Physiology
Oral Rehydration Solution vs Plain Water
Plain water alone is the wrong replacement fluid during active GI losses — it can cause hyponatremia. Oral Rehydration Solution combining water, glucose, sodium, and potassium exploits sodium-glucose cotransporters in the gut and is one of the most lives-saved medical interventions of the 20th century.
Short-Chain Fatty Acids: What Gut Bacteria Make From Fibre
Acetate, propionate and butyrate, produced when colonic bacteria ferment fibre humans cannot digest. Butyrate feeds colonocytes directly and supports the gut barrier with anti-inflammatory effects via HDAC inhibition; propionate goes to the liver for gluconeogenesis; acetate enters circulation. All act on host receptors FFAR2/FFAR3, making them signalling molecules rather than just fuel. A shift in SCFA-producing taxa is a compositional finding, not a demonstrated benefit.
Vomiting and the Renal Potassium Cascade
Most potassium lost during repeated vomiting does not come from the vomit itself — it comes from the kidney dumping potassium over days as a side effect of metabolic alkalosis, volume depletion, and aldosterone activation. This is why simple oral potassium supplementation cannot fix the deficit.
The Carotid Body Measures Oxygen Tension, Not Oxygen Content
The body's principal low-oxygen sensor responds to the partial pressure of dissolved oxygen in plasma, not total oxygen carried. The two usually move together — which creates a blind spot for anything that reduces delivery while leaving PaO2 normal: carbon monoxide poisoning, anaemia, methaemoglobinaemia. That's why CO victims feel no air hunger while suffocating people fight desperately for air, and why pulse oximetry can read normal in severe poisoning.
Thermoneutral Zone: Why 'Nude TNZ 27-31°C' Sounds Impossibly Warm
The textbook {{thermoneutral zone}} assumes nude, at-rest, still-air conditions; clothing, metabolic heat, body fat, and habituation shift real-world comfort down 8-12°C.
Your Atoms Turn Over Constantly, By Evaporation Rather Than Tunnelling
Atoms leave the body continuously through insensible water loss, exhaled CO2, shed skin and gut lining, and metabolic protein turnover. The popular '98% of your atoms per year' figure is a loose illustration: turnover varies from days (gut epithelium) to a lifetime — carbon-14 dating shows cerebral cortex neurons and eye lens crystallins are largely as old as the person. Not tunnelling, and not the body's ~7,000–8,000 decays per second either, which are weak-force processes.