In the given detailed video, the pathology of Hypersensitivity pneumonitis is explained. The video also talks about sarcoidosis, farmer's lung and Byssinosis. TIMELINE: 0:00 Introduction 2:58 What is Hypersensitivity Pneumonitis? 4:10 Pathogenesis 5:14 Examples 5:50 Important subtypes 7:04 Clinical features 8:12 Complications 8:39 Diagnosis 10:43 Treatment 11:32 Clinical pearls 11:48 Exam question 12:41 Byssinosis 14:30 Silo filler’s lung 14:57 Sarcoidosis 15:12 Farmer’s lung 15:57 Treatment