Resp Mechanics Lect 1 Flashcards
What is external respiration
Sequence of events that leads to exchange of oxygen and carbon dioxide between the external environment and the cells of the body
Involves four steps
What are the four steps for external respiration
Ventilation –> mechanical process of moving gas in and out of lungs
Gas exchange between alveoli and blood (of pulmonary capillaries)
Gas transport in the blood
Gas exchange at tissue level
What are the 3 a body systems involved in external respiration
Respiration syst
Cardiovascular syst
Haematology syst
Examine what ventilation is, including the involvement of boyles law
Ventilation is the mechanical process of moving air between alveoli and alveolar sacs
Air flows down a pressure gradient from a high to a low concentration. Therefore the intra alveolar air concentration must be less this is achieved by the contraction of the inspiratory muscles allowing the lungs and thorax to expand.
Boyles law –> at any constant temperature the pressure exerted by a a gas varies inversely with the volume of the gas
What are the two forces that hold the thoracic wall and the lungs in close opposition
Intra pleural fluid cohesiveness - water mols in the fluid are attracted to eachother and resist being pulled apart hence the pleural membranes tend to stick together
Negative intra pleural pressure - subatmospheric intra pleural pressure creates a transmural pressure gradient across the lung wall and chest wall
What are the 3 important pressures of ventilation
Intra pleural pressure - pressure in pleural sac 756mm Hg
Atmospheric pressure - varies at sea level, but at sea level is 760mm Hg
Intra alveolar pressure - in alveoli, 760mm Hg
Is inspiration an active or passive process and what does it depend on
Inspiration is active
Depends on muscle contraction, the volume is vertically increased by contraction of the diaphragm ( major inspiratory muscle) which is supplied by the phrenic nerve
The external intercostal muscles also contract and moves the sternum out (bucket handle analogy)
Is expiration an active or passive process
Passive brought about by the relaxation of inspiratory muscles
The recoil of the lungs make the intra alveolar pressure increase as more air molecules in a smaller volume
The air leaves the lungs down its pressure gradient as intralveoikar pressure greater than atmospheric
What is pneumothorax
Air in the pleural sac which abolishes he transmural gradient
Traumatic - puncture to chest wall
Spontaneous - lung rupture
What causes lungs to recoil in expiration
The elastic connective tissue in the lungs
Alveolar surface tension
What is alveolar surface tension
Attraction between water mols at the liquid air interface
In alveoli this produces a force which resists the stretching of the lungs
Alveoli are not just lined by water as this would be too strong and cause alveoli to collapse
What is pulmonary surfactant and why is it important, include the explanation of the law of LaPlace
Pulmonary surfactant is a complex mix of proteins and lipids secreted by type 2 alveoli
Lowers surface tension on alveoli by going between water mols
It works more on smaller alveoli than larger
Laplace law explains that smaller alveoli are more likely to collapse
Explain what difficulties a premature baby would have in terms of respiration
Premature babies may not have enough surfactant
Causes a respiratory distress syndrome
Baby will have to make very strenuous inspiratory efforts ina Na attempt to overcome the high surface tension
What is alveolar interdependence
If an alveolus begins to collapse the surrounding are stretched and then recoil exerting expanding forces in the collapsing alveolus to open it
What are the opposing forces acting on the alveoli
Keeping alveoli open - transmural pressure gradient, pulmonary surfactant, alveolar interdependence
Promoting closure of alveoli - elasticity stretched, alveolar space tension
