1- Overview of Respiration & Respiratory mechanics Flashcards
what is internal respiration?
intracellular mechanisms which consumes oxygen and produces carbon dioxide (once in tissues)
what is external respiration?
sequence of events that lead to exchange of oxygen and carbon dioxide between external environment and cells of the body
(has 4 steps)
what are the 4 steps of external respiration?
- Ventilation = mechanical process of moving gas in & out of lungs
- gas exchange between alveoli & blood = exchange of O2 and CO2 between air in alveoli and blood in pulmonary capillaries
- Gas transport in the blood = The binding and transport of of O2 and CO2 in the circulating blood
- gas exchange at tissue level = The exchange of O2 and CO2 between the blood in the systemic capillaries and the body cells
what 4 body systems are involved in external respiration?
- respiratory system
- cardiovascular system
- Haematology system
- Nervous system
what is ventilation?
first step of external respiration which is mechanical process from moving air between atmosphere & alveolar sacs
what influences movement of lungs? is it passive or active?
movement is entirely passive of the lungs - results form forces external to lungs
is inspiration active or passive? and what causes?
active process brought about contraction respiratory muscles
is expiration active or passive? and what causes it?
passive process brought about relaxation of inspiratory muscles
what are the opposing forces that act on the lungs?
= forces keeping alveoli open and forces promoting alveoli collapse
keeping open:
- transmural pressure gradient (important)
- pulmonary surfactant
- alveolar interdependence
promoting collapse:
- elastic recoil of lungs & chest wall
- alveolar surface tension
what is transmural pressure gradient?
gradient that can be across lung wall & across thoracic wall
(intrapleural should be lower so allows alveoli to expand more)
2 different transmural pressure gradients:
across lung wall= intra-alveolar pressure - intrapleural pressure
across thoracic wall = atmospheric pressure - intrapleural pressure
what are 2 factors that allow the lungs to adhere to chest and follow movement?
- transmural pressure gradient
- intrapleural fluid cohesiveness (water molecules in intrapleural fluid attracted to each other & resist being pulled apart)
what is normal pressure in
a) atmosphere
b) intra-alveolar pressure
c) intrapleural pressure
a) 760 mmHg
b) 760 mmHg
c) 756 mmHg
what is intrapleural/intrathoracic pressure?
pressure exerted outside the lungs within pleural cavity (usually less than atmospheric pressure)
what is intra-alveolar/intrapulmonary pressure?
pressure within lung alveoli - 760 mmHg when equilibrated with atmospheric pressure
what does increased transpulmonary pressure gradient mean?
=another name for transmural pressure gradient across lung wall
means lungs will expand (as increased gradient means lower intrapleural pressure so alveoli can spread out)
what is pneumothorax?
air in pleural space
what effect does pneumothorax have on transmural pressure gradient?
abolishes transmural pressure gradient as liquid in pleural space so disrupts the normally negative intrapleural pressure and raises it
= this can lead to lung collapse
what can cause pneumothorax?
can be spontaneous, traumatic, iatrogenic
= air enters pleural space from outside lungs or lung itself
what are symptoms of pneumothorax?
shortness of breath and chest pain
what are signs of pneumothorax?
hyperresonant percussion note and decreased/absent breath sounds
what must pressure levels be like to allow inspiration?
intra-alveolar pressure must be less than atmospheric pressure air to flow into lungs in inspiration (as air flows from high pressure to low pressure)
how does intra-alveolar pressure change during inspiration and expiration?
before inspiration = intra-alveolar pressure is same as atmospheric pressure
during inspiration = thorax & lungs expand (because of muscle contraction) and this expansion makes intra-alveolar pressure fall to become less than atmospheric due to Boyle’s law (as volume of gas increases the pressure exerted by gas decreases)
during expiration = muscles relax so intra-alveolar pressure rises (relax muscle = less space = higher pressure). higher intra-alveolar pressure allows air flow to leave again
how does contraction of diaphragm affect volume of thorax?
volume of thorax increased vertically by contraction of diaphragm - flattens out it’s dome shape
what does contraction of external intercostal muscles do?
causes elevation of ribs which increases side-side dimension of thoracic cavity. this pushes diaphragm down increasing vertical dimension of thoracic cavity
what happens in inspiration?
= active process brought about by contraction of inspiratory muscles
- chest wall & lungs stretched
- increase in size of lungs makes intra-alveolar pressure fall
- because air molecules become contained in a larger volume (Boyle’s Law)
- The air then enters the lungs down its pressure gradient until the intra-alveolar pressure become equal to atmospheric pressure
what happens in expiration?
= passive process brought by relaxation of inspiratory muscles
- The chest wall and stretched lungs recoil to their pre-inspiratory size because of their elastic properties
- The recoil of the lungs make the intra-alveolar pressure to rise because air molecules become contained in a smaller volume (Boyle’s Law)
- The air then leaves the lungs down its pressure gradient until the intra-alveolar pressure become equal to atmospheric pressure
what allows lungs to recoil during inspiration?
- elastic connective tissue in the lungs (bounces back whole structure)
- alveolar surface tension - IMPORTANT
what is alveolar surface tension and how does it help lungs recoil during expiration?
attraction between water molecules (alveoli lined with water molecules that are attracted to each other creating surface tension) - this tension would collapse the alveoli if not for surfactant
surfactant is interspersed between water molecules lowering surface tension = preventing collapse and therefore helping recoil
what is surfactant and it’s role in expiration?
surfactant = a complex mixture of lipids and proteins secreted by type II alveoli
Surfactant acts to decrease surface tension, particularly at smaller alveolar sizes. This reduces the pressure needed to keep the alveoli open and prevents their collapse during expiration
what does LaPlace’s Law help support?
supports the idea about alveolar surface tension and surfactant
the law says that the smaller alveoli the higher tendency to collapse so surfactant has to help smaller alveoli most
how can surfactant link to respiratory distress in newborns?
the developing fetal lung is unable to synthesize surfactant until late pregnancy so premature babies may not have enough causing respiratory distress by strenuous inspiratory efforts in attempt to overcome high surface tension & inflate the lungs
what is alveolar interdependence?
= factor that helps keep alveoli open
If an alveolus start to collapse the surrounding alveoli are stretched and then recoil exerting expanding forces in the collapsing alveolus to open it
