Understanding cardiac physiology 006 – the pulmonary interstitium.


The function unit of the lung : the Alveolar-Capillary unit.

A “functional unit”¬† is the basic unit that still represents the function

of the full organ system.

In other words, the lungs will oxygenate and ventilate the patient.

And the alveolar-capillary unit will also oxygenate and ventilated the patient.


pictured above : oxygen enters the alveolus


next, the unoxygenated blood is flowing by in the capillary.


the oxygen enters the capillary and starts oxygenating the blood.


oxygen is now entering “full blast” into the blood vessel and oxygenating all the

hemoglobin molecules.

oxygen is also entering the tissue around the alveolus and capillary (known as

the pulmonary interstitium).


oxygenation is occurring at “full blast” into the hemoglobin of the blood vessel

as well as the pulmonary interstitium tissue.


If the alveolus stopped receiving oxygen, oxygenation stops abruptly.


oxygenation stops in the blood vessels.

oxygenation stops in the pulmonary interstitium.


The pulmonary capillary “notices” that there is no more oxygen around that area.


The pulmonary interstitium starts to vasoconstrict  >> this is the phenomenon of

hypoxic pulmonary vasoconstriction (HPV).


The pulmonary vasoconstriction (HPV) now starts the misadventures

of cardiopulmonary demise : RV overdistention and concomitant

LV underfilling with resultant systemic hypotension.






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