Respiratory microanatomy

Question 1

Learning outcomes

Answer 1

•List the key parts of the respiratory system, summarise the histological and ultrastructural features of each and relate these to their different functions
•Describe the histological and ultrastructural features of the trachea
•Describe the histological and ultrastructural features of the lung, including the blood/air barrier
Open lecture 45 blood resp

Question 2

Functions of respiratory system

Answer 2

• Moves air to and from exchange surfaces
• Exchange of CO₂ and O₂ between atmosphere and blood
• Protects:
• Airways from environment e.g. mucociliary escalator: hair like projections have assoc. mucus that traps pathogens
• Airways & other tissues from pathogens
• Sensation of smell
• Sound production
• Assists in regulation of blood volume, blood pressure, & control of body fluid pH

Question 3

Respiratory system- conducting vs respiratory portion

Answer 3

Conducting portion:
 Nasal Cavities
• Nasopharynx
• Larynx
• Trachea
• Bronchi
• Bronchioles

Respiratory portion
• Respiratory bronchioles
• Alveolar Ducts
• Alveolar Sacs
• Alveoli

Question 4

Nasal cavities and conchae

Answer 4

• Divided medially by nasal septum – hyaline cartilage
• Lined with pseudostratified columnar ciliated (PSCC) epithelium (roof lined with olfactory epithelium)
• Conchae (turbinate bones) – vascular bony shelves
• Filter and warm incoming air

Question 5

Nasal conchae

Answer 5

• Increase surface area of nasal cavity
• Lined with PSCC (pseudo ciliated columnar) epithelium
• Contain tubuloacinar seromucous glands
• Cause air turbulence to trap foreign matter
• Blood acts as a heat exchanger, warming the incoming air
• Filters air – pollutants are trapped in the mucus

Question 6

Nasopharynx

Answer 6

• Lined with PSCC epithelium (“respiratory” epithelium)

* Contains the Pharyngeal tonsil (immune gateway) –also known as the adenoids

Question 7

Larynx

Answer 7

• Connects pharynx to trachea
• Framework of cartilages, CT, skeletal muscle, vocal cords, epiglottis
• Lined by PSCC epithelium, except epiglottis & vocal cords – SSNK
• Responsible for phonation
• Guards against entry of foreign bodies

Question 8

Trachea

Answer 8

• Conducts air into thorax
• Connects larynx to primary bronchi
• Withstands stretch
• PSCC (+ goblet cells) epithelium
• Tubuloacinar seromucous acinar glands within a submucosa layer of DIRCT
• Horse-shoe shaped rings of hyaline cartilage (approx. 20) –ends connected posteriorly by the trachealis muscle (composed of smooth muscle)
• Transports mucous blanket – mucociliary escalator

Question 9

Bronchi

Answer 9

• Conduct air into and out of lungs
• PSCC (+ goblet cells) epithelium
• Tubuloacinar seromucous glands
• Cartilage: complete C-shaped rings (extrapulmonary)
• Cartilage: incomplete plates (intrapulmonary)•Spirally arranged smooth muscle

Question 10

Bronchioles

Answer 10

• Conducts air into respiratory passages
• < 1mm in diameter
• Simple columnar/cuboidal epithelium•Gradual decrease in goblet cells & cilia
• NO GLANDS
• NO CARTILAGE
• Prominent smooth muscle
• Presence of Clara cells in the Respiratory Bronchioles
• Protect bronchiolar epithelium
• Secrete solution similar to surfactant

Question 11

Alveoli

Answer 11

• Main site of gas exchange
• Each lung contains ~ 150 million alveoli
• Thin walls lined by simple squamous epithelium
• Type I pneumocytes (gas exchange)
• Type II pneumocytes (surfactant production)
• Surfactant reduces surface tension
• Capillaries in mid-wall of adjoining alveoli alongside elastic and reticular fibres
• Alveolar macrophages