# Disease

**Cellular Adaptations to Stress**

Hypertrophy → increased size, cell and organ

Hyperplasia → increased number of cells

Atrophy → decreased size, cell and organ

Metaplasia → change in phenotype of differentiated cells, often in response to chronic irritation where the alteration makes the cell better withstand the stress

**Mechanisms of Cell Injury**

* ATP depletion
* Mitochondrial damage
* Influx of calcium
* Accumulation of reactive oxygen species
* Increased permeability of cellular memberanes
* Accumulation of damaged DNA and misfolded proteins

PD-1 → [Programmed Death receptor](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5807740/)