13,14-Lung Function Flashcards
Anatomy of human respiratory system ?
Upper respiratory system: includes all structures from nose to larynx.
* Lower respiratory system: larynx or trachea and all others below
* Lower respiratory system: larynx or
trachea and all others below…
o This system consists of conducting
and respiratory zone structures.
First airway branches that no longer
contain cartilage are termed the
bronchioles → branch into smaller,
terminal bronchioles.
* Alveoli first appear attached to
walls of respiratory bronchioles →
their number increases in alveolar
ducts; airways end in ‘grape-like’
clusters, i.e. alveolar sacs
Structure of Trachel wall ?
From the nasal passages to the small bronchi, the airways are lined with pseudo-stratified columnar ciliated epithelium:
o Contains mucus-secreting goblet cells.
* In bronchioles (not shown), epithelial layer
changes to become a simple ciliated cuboidal epithelium:
o Cilia beat, slowly moving mucus towards mouth → remove inhaled particles.
What is cystic fibrosis ?
genetic (inherited) disorder that affects
(Cl-) ion channels.
* Failure of channel to function causes
affected cells to produce thick, viscous secretions:
o Most profound effects are in the
lungs and pancreas.
Pancreas: thick secretions block release
of digestive enzymes; inability to digest
certain nutrients/foodstuff may lead to
inflammation, i.e. pancreatitis.
What is the site of gas exchange ?
Alveoli
o Huge surface area
O2 into blood (via the pulmonary vein), CO2 into alveoli (via pulmonary artery)!
* Walls of alveoli consist of a thin epithelial cell layer comprising:
o Alveolar Type I;
o Alveolar Type II.
Alveolar type 1 and type 2 cells ?
Type I: thin, squamous epithelial cells; major part of alveolar walls.
* Type II: rounder, cuboidal cells; produce fluid layer that lines alveoli:
o Produce and secrete pulmonary surfactan
Surfactant: reduces surface tension of alveoli → prevents alveoli from
collapsing during exhalation & easier to
expand during inhalation
Ventilation in mammals ?
- In all air breathing vertebrates (except birds), breathing is tidal.Volume of air exchanged with each breathe may vary, but inhaled air is always mixed with ‘stale’ air (not fresh air; relates to dead space):.
o Mixing with stale air lowers the PO2 gradient → blood PO2 leaving the
lungs is just below PO2 of exhaled medium… Not very efficient..
Mamallian respiratory adaptation ?
To compensate for tidal ventilation,
o A large gas exchange surface area (A), owing to the extensive
branching (particularly in respiratory zone).
o A short diffusion path length (L): distance between air & blood is
* ‘Indirect’ adaptations (aid breathing
without affecting gas exchange):
1. Mucus: mucus escalator clears
inhaled dirt particles and micro-
organisms (see pre-lec. slides).
2. Surfactant: forms a phospholipid
layer at air-liquid interface; helps
reduces surface tension
What is lung inflation fascillitaed by ?
Surfactant
Requires great effort to inflate lungs against surface tension. Untreated, may result in exhaustion, the inability to
breathe, lungs collapse… May lead to death.
Lack of surfactant in premature infants (those born before week 28)
→ newborn (/infant) respiratory distress syndrome (NRDS).
What are Alveoli ?
Alveoli: thin-walled air
sacs; alveolar ducts lead
into these terminal
clusters (i.e. alveoli)
Mechanics of Breathing ?
During breathing (ventilation):
o Muscles of inspiration act to ↑ volume of thoracic cavity; include:
o Diaphragm, external intercostals, pectoralis minor & scalene muscles.
o Muscles of expiration act to ↓ volume of thoracic cavity; include:
o Internal intercostals & transversus thoracis muscles; assisted by the
abdominal muscles.
Mechanics of breathing: anatomy intro
*
Mechanics of breathing and physics ?
Inspiration: an active process; lung volume↑, and lung pressure ↓:
o Air flows into lungs, down its pressure gradient.
* Expiration: a passive process; lung volume ↓, and lung pressure ↑:
o Air flows out of lungs, down its pressure gradient.
o When tension is removed, lungs (and co) ‘spring back’ (recoil) into a
smaller, relaxed state; e.g. diaphragm relaxes; moves upward.
What is Intrapulmonary & intrapleural pressure ?
Pleurae (singular: pleura) form a
thin, double-layered serosa.
* Outer parietal pleura covers the
thoracic wall and superior face of
the diaphragm (covers).
* Inner visceral pleura covers the
external lung surface (dips in too).
* Pleural cavity: filled with fluid
(10ml) produced by the pleurae:
o Allows lungs to ‘glide’ over
the thoracic wall during
breathing movements
- Pleurae (singular: pleura) form a thin, double-layered serosa.
- Outer parietal pleura covers the thoracic wall and superior face of the diaphragm (covers).
- Inner visceral pleura covers the external lung surface (dips in too).
- Pleural cavity: filled with fluid (10ml) produced by the pleurae:
o Allows lungs to ‘glide’ over the thoracic wall duringbreathing movements.
Pressure relationships in thoracic cavity ?
Inntrapulmonary (i.e. alveolar) pressure is that within alveoli. While intrapleural
pressure is that within pleural cavity. Latter is always –ve to/than atmospheric pressure, this is because of the opposing forces that exist in the thorax (chest)
What if the intrapleural pressure becomes
equal to atmospheric pressure?
Pneumothorax: air enters pleural cavity; could be caused by e.g. puncture of
the thoracic cavity → the lung(s) collapse (breathing brings air into pleural cavity instead of into lungs).
Control of breathing /respiration ?
The basic respiratory rhythm is generated in the brainstem;
specifically, in the medulla oblongata:
o Involves 2 groups of neurons (a neural circuit): dorsal and ventral
respiratory neurons (DRG and VRG neurons, respectively).
o Reflexes such as the cough reflex, swallowing, the Hering-Breuer
(lung inflation) reflex can influence the breathing pattern
