Transcription
Peace be upon you. Take a deep breath. Let it out. Isn't that amazing? The human respiratory system, I mean. The system that allows us to do that – gas exchange. Now don't confuse the respiratory system with cellular respiration. If you watched our cellular respiration video, you learned why our cells need oxygen. Your cells need oxygen to produce ATP (adenosine triphosphate), the energy currency, and the gaseous byproduct is carbon dioxide that the body needs to get rid of. That's part of the aerobic cellular respiration equation that your cells do. But the respiratory system that takes in oxygen and expels carbon dioxide – it works closely with the circulatory system and other systems to do that – is how we get that oxygen into the human body in the first place. And that oxygen is essential for cellular respiration. So you inhale. Air passes through your nasal cavity. The air is warmed, humidified, and filtered. This includes mucus and hairs. Nasal hairs that you can see and then microscopic cilia that are like hair-like structures. Now, we come to the pharynx. A crossroads, if you will, of both food and air. From the pharynx, we pass through the larynx (often called the voice box). Then the trachea. By the way, food should go down the esophagus, not the trachea. We mention in the digestive system video that the epiglottis prevents food from going down the trachea. The trachea is a really cool cylindrical tube with rings of cartilage. This cartilage helps to support the trachea and keep it open so that air can pass through. The trachea goes down, down, down into the primary bronchi. One on each side because this branches into the lungs. Just a little bit about the lungs. There are two. Each lung has divisions called lobes. Three lobes on the right and two on the left. There's an indentation on the left side of the lung where there's a little bit of space to give the heart some room. The left lung is generally smaller than the right. Our main focus will be on what happens inside the lungs, so let's go ahead and continue. The primary bronchi. The primary bronchi divide into secondary bronchi, then tertiary bronchi, and then smaller bronchioles. And as you know, it kind of looks like an upside-down tree. I love trees. So, a general recap of where we've gone: Nasal cavity -> Pharynx -> Larynx -> Primary Bronchi -> Secondary Bronchi -> Tertiary Bronchi -> Bronchioles. The diameter gets smaller as you go through these different areas. Beyond the terminal bronchioles, there will be branching into respiratory bronchioles and then into alveolar ducts. Each alveolar duct is surrounded by alveolar sacs. Alveoli are very much like... a bunch of grapes. I'm not the only one who thinks so. Each of these alveolar sacs contains alveoli, and this is where gas exchange will actually occur. This is because these alveoli are made of thin-walled cells, they have a large 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 pick up the inhaled oxygen to deliver throughout the body and also pick up carbon dioxide – a waste gas that needs to be removed – so that it can be exhaled. Along with the circulatory system, there are other body systems that work with the respiratory system. The skeletal system includes the ribs that protect the lungs like a cage around them. But muscles of the muscular system are also involved. Muscles involved in breathing include the muscles between the ribs called the intercostal muscles. It includes a large muscle underneath called the diaphragm. And it includes the abdominal wall muscles. All of these are part of the muscular system – and they are involved in helping to expand or contract the thoracic cavity. While you have voluntary control over your breathing, you'll notice that your breathing is involuntary most of the time: this means you're not consciously controlling it. The nervous system regulates this, and here's something cool: it uses pH to do so. pH is based on the concentration of hydrogen ions (H+). Acids – shown here as lower numbers on the pH scale – have a higher concentration of hydrogen ions compared to bases, which have a lower concentration of hydrogen ions. Finally, an increase in the concentration of carbon dioxide in the blood increases the concentration of H+. If you want to learn more about how that happens – fascinating chemistry – check out the further reading links. So the more carbon dioxide there is in the blood, the slightly lower the blood pH is on the pH scale – it's become more acidic. The increase in acidity is detected and sent as signals to the brain. The brain can then control the intercostal muscles, the abdominal muscles, and the diaphragm, and that's to increase the rate and depth of breathing. This can bring the blood back to a normal blood pH and keep blood pH stable. Around 7.4. A great example of homeostasis. Just think about when you exercise and how amazing it is to have such a precise system that the rate and depth of breathing can be increased 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 two final notes I'd like to mention. First, we want to remind you we're focusing on humans. But obviously, gas exchange isn't just humans. In fact, earthworms exchange gases through their skin. Fish can use gills for gases to diffuse, insects can have a tracheal system which means they can have small openings in their bodies – called spiracles – that connect to small 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 diseases or respiratory problems that may arise. There are many professions that focus specifically on the respiratory system – and examples of these are pulmonologists and respiratory therapists. They may be involved in treating respiratory conditions like asthma or emphysema, and an example I'd like to conclude with: they may be involved in treating premature infants who may not have fully developed lungs. To expand on this: remember we were talking about alveoli – we mentioned that alveoli have a large surface area? Perfect for gas distribution. But without something called surfactant inside, the alveoli can be prone to collapse due to the surface tension of the water inside the alveoli. Surface tension is a great thing to review in the properties of water video. So, write 2 alveolar cells make surfactant, which is a substance containing phospholipids and proteins. Surfactant interferes with the cohesion of water which contributes to reducing surface tension, making it easier to inflate the alveoli. But sometimes, premature infants may not have enough surfactant in their lungs. This can make it difficult for the alveoli to inflate properly; it can cause collapse. This can lead to respiratory distress syndrome (RDS). But now... because of a better understanding of this, synthetic surfactants can be used to treat preemies and that has saved many lives. Translated by Fatima Khalid Mahdi Al-Araji. Well, that's all for Amoeba Sisters, and we remind you to stay curious.