M12: Respiratory System - Ventilation

Question 1

3 main steps to repsiration

Answer 1

1. PULMONARY VENTILATION
   - mechanical flow of air into and out of lungs
2. EXTERNAL RESPIRATION
   - exchange of gasses between air in lungs and blood in pulmonary capillaries
3. INTERNAL RESPIRATION
   - exchange of gasses between blood in systemic capillaries and tissue cells

Question 2

air moves into/out of the lungs when…

Answer 2

IN
- pressure inside lungs is less than atmospheric pressure
- diaphragm contracts + thorax expands to increase lung volume

OUT
- pressure inside lungs is more than atmospheric pressure
- diaphragm relaxes + thorax recoils to decrease lung volume

Question 3

Boyles law

Answer 3

pressure inversely proportional to volume

Question 4

structures that change dimensions of thoracic cavity

Answer 4

diaphragm
- contraction/relaxation change vertical dimesions
ribs
- movement changes lateral and anterior/posterior (via sternum) dimensions

Question 5

muscles involved in inhalation

Answer 5

• diaphragm (brings 75% of air)
• external intercostals (brings 25% of air)
• pec minor*
• scalenes*
• sternocleomastoid*
  *only involved during heavier breathing

Question 6

muscles involved in exhalation

Answer 6

normal expiration just means muscles relax

Forced expiration
- abdominals
- internal intercostals
- transvers thoracis

Question 7

quiet inspiration/expiration

Answer 7

regular breathing

Question 8

steps to quiet inspiration

Answer 8

• diaphragm moves a bit, ribs lifted by external intercostals
• intrathoracic pressure falls, ~500mL inhaled
• 75% air from diaphragm, 25% from external intercostals

Question 9

role of pleura during breathing

Answer 9

• keeps lungs from collapsing
  
  • pressure in pleural cavity less than atmospheric and intra-alveolar pressure

Question 10

typical volume of air inhaled at rest

Question 11

factors effecting ventilation

Answer 11

1. SURFACE TENSION OF ALVEOLAR FLUID
   - thin layer of alveolar fluid coats alveoli lumen
   - alveolar surface tension must be overcome to expand them, but they also help with elastic recoil
   - SURFACTANT reduces surface tension
2. COMPLIANCE OF THE LUNGS
   - effort required to stretch lungs and chest wall
   - 2 factors: elasticity + surface tension
3. AIRWAY RESISTANCE
   - bronchioles: smooth muscles change resistance
   - SNS (NE) relaxes smooth muscle in airway = less resistance
   - PNS (ACh) contracts smooth muscle = more resistance

Question 12

infant respiratory distress syndrome

Answer 12

• premature babies might not have mature type II pneumocytes
• no surfactant produced, so alveolar surface tension too high. Baby can’t inspire