In cell injury, Mitochondria damage starts, when the oxygen level gets low. First, it’s a reversible process but in the chronic condition, it gets irreversible. When oxygen level gets down due to any condition like ischemia, inflammation, or any type of wound. The oxidative phosphorization process gets decreases.  Due to that less ATP synthesize. So, the Na/K pump gets reverse. Due to which a huge amount of water enters the Mitochondria. And Mitrochondia gets swell. We called this Cloudy/ Hydropic Swelling. 

This Cell swelling is the earliest sign of cell injury. After some time apoptosis happened. A small amount of calcium gets deposited in Mitrochondia at this time its reversible cell injury. After some time calcium deposits get increase then its Irreversible injury.

In short, Mitrochondia gets swell and calcium deposits increase.