Question

1. explain the effects of pneumococcal pneumonia on the respiratory tract. You should mention specific cell types and specific respiratory structures

Answer 1

Pneumococcal pneumonia

More than 90% of all lobar pneumonias are caused by Streptococcus pneumoniae, a lancet-shaped diplococcus. Out of various types, type 3 S. pneumoniae causes particularly virulent form of lobar pneumonia. Pneumococcal pneumonia in majority of cases is community-acquired infection.

MORPHOLOGIC FEATURES

Laennec’s original descrip- tion divides lobar pneumonia into 4 sequential pathologic phases: stage of congestion (initial phase), red hepatisation (early consolidation), grey hepatisation (late consolidation) and resolution. However, these classic stages seen in untreated cases are found much less often nowadays due to early institution of antibiotic therapy and improved medical care.
In lobar pneumonia, as the name suggests, part of a lobe, a whole lobe, or two lobes are involved, sometimes bilaterally. The lower lobes are affected most commonly. The sequence of pathologic changes described below represents the inflammatory response of lungs in bacterial infection.
1 STAGE OF CONGESTION: INITIAL PHASE The initial phase represents the early acute inflammatory response to bacterial infection that lasts for 1 to 2 days. Grossly, the affected lobe is enlarged, heavy, dark red and congested. Cut surface exudes blood-stained frothy fluid. Histologically, typical features of acute inflammatory response to the organisms are seen. These are as under
i) Dilatationandcongestionofthecapillariesinthealveolar walls.
ii) Paleeosinophilicoedemafluidintheairspaces.
iii) A few red cells and neutrophils in the intra-alveolar fluid.
iv) Numerous bacteria demonstrated in the alveolar fluid by Gram’s staining.
2. RED HEPATISATION: EARLY CONSOLIDATION
This phase lasts for 2 to 4 days. The term hepatisation in pneumonia refers to liver-like consistency of the affected lobe on cut section.
Grossly, the affected lobe is red, firm and consolidated. The cut surface of the involved lobe is airless, red-pink, dry, granular and has liver-like consistency. The stage of red hepatisation is accompanied by serofibrinous pleurisy. Histologically, the following features are observed
i) The oedema fluid of the preceding stage is replaced by strands of fibrin.
ii) There is marked cellular exudate of neutrophils and extravasation of red cells.
iii) Manyneutrophilsshowingestedbacteria.
iv) The alveolar septa are less prominent than in the first stage due to cellular exudation.
3. GREY HEPATISATION: LATE CONSOLIDATION
This phase lasts for 4 to 8 days.
Grossly, the affected lobe is firm and heavy. The cut surface is dry, granular and grey in appearance with liver-like consistency . The change in colour from red to
grey begins at the hilum and spreads towards the periphery. Fibrinous pleurisy is prominent.
Histologically, the following changes are present
i) Thefibrinstrandsaredenseandmorenumerous.
ii) The cellular exudate of neutrophils is reduced due to disintegration of many inflammatory cells as evidenced by their pyknotic nuclei. The red cells are also fewer. The macrophages begin to appear in the exudate.
iii) The cellular exudate is often separated from the septal walls by a thin clear space.
iv) The organisms are less numerous and appear as degenerated forms.
4. RESOLUTION This stage begins by 8th to 9th day if no chemotherapy is administered and is com- pleted in 1 to 3 weeks. However, antibiotic therapy induces resolution on about 3rd day. Resolution proceeds in a pro- gressive manner.
Grossly, the previously solid fibrinous constituent is liquefied by enzymatic action, eventually restoring the
normal aeration in the affected lobe. The process of softening begins centrally and spreads to the periphery. The cut surface is grey-red or dirty brown and frothy, yellow, creamy fluid can be expressed on pressing. The pleural reaction may also show resolution but may undergo organisation leading to fibrous obliteration of pleural cavity.
Histologically, the following features are noted:
i) Macrophages are the predominant cells in the alveolar spaces, while neutrophils diminish in number. Many of the macrophages contain engulfed neutrophils and debris.
ii) Granular and fragmented strands of fibrin in the alveolar spaces are seen due to progressive enzymatic digestion.
iii) Alveolarcapillariesareengorged.   
iv) There is progressive removal of fluid content as well as cellular exudate from the air spaces, partly by expectoration but mainly by lymphatics, resulting in restoration of normal lung parenchyma with aeration.