Effects of influenza on the respiratory system
Left: Acute hemorrhagic and ulcerative laryngotracheitis
Right: Right lung - showing consolidation, grey hepatization (lower lobe), and congestive edema (upper lobe). There is a large hemorrhage in the center of the hepatized lobe.
Happy Flu Season!
I’ve said it before, and I’ll say it again - even if the flu is just a few days of misery for you, it’s often far more serious than you might think for many others out there. It’s worth making sure you get the vaccine every year so you don’t spread infection, and, if you do get infected, stay the hell at home.
Hepatization is the conversion of a tissue or organ to a “liver-like” substance. In the lungs, this occurs when they become engorged with effused matter, such as red blood cells, neutrophils, and fibrin, which clog up the alveoli to the point that the lungs are impervious to air, where this has occurred. Grey hepatization is the second stage in lung hepatization - at this point, the red blood cells have broken down, leaving only the fibrinogen exudate and dead tissue behind.
Laryngotracheitis is an inflammatory response in the larynx and trachea. The trachea is lined with the same epithelial cells as much of the bronchial tree, and all influenza strains are able to infect those cells. This is why, whether you have a “light” case of the flu or a deathly-serious case, coughing and throat pain still occur. When the infection is bad enough, the coughing can lead to ulceration of the tissue below the epithelium, which can lead to bleeding into the lungs, or coughing up blood.
In cases involving “consolidation”, there is generally an opportunistic pneumonia taking hold. The bacterial exotoxins and sometimes the patient’s own immune system, break down epithelial cells that separate and define the alveolar sacs. The surface area given by these epithelial layers is what allows a high volume of oxygen to be absorbed with each breath we take. When those cell layers are destroyed, the oxygenation of blood is severely decreased.
Pathology of Influenza. Charles Winternitz, Isabel Wason, and Frank McNamara, 1920.