Anatomy, Pathophysiology, and Public Health Foundations

1. Everything comes down to the cell

A cell needs two deliveries. Oxygen. And glucose. And it needs one pickup: carbon dioxide and waste. Perfusion is what moves all three.

When perfusion is adequate, the cell runs aerobic metabolism. When it is not, the cell switches to anaerobic metabolism. That switch is the entire story of shock.

	Aerobic metabolism	Anaerobic metabolism
Requires	Glucose and oxygen	Glucose, without oxygen
ATP yield	High	Low
Byproducts	Carbon dioxide and water	Lactic acid
Effect on the patient	None — this is normal	Acid builds up and degrades cell structure and function

So follow the failure all the way through. No perfusion means no oxygen and no glucose. No oxygen and no glucose means not enough ATP. Without ATP, the sodium/potassium pump shuts down. The pump shutting down means the cell membrane ruptures. And the cell dies.

That's why "shock" is not a blood pressure number. Shock is inadequate perfusion — cells forced into anaerobic metabolism. Every EMT intervention you have exists to stop that chain: airway, oxygen, ventilation, bleeding control, position, warmth, rapid transport. All of it is aimed at keeping cells aerobic.