Intro to the Respiratory System

Question 1

Why do we need a respiratory system?

Answer 1

1. Cells require energy to function, and we need O2 to make that energy.
2. Aerobic respiration requires O2 and produces CO2.
3. The atmosphere provides a source of O2, and CO2 can be expelled.
4. Our bodies are too large to rely on simple diffusion of gases from the atmosphere to the tissues.

Question 2

What is the division, diameter (mm), how many and what is the cross sectional area of the different structures gas has to pass thorugh?

Answer 2

Question 3

How are alveoli adapted to maximise the rate of gas exchange?

Answer 3

1. They have a large surface area (lungs have a high surface area to volume ratio due to their 3D structure).
2. Their walls are one cell layer thick and they have basement membrane fused with blood vessel.
3. They are richly innervated by capillaries (adequate blood supply)

Question 4

What functions does the respiratory system have within the body?

Answer 4

• It provides (and ventilates) a specialised surface where gas exchange can take place between the atmosphere and the blood.
• It contributes to the acid-base balance in the body (eg. the pH of the blood).
• Communication.
• Metabolism and production of specific mediators.
• The pulmonary circulation filters particulate matter and emboli reducing systemic circulation exposure.
• Immunological defence.

Emboli meaning - a blood clot, air bubble, piece of fatty deposit, or other object which has been carried in the bloodstream to lodge in a vessel and cause an embolism.

Question 5

How does oxygen get from the atmosphere to the cells?

Answer 5

1. O2 is inhaled from the atmosphere into the alveoli within the lungs.
2. O2 diffuses from the alveoli into the blood within the pulmonary capillaries.
3. O2 is transported in the blood, predominantly bound to haemoglobin.
4. O2 diffuses into cells/tissues for use in aerobic respiration.
5. CO2 diffuses from the respiring tissues to the blood (the exchange occurs at the lungs).

Question 6

What are the different lung volumes and capacities?

Answer 6

Lung volumes and capacities depend upon factors like age, sex, height, as well as lung properties (compliance, obstruction / damage due to disease).

Question 7

What is the functional residual capacity (FRC)?

Answer 7

• Functional Residual Capacity (FRC) is the volume of air present in the lungs at the end of passive expiration.
• At FRC, the opposing elastic recoil forces of the lungs and chest wall are in equilibrium and there is no exertion by the diaphragm or other respiratory muscles.

Question 8

What is the inspiratory reserve volume (IRV)?

Answer 8

• Inspiratory reserve volume is the maximal volume that can be inhaled after normal inspiration.

Question 9

What is the expiratory reserve volume (ERV)?

Answer 9

• Expiratory reserve volume is the maximal volume of air that can be exhaled after normal expiration.

Question 10

What is tidal volume (V_T)?

Answer 10

• Tidal volume is the volume of air moved into or out of the lungs during a normal breath.

Question 11

What is total lung capacity (TLC)?

Answer 11

• Total lung capacity is the volume in the lungs at maximal inflation.
• It is the sum of VC and RV (or sum of IRV + V_T + ERV + RV).

Question 12

What is residual volume (RV)?

Answer 12

• Residual volume is the volume of air remaining in the lungs after a maximal exhalation.

Question 13

What is vital capacity (VC)?

Answer 13

• Vital capacity is the maximum volume of air breathed out after the deepest inhalation.
• It is the sum of the ERV + TV + IRV.

Question 14

What is total ventilation / respiratory minute volume? How to calculate it?

Answer 14

• Total ventilation / Respiratory minute volume is the volume of gas inhaled (inhaled minute volume) or exhaled (exhaled minute volume) from a person’s lungs per minute.

Question 15

Why isn’t the alveolar air equal to the inspired air?

Answer 15

• The lungs contain a mixture of ‘fresh’ and ‘stale’ air.
• Gas exchange only takes place in alveoli, bu air must first pass through the airways. (The airways are where gas exchange does not take place and hence they are called “anatomic dead space”).
• The respiratory system is a two-way system; air enters and leaves via the same path. Also, a residual volume of air remains in the airway and lungs at the end of expiration.
• This means that the final ~ 150mL (dead space volume) of each inspiration never reaches the alveoli or takes place in gas exchange.

Question 16

What is alveolar minute ventilaton? How to calculate it?

Answer 16

Question 17

What is the ideal gas law?

Answer 17

• It is the equation of state of the hypothetical gas.
• It helps us model and predict the behaviours of gases.
• It’s what helps us understand that gases naturally move from (connected) areas of higher pressure to lower pressure, until an equilibrium is re-established.
• PV=nRT
• where P is pressure (pascals), V is volume (m³), n is the number of moles (moles), R is the gas constant (8.314) and T is the temperature (kelvin).

Question 18

We can manipulate the ideal gas law to produce Boyle’s Law. Describe Boyle’s Law.

Answer 18

• Boyle’s Law states that the pressure of a gas is proportional to the number of has molecules within a given volume.
• P ∝ n/v
• If the n remaines constant, increasing the volume will decrease the pressure.

Question 19

What is partial pressure of gas? How can we calculate partial pressure?

Answer 19

• It is the pressure that would be exerted by one of the gases in a mixture if it occupied the same volume on its own.
• It can be calculated by multiplying the total pressure by the mole fraction.

Question 20

What is the partial pressures of gases dissolved in liquid?

Answer 20

• The partial pressure of gas dissolved in a liquid reflects the amount of gas that would dissolve (at equilibrium) if the liquid was placed in contact with a gas phase of equivalent partial pressure.