Lecture 15- The lower respiratory tract Flashcards
What are the key components of the lower respiratory tract?
- Larynx
- Trachea
- Bronchi
- Bronchioles
- Alveoli
What are the 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
What passes through the larynx?
Only air
Where is the larynx positioned?
- Anterior to esophagus
- From hyoid bone to trachea
What are the three types of cartilage in the larynx? What are their functions?
-Epiglottis: Most important, sit underneath tongue and
runs diagonally to stop food getting into airway. Pressure causes it to flap down.
- Thyroid cartilage: If you press on your throat you can feel this. Includes the Laryngeal prominence which is more obvious in men.
- Cricoid cartilage: Thick, complete ring holds airway to keep its shape.
What part of the larynx is responsible for voice?
- The glottis= voice box
- Has folds attached to cartilage
What are the two types of folds in the glottis, how does their function vary?
- Vocal folds:
- Are the ‘True’ vocal cords responsible for normal sounds that come out of mouth
- Passing air causes vibrations = sound waves - Vestibular folds
- ’False’ vocal cords
- Superior to vocal folds
- Prevent foreign object entry to glottis
- Can produce very deep sounds
Why are men’s voices deeper than female voices?
Testosterone affects cartilage and muscle, resulting in longer, thicker folds and therefore a deeper voice
What is below the larynx? Where is this in relation to other parts of the respiratory system?
- The trachea
- Anterior to esophagus
- Between larynx and primary bronchi
What is the function of the trachea?
- Maintain patent airway
- Clean, warm, humidify air as has respiratory epithelium
- Rings provide some protection
How does the trachea maintain a patent airway?
- C-shaped cartilage rings (gives support)
- Ends connected by band of smooth muscle at posterior: the trachealis which contract for coughing to clear any obstructions
- Has many elastin fibres in lamina propria/submucosa layers which recoil when coughing
Why in the trachea is a C shape ring used rather than a full ring?
Means the cartilage doesn’t protrude into the esophagus. This would limit the amount of food that could go down.
What are the tiny structures within the submucosa of the trachea?
- Submucosal glands
- Tells us that making air moist and clean is important in the trachea as mucus is made in the underlying tissue as well as goblet cells of epithelium
What is the mucociliary escalator and why is it needed?
- Mucus from goblet cells and mucous glands coat surface of epithelium. Debris becomes trapped. Cilia move mucus up to pharynx where debris can be swallowed
- Called the escalator as having to move against gravity unlike in URT
- Found in the trachea
Which structure prevents food from entering the larynx?
The epiglottis
Why does the amount of lobes in the left and right lungs differ?
- 3 lobes on the right
- 2 lobes on the left as the heart takes up space
What is the Hilum of the lungs?
Where bronchi, lymphatics & blood vessels enter
Where do the different parts of the lungs sit?
- Apex is pointing and sits against the clavicle
- Dome shaped base sits against the diaphragm
- Costal surface sits against the ribs
What is the bronchi tree?
- Trachea
- Primary bronchi (head into the lungs)
- Secondary (lobar) bronchi (head into the lobes)
- Tertiary (segmental) bronchi
- Bronchioles
- Lots of branching to get smaller and smaller
- Terminal bronchioles (last in series before alveoli)
How many secondary (lobar) bronchi will there be for each lung?
- 2 for the left lung
- 3 for the right lung
Reflects the number of lobes
What are the primary bronchi like in terms of cell shape and cartilage?
- Respiratory epithelium (moisten, warm, clean)
- Cartilage and smooth muscle rings complete to keep airways open
What are the secondary and tertiary bronchi like in terms of cell shape and cartilage?
- Respiratory epithelium starts to decrease in height, goblet cell numbers reduce. Both these changes reflect lumen becoming thinner so not enough space for tall cells.
- Cartilage plates: air pressure helps to keep vessels open therefore don’t need full rings
What are the bronchioles like in terms of cell shape and cartilage?
- Less than 1 millimeter
- Cuboidal epithelium. Purely a barrier with no mucus produces as this would block thin tubes as there is no cilia to move it.
- No cartilage but thick smooth muscle for bronchoconstriction/dilation
What are the terminal bronchioles like in terms of cell shape and cartilage?
- Less than 0.5 millimeters
- Each supplies a pulmonary lobule
What are pulmonary lobules made up of?
- Many alveoli (air sacs)
- Arranged like bunches of grapes
How many alveoli are there per lung? What does this mean?
- ~150 million alveoli per lung
- This takes most of the lungs’ volume and creates an enormous surface area for gas exchange
What are the walls of the alveoli like?
-Alveolar walls very thin: simple squamous epithelium
on a thin basement membrane
What is the external surface of the alveoli covered in?
- Covered in fine network of pulmonary capillaries
- This is where the pulmonary veins and arteries connect
Where are the openings in the alveoli? What do they allow?
- Pocket-like opening at one side
- Allows air to get in and out
What are lung epithelial cells called?
Pneumocytes
What are the two types of Pneumocytes?
- 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
What is a roaming macrophage?
Remove debris that makes it to alveoli
What is the blood air barrier and what are the three layers?
-Alveolus and capillary come next to each other
3 layers:
- Alveolar cell layer
- Fused basement membranes
- Capillary endothelium (can tell it is blood side if there is a red blood cell shown)
What is the trend in both cartilage and smooth muscle in the lower respiratory system?
- Cartilage goes from full in the larynx to C shaped in the trachea, then full again in the primary bronchi. In primary and secondary bronchi becomes fragmented and then in bronchioles there is none at all
- Opposing trend in seen in smooth muscle starts as not much at all and then as cartilage is less it is replaced by smooth muscle
What is the trend in cell shape/shape across the bronchi tree?
- Start as columnar and then as the diameter gets smaller and smaller becomes cuboidal in the bronchioles and squamous for thinnest gas exchange surface possible in terminal bronchioles.
- Also get less goblet cells and mucus as go down as this blocks the narrow spaces
