Respiration: Structure and Function Flashcards
What are the steps of external respiration?
- ventilation between atmosphere and alveoli in lungs
- O2 enters lungs
- CO2 exits lungs - gas exchange between air in alveoli and blood in pulmonary capillaries
- O2 enters blood
- CO2 exits blood, enters alveoli - blood transports O2 and CO2 between lungs and tissues
- gas exchange between blood in systemic capillaries and tissue cells
- O2 enters tissue cells
- CO2 exits tissue cells, enters blood
(tissue cells use O2 to make CO2, H2O, and ATP)
What are the two types of transport/movement of air, blood, and gases?
- bulk transport (long distance)
- diffusion (short distance)
What processes use bulk flow? (2)
- ventilation/breathing
- blood gas transport
What is ventilation/breathing driven by?
air pressure gradient
What is blood gas transport driven by?
blood pressure gradient – pumped by heart
What process uses diffusion?
gas exchange
What is gas exchange driven by?
partial pressure gradient of individual gases
What structures do the upper airways consist of?
- nasal passages
- mouth
- pharynx
- larynx (throat)
What structures does the tracheobronchial tree consist of?
- trachea (windpipe)
- bronchus
- bronchioles
- terminal bronchiole
What structures does the chest wall consist of, and associate with?
- ribs + associated muscles
- dorsal vertebrae
- diaphragm
What is the diaphragm?
key muscle of inspiration, separates abdominal and thoracic cavities
Why does UAW size need to be regulated?
negative pressure is generated when drawing air in (breathing), which can cause the UAW to collapse
UAW size needs to be regulated to be kept open for air to be able to continue to be drawn in through them
What are the 3 structures that close during swallowing, and what do they do?
- uvula: inhibits nasal regurgitation
- epiglottis: inhibits entrance to trachea → directs food into esophagus instead
- vocal cords: (across laryngeal opening) allows phonation, and prevents aspiration of food into lungs
What controls upper airway patency (keeping it open)?
- 20+ muscles control the position of tissues
- dilator muscles keep airway open during inspiration (controlled by CNS)
What happens during obstructive sleep apnea (OSA)?
decrease in genioglossus dilator muscle activity leads to airway obstruction – tongue falls back, which stops airflow to lower airways
What does UAW mucosal lining do?
provides heat and humidity to the air you breathe in
Air Conditioning by UAW Mucosal Lining
see notes
Where is the isothermal boundary?
bifurcation of trachea into bronchi
What are the 2 functional zones of the tracheobronchial tree?
- conducting zone
- respiratory zone
What does the conducting zone do?
DRAWS AIR IN
- bulk transport – requires energy
- muscle activity alters thoracic volume → changes thoracic pressure relative to atmosphere → drives movement of air (airflow)
What structures of the TBT does the conducting zone consist of?
(first half)
trachea main bronchus bronchus bronchiole terminal bronchiole
What structures of the TBT does the conducting zone consist of?
(last half)
respiratory bronchiole
alveolar duct
alveolar sac
What does the respiratory zone do?
GAS EXCHANGE
- diffusion – no energy required
- individual gases diffuse across alveolar-capillary membrane, driven by partial pressure differences of individual gases
What are the two types of cartilage?
trachea cartilage: C-shaped, closed into ring by trachealis muscle
bronchi cartilage: plates interspersed in smooth muscle ring
What does cartilage do for airways?
airways with cartilage resist collapse
What are the bronchioles composed of?
mostly smooth muscle with NO CARTILAGE
What are the terminal bronchioles?
last generation of bronchioles with only conducting function
What do respiratory bronchioles do?
allow gas exchange across their alveoli
What are alveolar ducts?
walls covered with alveoli that terminate in alveolar sacs
What are 2 other names for alveoli?
- acini
- respiratory zone
What are the 3 types of alveolar cells that make up the alveolar epithelium?
- type I: pneumocyte
- type II: granular pneumocyte / septal cell
- type III: alveolar macrophage / dust cell
What are type I pneumocytes? Describe their structure.
cells that line alveoli – flat ‘squamous epithelium’
- mostly thin
- thick centre – nucleus
- covers 95% of alveolar surface area ≈ 80-200 m2
- 0.1-0.3 microns in width
What are type II granular pneumocytes (septal cells)?
cuboidal cells that store and produce surfactant
- lamellar inclusion bodies (typically only seen in lungs and few other structures) stores pulmonary surfactant
What is pulmonary surfactant?
mixture of lipids and proteins that reduces alveolar surface tension
- SA reducing agent is diphosphatidylcholine (DPPC)
Why is pulmonary surfactant needed?
air coming in is moistened, heated, and saturated in water vapour – means that airways (including alveoli) are coated with water, which causes surface tension and may cause lung to collapse
pulmonary surfactant reduces alveolar surface tension to prevent collapse
What are type III alveolar macrophages (dust cells)?
migratory and phagocytic cells located on extracellular lining of alveolar surface, that defend against foreign particles
What is the 0.5 µm air-blood barrier?
barrier separating air and blood – distance O2 and CO2 in air has to travel to reach blood in pulmonary capillary
Describe the path of O2 from air in alveolus to blood.
O2 from air passes through surfactant epithelium (type II) → alveolar epithelium (type I) → travels 0.5 µm through interstitium to pulmonary capillary endothelium → plasma → RBC
What are the 2 functions of the alveolar interstitium?
- joins and supports structural elements by elaborate collagen and elastin fibre system (matrix)
- more elastin = more stretchy
- more collagen = more stiff
- contributes to mechanical characteristics of lung – ie. its compliance, allowing airways to expand during inspiration, and spring back during exhalation
- fluid space in series with lymphatic system, which allows excess fluid drainage into lymphatic system
- excess fluid (plasma) due to high BP that leaks into interstitium will not enter lungs – drained into lymphatic system instead
- HOWEVER, sometimes if BP is very high, some fluid associated with plasma can get through and overwhelm lymphatic drainage, and fluid will therefore enter alveoli
How does the structure of the airway wall change as we move from trachea to alveoli?
- decreasing epithelial height
- loss of cartilage, smooth muscle, mucous glands
- decreasing thickness
Structural Changes of Airway Wall – Trachea/Bronchus, Bronchiolus, Alveolus
Trachea/Bronchus
- smooth muscle
- cartilage
- mucus/surfactant layer
- columnar cells with villi – moves mucus and surfactant layer
- cell types without villi – secrete mucus to top
- glands – secrete mucus to top
Bronchiolus
- no cartilage
- decreased epithelial height
Alveolus
- no smooth muscle
- no cartilage
- alveolar epithelium – made of three types of alveolar cells
How are particles > 10 µm in diameter cleared from airway?
- filtered and trapped by nasal hairs
- irritant receptors lining nasal passages initiate sneeze reflex
How are particles 2-10 µm in diameter cleared from airway?
- mucociliary clearance (MCC) system lines airways proximal to terminal bronchioles
- irritant receptors in airway lining initiate cough reflex
How are particles < 2 µm in diameter (that reach the alveoli) cleared from airway?
- migrating and phagocytic macrophages engulf foreign particles and degrade them
- non-degradable particles with sharp profiles (ie. silica dust, asbestos fibres) injure alveolar epithelium and alveolar macrophages → damaged macrophages release toxins → inflammation, scar formation (collagen deposition), and pulmonary fibrosis
MCC Transport System
- mucus blanket produced by submucosal glands or goblet cells
- metachronal beat synchronization of cilia associated with epithelium of airway move mucus blanket from terminal bronchiole to mouth
- move mucus through vocal cords into pharynx
- move mucus blanket from nose to mouth - cough up mucus + any particles stuck to it
What are the two layers of the mucus blanket produced in the MCC transport system?
GEL mucus: viscous, sticky
SOL: aqueous perciliary (PCL), low viscosity, facilitates stroke of cilia
What does impairment of MCC do?
↓ airway clearance and ↑ chest infection
What are 4 factors that impair MCC?
- cigarette smoking
- pathogenic microbes
- primary ciliary dyskinesia
- cystic fibrosis
How does cigarette smoking impair MCC?
- ↓ ciliary length, number, and motility
- ↑ mucus production
How do pathogenic microbes impair MCC?
ie. HIV virus, Pseudomonas aeruginosa, and haemophilus influenza bacterias
release substances that paralyze and slow ciliary motion
How does primary ciliary dyskinesia impair MCC?
primary ciliary dyskinesia: (inherited disease) genetic mutations of cilia’s ultrastructure
↓ ciliary motility
airway particle clearance takes 1 week in PCD vs. 12 hrs in healthy non-smokers
How does cystic fibrosis impair MCC?
cystic fibrosis: (inherited disease) genetic mutation of CFTR – Cl- ion channel involved in H2O and Na+ transport across epithelial, responsible for maintaining mucus osmolarity
↑ mucus viscosity – reduces clearance in lungs and pancreatic ducts
What are club cells (Clara cells)?
non-ciliated, dome-shaped cells found mostly in terminal and respiratory bronchioles (corridor of functional transition from conducting to respiratory zone of airways)
What do club cells (Clara cells) do?
secrete variety of products that provide clues to its potential roles:
- surfactant-like substance – compliance of lungs
- defence through phagocytic activity engulfing airborne toxins
- lung remodeling in response to injury/disease – like basal cells, can act as stem/progenitor cells that multiply and differentiate into different epithelial cell types in response to injury
Where in the TBT epithelium are ciliated cells found?
everywhere – a little more in respiratory zone
Where in the TBT epithelium are goblet cells found?
conducting zone
Where in the TBT epithelium are Clara cells found?
mostly in terminal and respiratory bronchioles (corridor of functional transition from conducting to respiratory zone of airways)
Where in the TBT epithelium are basal cells found?
everywhere – a little more in conducting zone
