Kinesiology 132 Systems Physiology II Respiratory System PDF

Kinesiology 132 Systems Physiology II Respiratory System – RS1 Today’s topics: Respiratory System – overview Ventilation General principles Boyle’s Law Pressures Inspiration and expiration Respiratory (RS) System – overview Focus of course:...

Kinesiology 132 Systems Physiology II Respiratory System – RS1 Today’s topics: Respiratory System – overview Ventilation General principles Boyle’s Law Pressures Inspiration and expiration Respiratory (RS) System – overview Focus of course: Ventilation: Air exchange between atmosphere and alveoli. Gas exchange: External respiration: gas exchange between alveoli and pulmonary capillaries. Internal respiration: gas exchange between tissue capillaries and interstitial fluid/tissue cells. Gas transport: Gas movement by pulmonary and systemic circulations between gas exchange locations. Ventilation – general principles At sea level atmospheric pressure varies; typically ~760 mmHg. Often report pressure changes as a relative change from atmospheric: 756 mmHg 758 mmHg 760 mmHg 762 mmHg 764 mmHg -4 -2 0 +2 +4 Ventilation driven by air pressure gradient: high to low pressure Breath in – inspiration: atmosphere (high pressure) to alveoli (low pressure). Breath out – expiration: alveoli (high pressure) to atmosphere (low pressure). Between breaths – pressures equalize between alveoli and atmosphere; no pressure gradient so no air movement for a moment. To get pressure gradient for ventilation: Need to manipulate pressure at alveolar level to get pressure gradients no matter what atmospheric pressure is doing. Ventilation – Boyle’s Law In a closed system at constant temperature, pressure (P) and volume (V) are 1 inversely related (P ∝ ). V Increase volume – decrease pressure. Decrease volume – increase pressure. Change volume – change pressure – create pressure gradient – produce ventilation. Boyle’s Law in action – interesting – but not testable Diving underwater into a hyperbaric (increased pressure) environment. Boyle’s Law at play in both directions: Descending: Pressure is increasing – volume decreasing. “Equalize” pressure – avoid pressure compression limits of some tissues. Ascending: Pressure is decreasing – volume is increasing. Expiration – avoid expansion limits of some tissues. Ventilation – 3 pressures Atmospheric Pressure (Patm ): Also known as air pressure or barometric pressure. Surrounding environment. Alveolar Pressure (Palv ): Within alveoli. Intrapleural Pressure (Pip ): Within intrapleural space between visceral and parietal pleura. Ventilation – intrapleural pressure Variable but always subatmospheric (lower than Patm ). Creates a pressure gradient: Between alveolar and intrapleural: outward pressure – opposes lung elastic recoil (without this pressure gradient – lung collapses). Between atmospheric and intrapleural: inward pressure – opposes chest wall elastic recoil (without this pressure gradient – chest wall springs out). Pressures working together link lung and chest wall together so move as a unit. Atmospheric (Patm ) / Alveolar (Palv ) / Intrapleural (Pip ).  Ventilation – inspiration Diaphragm/external intercostals contraction Eupnea: 75% Diaphragm Contraction – downward flattening (~ 2cm). Thoracic cavity volume increases 25% External intercostals Contraction – outward and upward movement of chest wall. Lung volume increases Palv becomes subatmospheric Air flows into lungs Eupnea: quiet, resting, unlaboured breathing Ventilation – inspiration More forceful breathing: Diaphragm Contraction – stronger; more downward flattening (up to 10 cm). External intercostals Contraction – stronger; more outward and upward movement of chest wall. Accessory muscles of inspiration recruited (scalenes, sternocleidomastoid, pectoralis minor). Contraction – more outward and upward movement of chest wall. Result Greater increase in lung volume. Palv decreases below atmospheric to greater extent (larger pressure gradient). Even more air flows into lungs.  Ventilation – expiration Diaphragm/external intercostals stop contraction Eupnea: Recoil to pre-inspiration positions. Recoil – thoracic cavity volume decreases Diaphragm Contraction ends – recoil back to dome shape. Lung volume decreases returning to pre- inspiration size (compresses alveoli) External intercostals Contraction ends – inward and downward recoil of chest wall. Palv becomes greater than Patm Air flows out of lungs Eupnea: quiet, resting, unlaboured breathing Ventilation – expiration More forceful breathing: Diaphragm Contraction ends – recoil back to dome shape. External intercostals Contraction ends – inward and downward recoil of chest wall. Accessory muscles of expiration recruited (internal intercostals, abdominals). Contraction – more inward and downward movement of chest wall. Result Greater decrease in lung volume; more compression of alveoli. Palv increases beyond atmospheric to greater extent (larger pressure gradient). Even more air flows out of lungs.