Resp Lecture 4 โ๏ธ๐ช Flashcards
RECOIL FORCE
ELASTICITY
SURFACE TENSION
Defining Elasticity
Ability to recover original size & shape after deformation
How Does Expiration Occur at Rest?
RECOIL FORCE
ELASTICITY of the Lungs
Lungs are Distensible
Inspiration Expiration
COMPLIANCE
1/ Elasticity
COMPLIANCE =
change in Volume/ change in Pressure
What is Surface Tension
Molecules within a liquid have cohesive forces with all neighbouring atoms. But, those on the surface (i.e. at a liquid- gas interface) have no neighbouring atoms above, and so exhibit stronger attractive forces upon their nearest neighbours on the surface. This enhancement of the intermolecular attractive forces at the surface is called surface tension.
Laplaceโs Law
P = 2T/R
COPD
Massively expanded lungs
Flattened diaphragm
Mid-sternal space reduced
Fibrosis
Deflated lungs Mid-sternal space wide Fluffy areas fibrotic tissue
COPD
chronic obstructive pulmonary disease
Parasympathetic Nerves
Contained within the vagus nerve Bronchoconstriction Muscarinic receptor
Sympathetic Nerves
From the spinal cord Bronchodilator Beta-adrenoceptors
Asthmatics take
salbutamol - beta-adrenoceptor agonist
Lung stretch
receptors
mechanoreceptors
in bronchioles
Hering-Breuer Reflex
SENSORY RECEPTOR lung stretch receptor = Vagal afferents = Medulla Oblongata respiratory centres = Sympathetic efferent= EFFECTOR or TARGET ORGAN = bronchioles: BRONCHODILATE NA โฮฒ-adrenoceptor
At rest, expiration is a passive process relying on
radial traction which depends on physical properties of the lungs (elasticity and surface tension)
La Placeโs law To measure the surface tension induced pressure within the alveoli (PA) we 2T use La Placeโs law where
PA = 2 x surface tension divided by the alveolar P =
Lung compliance
change in volume of lung divided by change in pressure and tends to collapse lungs at functional residual capacity (FRC)
Pulmonary disease states typically afect compliance of the lung and/or chest wall: e.g
chronic obstructive pulmonary disease or COPD (increased lung compliance caused by smoking) and ibrosis (โstif lungโ caused by air contaminants).
The upper tree
irst 16 generations are non-respiratory in function and form the conducting zone โ which makes up anatomical dead space
Dead space causes contamination of freshly inhaled air diluting the oxygen content. It is approximately 2.2 ml per kg. The respiratory zone (or unit) comprises
respiratory bronchioles, alveolar duct and alveolar sac. These latter structures are free of cartilage and are kept open by the lung parenchyma.
Cross sectional area and air low down the airway The cross sectional area increases from the trachea to the alveoli x500 - so called
funnel efectโ.
300 million alveoli. The low of air in the conducting zone is rapid and
highly turbulent but becomes slow and laminar in the respiratory zone due to large surface area.
Airway resistance is dependent on
airway resistance
The highest is in the upper airway and lowest in the bronchioles. Airway resistance is dependent on lung volume a inlating the lung pulls airways open via radial traction. The airways contain smooth muscle and are innervated
by parasympathetic (PS) and sympathetic nerves. The PS nerves cause bronchoconstriction and the sympathetic nerves bronchodilatation
The bronchal smooth muscle also has numerous receptors sensitive to humoral and hormonal inluences. The bronchiole smooth muscle contains
beta2- adrenoceptors, which are targeted using agonists in people with asthma, for example.
The bronchioles are innervated with sensory stretch receptors that generate action potentials during lung inlation that are
sent to the brainstem
This triggers a relex bronchodilatation mediated via the sympathetic nervous system to reduce
airway resistance and facilitates air low into the alveoli.
