Explain why nerves are not diffusely numbed or affected throughout the epidural space during an Epidural Steroid Injection.
An epidural steroid injection is administered to provide pain relief for a patient with inflamed, pinched nerves. The injection consists of a mixture of lidocaine, and steroids. The steroids reduce the inflammation of the nerve, while lidocaine provides local numbing. However, since the epidural space is continuous up and down the spine, the injected medicine WILL flow throughout the space and hit nerves both above and below the level injected. Why doesn't this matter? Well, the lidocaine is short-acting, (a couple of hours max) so even it other nerves are affected, the anesthetic effect will wear off with no long term consequences. The steroid, on the other hand, will only reduce inflammation in the nerves that are inflammed in the first place. Any normal, healthy nerves will not be affected by the steroids.
Explain the Starling Equation as it relates to the flow of blood in the blood vessels of your body.
Starling's equation is essentially a way to measure the NET movement of fluid through your capillaries. This movement will depend on the pressure created by proteins, blood and other components of the blood INSIDE the vessels, as well as the interstitial fluid and its components OUTSIDE the vessel. Starlings equations is: FLOW = (hydrostatic pressure)- (oncotic pressure) in other words: FLOW= (Pressure of blood inside the vessel- the pressure of interstitial fluid) + (pressure of proteins in interstitial space attracting fluid- proteins in blood attracting fluid) Think about it this way: the blood vessel is always under pressure with all the blood and proteins flowing through it. It is at the same time submerged in interstitial fluid that exerts its own pressure as well. So, depending on whether the pressure of the blood vessel or the pressure the interstitial fluid is higher, fluid will either seep into the blood vessel or out of it. Generally, proteins pull fluid into space they are in, and fluid tries to get out of spaces under pressure. So going back to the equation! Hydrostatic pressure, ie net pressure of the fluids is equal to: fluid trapped inside the blood vessel trying to push and seep its way out, MINUS the fluid in the interstitial space trying to push and seep into way into the vessel. Oncotic pressure, ie net pressure from proteins is equal to the net pressure of proteins drawing fluid into the interstitial space MINUS the proteins drawing fluid into the blood vessel. The whole system is sort a tug-of-war of fluids and proteins. If it confuses you, try drawing it out. With forces pushing teh fluid in/out of the vessel, and proteins pulling fluids in/out of the vessel!
What is the central dogma of biology, and name one circumstance under which it fails!
For many, many years, the central dogma of biology was set in stone as the way DNA turned into RNA and then finally into proteins! DNA, is a double-stranded spiral of genetic information trapped in the nucleus of a cell. This DNA is transcribed into RNA by RNA polymerases. This new single-stranded RNA can then leave the nucleus and get TRANSLATED into proteins that have lots of different functions in the cell! Simple right? Well as it turns out this one-way street can go backward, particularly in the case of viruses such as HIV. These viruses have figured out a way to essentially hijack this dogma and take over normal functioning, healthy cells. They will use several different mechanisms (which we won't get into here) to inject their own single-stranded RNA that codes for a protein called reverse transcriptase and DNA integrase into the cytoplasm of a cell. The cells own RNA polymerases will see this new RNA and translate it into its resulting proteins...aka REVERSE TRANSCRIPTASE and DNA INTEGRASE!!. This reverse transcriptase is the culprit. It will then turn around and start reverse transcribing the RNA from the viruses that was injected into the cytoplasm. The Reverse transcribing here DOES NOT PRODUCE RNA....infact it produces DNA!! The DNA integrase will then take this viral DNA and integrate it into the cells own DNA in the nucleus. This disrupts its own natural DNA and causes cell death.