week 1 - introduction to the respiratory system

Question 1

which divisions are the conducting airways and which are the respiratory zone?

Answer 1

divisions between the trachea and alveoli:
divisions 1-16: conducting airways - NOT in gas exchange
divisions 17-23: respiratory zone - in gas exchange

Question 2

what are the alveoli surrounded by?

Answer 2

capillaries which receive the entire output of the right ventricle via the pulmonary arteries and its branches

Question 3

where does gas exchange occur?

Answer 3

across the very thin (0.3 micrometer) alveolar capillary membrane

Question 4

what is ventilation?

Answer 4

the process of inspiration and expiration

Question 5

how does a breathing pattern occur?

Answer 5

neurones in the respiratory centre in the medulla of the brain generate automatic rhythmic impulses - responsible for the normal rhythmic involuntary breathing pattern

Question 6

where do the impulses from the medulla of the brain travel via?

Answer 6

spinal cord and peripheral nerves to the inspiratory muscles

Question 7

what expands the chest and lungs?

Answer 7

inspiratory muscles contract

Question 8

how does pressure and volume change in lungs following Boyle’s law?

Answer 8

when the volume of air in the lungs increase, its pressure decreases

Question 9

when does air flow into lungs?

Answer 9

when the pressure within lungs drop below the atmospheric pressure

Question 10

what happens in expiration?

Answer 10

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

Question 11

how does oxygen travel into the blood from lungs?

Answer 11

oxygen diffuses across the air-blood interface down its partial pressure gradient into the capillary blood

Question 12

what is partial pressure?

Answer 12

the measure used to indicate the availability of gases for respiration - denoted by p e.g. pO2

Question 13

how does oxygen travel in blood once diffused?

Answer 13

most of it carried bound to Hb, small amount carried dissolved in blood

Question 14

what happens to the CO2 from venous blood?

Answer 14

CO2 in venous blood arrive in the pulmonary capillaries diffuses into alveolar air and is breathed out in exhalation

Question 15

what are gases?

Answer 15

a collection of molecules moving around a space

Question 16

how is pressure generated?

Answer 16

by collisions of gas molecules with the walls

the more frequent & harder the collisions, the higher the pressure

Question 17

how does the universal gas law describe volume and pressure changes with temperature?

Answer 17

P.V = nR.T
n=amount of gas
R = gas constant

Question 18

what is Boyle’s law?

Answer 18

the pressure is inversely proportional to volume for a fixed quantity of gas at a constant temperature e.g. lung ventilation

Question 19

what is pressure measured in?

Answer 19

kilopascals (kPa)

Question 20

what is Dalton’s law (of partial pressure)?

Answer 20

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

Question 21

what happens in high altitudes?

Answer 21

atmospheric pressure is lower

Question 22

what can happen if a gas mixture is in contact with water?

Answer 22

1. gas molecules enter the liquid to dissolve (become 1 liquid mixture)
2. water molecules evaporate to enter the gas phase (become 1 gaseous mixture)

Question 23

what happens when a gas and liquid are in contact?

Answer 23

gas molecules will enter the liquid until an equilibrium is established between the rate of solution and dissolution of gas

Question 24

what is the partial pressure of a gas in a liquid?

Answer 24

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

Question 25

what happens at equilibrium?

Answer 25

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)

Question 26

what does partial pressure determine?

Answer 26

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

Question 27

what is the solubility coefficient of a gas?

Answer 27

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)

Question 28

what happens when the partial pressure of a gas increases?

Answer 28

more of the gas will dissolve

Question 29

how do you work out the amount of gas dissolved?

Answer 29

amount of gas dissolved = solubility coefficient of that gas x the partial pressure it is exposed to

Question 30

what is saturated vapour pressure (SVP)?

Answer 30

at equilibrium, the gas mixture is saturated with water vapour, and the pressure it exerts is called SVP

Question 31

what does SVP depend upon?

Answer 31

only temperature (INdependent of total pressure)
e.g. water SVP at 37 degrees = 6.28kPa

Question 32

why does the total pressure of humidified air always remain at 101kPa?

Answer 32

gas is continuous with the outside air, and pressure will equilibrate to atmospheric pressure

Question 33

how does pressure in systemic and pulmonary circulation differ?

Answer 33

same total flow

systemic under much higher pressure than pulmonary

Question 34

how is the pulmonary and systemic circulation ran?

Answer 34

pulmonary circulation: low resistance, supply driven (driven by how much travels through veins)
systemic: demand led (more blood if body requires more)

Question 35

what do pulmonary resistance vessels influence?

Answer 35

only the distribution of blood within it

does NOT influence the total flow through the pulmonary circulation

Question 36

what is the rate of movement of fluid across the capillary endothelium into the interstitium determined by?

Answer 36

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

Question 37

in a normal lung, is oncotic pressure higher or hydrostatic pressure? why?

Answer 37

oncotic pressure is higher - tend to draw fluid back into the circulation so tissue fluid is not normally formed (fluid buildup in lungs)

Question 38

except where is oncotic pressure higher than hydrostatic pressure in the lungs? why?

Answer 38

except occasionally in the base of the lungs where the effects of gravity increases transmural hydrostatic pressure

Question 39

what is atmospheric pressure? how does it arise?

Answer 39

arises from the weight of air

the mass of air is pulled down by gravity and exerts a force