The Importance of Receptors
In order for a substance to have an effect on you, your body must have receptors for the substance to bind to. For example, people with Congenital Insensitivity to Pain (CIP) have a mutated protein in their pain receptor neurons.  As such, these neurons cannot receive the message of pain and the person cannot feel pain. Therefore, since you feel the effects of the CBD hemp oil that you ingest, this must mean that there are natural receptors for it. In fact, your body actually creates its own cannabinoids, as do many other plants that we ingest on a regular basis, like Echinacea, broccoli, ginseng, and carrots.
Components of the ECS
The Endocannabinoid System (ECS) was discovered after the discovery of cannabinoids in the cannabis plant. This is why scientists named the ECS after the cannabis plant. This system is made up of receptors, ligands (things that bind to receptors), and enzymes (that modify the ligands). 
- Receptors: CB1, CB2
- Ligands: endocannabinoids
- Enzymes: things that breakdown or create more endocannabinoids
Role of Receptor and Ligands
The receptors, CB1 and CB2, are found throughout the body of almost all organisms, except insects. Even simple organisms like the hydra (which is basically a giant stomach with tentacles and a nerve net) have an endocannabinoid system.  In humans, CB1 is found in the central and peripheral nervous system, while CB2 is mostly found on immune system cells. 
CB1 is found in parts of the brain that are responsible for memory, mood, movement, and pain. While only THC has a direct effect on these areas, CBD is able to indirectly affect them. One interesting (and reassuring) fact is that there are very few CB1 receptors found in the brain stem. This means that basic functions like breathing and heart rate are not affected by cannabinoids, THC or CBD. 
CB2 receptors are found on microglial cells and immune system cells. Since the brain is an immune-privileged site, normal immune system cells cannot cross the blood-brain barrier and enter the brain.  Therefore, it’s up to the microglial to keep things in order upstairs. These cells clean up the debris left by neurons that have gone through apoptosis (programmed cell death) and also help with pruning synapses as the brain develops. 
What all this means is that hemp extracts can affect your body through two pathways, either via the nervous system or via the immune system. It might even affect other organs and systems, but this is still an area of research that is being investigated. 
CBD in the Blood
It’s difficult to do CBD research on live animals and humans. The reason for this is that CBD doesn’t show up easily in a blood test. This is likely due to the fact that these are fat-loving (hydrophobic) molecules and humans contain a lot of water, making absorption more difficult. [9, 10] In order to test the effects of CBD, scientists need to be able to measure how much of it is circulating around the body.
A Somewhat Hazy Conclusion
The role of the ECS is complex and widespread throughout organisms and body systems. Since CBD is able to interact, directly or indirectly, with the human endocannabinoid system, this hemp extract oil does indeed exert some effect on us. What these effects are, however, are still being investigated.
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