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Full summary; all lectures Medical Physiology
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Medical Physiology SummaryRespiratory System & Work of breathing:
Aim of breathing: Supply the cells in the body with O2 and get rid of the CO2 that is produced in the
cellular metabolism.
Aim & components of breathing:
Transport of gasses in and out of the lungs: ventilation
Diffusion between alveoli and blood: gas exchange/Alveolar
diffusion
Passage of blood: perfusion
Tuning ventilation and lung perfusion: ventilation/perfusion ratio
Transport of gasses in the blood, O2 to tissues & CO2 back to lungs
: gas transport
Exchange of gas between blood and cells: gas exchange (or tissue
diffusion)
Use of O2 and production of CO2 in cells : cellular respiration
Anatomy of the airways:
Spirometry: measure the volume that someone breaths. Spirometer: filled with air, connect to
person. If you suck in air, you pull the chamber downwards and the pen will go upwards →
spirogram.
,Static lung volumes and capacities:
• Tidal volume VT= quietly
breathing, in healthy person =
500 ml/breath.
• Inspiratory Reserve Volume IRV=
amount of air that we can breath in
extra = 3L.
• Expiratory Reserve Volume ERV=
what someone can breathe out
extra, after a normal expiration.
• Residual Volume RV= if someone
breathes out completely, there is still some air in the lungs left.
• Functional Residual Capacity FRC = ERV + RV (residual volume +expiratory reserve volume) = air
that you already have if you start breathing in = 2,5 → 3 L.
• Inspiratory Capacity IC = VT + IRV (tidal volume + inspiratory reserve volume)
• Vital Capacity VC = IC + ERV = amount that you can breath in maximally + amount that you can
breath out maximally. VC is a measure of the maximum volume of gas in the respiratory system that
can be exchanged with each breath.
• Total Lung Capacity TLC = VC + RV (residual volume + vital capacity)
• Forced vital capacity FVC = test in which someone has to breathe out maximally at once.
Ventilation:
Inspiration: contract the diaphragm → it flattens; enlarge the thorax; volume increases.
Pressure* Volume = constant {Boyle’s law}
If you enlarge the volume, pressure goes down. Air flows from a high to low pressure so lowering
pressure inside the lung → air will flow from the outside air into the lungs.
Relax muscles of inspiration: thoracic volume decreases; air pushed out of the lungs again to the
outside air.
Ventilation; cause pressure differences; create flow of air.
For inspiration; 2 muscle layers between ribs used; external intercostal muscles; lift the lungs up and
out.
Space between lung and thoracic cavity; pleural space.
, During inspiration: volume in the pleural
space is increased as well so : Ppleura goes down. Pressure in pleural space pulls on the lungs, lungs will
expand.
The amount that the lung expands depends on how compliant the lung is. If the lung is very stiff, we
need to create a large pressure difference to expand the lung.
Amount of air that starts flowing- depends on the resistance. Resistance depends on how narrow the
bronchioles are and how much air is flowing.
Forces to be overcome during breathing:
• Elastic forces (‘static’):
– retraction forces lung
– retraction forces thorax wall
• Resistance forces (‘dynamic’):
– airway resistance
– tissue resistance
Two membranes:
-parietal pleura: lining the thorax
-pulmonary pleura: lining the lungs
^in between the two membranes: pleural space
Little layer of fluid in between; pulls the membranes together. The thorax wants to be big, lungs want
to be small.
Thorax; pulling to the outside
Lungs; pulling to the inside
^ Pressure in the pleural space = lower that outside world & lower than pressure inside the lungs.
Outer pressure = 760 mm Hg.
Pretend that the pressure outside & in the lungs is zero, so pressure pleural space is negative- at FRC.
Pressure over the lung wall ( pulmonary pressure ); PI = P Alv – PPL
If we’re not breathing; pressure Alveoli = 0, PL= negative → so pressure over the lung wall is positive.
, If the PI is negative; it is a net force trying to deflate the lung.
If the PI is 0 → no pressure to keep the lung open so it collapses.
Pressure over the thoracic wall; Pth = PPL – Pb
Pb= outside air.
If Ppl is negative and Pb is zero → negative pressure. ( At FRC) – the chest is slightly deflated because
of the negative pressure.
Forces pushing the lungs to the outside and the thorax to the inside are equal; at FRC no extending or
collapsing force.
Pressure over the 2 membranes: PL+th = Palv – Pb
Not breathing; P alv = 0 and Pb = 0 → so the pressure = 0.
^Transmural pressures: Pin – Pout.
Static volume/pressure relationship:
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