help to block out harmful substances and other large particles. The first barrier is our vibrissae, a fancy term for nose hair, which forms a screen or sieve that blocks the passage of large particles and dust.

Extra nasal protection!!!

Additionally, our nose and throat contains mucus that traps smaller particulates and pathogens. Our mucus doesn’t just play a passive role though it also contains an enzyme called lysozyme (lyso = to lyse or break) that breaks apart bacteria whose walls have a high quantity of peptidoglycan.

Furthermore, the mucus houses a wide variety of immune cells and antibodies all of which are poised and ready to attack any unwary invaders. Eventually, this mucus will end up oozing down our throat (kinda gross I know!) where cilia, small moving hair-like structures, will propel the mucus into our oral cavity or pharynx for elimination.

Summary Image: Wondering if it is possible to create a big picture zoom out that incorporates the different parts so people can see the whole system at a glance. Sketchy comes to mind. This is super extra though so feel free to skip it.