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03-18-2009, 10:00 AM
Anatomy and physiology
The upper respiratory tract includes the nose, nasopharynx and larynx. It is lined by vascular mucous membranes with ciliated epithelium on their surface.
The lower respiratory tract includes the trachea and bronchi. It is lined by ciliated epithelium.
The larynx and large bronchi are rich in sensory receptors involved in the cough reflex.
The alveoli are lined with flattened epithelial Cells (type I pneumocytes) and cuboidal type II pneumocytes.
(Type II pneumocytes) can divide and reconstitute (type I pneumocytes) after injury.
There are about 300 million alveoli in each lung, their total surface area is 40-80m2
Nerve supply to the lung:
The parasympathetic supply is from vagus and the sympathetic from the sympathetic Chain.
The parietal pleura is innervated from intercostal and phrenic nerves while the visceral pleura has no innervation.
Factors controlling breathing:
Discharges arising form respiratory center in brain stem motor discharges from respiratory center travel via the Phrenic and intercostal nerves to the respiratory musculature.
Neurogenic factors
Impulses from limb receptors as in exercise
Impulses form pulmonary receptors sensitive to stretch
Juxtapulmonary capillary receptors (J receptors).
Chemical stimuli
Central chemo receptors sensitive to Co2 and H+ ions in blood due to acidosis
Peripheral chemo-receptors sensitive to O2
In Pts with GOAD the sensitivity to Co2 lost so that in these pts hypoxia is the chief stimulus to respiratory drive, see later