12. The Walls: Epithelial Barriers And How Infection Begins

Every pathogen must first get past the epithelium. This episode covers the walls of the body (skin, airways, gut, urogenital tract): their shapes and tight junctions, the mucus and cilia that sweep microbes out, why cystic fibrosis leads to lung infection, the microbiota as part of the barrier, and how an infection actually begins, stage by stage. Episode 12 of Primer on Immunology: In this episode • Every surface facing the outside world is epithelium, and none is a perfect barrier • Stratified, simple columnar and pseudostratified epithelium; tight junctions • Three kinds of defence: mechanical, chemical, microbiological • Mucus, mucins and the mucociliary escalator • Cystic fibrosis: CFTR, thick mucus, bacteria colonising the surface • Peristalsis, and the colon's two mucus layers • The microbiota: lactic acid, bacteriocins, short-chain fatty acids • Antibiotics and the empty space; when commensals cause disease • Breach vs adherence: how an infection begins • The four stages of an infection through a wound in the skin, and the defences at each • Routes in: airways, gut (typhoid, cholera), skin, direct contact • Why infectious disease is infrequent • Athlete's foot vs tetanus; inflammation and clotting downstream • The hand-over to adaptive immunity and memory Chapters 0:00 Welcome 0:16 Every surface is epithelium 0:47 Three shapes of epithelium 1:12 Three kinds of defence 1:26 Mucus and the mucociliary escalator 1:56 Cystic fibrosis 2:26 Peristalsis 2:38 Two layers of mucus, and the microbiota 3:39 Antibiotics and the empty space 3:55 How an infection begins 4:34 Four stages of an infection 5:33 Disease and the ways in 6:08 Most infections pass undetected 6:25 Local or devastating 6:51 Inflammation, clotting and the adaptive hand-over 7:27 Next: the chemical weapons, and links Next: the chemical weapons epithelial cells make — enzymes and peptides that kill microbes on contact. Everything we make is at rheumatologydigest.org WhatsApp channel (new material first): https://whatsapp.com/channel/0029Vb6P... Icons from Noun Project (CC BY 3.0): Human by Peleg Red; Foot by pojok_icon. For educational purposes only. Rheumatology Digest is made for students and clinicians; it is not medical advice. #immunology #innateimmunity #microbiome