BIOL 2420 Lecture Notes - Lecture 4: Functional Residual Capacity, External Intercostal Muscles, Lung Volumes

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Unit 5 Lecture 4
Lung Capacities
- Capacity: the sum of two or more lung volumes
o Vital capacity (VC): sum of the inspiratory reserve volume, expiratory reserve volume,
and tidal volume
Represents the maximum amount of air that can be voluntarily moved into or
out of the respiratory system with one breath
Decreases with age as muscles weaken and the lungs become less elastic
To measure VC
Asked to take in as much air as possible, then blow out as fast as
possible
Forced VC test allows the clinician to measure how fast air leaves the
airways in the first second of expiration
o FEV1 (forced expiratory volume in 1 second)
decreases in certain lung diseases
asthma
decreases with age
VC plus the residual volume = total lung capacity (TLC)
o Inspiratory capacity = tidal volume + inspiratory reserve volume
o Functional residual capacity = expiratory reserve volume + residual volume
During Ventilation, Air Flows Because of Pressure Gradients
- Breathing requires muscle contraction and is an active process
o Air flows into the lungs because of pressure gradients created by a pump
muscles of the thoracic cage and diaphragm function as the pump because most
lung tissue is thin exchange epithelium
when muscles contract, the lungs expand, held to the inside of the chest wall by
the pleural fluid
- primary muscles involved in quiet breathing (breathing at rest) are
o diaphragm
o external intercostals
o scalenes
- during forced breathing, other muscles of the chest and abdomen may be recruited to assist
o examples: exercise, playing a wind instrument, blowing up a balloon
- air flow in the respiratory tract obeys the same rule as blood flow
Flow ∆P/R
1. air flows in response to a pressure gradient ∆P
2. flow decreases as the resistance ® of the system to flow increases
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