How does THCa interact with the human body?

The human body (and some animals) contains a unique set of receptors that are part of the Endocannabinoid System. This system was discovered relatively recently by Raphael Mechoulam. ECS has a critical role in maintaining the homeostasis of the human body, which affects our brain, immune and other systems. [Source] https://pmc.ncbi.nlm.nih.gov/articles/PMC7593926/

Unlike THC, THCA is a non-psychotropic cannabinoid. In other words, it does not produce the intoxicating effect that is commonly associated with cannabis and THC. 

This is a result of the size of the THCA molecule. This is a large molecule that does not bind to cannabinoid receptors in the endocannabinoid system. 

Current research suggests that THCA does not bind much to either CB1 or CB2 receptors, the two major cannabinoid receptors. 

This does not mean that THCA has no effects on your system, however. 

Recent research has suggested that marijuana extracts comprised primarily of THCA may have anti-inflammatory and neuroprotective properties for some people. It has also been suggested by some studies to reduce nausea and vomiting.