physiology of the respiratory system. pulmonary ventilation breathing, 2 phases inspiration: air...
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Pulmonary Ventilation Breathing, 2 phases
Inspiration: air moves into the lungs Expiration: air moves out of the lungs
Gas moves down a pressure gradient Air in the atmosphere exerts pressure
of 760 mm Hg
Inspiration Diaphragm contracts, it flattens,
which makes thoracic cavity longer
Intercostals muscles contract, elevated sternum & ribs, which enlarges thoracic cavity
Lungs pulled out because of cohesion of the pleura
Air pressure in alveoli & tubes decrease & air moves into lungs
Expiration
Inspiratory muscles relax, decreasing size of thorax
Alveolar pressure increases thus positive pressure gradient from alveoli to atmosphere & expiration occurs
Pulmonary Volumes Tidal volume= volume of air exhaled after a
typical inspiration; normal TV=500 ml Expiratory reserve volume= largest additional
volume that can be forcibly expired after expiring tidal air; normal ERV=1000-1200 ml
Inspiratory reserve volume= amount of air that can be forcibly inspired over and above normal inspiration; normal IRV=3300 ml Residual volume= air that can not be forcibly
expired but is trapped in alveoli, RV=1200 ml
Vital capacity
Largest volume of air that an individual can move in and out of the lungs
VC=IRV=TV=ERV
Alveolar Ventilation Volume of inspired air
that actually reaches the alveoli
Part of air inspired fills our air passageways, this is the anatomical dead space
Anatomical dead space is approximately 30% of TV, thus alveolar ventilation is 70 % of TV
Pulmonary Gas Exchange
A gas diffuse “down” its pressure gradient
Concentration of O2 in air is about 21% thus the partial pressure of O2 is about 160 mmHg 21% x 760 mm Hg = 160 mm
Hg
Amount of Oxygen that diffuses into blood
depends on: Oxygen pressure gradient Total functional surface area of
alveolus Respiratory minute volume Alveolar ventilation
Hemoglobin 4 polypeptide chains
(2 alpha & 2 beta) each with an iron containing heme molecule
Oxygen can bind to iron in heme group
CO2 can bind to amino acids in chain
Transport of Oxygen Oxygen travels in two
forms in blood: Dissolved in plasma Associated with
hemoglobin as oxyhemoglobin (most)
Increasing PO2 in blood accelerates hemoglobin association with O2
Transport of Carbon Dioxide Dissolved carbon dioxide
(10%) Bound to amine (NH2)
groups of amino acids to form carbaminohemoglobin (20%)
In the form of bicarbonate ions (more than 2/3) CO2 + H20 H2CO3
H + HCO3
Catalyzed by carbonic anhydrase
Carbon Dioxide and pH
Increasing carbon dioxide content of blood increases H ion concentration thus increases the acidity and decrease the pH
Respiratory Control Centers Main integrators that control
nerves that affect inspiratory & expiratory muscles are located in brainstem Medullary rhythmicity center
generates basic rhythm of respiratory cycle
Can be altered by input inputs from: Apneustic center in pons
stimulates to increase length and depth of respiration
Pneumotaxic center in pons inhibits apneustic center to prevent overinflation of the lungs
Factors that influence breathing PCO2 acts on chemoreceptors in medulla:
Increasing PCO2 increases RR
Decreasing PCO2 decreases RR
Decrease in blood pH stimulates chemoreceptors in carotid & aortic bodies
Arterial blood PO2 has little influence if it stays above a certain level Decrease in PO2 below 70 mmHg increases RR
Arterial blood pressure & breathing Sudden rise in blood pressure results in
reflex slowing of respirations
Miscellaneous factors
Sudden painful stimulations produces reflex apnea (no respirations) but continued painful stimulus cause faster & deeper respirations
Sudden cold stimuli on skin causes reflex apnea
Stimulation of pharynx or larynx by irritating chemicals or touch causes temporary apnea-choking reflex