Lecture 15 - Respiratory system II - The Lower Respiratory Tract

Question 1

Where in the URT would we find stratified squamous epithelium?

Answer 1

Oropharynx, laryngopharynx and the vestibule of the nose

Question 2

Where does olfaction occur?

Answer 2

Nasal cavity

Question 3

Components of the Lower Respiratory Tract

Answer 3

Starts from ….
Larynx
Trachea - windpipe 
Bronchi - tubes that branch off the trachea 
Bronchioles - tiny bronchi
Alveoli - where gas exchange occurs

Question 4

Functions of the Lower Respiratory Tract

Answer 4

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

Question 5

Larynx

Answer 5

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

Question 6

Structures in the larynx

Answer 6

Epiglottis
Hyoid bone 
Thyroid cartilage 
Laryngeal prominence 
Circoid cartilage 
Tracheal cartilage 
Glottis
Vestibular fold 
Vocal fold

Question 7

Laryngopharnyx

Answer 7

Diverges into 2 parts - anteriorly down the larynx for air and posteriorly down the esophagus for food

Question 8

Epiglottis

Answer 8

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

Question 9

Hyoid bone

Answer 9

a U-shaped bone in the neck which supports the tongue

Question 10

Thyroid cartilage

Answer 10

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

Question 11

Laryngeal prominence

Answer 11

protrusion in the human neck formed by the angle of the thyroid cartilage surrounding the larynx seen especially in males

Question 12

Cricoid cartilage

Answer 12

The cricoid cartilage is a ring of cartilage that surrounds the trachea (encapsulates the whole of the larynx)

Question 13

Tracheal cartilage

Answer 13

The tracheal cartilages help support the trachea while still allowing it to move and flex during breathing.

Question 14

Glottis

Answer 14

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.

Question 15

What are the fold attached to?

Answer 15

Cartilages

Question 16

Vestibular folds

Answer 16

‘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

Question 17

Vocal folds

Answer 17

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

Question 18

Trachea

Answer 18

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

Question 19

C shaped cartilage rings

Answer 19

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

Question 20

Esophagus

Answer 20

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.

Question 21

Trachealis

Answer 21

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.

Question 22

Trachea - mucociliary escalator

Answer 22

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

Question 23

Which structure prevents food from entering the larynx?

Answer 23

Epiglottis

Question 24

The lungs

Answer 24

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

Question 25

How many lobes on the right lung?

Answer 25

3

Question 26

How many lobes on the left lung?

Answer 26

2

Question 27

Hilum

Answer 27

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)

Question 28

Apex of the lung

Answer 28

Is the superior region of the lung

Question 29

Costal surface describes

Answer 29

Outer surface against the ribs - sits right up against the thoracic wall

Question 30

Base of the lung

Answer 30

Is inferior, sits on the diaphragm (between the thorax and abdomen)

Question 31

Bronchial tree flow

Answer 31

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

Question 32

Bronchial tree descriptions of each sections

Answer 32

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

Question 33

What changes occur to the cartilage and epithelial tissue along the LRT?

Answer 33

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

Question 34

Why does the left lung have one less lobe than the right?

Answer 34

Because of the location of the heart - it is located on the left side

Question 35

LRT - Respiratory zone

Answer 35

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

Question 36

Alveolus (pl. alveoli)

Answer 36

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

Question 37

Type I pneumocyte

Answer 37

squamous, forms the respiratory membrane/blood-air barrier with capillary wall and shared basement membrane

Question 38

Type II pneumocyte

Answer 38

cuboidal, scattered amongst type I, secrete surfactant - a complex lipoprotein (phospholipid) that reduces the surface tension of alveolar fluid

Question 39

Roaming macrophages

Answer 39

Remove debris that makes it to alveoli

Question 40

Respiratory membrane

Answer 40

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

Question 41

How does the structure of the LRT vary along its length?

Answer 41

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

Question 42

What is the structure of the alveoli?

Answer 42

Type I pneumocytes form wall of alveoli, type II pneumocytes secrete surfactant

Question 43

What structures form the respiratory membrane?

Answer 43

Alveolus wall, fused basement membrane, capillary wall

Question 44

Compare the epithelia found in the upper respiratory tract to the epithelium four in the alveoli

Answer 44

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.