RESPIRATORY SYSTEM - LECTURE 1 Flashcards
Overview of the respiratory system (functions, structures)
The respiratory system is related to the intake of oxygen and expelling CO2 (gas exchange - what we wil focus on), but also helps with sound/voice production, regulating/removing health (panting), regulating moisture, and smell
The respiratory systems starts from the nose, goes through the throat, and goes all the way down to the alveoli air sacs (where gas exchange occurs)
It is often called the respiratory tree - as form the windpipe of the trachea onwards is like an upside down tree with many branches and therefore massive surface area
Introduction to the lungs (what are they, what do they do, differences between lungs, structures aroung them)
The trachea branches off into two and then into each of the lungs
The lungs are internal pockets of the body surface in which atmospheric air is brought close to pulmonary capillaries so that gas exchange can take place
Anatomically, the right and left lung are slightly different - the left lung is slightly smaller to accommodate for the heart
We can split the lungs into compartments/lobes: the left has two lobes while the right has three
Furthermore, the lungs are encased in a membrane called the pleura, and as they are so delicate they are also protected and attached to the ribcage (they follow them as we breath)
There is also the diaphragm that sites under the lungs, The diaphragm is a dome shaped tendinous muscle which sits below the lung and is important with the mechanics of breathing (related to lectures 3-6)
Two things that are essential for efficient gas exhange
The diffusion distance between the air and blood must be small (need the tiniest possible distance to allow this to happen, it is called the diffusion/blood-air barrier, most of which is established during lung development)
- The diffusion distance is about 0.5micrometres, which is one fifteenth of the diameter of a RBC
The surface area over which exchange takes place must be large - we have millions of alveoli at the end of the ‘tree’ which allows for a large surface area despite the fact that the lungs are tightly packed in the thorax and thoracic cage in the ribs.
- The internal surface area of the lungs is about 100m^2, which is half the size of a tennis court
1 - Respiration vs Ventilation
Respiration is the transfer/exhange of gases across a distance
Respriation occurs at three different levels:
- External respiration is the process in the lungs by which oxygen is absorbed from the atmosphere into blood within the pulmonary capillaries, and carbon dioxide is excreted.
- Internal (or tissue) respiration describes the exchange of gases between blood in systemic capillaries and the tissue fluid and cells which surround them. It is not the subject of this lecture.
- Cellular respiration is the process within individual cells through which they gain energy by breaking down molecules such as glucose. It occurs in mitochondria, consumes oxygen and generates carbon dioxide. It is not the subject of this lecture.
Ventilation:
In comparison, pulmonary ventilation (breathing) describes the bulk movement of air into and out of the lungs. Sometimes it is called the mechanics of breathing as it is a mechanical process where you need to change the volumes to change the pressure and move the air. The ventilatory pump (what allows for pulmonary ventilation) comprises the rib cage with its associated muscles, and the diaphragm.
Two functional sections of the respiratory system:
As air moves into and through the respiratory tree, it goes through parts that can be split into two function classifications:
Conducting zone/part:
The conducting part of the respiratory system is a series of cavities and thick-walled tubes which conduct air between the nose and the deepest recesses of the lungs, and in doing so warm, humidify and clean it (preparing the air for gas exchange - the large surface area allows for this to happen). The conducting airways are the nasal cavities, pharynx, larynx, trachea, bronchi, and bronchioles. No gas exchange occurs
Respiratory zone/part:
The respiratory part of the respiratory system comprises the tiny, thin-walled airways where gases are exchanged between air and blood. The airways are respiratory bronchioles, alveolar ducts and sacs, and the alveoli themselves (large surface area as a lot of branching beforehand).
Note that this differs form the lower and upper respiratory tract:
Difficult to treat and manage a lower respiratory tract infection
The movement of gas into and out of the blood
The oxygen from the atmosphere enters the lungs
The pulmonary capillaries pick up the oxygen (external respiration) and send blood to the left side of the heart (let cardiac pump)
Then the blood is pumped out and sent to the neccessary tissues (internal respiration)
Then there is cellular respiration within cells
Then the CO2 produced leaves the tissue (internal respiration) and goes to the right side of the heart
Then the oxygen-poor or carbon-dioxide rich blood goes through the right ventricle into and out through the lungs (external respiration)
Overall, we mechanically ventilate to allow the air to pass through the conducting and into the respiratory zone, and from there the three types of respiration can occur
What are the three characteristics of air to breath that we need surfaces to regulate
We need air to go from room temperature to 37 degrees within one breath (large surface area allows for this)
We need the air to be 100% saturated with water (normally the air is roughly 70%), to allow for it to travel into the liquid of the bloodstream
Arguably most importantly, we need the air to be clean/filtered - remove virus, particles, dust, bacteria etc.
- The airway lining is very delicate and is one of the only places where we expose the sterile environment of ouy bodies to the external environment, so damaged easily and need a good defence system
2 - THE NASAL CAVITY (basics)
The nasal cavity is the start of the respiratory system
It is a tall, narrow chamber lined with mucus membrane.
The medial surface is flat, the lateral surface carries three sloping shelves - conchae. It is divided in two by the nasal septum
Air is conditioned in all 3 ways - similar principles occur in other area of the respiratory tree, just at quicker rates as go through the different tubes
For healthy and rested people, by the time air gets to our throat, it is about 90% saturated, about 32 degrees, and on its journey of getting cleaned
If we are running then there is less time for this conditioning (hence air feels colder)
The nasal cavity mucus membrane structure and function
It is covered in a wet mucous membrane, which has pseudostratified columnar ciliated epithelium along with mucous cells called the goblet cells (like digestive system)
Due to this, there is a layer of mucus on top of the layer of ciliated epithelium
The mucus is sticky but also watery, to allow for humidifying, warming, and filtering process
Note that the goblet cells do not have cillia, they secrete the mucous that sits slightly on top of the cillia (it is too thick to be in them)
The cillia beat 20 - 30 times a second, and they beat towards our throat
The cillia have a very unique action - they do a power stroke to move the mucus and whip down, then will come back under the mucus for another go. In this movement, they move the ‘mucosilary escalator’
Most of the time we are swallowing mucous, and if we have excess mucous we can spit it out
The nasal cavity mucus membrane extras
When we get a cold we get excess mucus, and with hayfever can get streamy mucus. If we have excess mucous we can spit it out
If you have a genetic defect in the motor proteins responsible for the movement of cilia, you can have many infections and respiratory conditions, as the mucus will not be cleared and then the bacteria will stay there
If you smoke, the cilia become disorganised so the mucus doesn’t go anywhere. Furthermore the mucus becomes thicker and it paralyses the cilia, so you can get smoker cough (or snorting), in order to cough the mucus up (note that cilia are all the way down the conducting zone). Eventually the cilia get lost and fall off due to the toxic particles and you really have to cough
Nasal cavity conchae structure and function
The nasal cavity is the only place in the journey the air takes where we want to slow the air down, as there are bones that stick out and get in the way of the air
- All of the other tubes are straight as we want the air to be laminar/go in a straight line as quickly as possible)
We slow down air because we want to start the filtration and warming process as quickly as possible
There are three conchae in the nasal cavity, the bottom one being the biggest, and they are structures of bone covered in a membrane
The bones are called turbinate bones. They create turbulence, which causes the air to mix around. This allows for heat exchange form the blood vessels (under the cell layer of the mucous membrane), and means that the particles are more likely to get into the mucus membrane, which can help with humidification because you can add water to the air
It also leads to increased surface area.
Note that the rich blood supply in the nasal cavity is why we get bloody noses
Nasal cavity surrounding structures
We also have air filled (paranasal) sinuses in the face (holes in the facial bones), which allows for our heads to be lighter and for our voices to have resonance
- If we get a cold mucus can fill up in the sinuses and cause the voice to be flat
We also have olfactory epithelium at the top/roof of the nasal cavity which is why we can smell (this is what was impaired with early covid). Turbulence caused by sniffing carries air up to this epithelium. Axons of olfactory receptor cells lead towards the brain through perforations (holes) in the overlying bone, the cribriform plate.
The three parts of the pharynx/throat
When we breath through our nose, before we head into the respiratory tree itself, the air needs to pass through shared spaces
After going through the nasal cavity, it will go into the pharynx/throat - a vertical passage that acts as both an airway and a foodway
The pharynx can be divided into three parts which all have an anterior opening (depending on what structure it is fed by or connected to)
Nasopharynx - the posterior aspect of the nasal cavity
Oropharynx - posterior aspect from the mouth/buccal cavity
Laryngopharynx - region just above the larynx/voice box (not the subject of the lecture)
The pharynx is mainly considered part of the GI tract, but there is a shared passage of air and food from the oropharynx and laryngopharynx
What is below the pharynx
Below the pharynx is the larynx.
The laryngopharynx and the larynx is where we might get a sore throat - as it is higher up and not near delicate alveoli, not high risk (so hopefully short and low-risk infection)
Below the larynx is the trachea and oesophagus
The trachea is anterior and the oesophagus is posterior - a tiny muscular tube that only stretches with food (so we have the trachea open if not eating or swallowing)
4 - Swallowing
In order to protect the trachea from food or drink going down it (can cause chocking), when we swallow food, the soft palate is pushed and closes the nasal pharynx to make sure food/drink doesn’t go up the nose
Then, in a passive movement (no contraction/nerves involved), the food pushes the epiglottis (a rubbery elastic cartilage structure on top of the trachea/glottis - cartilaginous) to make it fold on top of the trachea (so epiglottic functions mechanically), which makes the food go posteriorly to the oesophagus
When the food has gone down, the epiglottis it will flip back up
Normally (when not eating/swallowing) the air just goes smoothly through the pharynx and larynx to the trachea
