In the Hepatic Portal System, the blood is transferred from abdominal organs directly to the liver through a network of veins. As a result, chemicals ingested from the digestive tract are initially accessible to the liver. These organs include the lower esophagus, stomach, small intestine, large intestine, spleen, pancreas, and gallbladder. The hepatic portal vein is the largest vessel of the hepatic portal system. It is formed by the union of the splenic and superior mesenteric veins. The splenic vein drains the spleen, pancreas, and portions of the large intestine.
Table of Content
What is a Portal System?
A Portal System is a system of blood vessels that has a capillary network at each end. In other words, a portal system is an arrangement of blood vessels such that blood passes from a capillary bed into larger blood vessels and then into another capillary bed. Ordinarily, blood flows from a capillary bed into the venous system and eventually back into the heart. In the case of a portal system blood flows from a capillary bed into the venous system but then flows through another capillary bed before returning to the heart.
There are three portal systems in mammals:
- Hypophoseal Portal System
- Renal Portal System
- Hepatic Portal System
What is the Hepatic Portal System?
In the Hepatic Portal System, venous drainage from most of the gastrointestinal tract, the spleen, and the pancreas, pools into the portal vein to reach the liver, before returning to the heart. This way, all substances absorbed through the GI tract, including nutrients, toxins, and pathogens, are first processed in the liver before they can reach the general circulation.
Veins that make up the Hepatic Portal System
These are the veins that collectively make a hepatic portal system:
- Hepatic Portal Vein
- Splenic Vein
- Superior Mesenteric Vein
- Inferior Mesenteric Vein
Anatomy of the Hepatic Portal System
It is the hepatic portal vein that receives blood from the organs of the gastrointestinal tract and provides blood to the liver. More specifically, the inferior mesenteric vein and the small gastric vein drain into the splenic vein, and the splenic vein drains into the hepatic portal vein. The superior mesenteric vein, right gastric vein, and left gastric vein all drain into the hepatic portal vein. Thus the hepatic portal vein receives venous blood from the stomach the small intestines, and the large intestine as well as venous blood from the gallbladder, spleen, and pancreas.
The hepatic portal vein allows for blood from all major organs of the gastrointestinal tract to enter the liver through one vein. The hepatic portal vein enters the liver and splits into the left and right hepatic veins as well as a smaller, middle, or intermediate vein. There are also small hepatic veins referred to as short hepatic veins. All of these hepatic veins eventually drain into the inferior vena cava. Thus, before blood from the gastrointestinal tract reaches the inferior vena cava, the gastrointestinal blood passes through the liver. The hepatic portal vein is called a portal vein because it leads into the hepatic portal system.
Hepatic Portal System Diagram
The following is a labelled diagram of hepatic portal system:
Function of the Hepatic Portal System
The function of Hepatic Portal Systems is:
- At first, the nutrients are processed by the liver, which also controls the quantity of nutrients that can reach the circulation. For example, the liver stores extra glucose as glycogen when it surges after a meal due to the breakdown of carbohydrates.
- During a fast, the body changes glycogen back into glucose, which is then released into the bloodstream. In other words, the liver prevents excessive fluctuations in blood sugar levels by maintaining a balance.
- The liver is another organ where the free amino acids from digesting proteins are utilized to create new proteins and pro-enzymes.
- Excess amino acids are broken down to urea to be eliminated from waste or transformed into other energy-storing molecules, both of which can be hazardous.
- This brings us to the second function of the liver as a detoxification organ. The liver screens the blood for potentially toxic substances and pathogens and removes them before they can reach the rest of the body.
Significance Of Hepatic Portal System
Hepatic Portal System is important because of the following reasons:
- It is the hepatic portal vein that receives blood from the organs of the gastrointestinal tract and provides blood to the liver.
- Blood that flows through the liver is mixed. Most organs receive blood flow from arteries and blood flows out of the organs through venules or veins.
- Blood from the hepatic portal vein provides 75 to 80 percent of all blood that circulates through the liver. The hepatic artery only provides around 20 to 25 percent of the blood circulating through the liver. The liver overall demands about 25 percent of cardiac output.
- In a Hepatic portal system, the liver receives blood from the gastrointestinal tract and performs functions like receiving blood from numerous organs to receive the biomolecules necessary for the many tasks the liver performs.
- Blood that comes from the alimentary canal contains glucose, amino acids, and other nutrients. The liver absorbs excess fat and glucose and uses them in the time of starvation.
- Harmful nitrogenous waste like ammonia is converted into areas which later removed by the kidney.
- The liver produces proteins that are transported through blood circulation.
Also Read:
FAQs on Hepatic Portal System
1. What are the Three Portal systems Found in the Human Body?
There are three portal venous systems – the hepatic portal system, the hypophyseal portal system, and the renal portal system. Unqualified, portal venous system usually refers to the hepatic portal system.
2. What is the Portal Vein System?
The portal vein (PV) is the main vessel of the portal venous system (PVS), which drains the blood from the gastrointestinal tract, gallbladder, pancreas, and spleen to the liver.
3. What is the Function of the Hepatic Vein?
Hepatic veins are blood vessels that return low-oxygen blood from your liver back to the heart. The veins are key players in the supply chain that moves the blood that delivers nutrients and oxygen to every cell in your body.
4. What is the Meaning of a Portal System?
A portal system is a system in which the veins start and end in capillaries. It delivers nutrient-rich blood to the liver for purification before it is carried to the heart.
5. What are the Three Branches of the Hepatic Portal Vein?
The portal vein and its 3 tributaries are formed by the superior mesenteric vein, inferior mesenteric vein, and splenic vein.