Ventilation:

Question 1

Ventilation:

Answer 1

the volume of air that moves in or out of the lungs per minute.

Question 2

2 phases of pulmonary ventilation:

Answer 2

1. Inspiration – air flows into lungs

2. Expiration – flows out of lungs

Question 3

Ventilation governed by

Answer 3

Boyles Law

Question 4

Boyles Law:

Answer 4

As volume increases, pressure decreases, vice versa.

• The direction of airflow is determined by the relationship between atmospheric pressure and intrapulmonary/intra- alveolar pressure
• The diaphragm, ribs and muscles involved with respiration are important components of the this mechanism

Question 5

2 types of breathing:

Answer 5

1. Quiet (normal) - Governed by parasympathetic nervous system
2. Forced (deep) – under exercise or pathological conditions

Question 6

1. Quiet (normal) inspiration:

Answer 6

• Volume of thoracic cavity increases – driven by muscular action
  (Diaphragm and intercostals)
• Decreases internal gas pressure
• Causes air to flow into the lungs (through the airways) , into the
  lobes, to try and equalize the pressure

Diaphragm:
Contracts- Flattens – The muscle fibers shorten, causes it to move down and flatten – pulls the central tendon downwards -increases the superior- inferior dimensions of thoracic cavity
- Innervated by the phrenic nerve

External intercostal muscles:

• Contraction raises the ribs – increases the lateral dimensions and anterior – posterior dimensions of the thoracic cavity
• Innervated by intercostal nerves

Question 7

At the Start of a breath

Answer 7

pressures inside and outside the thoracic cavity are identical
- no movement of air

Question 8

Enlargement of thoracic cavity

Answer 8

• pleural cavities and lungs expand to fill the additional space.
• expansion lowers the pressure inside the lungs,
• air enters respiratory passageways - pressure inside the lungs is
  lower than atmospheric pressure.
• air continues to enter until the volume stops increasing and the
  internal pressure is the same as the outside.
• Inspiration stops

Question 9

2. Forced (deep) inspiration:

Answer 9

• Needs action of additional muscles
  >Scalene muscles
  >Sternocleidomastoid
  >Pectoralis minor

Question 10

1. Quiet expiration

Answer 10

• mainly a passive process
• Inspiratory muscles relax
  > Diaphragm relaxes and moves up (moves superiorly)
  > external intercostals relax – ribs move down
• Volume of thoracic cavity decreases
• Elastic recoil of lung to original shape
• Volume in the lungs decreases and pressure increases
  = Air moves out from the lungs, through the airways to the outside
  Moves down pressure gradient

Question 11

2. Forced expiration

Answer 11

-	An active process
Produced by contraction of: 
•	Internal intercostal muscles 
•	Internal and external oblique muscles 
•	Transversus abdominis muscle 
These increase intra-abdominal pressure inside abdominal cavity – forces diaphragm upwards – further decreases volume of thorax

Question 12

General expiration summary:

Answer 12

1. Inspiratory muscles relax- diaphragm rises, ribcage decends
   because of recoil of costal cartilage
2. Thoracic cavity and pleural cavity decreases in volume
3. Elastic lungs recoil passively, lung volume decreases
4. Air pressure in lungs rises
5. Air flows out of lungs
   Note: alveoli don’t collapse during expiration as surfactant decreases surface tension