Lecture 15 - Respiratory system II - The Lower Respiratory Tract Flashcards
Where in the URT would we find stratified squamous epithelium?
Oropharynx, laryngopharynx and the vestibule of the nose
Where does olfaction occur?
Nasal cavity
Components of the Lower Respiratory Tract
Starts from …. Larynx Trachea - windpipe Bronchi - tubes that branch off the trachea Bronchioles - tiny bronchi Alveoli - where gas exchange occurs
Functions of the Lower Respiratory Tract
Conducts air to/from site of gas exchange
Completes cleaning, warming and humidifying of air
Provides a barrier between the air and blood, and a large surface area for gas exchange
Larynx
LRT
Passage of air only
Anterior to the esophagus
From the hyoid bone to trachea
Cartiilages protect (since it is so close to the surface, biggest cartilage is the thyroid cartilage) and maintain open airway - keeps it patent and open
Epiglottis closes over airway when swallowing
Structures in the larynx
Epiglottis Hyoid bone Thyroid cartilage Laryngeal prominence Circoid cartilage Tracheal cartilage Glottis Vestibular fold Vocal fold
Laryngopharnyx
Diverges into 2 parts - anteriorly down the larynx for air and posteriorly down the esophagus for food
Epiglottis
Top of the larynx, important piece of cartilage because it is what prevents food getting into your airway
When you swallow, the tongue pushes backwards and so pushes on the epiglottis and the larynx itself lifts up so the epiglottis flaps down and covers over the larynx and so the only way for food to flow down is down the esophagus - clever way of preventing food from getting into the larynx and the further down into the lungs
Hyoid bone
a U-shaped bone in the neck which supports the tongue
Thyroid cartilage
The thyroid cartilage is a hyaline cartilage structure that sits in front of the larynx and above the thyroid gland. The cartilage is composed of two halves, which meet in the middle at a peak called the laryngeal prominence
Laryngeal prominence
protrusion in the human neck formed by the angle of the thyroid cartilage surrounding the larynx seen especially in males
Cricoid cartilage
The cricoid cartilage is a ring of cartilage that surrounds the trachea (encapsulates the whole of the larynx)
Tracheal cartilage
The tracheal cartilages help support the trachea while still allowing it to move and flex during breathing.
Glottis
Voice box, is used to produce sound
the part of the larynx consisting of the vocal cords and the opening between them. It affects voice modulation through expansion or contraction.
What are the fold attached to?
Cartilages
Vestibular folds
‘False’ vocal cords
Superior to vocal folds
Prevent foreign object entry to glottis - prevent damage to the true vocal cords
Can produce very deeps sounds
Vocal folds
True’ vocal cords
Passing air causes vibrations = sound waves
Used for normal phonation
Testosterone affect cartilage and muscle, resulting in longer, thicker folds = deeper voice
Trachea
Anterior to the esophagus
Between larynx and primary bronchi
Functions
1 - Maintain patent airway (kept open so that air can come through) and it does this through…
C-shaped cartilage rings
Ends connected by band of smooth muscle: trachealis - contracts for coughing (helps with the spasms of the muscles)
Many elastin fibres in lamina propria/submucosa layers
2- Clean, warm and humidify air - respiratory epithelium, lines the larynx and trachea
C shaped cartilage rings
Why is it C shaped - to provide protection and keep airway open, but allow for the esophagus (posterior) and the trachealis muscle to expand and to allow for coughing to clear obstructions
If there was a complete ring of cartilage here then the esophagus wouldn’t be able to expand out as much so you would have to swallower tinier portions than usual.
Another reason for it being C-shaped is because of the trachealis muscle, band of muscle that runs all the way down and is important in coughing and this is how you force things out, coughing causes the muscles to contract and causes spasms meaning that anything is going to be pushed upwards so it is an important protective measure
Esophagus
The esophagus is a muscular tube connecting the throat (pharynx) with the stomach.
The esophagus runs behind the windpipe (trachea) and heart, and in front of the spine.
Only needs to be open when swallowing food whereas trachea needs to be constantly open to allow for air flow.
If there was a complete ring of cartilage here then the esophagus wouldn’t be able to expand out as much so you would have to swallower tinier portions than usual.
Trachealis
The trachealis muscle is a smooth muscle that bridges the gap between the free ends of C-shaped cartilages at the posterior border of the trachea, adjacent to the esophagus. The primary function of the trachealis muscle is to constrict the trachea, allowing air to be expelled with more force, e.g., during coughing.
Trachea - mucociliary escalator
Mucocillary escalator removes debris to the pharynx, to be swallowed and digested
Mucus from goblet cells and mucous glands coat surface of epithelium
Debris becomes trapped
Cilia move mucus to pharynx - can swallow without even noticing most of the time or oral uptake which involves spitting it out
Cleans the air
Which structure prevents food from entering the larynx?
Epiglottis
The lungs
2 lungs
3 lobes on the right (superior, middle and inferior lobes) and 2 lobes on the left (superior and inferior lobe)
Only 2 lobes on the left because of the heart, because the heart sits to the left and takes the space where the third lobe would have been
Hilum - where bronchi and blood vessels enter
Base of the lungs are domed shaped because they sit on the diaphragm
How many lobes on the right lung?
3
How many lobes on the left lung?
2
Hilum
where bronchi and blood vessels enter
Part of an organ where blood vessels, nerves and lymphatics go in and out (sometimes other structures too such as bronchi)
Apex of the lung
Is the superior region of the lung
Costal surface describes
Outer surface against the ribs - sits right up against the thoracic wall
Base of the lung
Is inferior, sits on the diaphragm (between the thorax and abdomen)
Bronchial tree flow
Trachea (trunk) - only one and we have two lungs so need to branch into two so here is our first branching
Primary bronchi - one on each side
Secondary (lobar) bronchi - head towards each of the lobes, right has three lobes therefore there are three of these, left has two lobes therefore there are two of these
Tertiary (segmental) bronchi
Bronchioles
Branching, branching, branching
Terminal bronchioles - end of the conducting region by the time we are here we are heading into the respiratory region
Note - as the branching happens, the diameter of the vessels gets smaller and smaller
Bronchial tree descriptions of each sections
Trachea
Respiratory epithelium
C-shaped cartilage rings
Trachealis muscle on posterior
Primary bronchi
Respiratory epithelium
Cartilage and smooth muscle rings are complete (because there is no trachealis muscle)
Secondary and tertiary bronchi
Respiratory epithelium start to decrease in height, goblet cell numbers reduce - goblet cells get smaller due to the decrease in diameter
Cartilage plates - gives some support but not as much
Bronchiole <1mm - because they are so tiny we do not want any mucus here so not goblet cells and the cells become so short that they are now cuboidal cells
Cuboidal epithelium
No cartilage but thick smooth muscle for bronchoconstriction/dilation
Terminal bronchioles <0.5mm
Each supplies a pulmonary lobule
What changes occur to the cartilage and epithelial tissue along the LRT?
Cartilage - complete ring in larynx (circoid), c-shaped in trachea, complete rings in primary bronchi, become plates and then absent in the bronchioles
Epithelium - respiratory mucosa that decreases in height by the secondary bronchi. Becomes cuboidal in the bronchioles, with no goblet cells present
Why does the left lung have one less lobe than the right?
Because of the location of the heart - it is located on the left side
LRT - Respiratory zone
Pulmonary lobules made of many alveoli (air sacs)
Arranged like bunches of grapes
Approx 150 million alveoli per lung — this is most of the lung volume and it covers an enormous surface area
Alveolar walls very thin: simple squamous epithelium on a thin basement membrane
External surface of alveoli covered in fine network of pulmonary capillaries - capillaries are very close by to ensure that the exchange can occur
Alveolus (pl. alveoli)
Pocket-like - open at one side so that air can come in
Covered by dense capillary network
Pneumocytes (lung epithelial cells)
Type I squamous - forms the respiratory membrane/blood-air barrier with capillary wall and shared basement membrane
Type II cuboidal - scattered amongst type I, secrete surfactant - a complex lipoprotein (phospholipid) that reduces the surface tension of alveolar fluid
Summary - Type I pneumocytes form wall of alveoli, type II pneumocytes secrete surfactant
Type I pneumocyte
squamous, forms the respiratory membrane/blood-air barrier with capillary wall and shared basement membrane
Type II pneumocyte
cuboidal, scattered amongst type I, secrete surfactant - a complex lipoprotein (phospholipid) that reduces the surface tension of alveolar fluid
Roaming macrophages
Remove debris that makes it to alveoli
Respiratory membrane
Where capillary meets alveolar wall
Wall of the alveolar contains type I pneumocytes (very thin and flat)
Type II aren’t part of the membrane itself
Bloodside is the wall of the capillary which is made up of capillary endothelial cells
There is a fused basement membrane connecting them together - shared basement membrane, ensures anchorage and that these structures don’t move apart, it attaches onto another cell
How does the structure of the LRT vary along its length?
The structure of the larynx allows production of sound and ensures only air can pass. From the trachea to the bronchioles, the airway becomes narrower, with less cartilage support, more smooth muscle, and flattening of the epithelia
What is the structure of the alveoli?
Type I pneumocytes form wall of alveoli, type II pneumocytes secrete surfactant
What structures form the respiratory membrane?
Alveolus wall, fused basement membrane, capillary wall
Compare the epithelia found in the upper respiratory tract to the epithelium four in the alveoli
The roles of the URT is to conduct air to the LRT, and to ensure that the air is warmed, cleaned and moistened.
The nasal cavity, paranasal sinuses and nasopharynx are lined with respiratory mucosa, a pseudostratified ciliated columnar epithelium with goblet cells. The goblet cells secrete mucus which moistens the air, and traps debris. The cilia beat to move the mucus to the pharynx to be swallowed. The lamina propria of the nasal cavity contains a venous plexus that warms the air.
Areas of the URT where both food and air pass are protected by stratified squamous epithelium. These areas are the oropharynx and laryngopharync. Similarly, the vestibule of the nose is lined with skin to protect against abrasion.
The nasal cavity also contains an area of olfactory mucosa, which is where we detect smell.
In comparison, the alveoli are located at the end of the LRT. By this point, air is in optimum condition for gas exchange.
There are two types of epithelial cells within the alveoli - type I and type II pneumocytes
Type I pneumocytes are simple squamous epithelial cells which form the wall of the alveoli. These are attached to the endothelial cells of capillaries by a fused basement membrane. These three structures form the respiratory membrane.
Type II pneumocytes are cuboidal cells which are found scattered throughout the alveoli. They do not form part of the respiratory membrane, but instead secrete surfactant, which reduces surface tension within the alveoli.
