How do drugs work when taken orally and snorted? And how do they differ in action?

I wanted to know how drugs work inside our body and specially about snorting.I read about it on the internet.It says snorting puts the drugs directly into our blood stream.How does it go into bloodstream?

• When orally taken the drug is absorbed slowly over a long range of time,the drug goes through the whole digestion process and gets absorbed in the bloodstream from the intestines?

• But when taken by snorting it,the whole drug goes at once in the bloodstream,will act intensively but for short duration? The drug goes from nasal passage into the lungs,from lungs it gets absorbed into bloodstream and then to heart and then to all organs of the body?

• Is this the only difference between action of drugs when taken orally and when snorted? Add more as much as you know and please give analogies so I can understand better and make someone understand in lame language the difference in their action.

• When taken orally the drug amount in bloodstream remains normal/optimum/safe always or it gradually rises and reaches the level that would in case of snorting? Please clear this thing to me,if possible with some analogy or in lame language too.

• The drugs might be made in away that when it gets metabolized,it releases the main chemical compound; so what happens when it is snorted? How does it get metabolized?

• If only those drugs that need not be metabolized to release the main chemical compound are snorted, then why are potentially abused drug not made such that they need to be metabolized and don’t work when snorted?

• And I also read somewhere that when snorted,the drugs directly go to the brain,what does this mean? When taken either way,the drug enters bloodstream and will go to brain similarly in both cases,no? And only the quantity of drug carried to the brain will be more in case of snorting?

• If the drugs taken orally are absorbed slowly with time as opposed to snorting,then what is sustained release (SR) and immediate release (IR)? Is extended release (XR) different from SR?

• Can SR or XR be snorted?

• Considering the rate of absorption/action of drug; Snorting > immediate release > sustained release ,right? What else can be added here?

• What are other ways that puts the drug fast into the bloodstream? I read somewhere injecting stuff rectally,means that will get absorbed from the intestinal walls into the bloodstream,right? And so it will be safer than snorting because nasal tissue and lungs are safe from this? But the large intestine is supposed to absorb water only,no? Or will it also absorb the drugs? And it also does selective absorption,so it may not absorb the extra things in the drug other than the main chemical?

I am not doing any of these,except I take drugs orally and use my nasal passage for air only,I am just curious to know how this works :)