Inspiration

Question 1

Initiation

Answer 1

neurally induced contraction of diaphragm and external intercostal muscles (phrenic nerves C3,4,5 and intercostal nerves) - diaphragm dome moves downward into abdomen, englarging the thorax. external intercostals move ribs upwards and outwards - increased thoracic size.

Question 2

what does contraction of inspiratory muscles cause?

Answer 2

an upset in purely elastic forces present between breaths
thoracic wall moves slightly away from lungs, making IP more subatmospheric - increases transpulmonary pressure (now greater than elastic recoil) -> expand lungs further

Question 3

how and when is equilibrium established across the lungs?

Answer 3

end of inspiration/expiration, no airflow.
more inflated lungs exert greater elastic recoil - increases transpulmonary pressure
transpulmonary pressure equal to elastic recoil

Question 4

alveolar pressure during inspiration

Answer 4

enlargement of lungs increases size of alveoli
pressure decreases to less than atmospheric
causes bulk flow
increased air flow equalises pressures, ceases airflow

Question 5

flow chart

Answer 5

diaphragm and inspiratory intercostals contract
thorax expands
IP becomes more subatmospheric
increased transpulmonary pressure
lungs expand
alveolar pressure becomes subatmospheric
air flows into alveoli

Question 6

end of expiration pressures

Answer 6

atmospheric pressure 0mmHg
no flow
alveolar pressure 0mmHg
transpulmonary pressure 4mmHg
intrapleural pressure -4mmHg

Question 7

mid inspiration pressures

Answer 7

atmospheric pressure 0mmHg
airflow in
alveolar pressure -1mmHg
transpulmonary pressure 5mmHg
intrapleural pressure -6mmHg

Question 8

end of inspiration/beginning of expiration pressures

Answer 8

atmospheric pressure 0mmHg
no flow
alveolar pressure 0mmHg
transpulmonary pressure 7mmHg
intrapleural pressure -7mmHg

Question 9

mid expiration pressures

Answer 9

atmospheric pressures 0mmHg
airflow out
alveolar pressure 1mmHg
transpulmonary pressure 6mmHg
intrapleural pressure -5mmHg

Question 10

expiration flowchart

Answer 10

diaphragm and inspiratory intercostals stop contracting
chest wall recoils inward
intrapleural pressure moves back towards preinspiration value
transpulmonary pressure moves back towards preinspiration value
lungs recoil towards preinspiration size
air in alveoli becomes compressed
alveolar pressure becomes greater than atmospheric pressure
air flows out of lungs

Question 11

what causes the lungs to passively recoil?

Answer 11

transpulmonary pressure is smaller than the elastic recoil, due to intrapulmonary immediately becoming less subatmospheric when the chest wall and lungs recoil.

Question 12

contraction of internal intercostal muscles

Answer 12

contraction pulls chest wall downward and inward - decreases thoracic volume

Question 13

contraction of abdominal muscles

Answer 13

increases intraabdominal pressure and forces relaxed diaphragm into thorax

Question 14

accessory muscles in inspiration

Answer 14

sternocleidomastoid - elevates sternum
scalenes - fix/elevate ribs 1-2
pectoralis minor - elevates ribs 3-5
internal intercosatals, intercartilaginous part - aid in elevating ribs

Question 15

muscles used in forced expiration

Answer 15

internal intercostals, interosseous part - depresses ribs 1-11, narrow thoracic cavity
diaphrapgm - ascends and reduces depth of thoracic cavity
rectus abdominis - depresses lower ribs, pushes diaphragm by compressing abdominal organs
external abdominal oblique - same as rectus abdominis