Lecture 18 – Introduction to Respiratory System

Question 1

Why do we need a respiratory system? 4

Answer 1

Why do we need a respiratory system?

1) Cells require energy to function.
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 tissues.

Question 2

WHY IS ALVEOLI GOOD 3

Answer 2

• Alveoli have intricate structures & multiple adaptations to maximise the rate of gas exchange.
• Large surface area (lungs have high surface area-volume ratio due to 3D structure).
• Wall = one cell layer thick + basement membrane fused with blood vessel.
• Richly innervated by capillaries (adequate blood supply).

Question 3

What functions does the respiratory system have within the body? 6

Answer 3

• Provides (and ventilates) a specialised surface where gas exchange can take place between the atmosphere and blood.
• Contributes to acid-base balance (e.g. 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.

Question 4

How does oxygen get from the atmosphere to cells? 5

Answer 4

How does oxygen get from the atmosphere to cells?

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

Question 5

Ventilation 2

Answer 5

• Total level of ventilation = The total volume of air that is inspired over a given time period, per minute.
V = VT x f
• V: minute volume (mL), the total volume of air inhaled in all breaths over one minute.
• VT : tidal volume (mL), the volume of air inhaled in each breath.
• f = frequency (min-1), the number of breaths per minute

Question 6

Alveolar air ≠ Inspired air 4

Answer 6

• The lungs contain a mixture of ‘fresh’ & ‘stale’ air.
• Gas exchange only takes place in alveoli, but air must first pass through the airways (airways = “anatomic dead space”).
• The respiratory system is two-way system.
A residual volume of air remains in the airway & lungs at the end of expiration, the final ≈150mL (dead space volume) of each inspiration never reaches the alveoli or takes place in gas exchange.

Question 7

Alveolar ventilation (2)

Answer 7

• Alveolar ventilation corrects for the volume of inspired air which doesn’t take part in gas exchange (due to the dead space).
VA = (VT - VD) x f
• VA = alveolar minute volume (mL), the total volume of fresh air entering the alveoli across all breaths over one minute.
• VT = Tidal volume.
• 𝑉D = Dead space volume (mL), the volume of air remaining in the respiratory system at the end of expiration.
• VT - VD= The volume of fresh air entering the alveoli in each breath.
• f = frequency (min-1).

Question 8

How do gases behave? (4)

Answer 8

Move from high to low P.
If T is constant, no of gas molecules per unit of volume can be determined.
Pressure within a contaiend space can be changed by altering Volume.
Boyles law P proportional n/v. derived from ideal gas law.

Question 9

Partial pressure (2)

Answer 9

PP = Total pressure x Mole fraction

MF in air
N - 0.78
O - 0.21
CO2 - 0.03

Question 10

Partial pressures of gases dissolved in liquids

Answer 10

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.

Question 11

If the pressure of the surrounding gas phase is doubled, what will happen to the partial pressure of dissolved gas?

Answer 11

Double the pressure of surrounding gas = double the concentration of dissolved gas.