Could two humans have some differences in their dna sequences for insulin, yet still make the exact same insulin proteins? give a brief explanation.

DNA is copied and these copies are single stranded and called mRNA. mRNA gets translated and the information these mRNA-molecules have gathered from the DNA, triggers specific amino acids to bind and form proteins. 
One amino acid is coded from three bases on the RNA. So for example: ATG codes for one amino acid, and CGA codes for another. 
In many cases, different sequences can code for the same amino acid. For example: ATG and ATC results in the same amino acid.

That means that a difference in base sequence in the DNA can still result in the same protein being made. 

The Circulatory System

Explanation:

The circulatory system carries oxygen, nutrients , circulation carries blood from the heart to all the other parts of the body and back again, through the veins and arteries.

hope i helped