Topic 10 - Ventilation

Question 1

What is ventilation?

Answer 1

The movement of air into & out of lungs (breathing)

Question 2

What is the flow air in relation to pressure?

Answer 2

Molecules will move from high to low pressure

Question 3

What is the equation in relation to ventilation?

Answer 3

F (is directly proportional to) = ∆P/R

This means the greater the pressure diff., the faster the movement

Question 4

What are the 4 pressures to remember?

Answer 4

1. Atmospheric (P.ATM) = rel. constant as its air around you
2. Intraalveolar (P.A) = pressure in alveoli - it does change depending on stage of respiratory cycle
3. Intrapleural (P.PL) = pressure in pleural fluid, spec. intrapleural space. NOTE: usually neg. in respect to P.ATM & P.A
4. Transpulmonary (P.TP) = Not actual pressure, its value indicating pressure gradient -> P.TP = P.A - P.PL NOTE: It’s normally pos. value b/c P.PL norm neg.

Question 5

What occurs at rest (pressure)?

Answer 5

No air flow b/c no pressure difference -> P.A = P.ATM

Question 6

What occurs during inspiration (pressure)?

Answer 6

NEGATIVE PRESSURE DIFFERENCE -> P.A < P.ATM

Question 7

What are the order of events for inspiration? (7)

Answer 7

NEGATIVE PRESSURE DIFFERENCE:
1. Inspiratory muscles contract
2. Pleural fluid > vol. to occupy (P.PL less thus more neg.)
3. Pressure diff. b/w P.A & P.PL greater (thus P.TP greater)
4. Lung drawn out into area low pressure (lung inflates = alveoli enlarge)
5. Air in alveoli greater vol. occupy (P.A decrease)
6. Now, P.A < P.ATM
7. Air flows into lungs through tubes of conducting zone

Question 8

What are the order of events for expiration?

Answer 8

POSTIVIE PRESSURE DIFFERENCE:
1. Inspiratory muscles relax
2. Pleural fluid less vol. occupy (P.PL more thus less neg.)
3. P.TP decrease as less diff. b/w P.PL & P.A
4. The lungs deflate/recoil
5. Air in alveoli smaller vol. occupy (P.A increase)
6. Now, P.A > P.ATM
7. Air flows out of lungs

Question 9

What sort of neuronal activity is there for control of ventilation?

Answer 9

• Somatic motor neurons (phrenic nerve)
• Automaticity in that it’s usually controlled & reg. subconsciously

Question 10

What controls ventilation (3)?

Answer 10

Medulla oblongata (in brain stem) = signif. automatic regulator, 2 parts:
- Have neurons in DRG (dorsal respiratory group) which can gen. own AP’s. It stim. phrenic nerve, diaphragm contract -> inspiration
- VRG (ventral respiratory group) has expiratory & inspiratory actions. Usually active during more forceful contractions/relaxations.

Brain stem above medulla oblongata = pons region:
- Modulates medulla oblongata activity/ infl. DRG &/or VRG. Helps control pattern of breathing & coord. reflexes.
- 2 parts of it: pneumotaxic area (DRG control - switch off = inhibitory action on inspiration) & apneustic area (prevent switch off = excitatory action on inspiration)

Cerebral cortex:
- infl. above in spinal cord thus explain voluntary control over breathing
*Note: Ondine’s curse is where consciously breathe until asleep b/c damage to automatic control of breathing

Question 11

What do chemoreceptors do in relation to control of ventilation?

Answer 11

They detect changes in O2 & CO2 (via pH) & adjust respiratory rate/depth accordingly