RESPIRATORY SYSTEM - LECTURE 2 Flashcards
7 - Bronchi (features)
1 cm in diameter or a bit less
Cell type transitions from pseudostratified columnar ciliated epithelium to columnar ciliated epithelium
We will also have goblet cells - source of mucus, so we still have a mucocillary escalator
Under the epitheluium there is a bit of connective tissue
Under this CT there is some smooth muscle - allows for contracting and constricting, although it is very limited due to outer cartialge in the walls
Under the smooth muscle layer there are heaps of mucous glands - another source of mucous (some more sticky, some more watery). There will be ducts that go up to the lumen for secretion of the mucus
Then there are cartilage plates underneath the mucous glands.
Underneath the cartilage there is a wall/bronchi wall - this is where the bronchus ends
7 - Bronchi (function)
Still allows for the airway to be open, and thinking about how to condition the air - no gas exchange occurs, as the barrier between the lumen and the blood is too thick
By the time air gets into the bronchi, it is going o be pretty warm as deep in the chest, but still focused on hydration (and stopping cells dying as the air can be drying for them) and allowing for mucocillary escalator:
Additionally, alveoli will be aorund the bronchi - the lungs are efficient in that everywhere there is not an airway or blood vessel there will be alveoli to fill in the space - like leaves/flowers on a tree fil - the alveoli and bronchi are not connected at all (no gas exchange through them) but just next to each other
8 - Bronchiole (structure)
Most bronchioles are less than 1mm in diameter - so very small (but still much bigger than alveoli, in the micron range). This means that bronchioles are much simpler
There is a layer of ciliated (and mainly) cuboidal epithelium
There are cells called club cells (used to be called clara cells). They secrete more of a watery secretion - called club cell secretions, things will still get captured, but it is not as sticky (should only have small things like viruses and small bacteria which float better and may get through but get captured by this). Club cell secretions have antibacterial properties. Enzymes and lysosymes are in this mixture
The only other thing present in the bronchiole is the smooth muscle (under the CT of the ciliated cells)
It looks about the same size, but is quite a significant proportion of the wall (the only other thing that is present in large quantities)
Then there is the wall of the bronchiole
How do we measure what is in the club cell secretion
We can measure what is in the secretion by doing a lavage - stick a tube down and wash out and measure what in ti
8 - Bronchiole (function
Because the majority of the conditioning of air should have already happened and the airways become smaller
The main role of the bronchiole, along with increase surface area, is to control the flow of air - this is done using the smooth muscle. Because there are 1000s of bronchioles, a small contraction/relaxation of the smooth muscle in these tubes can have a dramatic effect on flow into the respiratory zone and into the alveoli (helps w/ excersize and capcity). This is why we say it provides the tone of the airways.
Asthma
When we have uncontrolled and unmedicated asthma, and we have an asthma attack, there is bronchoconstriction - smooth muscle contracts abnormally due to being triggered by something (pollens, allergens, exercise, temperature etc.)
During the acute phase, people take an inhaler with salbutamol/ventalin which is a relaxant - causes relaxationg of the muscle
This is called a Bronchodilator
Asthma is very prevalent in NZ, it is higher than the OECD average
9 - Terminal and respiratory bronchioles (what should have happened by now
At this point there are many branches, the air should be 100% saturated with water, 37 degrees, and should be clean
Terminal bronchiole
The terminal bronchiole is the last airway/tube of the conducting zone - no gas exchange
Respiraotry bronchiole
First part of the respiratory zone
It has some parts like a normal brociole (no gas exchange) BUT also some alveolar buds that allow for gas exchange
Therefore there is a transition
Due to these alveoli, it can undergo gas exchange and therefore is part of the respiratory zone
Alveolar ducts
After the respiratory bronchioles there could be alveolar ducts - a line/row of alveoli which makes a tube (increases surface area even more)
These are hard to find as need to cut a parallel section
Alveolar sacs
After the respirtory bronchioles there could also be alveolar sacs - a bunch of alveoli, great way to get a large surface area
10 - Alveoli
A single alveolus is one air sac:
There is a network of tiny pulmonary capillaries wrapped and attached around (intimate with) the alveolar wall (rich blood supply)
Specifically, the pulmonary vessels will go and branch into capillaries to wrap around the air sac completely (dense), and then they will leave the lung and go back to the heart
What will the majority of tubes in the respiratory zone have
Importantly, the majority of tubes in the respiratory zone will have a rich capillary network around it for gas exchange
11 - Cells in the alveolar wall, what are they
Type 1 pnuemoyte, type 2 pneumocyte, macrophages (capillariy endothelium)
Describe a type 1 pneumocyte
The first cell to note is the type 1 alveolar cell/AT1 cell/type 1 pneumocyte
These are the squamous cells - there is a cell nucleus, and then a very thin cytoplasm that goes around to cover the majority of the surface area of the wall
This is thin to allow for minimal distance to travel by air
Because it is so thin, it wants to collapse on itself when you breath out - which is why we need the second type of alveolar cells
Describe a type 2 pneumocyte
These cells secretes surfactant
Surfactant is like soap in that it breaks down the surface tension of water and can create bubbles (dishwashing liquid is a surfactant)
The water that lines the alveoli will attract/want to come together due to surface tension, which would cause the alveolus to close down - stick together and it would not be possible to open alveoli each time we breath (we wouldn’t survive)
The surfactant is a phospholipid and is not attracted to itself. In the water layer, it essentially just reduces the surface tension between the air and the liquid inface in the alveolus.
The consequence of this is that it keeps the alveoli open (may go in and out, but don’t collapse) and therefore decreases the work of breathing
Describe the singificance of surfactant in babies
These cells are clinically important in babies
These cells don’t start to appear until about week 26 of gestation and they don’t produce sufficient surfact until 32-34 weeks of development
With preterm birth, there is surfactant insufficiency, which causes them to have respiratory distress syndrome - huge amount of effort to generate enough change in volume to change pressure and air flow in (as have to reinflate the airways)
It can be treated if they are ventilated, and you can also provide surfactant and deliver it to the lungs until the baby makes it themselves
Describe alveolar macrophages
Then there are alveolar macrophages, which are not part of the wall and can travel around and squeeze in and out of space. They can get all of the last dust/fine particles that don’t stick to the mucus or liquid and can ingest that. They will also digest any bleeding/hemorrhage/trauma (will eat blood cells and take it away from the airspace).
What else surrounds the alveoli
Then there are capillaries, where the air travels into. There is an intimate boundary between the capillary and the lumen of the alveoli
There will be RBCs in the capillaries
What must every surface exposed to air have
NOTE - EVERY SURFACE EXPOSED TO AIR MUST HAVE A LIQUID (mucus, club cell secretions, water/surfactant)
12 - Diffusion or blood/air barrier:
All epithelial cells (including endothelial cells) sit on a basement membrane
In alveoli, there is the squamous pneumocyte (type 1 cell) that lines the alveolar air space, then there is a basement membrane for this
Importantly, flush against it/fused to it is the basement membrane of the capillary - so the BM’s are fused to reduce thickness
Then there is the capillary endothelium (which will go into blood plasma w/ RBCs)
These three things are known as the blood air barrier
This is about 0.5um, so very thin
Any condition that affects this barrier will limit the gas exchange - e.g. fluid in the lungs, fibrosis (BM thickens)
13 - Summary
Upper airways (trachea and bronchus): need to be open (cartilage), loads of SA, and load of conditioning (mucus and mucus glands)
Mid: we have conditioned the air, more for keeping them open, hydrated (club cells), and controlled (muscle)
Respiratory zone: efficient gas exchange (blood/air barrier) and efficient work of breathing (surfactant)
14 - Subdivisions of the lung + 15 - Lung segments:
Primary bronchi (2) are right and left main stem bronchi supplying each lung
Secondary bronchi are lobar bornchi supplying lobes (2 on the left - due to heart, 3 on the right)
Tertiary bronchi are segmental bornchi supplying segments of the lung (8 on the left, 10 on the right).
Each bronchopulmonary segment has its own air (via a segmental bronchus) , blood, and nerve supply, and are encased in a thin connective sheath.
This provides insurance/compartmentalization, as if one section gets damaged the others (as long as the pleura’s not affected) is kind of isolated. If it was on big air sac damage to one area would likely collapse all other regions
Segments can be seen with medical imaging, which allows for reporting of different areas as well
What happens with a localised tumur in the lung
Thus when a localised tumour occurs in the lung, a surgeon who knows the approximate boundaries can remove one or more segments containing the tumour without excessive leakage of air or blood of neighbouring segments
16 - Pleurae (strucutre)
The pleura are smooth membranes that cover each lung; and also lines the thoracic cavity in which the lung sits. They are very thin and smooth and very difficult to see.
There are two membranes (pleurae):
The visceral pleura sits absolute intimately with/touches the lung
The other part of the membrane is the parietal pleura, which is attached to the skeletal muscle of the thorax
The pleura are continuous at the root of the lung (hilum)
Within the pleura there is a pleural space/cavity which is filled with a thin film of fluid separate the pleurae.
Pleurae function
Although the fluid allows sliding movement between the pleurae, it mainly also prevents them from being separated - everything is stuck together in the pleura, and we want surface tension to allow for this sticking (the visceral pleura, through fluid, is stuck to the parietal pleura, and this parietal pleura is stuck to the ribs via muscle).
Therefore, when the thoracic wall moves inwards or outwards, the lungs must follow. This is important accounting for the fact that in order to get air in the lungs, we need a change in volume and therefore change in pressure. Note that the lungs will follow as they are spongy, soft, and compliant so will come with it.
Similarly, when the diaphragm moves upwards or downwards, the lungs must follow through the pleura in the same way
What happens with air or blood in the pleural cavity
Importantly, if we have air or blood in the pleural cavity, we will loose the surface tension and stickiness, so we get a collapsed lung and can’t breath properly - pneumothorax or hemothorax
17 - Ventilation: movement fo the ribs (quiet breahting vs excersise)
When we breath quietly, inspiration is an active process. Expiration is passive.
During exercise, we need to push the air out quicker than when relaxing. This means that both inspiration and expiration are active processes
Quiet breathing
Inspiration is active because it requires energy for contraction of the external intercostal muscles which run obliquely between ribs (on the exterior surface):
The ribs pivot around their joints with the vertebral column.
The orientation/angle of the external intercostal muscles means that contraction has the effect of lifting the ribs (roatating them around their pivot joints) - bucket handle analogy. This movement increases the volume of the thorax and takes the lung tissue with it
Expiration is passive.
The ribcage returns to its resting positing without requring muscular action - we just relax the external intercostals
What percentage of air movement is due to the ribcage when resting
Movement of the ribcage is responsible for about 25% of air movement into and out of the lungs (the majority happens in the diaphragm)
Breathing during exercise
During exercise, we need to push the air out quicker than when relaxing.
This means that both sets of intercostal muscles are now active so both inspiration and expiration are active processes; externals for inspiration, internals for expiration
The external intercostals are still used during inhalation
The internal intercostal muscles run at right angles to the externals (on the interior of the ribs). When they contract they drag the ribs downwards and inwards. Active contraction only occurs during forceful exhalation - when we need to push air out quicker. This movement makes the volume smaller pushing the air out
18 - Diaphragm structure
The diaphragm is a dome-shaped platform which forms the floor of the thorax and the roof of the abdomen - it separates the abdominal contents form the lungs.
THe diaphragm will be connected to the vertebrae and the very inferior aspect of the sternum
It is like a circle of muscle
There is a central part which is a thin sheet of connective tissue, (technically an aponeurosis) called the central tendon - this part doesn’t expand much, but is robust.
The lateral margins are muscular.
The muscle is fast-acting skeletal muscle innervated by the phrenic nerve
18 - Diaphram function
Contraction of the diaphragmatic muscle (like in inhalation) flattens the diaphragm, pulling its central dome downwards. This increases the volume of the thorax and causes inspiration as the top surface of the diaphragm has pleura on it which is attached to the lung, so will cause increased volume
Passive relaxation of the muscle allows the diaphragm to lift back towards the thorax, reducing thoracic volume (expiration).
If there are any injuries, including to the nerve supply, of the diaphram, there can be massive affects to breathing
What percentage of air movement is done via the diaphragm when resting
Movement of the diaphragm is responsible for 75% of bulk flow of air during quiet breathing, and a smaller proportion during exercise (rest is due to intercostal muscles)
Describe breath control in professionals
Those who control breathing - singers, ice bathers, meditators will be aware of how to control breathing. For example, when singers say ‘Breathing form the stomach’ rather than breathing from the ribs, it means controlling air flow using the diaphragm
