Unit 2 - Lungs Flashcards
describe the conducting zone and its respiratory tree
no gas exchange - transfer of gases to & from alveoli/ filtration/ warming & humidifying air
trachea - generation 0/ bronchi (1)/ lobar bronchi (2/3)/ segmental bronchi (4)/ small bronchi (5-11)/ bronchioles (12-15)/ terminal bronchioles (16)
describe the cell lining the airways in conducting zone
trachea to small bronchi - pseudostratified columnar ciliated epithelium
bronchioles - simiple ciliated cuboidal epithelium
describe the walls lining the airways in conducting zone
trachea/ bronchi - C-shaped rings of hyaline cartilage
smaller bronchi - overlapping cartilage
bronchioles - no cartilage
terminal bronchioles - thick walls due to smooth muscle
describe the transitional/ respiratory zones and the respiratory trree
gas exchane - large SA respiratory bronchioles (17-19)/ alveolar ducts (20-22)/ alveolar sacs (23)
what does an alveolar sac contain?
2 or more alveoli enveloped by pulmonary capillaries
what are the two types of cell found in alveolar septa?
Type I: squamous epithelial
Tupe 2: thicker cell which synthesis and secrete pulmonary surfactant
what is found between alveolar septa and capillaries?
lung parenchyma - connective tissue containing elastic fibres & collagen linking alveoli together
(pores of Kohn interconnect neighbouring alveoli)
give the definitions of: TV/ IRV/ ERV/ RV/ FRC/ VC
tidal volume - air taken in/ out in each breath
inspiratory reserve volume = difference in lung volume between normal and maximal inspiration
expiratory reserve volume = difference in lung volume between normal and maximal expiration
residual volume - air remaining after maximal expiration
functional residual capacity - ERV + RV - volume of air left at end of normal expiration
vital capacity - difference in lung volume between maximal inspiration and expiration
what is the formula for tidal volume?
dead space + alveolar ventilation
what is dead space?
anatomical - air taken in not mixing with air in alveoli
physiological - air taken in not taking part in gas exchange
Vd= Ve (1 -Fe/ Fa) where Ve = minute volume(fVt) and F is fractional content of CO2 in e- air exhaled/ a- alveoli
how do you calculate alveolar ventilation rate?
Va = (Vt - Vd) x f Va = Ve - (Ve x Vd/ Vt)
what is the dead space: tidal volume ratio?
Vd/ Vt = (PaCO2 - PeCO2)/ PaCO2
why is ventilation uneven?
progressive decrease in intrapleural pressure from apex to base
transpulmonary pressure decreased in lower regions at rest since Patm=Palv so increase more in volume during inspiration
- also lower ribs more curved
- descent of diaphragm expand lower lobes more than upright ones
- peripheral tissue more compliant than deeper tissue
describe perfusion at apex, middle and base of lungs
apex - Palv = Pa - high vascular resistance no blood flow
middle - Pa> Palv - blood flow increases down the zones
base - Pa» Palv - arterial pressure exceeds alveolar pressure considerably so increased blood flow
what do the dots mean on top of V and Q?
flow in litres per minute
what does it mean when Va: Q =1 = 0 < 1 > 1
Va: Q - ventilation: perfusion ratio
=1 optimum matching/ optimum gas exchange
= 0 right to left shunt - blood passes through lung without coming into contact with alveolar air
< 1 poorly ventilated alveoli - well perfused
> 1 well ventilated alveoli - poorly perfused
what happens in hypoventilation?
ventilation does not meet metabolic demands - increased PCO2/ decreased O2 - chest wall damage -increased dead space
what happens in hyperventilation?
ventilation exceeds metabolic demands - decreased PCO2/ increased O2 - asthma attack
what are the formulas for work?
mechanical work - force x distance moved
work done by gas - pressure x volume = Nm = J
what is the formula for transpulmonary pressure?
Pl= Pa - Ppl (alveolar - intrapleural pressure)
what is the behaviour of the curves in pressure-volume loop?
hysteresis - greater pressure change to inhale than to exhale due to static compliance of chest and non-elastic resistances of airways and tissue
difference between curves - cost of ventilation of lung during single respiratory cycle
what is compliance?
change in volume / change in pressure
higher compliance = lower resistance = greater elasticity and stretch - reduced work of breathing
what two properties determine the elasticity of the lungs?
- elastic fibres of parenchyma
- surface tension of liquid film lining alveoli
what is laplace’s law? describe the relevance
P = 2T/r - when lungs inflated with air surface tension and elasticity of parenchyma opposes expansion - this would suggest a higher pressure of 3 kPa to inflate lung when in reality maximum inflation occurs at <2 kPa
what accounts for the lower pressure <2kPa than expected to inflate the lungs?
surfactant secreted by Type II cells DECREASE SURFACE TENSION/INCREASE COMPLIANCE - phospholipid hydrophilic head in aqueous phase and hydrophobic tail in air space
during expiration phospholipids become compressed exclude water forming monolayer so decreases tension
during inspiration increase in area leads to slow increase in tension since phospholipid molecules separate slowly
describe stages of inspiration
contraction of diaphragm/ intercostal muscles increase in thorax volume decrease in intrapleural pressure expansion of alveoli reduction in alveolar pressure flow in air into the lungs
describe stages of expiration
relaxation of diaphragm/ intercostal muscles decrease in thorax volume increase in intrapleural pressure reduction of alveoli increase in alveolar pressure flow in air out of the lungs
what is FEV?
measurement of volume air expelled from lung during first second of a forced breath
how does FEV and VC change with a person with fibrosis?
reduced vital capacity
FEV to a lesser extent / unchanged
how does FEV and VC change with a person with acute asthma?
reduced FEV
VC to less extent
