week 1 - introduction to the respiratory system Flashcards
which divisions are the conducting airways and which are the respiratory zone?
divisions between the trachea and alveoli:
divisions 1-16: conducting airways - NOT in gas exchange
divisions 17-23: respiratory zone - in gas exchange
what are the alveoli surrounded by?
capillaries which receive the entire output of the right ventricle via the pulmonary arteries and its branches
where does gas exchange occur?
across the very thin (0.3 micrometer) alveolar capillary membrane
what is ventilation?
the process of inspiration and expiration
how does a breathing pattern occur?
neurones in the respiratory centre in the medulla of the brain generate automatic rhythmic impulses - responsible for the normal rhythmic involuntary breathing pattern
where do the impulses from the medulla of the brain travel via?
spinal cord and peripheral nerves to the inspiratory muscles
what expands the chest and lungs?
inspiratory muscles contract
how does pressure and volume change in lungs following Boyle’s law?
when the volume of air in the lungs increase, its pressure decreases
when does air flow into lungs?
when the pressure within lungs drop below the atmospheric pressure
what happens in expiration?
the neurones in medulla of the brain cease generating impulses, and the inspiratory muscles relax
the chest returns to original size (compress inflated lungs)
as air pressure in lung increases (greater than atmospheric), air flows out
how does oxygen travel into the blood from lungs?
oxygen diffuses across the air-blood interface down its partial pressure gradient into the capillary blood
what is partial pressure?
the measure used to indicate the availability of gases for respiration - denoted by p e.g. pO2
how does oxygen travel in blood once diffused?
most of it carried bound to Hb, small amount carried dissolved in blood
what happens to the CO2 from venous blood?
CO2 in venous blood arrive in the pulmonary capillaries diffuses into alveolar air and is breathed out in exhalation
what are gases?
a collection of molecules moving around a space
how is pressure generated?
by collisions of gas molecules with the walls
the more frequent & harder the collisions, the higher the pressure
how does the universal gas law describe volume and pressure changes with temperature?
P.V = nR.T
n=amount of gas
R = gas constant
what is Boyle’s law?
the pressure is inversely proportional to volume for a fixed quantity of gas at a constant temperature e.g. lung ventilation
what is pressure measured in?
kilopascals (kPa)
what is Dalton’s law (of partial pressure)?
in a mixture of gases, the molecules of each type behave independently, so each gas exerts a partial pressure
(each gas has a different pp provided that the gases don’t combine chemically)
each component of gas exerts a partial pressure proportional to its volume percentage in mixture
what happens in high altitudes?
atmospheric pressure is lower
what can happen if a gas mixture is in contact with water?
- gas molecules enter the liquid to dissolve (become 1 liquid mixture)
- water molecules evaporate to enter the gas phase (become 1 gaseous mixture)
what happens when a gas and liquid are in contact?
gas molecules will enter the liquid until an equilibrium is established between the rate of solution and dissolution of gas
what is the partial pressure of a gas in a liquid?
the collision of the dissolved gas molecules generates a pressure within liquid, which is the partial pressure (or tension) of that gas in the liquid
what happens at equilibrium?
the partial pressure (or tension) of a gas in the liquid is equal to the partial pressure of the gas (in the gas phase) to which the liquid is being exposed to
(rate of evaporation = rate of molecules water returning to liquid phase)
what does partial pressure determine?
partial pressure (tension / collisions) determines the equilibrium and therefore amount of gas in liquid partial pressure is NOT the amount or content of gas in liquid, it is just the factor which determines the amount
what is the solubility coefficient of a gas?
determines the amount of (in mmol) of a gas that will dissolve in a litre of plasma at 37 degrees (body temperature), when exposed to a given partial pressure
(it is a constant for a given gas)
what happens when the partial pressure of a gas increases?
more of the gas will dissolve
how do you work out the amount of gas dissolved?
amount of gas dissolved = solubility coefficient of that gas x the partial pressure it is exposed to
what is saturated vapour pressure (SVP)?
at equilibrium, the gas mixture is saturated with water vapour, and the pressure it exerts is called SVP
what does SVP depend upon?
only temperature (INdependent of total pressure) e.g. water SVP at 37 degrees = 6.28kPa
why does the total pressure of humidified air always remain at 101kPa?
gas is continuous with the outside air, and pressure will equilibrate to atmospheric pressure
how does pressure in systemic and pulmonary circulation differ?
same total flow
systemic under much higher pressure than pulmonary
how is the pulmonary and systemic circulation ran?
pulmonary circulation: low resistance, supply driven (driven by how much travels through veins)
systemic: demand led (more blood if body requires more)
what do pulmonary resistance vessels influence?
only the distribution of blood within it
does NOT influence the total flow through the pulmonary circulation
what is the rate of movement of fluid across the capillary endothelium into the interstitium determined by?
by the net hydrostatic pressure gradient, which favours movement of fluid out from the pulmonary microcirculation into the interstitium and oncotic pressures gradient which opposes it
in a normal lung, is oncotic pressure higher or hydrostatic pressure? why?
oncotic pressure is higher - tend to draw fluid back into the circulation so tissue fluid is not normally formed (fluid buildup in lungs)
except where is oncotic pressure higher than hydrostatic pressure in the lungs? why?
except occasionally in the base of the lungs where the effects of gravity increases transmural hydrostatic pressure
what is atmospheric pressure? how does it arise?
arises from the weight of air
the mass of air is pulled down by gravity and exerts a force
