Lecture 2: The Respiratory System/ Respiratory Tract infections

Question 1

What is the route that air can take from either the nasal cavity or oral cavity? 9 Points.

Answer 1

The air will travel through the pharynx, passing by the epiglottis (attached to top part of larynx), and the glottis (hole in larynx between vocal folds under epiglottis), as these will be open. It then passes through the larynx, then trachea, to reach a split between two primary bronchi, and then split again into secondary bronchioles (typically as many of these as lobes in lung). After the secondary bronchioles, it splits into tertiary bronchi, just before the bronchi become the narrowest passages before alveoli, the terminal bronchioles and respiratory bronchioles. Upon meeting alveoli gas exchange will occur.

Question 2

How many lobes do each of the lungs have? What reason is there for this difference? What other difference is there between the left and right lung?

Answer 2

The right lung has 3 lobes, however the left has 2. This size difference is to accomodate for the heart, as it sits in the cardiac notch.

As well as this the left lung has a projection from the upper lobe called the lingula (little tongue).

Question 3

What are the functions of the respiratory system? 5 Points

Answer 3

• To participate in gas exchange
• To defend against inhaled microbes/particles
• To produce sound (phonation)
• Detection of olfactory stimuli
• Helps regulate pH of blood

Question 4

What is the larynx?
What is the structure of the larynx?
What does this structure achieve?

Answer 4

The larynx is the structure connecting the pharynx to the trachea.

It has a complex structure of hyaline cartilaginous plates, this is to

Question 5

What is the difference in structure and function between the upper and lower respiratory system?

Answer 5

The upper respiratory system is more focused on protection of lower respiratory system.

The lower respiratory system is catered towards gas exchange.

Question 6

How does the upper respiratory tract protect the lower?

Answer 6

The upper respiratory system has many mucous membranes that can physically stop inhaled particles, as well as producing B-cells in MALT, these in turn will secrete large numbers of IgA to agglutinate pathogens, and prevent movement and infection, as well as target them for phagocytosis by macrophages and other immune cells.

The upper resp. tract also warms air, and adds moisture to prevent drying out and changing conditions of the more delicate lung tissue.

The larynx is also responsible for phonation.

The mucociliary escalator removes pathogen/particle laden mucous.

The epiglottis (top of larynx) provides a barrier that closes when swallowing to prevent food from entering the larynx.

Question 7

How does the epiglottis move during respiration and swallowing?

Answer 7

The epiglottis sits upright when respiring, and folds back over the larynx when swallowing, as the larynx is in front of the oesophagus.

Question 8

What structures make up the upper respiratory system?

Answer 8

• The oral cavity
• The nasal cavity/nose
• The sinuses
• Pharynx
• Larynx (transitional structure)

Question 9

What structures make up the lower respiratory system?

Answer 9

• Larynx (transitional structure)
• Trachea
• Primary bronchi
• Second./Tert. bronchi (lungs)
• Bronchioles (lungs)
• Alveoli (lungs)

Question 10

How else can components of the respiratory system be grouped besides upper and lower? Give these groupings.

Answer 10

Into the conducting zone and respiratory zone.

Conducting zone:
- Nose
- Nasal cavity, oral cavity
- Pharynx
- Larynx (+epiglottis)
- Trachea
- Bronchi
- Bronchioles + terminal bronchioles

Respiratory zone:
- Respiratory bronchioles
- Alveolar ducts
- Alveolar sacs
- Alveoli

Question 11

Where do the larynx and oesophagus sit in relation to each other?

Answer 11

The oesophagus is directly behind the larynx.

Question 12

What is respiratory epithelium? (type of epithelium and structure)

Answer 12

Ciliated pseudostratified columnar epithelium with goblet cells. Underneath the epithelium is a basement membrane and beneath this a spongy connective tissue called lamina propria.

Question 13

What tissues line each part of the respiratory system?

Answer 13

• The nasal cavity contains a variety of epithelial types, but the majority is respiratory epithelium (ciliated pseudostratified columnar epithelium with goblet cells).
• The upper nasopharynx has respiratory epithelium, and closer to oropharynx will transition to stratified squamous epithelium, as there is more mechanical stress
• Oropharynx and Laryngopharynx have stratified squamous epithelium
• The epiglottis has stratified squamous epithelium
• Larynx mostly has respiratory epithelium, vocal chords stratified squamous epithelium
• Trachea and bronchi have resp. epithelium
• Bronchioles have simple columnar to cuboidal epithelium.
• Alveoli have thin squamous lining.

Question 14

Describe the basic structure of the nasal cavity.

Answer 14

The nostrils (external nares) are the entrance to the nasal cavity, and the internal nares are the entrance to the throat from the nasal cavity.

The nasal cavity is partitioned by the nasal septum.

There are four paranasal sinuses, two above the eyes, and two under. The Nasolacrimal ducts run parallel to the nose, connecting around halfway down the nasal cavity.

Question 15

What is the pharynx? What is the basic structure?

Answer 15

The pharynx connects the nasal cavity and oral cavity to the larynx and oesophagus, so functions as a path for food and air.

The wall is composed of skeletal muscle lined with mucous membrane, can vary between whether the epithelium is respiratory (superior nasopharynx) or stratified squamous (inferior nasopharynx, oro- and laryngo-pharynx).

Question 16

What is the glottis?

Answer 16

The hole between the vocal folds of the larynx, under the epiglottis, that can close and open to protect airway or regulate airflow (and phonation, but that’s more vocal folds).

Question 17

What is the structure of the epiglottis?

Answer 17

A leaf-shaped flap of cartilage covered with muscle.

Question 18

What is the larynx?
What is its basic structure?

Answer 18

The larynx connects the pharynx with the trachea, and is responsible for preventing food from travelling into the lower respiratory system, or air travelling into the oesophagus, as well as being responsible for phonation.

The larynx consists of many (9), cartilaginous rings, connected by skeletal muscle and covered by mucous membrane (resp. epith.).

The epiglottis is connected at the top of the larynx, moving depending on whether oesophagus is open or larynx.

Below epiglottis is the glottis, this is an opening that can also open and close with action of vocal folds (vocal cords).

Question 19

What is the trachea?
What is the basic structure?

Answer 19

The trachea connects the larynx to the bronchi, it is a long tube of fibroelastic tissue braced with 15-20 cartilaginous horseshoe shaped ‘rings’ (gap in ring to accommodate for oesophagus) with gap connected by ‘trachealis’ muscle.

The trachealis muscle sits on the posterior side of the trachea, where the oesophagus rests, and gaps in cartilaginous rings are.

The lining of the trachea is respiratory epithelium.

Question 20

What is the purpose of having the trachealis muscle?

Answer 20

To allow some flexibility in the trachea, when swallowing, or expelling mucous, or differences in airflow depending on activities.

Question 21

What are the bronchi?
What are their general structure?

Answer 21

The bronchi connect the trachea to bronchioles, their purpose is to transport air.

The main (2) bronchi are extrapulmonary, but enter with each pulmonary artery, before dividing into bronchi (same number of secondary bronchi as lobes in lung).

They’re made up of broken rings of cartilage connected by smooth muscle, contain glands, and the lumen is lined with respiratory epithelium. Cartilage decreases down bronchi, smooth muscle increases.

Question 22

What are the bronchioles?
What is the general structure?
What changes in terminal and respiratory bronchioles?

Answer 22

The bronchioles branch off from secondary bronchi in each lung to supply air to the alveoli.

These structures have no hyaline cartilage, but instead elastic rings to prevent collapse when exhaling.
There is a relatively thick layer of smooth muscle.

Lamina propria gains more elastic fibers closer to the alveoli

Less goblet cells closer to alveoli

Number of clara cells (club cells) become present in bronchioles, becomes more prevalent closer to respiratory bronchioles,

From bronchioles to alveoli, order of epithelium goes:
- Ciliated simple columnar epithelium (no pseudo.)
- Non-ciliated cuboidal (no pseudo.)

Question 23

What are Clara cells?

Answer 23

Club cells (formerly Clara cells) are surfactant (glycosaminoglycans) secreting cells that decrease surface tension of the bronchiolar lumen to reduce surface tension and thus avoid collapse of terminal and respiratory bronchi.

Question 24

How does surfactant stop collapse of bronchioles and alveoli?

Answer 24

Water on the walls of these structures pulls other water molecules near it (polar forces of hydrogen and oxygen).

Because of this pulling, walls are also pulled inwards, causing collapse.

Surfactant acts like a detergent, disrupting these forces, decreasing the surface tension.

Question 25

What are alveoli?
What is the general structure? (not exact cells present besides epithelium).

Answer 25

Alveoli are tiny, hollow sacs involved in gas exchange due to very large surface area.

Surrounded by a vast capillary network to oxygenate blood from the pulmonary artery, and discharge oxygenated blood to the pulmonary vein.

The walls of the alveoli consist of very thin (1 cell) flat squamous cells on an elastic basement membrane and a very thin layer of elastic connective tissue to aid in recoil in exhalation.

Question 26

What cells are present in the alveoli?
What roles do they play?

Answer 26

Type 1 pneumocytes:
- Simple squamous epithelial cells.
- Scanty mitochondria and organelles.
- Thin, with flattened nuclei.
- 40% of cell population, but 90% of gas exchange surface.

Type 2 pneumocytes:
- 60% of cell population, around 10% of cell surface area.
- Rounded cells and nuclei, more rich in mitochondria, and smooth endoplasmic reticulum.
- Secrete surfactant.

Dust cells:
- Macrophages
- Phagocytosis, and can migrate after this to release contents into bronchioles or lymphatic system, aiding in immune response.

Question 27

What is pleurisy?

Answer 27

Inflammation of the pleural linings.

Question 28

What is the most common cause of upper respiratory infections?

Answer 28

Usually of viral origin. Rhinoviruses for example.

Question 29

What is the most common bacterial cause of upper resp. tract infections?

Answer 29

Streptococcus pyogenes (strep throat).

Question 30

What less common bacterial causes are there for upper respiratory tract infections?

Answer 30

Lancefield group C and G strep.

Corynebacterium Diphtheriae.

Question 31

What complications can arise from an upper resp. tract infection involving Corynebacterium diphtheriae?

Answer 31

Formation of a tough fibrous pseudomembrane in the throat and inflammation both can block the airway, causing respiratory failure.

The diphtheria toxin spreads through the blood and this dissemination of toxin can affect the heart (myocarditis) and nervous system.

The toxin is made of the active (a) and binding (b) domain, b binds to cell and is cleaved upon uptake of toxin into cell. ‘A’ portion binds to elongation factors 2, inactivating it, stopping the elongation stage of translation, and preventing further protein synthesis resulting in cell death.