intro to 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. The atmosphere provides a source of O2, and CO2 can be expelled.
3) Our bodies are too large to rely on simple diffusion of gases from the atmosphere to the tissues.

Question 2

What functions does the respiratory system have within the body?

Answer 2

• 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)
• its used for communication and metabolism
• pulmonary circulation filters particulate matter and emboli reducing systemic circulation exposure
• immunological defence

Question 3

How does oxygen get from the atmosphere to the cells?

Answer 3

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 4

Why is ventilation of gas exchange structures necessary?

Answer 4

Tissues continually demand O2 and produce CO2.
An adequate concentration gradient between the alveolar air and blood is required for efficient gas exchange (diffusion). Therefore, fresh air is required from the atmosphere to ensure that the alveolar oxygen pressure (PalvO2) is high and the alveolar CO2 pressure (PalvCO2) is low, relative to the blood.

Question 5

Alveoli have adaptations that maximize the rate if gas exchange. Name some of these.

Answer 5

1. Large surface area
   
   2. Wall is one cell layer thick (squamous) and basement membrane is fused with blood vessel to provide a short diffusion pathway for gaseous exchange
2. Richly innervated by capillaries (blood supply)

Question 6

What is the ideal gas law?

Answer 6

It is the equation of state of the hypothetical gas. It helps us model and predict the behaviors 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, V is volume, n is the number of moles, R is the gas constant and T is the temperature.

Question 7

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

Describe Boyle’s Law.

Answer 7

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 remains constant, increasing the volume will decrease the pressure.

Question 8

What is the mole fraction of nitrogen, oxygen and CO2 in the air?

Answer 8

Nitrogen: 0.78
Oxygen: 0.21
Carbon dioxide: 0.03
(water is variable)

Question 9

Air consists of a mixture of gases which behave in accordance with their partial pressure rather than concentration.
How can we calculate partial pressure?

Answer 9

Partial pressure can be calculated by multiplying the total pressure by the mole fraction.

P gas = (P barometric - P H2O) x n gas

P gas is the partial pressure of the individual constituent gas, P barometric is the atmospheric pressure, P H2O is the water vapor pressure and n gas is the mole fraction.

Question 10

What is the PO2 of dry air at the summit of mount Everest (8844m) if Pbarometric= 34kPa?

Answer 10

34kPa x 0.21 (n of oxygen) = 7.14 (PO2)

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

Question 12

What can be used to calculate ventilation?

Answer 12

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 or air inhaled in each breath
F: frequency (min-1) the number of breaths per minute

Question 13

Alveolar ventilation corrects the volume of inspired air which doesn’t take part in gas exchange (due to the dead space). State an equational expression of this adaptation.

Answer 13

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 (mL)
VD: dead space volume (mL) the volume of air remaining in the respiratory system at the end of expiration
F: frequency (min-1)

Question 14

The total inspired air is NOT EQUAL to the total alveolar air. Explain why.

Answer 14

• The lungs contain a mixture of fresh and stale air
• At the end of expiration, the dead space and alveoli are filled with stale air
• During inspiration:
- Dead space is filled with fresh air
- Only a fraction of fresh air reaches alveoli
- The first fraction of air into the alveoli is stale air from dead space, THEN fresh air
· At the end of inspiration the dead space is filled with fresh air
The first fraction of expired air will be the air previously occupying the dead space that has not taken part in gas exchange