Pulmonary ventilation

Question 1

Why do we need a respiratory system?

Answer 1

Cells require energy to function (O2 needed as terminal electron acceptor in ETC to produce ATP)

Aerobic respiration requires O2 and produces CO2.

Atmosphere provides a source of O2, and CO2 can be expelled.

Our bodies are too large to rely on simple diffusion of gases from the atmosphere to tissues.

Question 2

Give some Alveoli adaptations for maximum gas exchange.

Answer 2

Folded for large surface area

one cell layer thick wall + basement membrane fused with blood vessel

richly innervated by capillaries to ensure adequate blood supply

Question 3

Give some Functions of the respiratory system.

Answer 3

Gas exchange between atmosphere and blood

acid-base balance (pH of blood)

communication (vibration of vocal cords)

metabolism and production of specific mediators

pulmonary circulation filters particulate matter and emboli and prevents them from entering the systemic circulation

immunological defence

Question 4

Describe what Ventilation is.

Answer 4

Movement of fresh air from outside the body to the alveoli where gas exchange occurs, and the subsequent movement of alveolar gas back to the outside

Question 5

What is Total ventilation (minute volume)?

Answer 5

The amount of air breathed in during each respiration multiplied by the number of breaths per minute.

Question 6

What must inspired air go through before reaching alveoli?

Answer 6

Inspired air must first pass through the conducting airways which are:

• the nose
• mouth
• pharynx
• larynx
• trachea
• bronchi
• bronchioles

Question 7

What are the conducting airways responsible for?

Answer 7

They do not contain alveoli therefore they do not participate in gas exchange, however they participate in warming and humidifying inspired air.

Question 8

What does total ventilation equation not consider?

Answer 8

Doesn’t consider the warmed and humidified air remaining in the conducting airways known as the anatomic dead space (150 ml).

Question 9

What is the difference between Fresh and Stale air?

Answer 9

During inspiration, 500 ml (tidal volume) of fresh air is inspired, but only 350 ml reaches alveoli. Other 150 ml is fresh air in anatomic dead space.
-first 150 ml into alveoli is stale air from dead space

At the end of inspiration, anatomic dead space is filled with fresh air

The first 150 ml of an expiration will be the air previously occupying the dead space that has not taken part in gas exchange

At the end if expiration, the anatomic dead space and alveoli are filled with stale air.

Question 10

What is Alveolar ventilation (VA)?

Answer 10

The volume of fresh inspired air that reaches the alveoli for gas exchange

Question 11

Decribe the Behaviour of Gases.

Answer 11

Gases naturally move from an area of higher pressure to areas of lower pressure until an equilibrium is re-established

Question 12

What is Boyle’s Law?

Answer 12

A principle that describes the relationship between the pressure and volume of a gas at constant temperature

P = n/V

Question 13

What is the Partial pressure of a gas in a gas phase mixture?

Answer 13

The proportion of total pressure provided by an individual gas as part of a mixture of gases.

Partial Pressure= Total Pressure x Mole Fraction

Question 14

How is the partial pressure of humidified air calculated?

Answer 14

When air becomes humidified, the contribution of water vapour has to be considered when determining overall pressure. Before multiplying the total pressure by mole fraction, you have to subtract the contribution of water vapour.

Pgas= (Pbarometric - PH20) x mole fraction (n)

Question 15

What is the Partial pressure of a gas dissolved in a liquid?

Answer 15

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

E.g. if the pressure of the surrounding gas phase was double, the partial pressure of the dissolved gas in the liquid doubles (doubled concentration).

Question 16

What is needed to move air into and out of the lungs?

Answer 16

Pressure gradients caused by changes in alveolar pressure due to changes in lung volume

Question 17

How Pressure gradients needed for inspiration and expiration?

Answer 17

For inspiration, alveolar pressure must fall below atmospheric pressure

For expiration, alveolar pressure must rise above atmospheric pressure

Question 18

How are pressure gradients achieved?

Answer 18

By contraction and relaxation of respiratory muscles (e.g. diaphragm) which alters volume of thoracic cavity:

During inspiration the diaphragm contracts and the thoracic cavity increases, decreasing alveolar pressure

During expiration the diaphragm relaxes and lung recoils and the thoracic cavity decreases, increasing alveolar pressure

Question 19

What is the Pressure gradient at the end of expiration?

Answer 19

Pressure of alveoli is the same as atmospheric pressure therefore there is no movement of air.

Question 20

Describe the Pleural membranes and cavity.

Answer 20

Inner visceral pleura lines each lung

Outer parietal pleura lines the thoracic cavity surrounding the chest, diaphragm and mediastinum (which contains the heart)

Between the two pleura is the sealed, fluid-filled pleural cavity

Question 21

What is the Role of the pleural cavity?

Answer 21

Indirectly attaches the lungs and the chest wall and helps to:

• provide a frictionless surface
• aid in the movement of the lungs

Question 22

How is a negative pressure within the pleural cavity achieved?

Answer 22

Tissues attached to each pleura (lungs and chest wall) recoil in opposite directions.

The lungs recoil inwards and the chest wall recoils outwards, stretching the sealed pleural cavity between them, generating a negative pressure within the pleural cavity.

sealed cavity + increased volume= decreased pressure

Question 23

What does negative intrapleural pressure generate?

Answer 23

Generates a collapsing force pulling the two pleural membranes together during inspiration, and as a result, the lung and chest wall together

Question 24

What should happen in order For the lungs to expand during inspiration?

Answer 24

The collapsing force pulling the pleural membranes together has to become greater than the force generated by the elastic recoil of the lung, causing the visceral pleura to be pulled outwards

this increases lung volume, decreasing alveolar pressure (below atmospheric pressure) and air moves down pressure gradient into lungs, expanding the lungs

Question 25

What happens when level of negative intrapleural pressure increases

Answer 25

It will cause a collapsing force acting to pull the pleurae together during inspiration and pulling the lungs and chest wall together

Question 26

What does elastic recoil act to do?

Answer 26

Pull the visceral pleura inwards and compress the lung volume

Question 27

Why is lung volume decreased during expiration?

Answer 27

During expiration intrapleural pressure becomes more positive due to relaxation of inspiratory muscles providing an inward force on the parietal pleura, no longer generating sufficient collapsing force acting to overcome the elastic recoil of the lung, and so visceral pleura is pulled inward (along with pleural cavity and parietal pleura)

this decreases lung volume, alveolar pressure increases above atmospheric pressure, air moves down pressure gradient into atmosphere, deflating lungs

Question 28

What is Pneumothorax?

Answer 28

Air in the pleural cavity due to rupture in either of the pleural membranes

Question 29

What is the Effect of pneumothorax?

Answer 29

Entry of air causes an increase in intrapleural pressure (more positive) until it equals atmospheric pressure

loss of negative intrapleural pressure reduces the collapsing force pulling the pleurae together, allowing the lungs to collapse due to elastic recoil (elastic recoil not resisted due to no collapsing force)