Sunday, April 6, 2008

The Portal System...made EZ

The Portal system? I was asked that during my NCLEX review class last week by some Jr students, and figured there may be more that are more than confused by this term. So what follows is a simple description of this system that is involved in some of the more common pathologies in the hospital.

The liver is a selfish organ. It demands first access to blood that is bringing anything new into the system, kind of like a checkpoint at the border. At this checkpoint, the liver removes anything toxic by metabolism or excretion, converts nutrients into useable or stored forms, as well as a host of other responsibilites. There are four main areas that drain their blood to the liver, before it is dumped into the system. Check out the picture below, to get an idea before we discuss this.

The easiest to picture, is blood coming from the intestines, where new food was just absorbed. The liver wants first access to this blood, and gets it via the portal system. The problem is, what if the liver is congested or scarred and little blood can get through the liver. Well anyone who has ever been on the interstate understands, that there is backup, when something is blocking the road. The blood trying to get to the liver now backs up and dilates these portal veins. In the intestines, this blood can leak out into the tissue, becoming Ascites.

The next drainage, comes from the rectum. That is a port of entry into your body, right? Well the liver wants to analyze blood coming from this area of your body (that is good when there is a medication jammed in there) and gets that blood through the portal system. If this blood backs up, you will get big dilated veins in the rectum, called Hemorrhoids.

The Spleen also drains into the Liver before its blood has access to the main system. That is good, since broken down RBCs (bilirubin) get processed there. If this part of the portal system backs up you would see Splenomegaly.

The final system that drains via the portal system, is the other port of entry into your body, the esophagus. Veins partially drain this area in case there are invaders or new toxins to metabolize. If this backs up you would see big, dilated veins in the esophagus, called Esophageal Varices (Varicose veins in the throat). This is a significant issue...imagine our patient is eating a Dorito, and an edge of that cool ranch chip nicks the dilated vein. You would get bleeding into the esophagus. Remember that the liver also makes important clotting factors, and if the liver is damaged and congested we are not going to clot well. (Remember that PT measures one of the key clotting factors? It is also the fastest lab value to change with liver damage so check that PT/INR!)

So Esophageal Varices are a very important pathology to notice in any liver patient as we must stop that bleeding. Luckily, blood is very irritating and is usually thrown at you with very violent, bloody vomiting, so you shouldn't miss that sign. One you may miss is if you forget that the Liver also makes Albumin, which, because it is so attractive to water, is what keeps volume in your blood. If you lose this albumin from a diseased liver, you are already looking at a patient that has falling blood pressure. Now take some blood away via these Esophageal varices, and you may see significant Hypotension. So make sure you are measuring those vital signs frequently!

Here is a picture that hopefully summarizes what we just covered. Now you should at least be able to recognize what the portal system is, and why we see certain signs in Liver patients, like Splenomegaly, Ascites, Hemorrhoids, Esophageal Varices, and Hypotension.


Anonymous said...

Thank you for the nice overview of the portal system. Reading that just made 160 intense pages from my med surg book "click".

~a nursing student

addala said...

Its so valuable...thank u