Final answer:
To extend the duration of local anesthesia, vasoconstrictors like epinephrine are added. These drugs decrease blood flow at the injection site, slowing the absorption of the anesthetic into the bloodstream and thus extending its effect.
Step-by-step explanation:
To make the effects of local anesthesia last longer, vasoconstrictors such as epinephrine are often added to the local anesthetic solution. These vasoconstrictors work by constricting blood vessels at the site of injection, which decreases blood flow and prevents the rapid absorption of the anesthetic into the bloodstream. This action prolongs the duration of the anesthesia by keeping the anesthetic agent concentrated at the nerve site for a longer period.
Local anesthetics like lidocaine and novocaine act as sodium channel blockers, preventing sodium ions from entering nerve cells and halting the transmission of pain signals. Injecting them to the site of a minor surgery or dental work provides numbness in a specific area. However, without the addition of vasoconstrictors, the body would quickly absorb these local anesthetics, leading to a shorter period of numbness.