Functional histology of the respiratory system Flashcards
What are the 4 stages of mechanical respiration?
inspiration
gas conduction
gas transfer
exhalation
Where does gas transfer occur?
alveolar spaces
What is the conduction zone?
consists of all of the structures that provide passageways for air to travel into and out of the lungs: the nasal cavity, pharynx, trachea, bronchi, and most bronchioles
Function of the conducting zone?
passage of air from environment to lungs
airway protection
air humidification + warming
smell
speech
What is the shape of the trachea?
C-shaped to allow swallowing
no cartilage at junction with oesophagus so oesophagus can expand
What 3 types of protection are present in the conducting zone?
mechanical (cellular)
- mucociliary escalator
- physical environment between external environment and tissue
immunological
- identification and removal of pathogens
mechanical (anatomical)
- reflex protection
What happens to the number of mucus-secreting cells in response to irritation?
number increases
more mucus secreted
2 types of cells that secrete mucus
goblet cells (within epithelium)
seromucinous glands (within submucosa)
Is cilia action dependent on nervous control?
no, cilia action is independent of nervous control and can persist several hours after death
What is the difference between the mucus secreted by goblet cells and seromucinous glands?
serous cells produce more watery, thin mucus
goblet cells and mucus cells produce thicker mucus
Roughly how many cilia are there per cell and how fast do they beat?
200-300 cilia/cell
beat 20x/second
What do the cilia beat towards?
nasopharynx
What immunological protection is there in the airway?
MALT (mucosa-associated lymphoid tissue)
Nasopharynx:
- Waldeyer’s ring
- dense lymphoid tissue
Bronchial epithelial cell + serous cell secretions
- lysozymes, lactoferrin, antiprotease, IgA, epithelial peroxidase
What refexes are there in the airway?
Cough reflex
Gag reflex
Swallow reflex
Describe the cough reflex
pulmonary irritant receptors
mechanical and chemical stimuli
vagus nerve
carina = specialised nervous tissue
stimulated by foreign body = violent coughing
What does the swallow reflex involve?
enables the epiglottis to cover the larynx to prevent aspiration
Describe the gag reflex
(pharyngeal reflex or laryngeal spasm)
reflex contraction of the back of the throat
prevents foreign bodies entering the upper airways
stimulus = touch from back of throat, tonsils, uvula, roof of mouth of base of tongue
How do we smell odours?
odours dissolve in mucus secreted by olfactory mucosa
What are the 3 phases of speech?
respiration -> lung function
phonation -> laryngeal function
articulation -> vocal tract (upper airways and oral cavity)
Above what structure is classed as the upper airway?
above the larynx
Where are alveolar macrophages?
lie on top of pneumocytes or free in alveolar spaces
Function of alveolar macrophages
phagocytose particles from inspired air (often carbon which is why a smoker’s lung is blackened)
What are pores of Kohn?
small gaps between alveoli
not present at birth
provides channels for spread of pneumonia and cancer that grows along the walls of alveoli
What are Lambert’s canals?
tubular connections which connect terminal and respiratory bronchioles with adjacent peribronchial alveoli
Describe type 1 pneumocytes
flattened nuclei
thin for gas exchange
Describe type 2 pneumocytes
larger darker nuclei
surfactant production
Function of pulmonary veins
return oxygenated blood back to the heart
What are the lungs themselves oxygenated by?
bronchial arteries
arise from systemic circulation
Function of the pleura
facilitates respiratory movement
Describe the pleura
a pair of serous membranes lining the thoracic wall (parietal), and lungs (visceral)
mesothelial cell lining (secrete fluid rich in hyaluronic acid)
connective tissue submesothelium
elastin layer
How does the elastin layer of the pleura differ between the parietal and visceral pleurae?
visceral = double layer and thicker to account for lung movement
parietal = single layer and thinner
