2.2 - ventilation of the lungs (workbook) Flashcards
how is air drain into the lungs?
by expanding thoracic cavity
what is done during breathing?
work is done to move structures of the lung and thorax and to overcome the resistance to the flow of air through the airways
what type of structures are the lungs?
elastic structures and if removed from the chest cavity the inward elastic recoil of the lungs causes the lungs to totally collapse
how is the chest wall like?
recoils outwards, from its usual position when the thoracic cavity is open to the atmosphere e.g. thoracic surgery
what are the lungs like within the living respiratory system?
lungs are sealed within the chest by the pleural seal
the elastic forces of lung and chest walls are balanced in equal and opposite directions at the end of quiet expiration (respiratory muscles are at rest)
what happens when there is an absence of muscular activity?
(when the respiratory muscles are relaxed)
there is an equilibrium position, when the inward force of the elastic recoil of the lungs is balanced by the outward recoil of the chest wall - same state as the end of normal quiet expiration
what is the equilibrium position known as?
resting expiratory level
what are the lungs sealed within the chest by?
pleural seal
what forms the pleural seal?
the pleural space (filled with few ml of pleural fluid) forms a seal, holding outer surface of the lungs (visceral) to the inner surface of the chest wall (parietal)
what does the pleural seal ensure?
that the chest wall and lungs move together
when the chest expands increasing the volume of the thorax cage, the lungs also expand
what is the functional residual capacity (FRC)?
the lung volume that exists at the end of expiration (at resting expiratory level)
what is significant at FRC (functional residual capacity)?
the elastic forces of the lung and chest walls are balanced
what disrupts the FRC (functional residual capacity)?
the muscles involved in breathing apply force to disturb this equilibrium in an inspiratory and expiratory direction
what does breathing in from the equilibrium position involve?
contraction of the diaphragm (contract down) and the external intercostal muscles (pull up - increase AP length) - all increase volume of thorax
what does breathing out during quiet expiration involve?
only passive recoil of the lungs
what does breathing out during forced expiration require?
contraction of the abdominal muscles (push in and up) and the internal intercostal muscles (inferior posterior fibres)
what happens when muscle contraction stops?
the lungs and thorax will return to the equilibrium position by passive recoil
in inspiration, what happens (in terms of volume)?
the volume of thorax increases, so will volume of lungs (pleural seal)
what happens as lung volume increases?
Boyle’s law: pressure falls below atmospheric pressure, air flow into lungs
what happens as air flow into lungs?
alveolar pressure gradually rise back to atmospheric pressure, when inspiration ceases
what happens in quiet expiration?
muscle contraction ceases, elastic recoil of lung results in a decrease in volume of the thorax and lung
decrease in lung volume causes pressure in terminal and respiratory bronchioles to rise above atmospheric pressure, so air flows back out again (until alveolar pressure = atmospheric pressure)
where does fresh atmospheric air reach?
only a far as the terminal & respiratory bronchioles
how does exchange of oxygen and CO2 occur?
by diffusion between atmospheric air in the terminal and respiratory bronchioles and alveolar gas (maintains normal composition of alveolar gas)
describe how the pleural pressure is like
since lungs and chest wall recoil in opposing directions, pressure within the pleural cavity is slightly less than atmospheric pressure (negative in relation to atmospheric pressure - due to opposing forces)
in quiet respiration, what happens to the pressure in the pleural cavity?
increases, but still remains negative relative to atmospheric pressure, throughout the respiratory cycle
in inspiration, what happens to pleural pressure?
the chest wall expands out (increase vol.), pleural pressure becomes more negative (than normal), and returns to original negative pressure as the lung returns to the resting expiratory level in quiet expiration
what happens to the muscles in quiet breathing?
diaphragm (major muscle of inspiration), moves down to increase vertical dimensions
external intercostal muscles (inferior anterior fibres) move ‘bucket handle’ movement to increase AP & transverse diameters of thorax
in forced inspiration what happens? when does forced inspiration occur?
(when ventilation is increased - exercise / resistance to respiration is present - COPD)
accessory muscles of inspiration are used
what are the accessory muscles of INspiration used?
exercise: serratus anterior & pec major
COPD: sternocleidomastoid & scalene muscles
how does quiet breathing occur?
elastic recoil of lungs
what happens in forced EXpiration? when does this occur?
accessory muscles of expiration are used e.g. exercise
what are the accessory muscles of expiration?
internal intercostal muscles
abdominal wall muscles (external & internal oblique muscles & rectus abdominis muscles)
which muscle is the major muscle of inspiration? what does it do?
diaphragm
major work against forces required to stretch the lungs - stretch the elastic tissue of the lung & to stretch the film of fluid lining the alveoli (against surface tension pulling it in & VdW forces)
