The portal vein is a short vessel located in the upper right side of the abdominal cavity. It carries blood to the liver. The portal vein is formed from the junction of the mesenteric and splenic vein. Learn how the portal vein is structured, what functions the portal vein is, how to examine the condition of the portal vein and what conditions the portal vein may be related to.
The portal vein(Latin vena portae) is one of the most important venous vessels in the human body. Located in the abdominal cavity, the portal vein acts as a link between the gastrointestinal tract and the liver. Thanks to the portal vein, blood that drains from the abdominal organs goes to the liver. Along with the blood, nutrients are transported to the liver, as well as toxins and other undesirable components absorbed from the gastrointestinal tract. Substances reaching the liver from the portal vein are then appropriately metabolized or stored.
Portal vein - construction
The portal vein is located in the upper right side of the abdominal cavity. Compared to other veins in our body, the portal vein is not particularly long (about 7 cm on average). However, it is characterized by a relatively large width (up to 2 cm) and a rapid blood flow. The portal vein is directly adjacent to numerous organs of the abdominal cavity, including the liver, pancreas and duodenum.
The portal vein is the final stage of the outflow of blood from the abdominal organs. The entire human digestive tract is surrounded by a dense network of tiny vessels that allow the absorption of nutrients from the digestive process. Tiny veins connect to each other to gradually form vessels of increasing diameter.
The portal vein is formed from the fusion of two large vessels:
- superior mesenteric vein
- and the splenic vein.
The superior mesenteric vein "collects" blood from the small intestine, pancreas and a large part of the large intestine. In turn, blood from the stomach, pancreas and lower parts of the large intestine goes to the splenic vein.
The connection of these vessels - the portal vein - transports blood from most organs of the gastrointestinal tract.
We already know how the initial segment of the portal vein is built. What is happening at the other end of this vessel? The portal vein enters the liver, dividing into two branches - right and left. Inside the liverThe portal vein continues to divide into smaller and smaller vessels, allowing blood to flow to every part of this organ.
The dense network of vessels in the liver is called the portal circulation. As you can easily guess, the correct function of the portal vein depends primarily on the condition of the liver. One of the common symptoms of liver disease is portal vein blood flow disturbance.
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Portal vein - functions
The portal vein is the main source of liver vasculature. As much as 75% of the blood reaching this organ comes from the portal vein (the remaining 25% is provided by the hepatic arteries). Thanks to the portal vein, all components absorbed in the digestive tract are transported to the liver.
The liver is a kind of filter - it separates necessary substances from harmful ones and stores spare ingredients. The liver undergoes a multitude of metabolic reactions and the nutrients are transformed in a way that best suits the body's needs.
If the blood from the gastrointestinal tract did not reach the liver via the portal vein, our body would not be able to control the substances absorbed from the gastrointestinal tract. In this way, numerous toxins and microbes would be spread throughout the body. Thanks to the portal vein and the liver, most of them are quickly neutralized.
An interesting use of the structure and functioning of the portal vein in medicine is one of the methods of administering drugs. We are talking about the supply of drugs through the rectal route - most often in the form of suppositories or enemas.
As mentioned earlier, the portal vein "collects" blood from most of the digestive tract. Consequently, drugs administered by the traditional, oral route are primarily transported through the portal vein to the liver. This results in some delays in their action, and in the case of some drugs, their partial breakdown in the liver.
One of the ways to avoid this problem turned out to be the supply of drugs to the end of the digestive tract - the rectum. Blood from the last parts of the rectum bypasses the portal vein and the liver and goes directly to the general circulation. Drugs administered by the rectal route can therefore spread throughout the body more quickly. Rectal doses are often lower than those administered orally because they are not broken down in the liver.
Portal vein - diseases
The portal vein is a vessel that plays a significant role in the process of transporting and metabolizing nutrients in our body. Due to its direct connection to the liver, many portal vein disorders are caused by abnormalities in the portal vein.
Disorders of portal vein blood flow can affect the entire circulatory system. For this reason, portal vein diseases often cause atypical clinical symptoms from seemingly distant locations in our body. The most common conditions associated with the portal vein are:
Portal hypertension
Portal hypertension is one of the most common portal vein diseases. The essence of this disease is the increase in the pressure in the portal vein above 12 mmHg (in normal conditions it does not exceed 5 mmHg).
Where does portal hypertension come from? There are many causes of this condition, but the most common are due to liver disease. Multiple liver diseases can lead to the remodeling of this organ.
The change in the structure of the liver results in the obstruction of blood flow in the vessels running through its parenchyma. This creates stagnation of blood in the portal vein, leading to portal hypertension. A common condition described as described above is cirrhosis of the liver, which may be due to chronic alcohol abuse, viral infections, or congenital liver disease.
What are the effects of portal hypertension? At this point, it is worth recalling the portal vein anatomy. This vessel is formed from the anastomosis of the splenic and superior mesenteric veins, which in turn arise from the connections of other venous vessels. Portal vein hypertension affects blood pressure throughout the venous system. This results in stagnation of blood in all venous vessels surrounding the digestive tract.
The typical clinical symptoms of this condition are varicose veins, most often occurring in the esophagus, and also around the anus (so-called haemorrhoids or hemorrhoids). Esophageal varices are a particularly dangerous complication of portal hypertension. In advanced stages of the disease, they can lead to serious bleeding from the gastrointestinal tract.
Much less common, but quite spectacular effect of portal hypertension is the so-called head of jellyfish (Latin caput medusae). This symptom consists in a significant widening of the veins in the area of the navel, which, forming a characteristic shape, resemble the head of the mythological Medusa.
Portal vein thrombosis
Portal vein thrombosis is a blood clot that blocks blood flow in this vessel. The cause of this condition may be congenital hypercoagulability, neoplastic diseases, inflammatory processes, as well as liver diseases.
There is an acute portal vein thrombosis, which causes sudden abdominal discomfort, as well as chronic thrombosis, which is most often a consequence of long-term liver diseases.
Portal vein thrombosis is one possible cause of portal hypertension. The disease is diagnosed on the basis of the portal vein Doppler ultrasound examination. In most forms, treatment requires medications to help dissolve blood clots in the bloodstream.
Portal vein pneumatosis
Portal vein pneumatosis is not actually a separate disease, but rather a symptom that occurs in the course of other diseases. Pneumatosis is the presence of air bubbles inside a blood vessel. Where is the portal vein air coming from?
Most often it gets there from the intestines that are very inflamed. Portal vein pneumatosis can be one of the symptoms of necrotizing enterocolitis - a disease that is a typical complication of prematurity.
As you can see, portal vein anatomy and dysfunction may also occur in the pediatric population.
Congenital defects of the portal vein
The portal vein system is formed in the early stages of fetal development. Among the many possible anatomical disorders in the development of the organism, there are also irregularities in the structure of the portal vein.
Portal vein birth defects may vary in form and severity. Some of them do not cause any clinical symptoms and are never detected. Examples of portal vein developmental abnormalities include agenesis (complete absence of the portal vein), abnormal branching, and portal systemic fistulas (a defect in the presence of extra vessels that cause blood from the portal vein to flow into the systemic circulation bypassing the liver).
Portal vein - examination
There are several ways to assess the condition of the portal vein. The simplest of these is the physical examination, which can detect the symptoms of the most serious conditions of the portal vein. An example of such a condition is advanced portal hypertension, which can cause changes in the venous circulation visible to the naked eye. Such symptoms include "Jellyfish head", as well as anal and esophagus varicose veins.
The tool dedicated to the assessment of the anatomy and function of the portal vein is an ultrasound examination (USG) with the Doppler function. Its advantages include wide availability, low price, low invasiveness and fast execution time. In the Doppler ultrasound examination, the dimensions of the portal vein as well as the direction and speed of blood flow in this vessel can be assessed. The obtained parameters allow for the initial diagnosis of most diseases related to the portal vein.