Portal venous system - AbsoluteAstronomy.com

Human anatomy

Human anatomy is primarily the scientific study of the morphology of the human body. Anatomy is subdivided into gross anatomy and microscopic anatomy. Gross anatomy is the study of anatomical structures that can be seen by the naked eye...

, the hepatic portal system is the system of vein

Vein

In the circulatory system, veins are blood vessels that carry blood towards the heart. Most veins carry deoxygenated blood from the tissues back to the heart; exceptions are the pulmonary and umbilical veins, both of which carry oxygenated blood to the heart...

s comprising the hepatic portal vein

Hepatic portal vein

The hepatic portal vein is not a true vein, because it does not conduct blood directly to the heart. It is a vessel in the abdominal cavity that drains blood from the gastrointestinal tract and spleen to capillary beds in the liver...

and its tributaries. It is also called the portal venous system, although it is not the only example of a portal venous system

Portal venous system

In human anatomy, the hepatic portal system is the system of veins comprising the hepatic portal vein and its tributaries. It is also called the portal venous system, although it is not the only example of a portal venous system, and splanchnic veins, which is not synonymous with hepatic portal...

, and splanchnic veins, which is not synonymous with hepatic portal system and is imprecise (as it means visceral veins and not necessarily the veins of the abdominal viscera).^{Dead link}

Function

The portal venous system is responsible for directing blood from parts of the gastrointestinal tract

Gastrointestinal tract

The human gastrointestinal tract refers to the stomach and intestine, and sometimes to all the structures from the mouth to the anus. ....

to the liver

Liver

The liver is a vital organ present in vertebrates and some other animals. It has a wide range of functions, including detoxification, protein synthesis, and production of biochemicals necessary for digestion...

. Substances absorbed in the small intestine travel first to the liver for processing before continuing to the heart. Not all of the gastrointestinal tract

Gastrointestinal tract

The human gastrointestinal tract refers to the stomach and intestine, and sometimes to all the structures from the mouth to the anus. ....

is part of this system. The system extends from about the lower portion of the esophagus

Esophagus

The esophagus is an organ in vertebrates which consists of a muscular tube through which food passes from the pharynx to the stomach. During swallowing, food passes from the mouth through the pharynx into the esophagus and travels via peristalsis to the stomach...

to the upper part of the anal canal

Anal canal

The anal canal is the terminal part of the large intestine.It is situated between the rectum and anus, below the level of the pelvic diaphragm. It lies in the anal triangle of perineum in between the right and left ischioanal fossa....

. It also includes venous drainage from the spleen

Spleen

The spleen is an organ found in virtually all vertebrate animals with important roles in regard to red blood cells and the immune system. In humans, it is located in the left upper quadrant of the abdomen. It removes old red blood cells and holds a reserve of blood in case of hemorrhagic shock...

and pancreas

Pancreas

The pancreas is a gland organ in the digestive and endocrine system of vertebrates. It is both an endocrine gland producing several important hormones, including insulin, glucagon, and somatostatin, as well as a digestive organ, secreting pancreatic juice containing digestive enzymes that assist...

.

Many drugs that are absorbed through the GI tract are substantially metabolized by the liver before reaching general circulation. This is known as the first pass effect

First pass effect

The first-pass effect is a phenomenon of drug metabolism whereby the concentration of a drug is greatly reduced before it reaches the systemic circulation. It is the fraction of lost drug during the process of absorption which is generally related to the liver and gut wall...

. As a consequence, certain drugs can only be taken via certain routes. For example, nitroglycerin cannot be swallowed because the liver would inactivate the medication, but it can be taken under the tongue

Sublingual

Sublingual, literally 'under the tongue', from Latin, refers to the pharmacological route of administration by which drugs diffuse into the blood through tissues under the tongue...

or transdermal (through the skin) and thus is absorbed in a way that bypasses the portal venous system. Inversely, dextromethorphan

Dextromethorphan

Dextromethorphan is an antitussive drug. It is one of the active ingredients in many over-the-counter cold and cough medicines, such as Robitussin, NyQuil, Dimetapp, Vicks, Coricidin, Delsym, and others, including generic labels. Dextromethorphan has also found other uses in medicine, ranging...

, a cough suppressor, is best taken orally because it needs to be metabolised by the liver into dextrorphan

Dextrorphan

Dextrorphan is a psychoactive drug of the morphinan chemical class which acts as an antitussive or cough suppressant and dissociative hallucinogen. It is the dextro-stereoisomer of racemorphan, the levo-half being levorphanol. Dextrorphan is produced by O-demethylation of dextromethorphan by CYP2D6...

in order to be effective. This latter principle is that of most prodrugs.
The use of suppository is a way to by-pass partially the portal vein: the upper 1/3 of the rectum

Rectum

The rectum is the final straight portion of the large intestine in some mammals, and the gut in others, terminating in the anus. The human rectum is about 12 cm long...

is drained into the portal vein while the lower 2/3 are drained into the internal iliac vein

Internal iliac vein

The internal iliac vein begins near the upper part of the greater sciatic foramen, passes upward behind and slightly medial to the Internal iliac artery and, at the brim of the pelvis, joins with the external iliac vein to form the common iliac vein.-Tributaries:With the exception of the fetal...

that goes directly in the inferior vena cava

Inferior vena cava

The inferior vena cava , also known as the posterior vena cava, is the large vein that carries de-oxygenated blood from the lower half of the body into the right atrium of the heart....

(thus by-passing the liver).

Blood flow to the liver is unique in that it receives both oxygenated and (partially) deoxygenated blood. As a result, the partial gas pressure

Partial pressure

In a mixture of ideal gases, each gas has a partial pressure which is the pressure which the gas would have if it alone occupied the volume. The total pressure of a gas mixture is the sum of the partial pressures of each individual gas in the mixture....

of oxygen (pO₂) and perfusion pressure of portal blood are lower than in other organs of the body. Blood passes from branches of the portal vein through cavities between "plates" of hepatocytes called sinusoids

Liver sinusoid

A liver sinusoid is a type of sinusoidal blood vessel that serves as a location for the oxygen-rich blood from the hepatic artery and the nutrient-rich blood from the portal vein....

. Blood also flows from branches of the hepatic artery

Hepatic artery

Hepatic artery can refer to:* Common hepatic artery * Hepatic artery proper...

and mixes in the sinusoids to supply the hepatocytes with oxygen. This mixture percolates

Percolation

In physics, chemistry and materials science, percolation concerns the movement and filtering of fluids through porous materials...

through the sinusoids and collects in a central vein which drains into the hepatic vein

Hepatic vein

In human anatomy, the hepatic veins are the blood vessels that drain de-oxygenated blood from the liver and blood cleaned by the liver into the inferior vena cava....

. The hepatic vein subsequently drains into the inferior vena cava

Inferior vena cava

The inferior vena cava , also known as the posterior vena cava, is the large vein that carries de-oxygenated blood from the lower half of the body into the right atrium of the heart....

.
The hepatic artery

Hepatic artery

Hepatic artery can refer to:* Common hepatic artery * Hepatic artery proper...

provides 30 to 40% of the oxygen to the liver, while only accounting for 25% of the total liver blood flow. The rest comes from the partially deoxygenated blood from the portal vein. Interestingly, the liver consumes about 20% of the total body oxygen when at rest. That is why the total liver blood flow is quite high, at about 1 liter a minute and up to two liters a minute. That is on average one fourth of the average cardiac output

Cardiac output

Cardiac output is the volume of blood being pumped by the heart, in particular by a left or right ventricle in the time interval of one minute. CO may be measured in many ways, for example dm3/min...

at rest.

Large veins that are considered part of the portal venous system are the:

Hepatic portal vein
Hepatic portal vein
The hepatic portal vein is not a true vein, because it does not conduct blood directly to the heart. It is a vessel in the abdominal cavity that drains blood from the gastrointestinal tract and spleen to capillary beds in the liver...
Splenic vein
Splenic vein
In anatomy, the splenic vein is the blood vessel that drains blood from the spleen.It joins with the superior mesenteric vein, to form the hepatic portal vein and follows a course superior to the pancreas, alongside of the similarly named artery, the splenic artery.It collects branches from the...
Superior mesenteric vein
Superior mesenteric vein
In anatomy, the superior mesenteric vein is a blood vessel that drains blood from the small intestine . At its termination behind the neck of the pancreas, the SMV combines with the splenic vein to form the hepatic portal vein...
Inferior mesenteric vein
Inferior mesenteric vein
In human anatomy, the inferior mesenteric vein is a blood vessel that drains blood from the large intestine. It usually terminates when reaching the splenic vein, which goes on to form the portal vein with the superior mesenteric vein...

The superior mesenteric vein

Superior mesenteric vein

In anatomy, the superior mesenteric vein is a blood vessel that drains blood from the small intestine . At its termination behind the neck of the pancreas, the SMV combines with the splenic vein to form the hepatic portal vein...

and the splenic vein

Splenic vein

In anatomy, the splenic vein is the blood vessel that drains blood from the spleen.It joins with the superior mesenteric vein, to form the hepatic portal vein and follows a course superior to the pancreas, alongside of the similarly named artery, the splenic artery.It collects branches from the...

come together to form the actual hepatic portal vein

Hepatic portal vein

. The inferior mesenteric vein

Inferior mesenteric vein

In human anatomy, the inferior mesenteric vein is a blood vessel that drains blood from the large intestine. It usually terminates when reaching the splenic vein, which goes on to form the portal vein with the superior mesenteric vein...

connects in the majority of people on the splenic vein

Splenic vein

, but in some people, it is known to connect on the portal vein or the superior mesenteric vein

Superior mesenteric vein

.

Roughly, the portal venous system corresponds to areas supplied by the celiac trunk, the superior mesenteric artery

Superior mesenteric artery

In human anatomy, the superior mesenteric artery arises from the anterior surface of the abdominal aorta, just inferior to the origin of the celiac trunk, and supplies the intestine from the lower part of the duodenum through two-thirds of the transverse colon, as well as the pancreas.-Location...

, and the inferior mesenteric artery

Inferior mesenteric artery

In human anatomy, the inferior mesenteric artery, often abbreviated as IMA, supplies the large intestine from the left colic flexure to the upper part of the rectum, which includes the descending colon, the sigmoid colon, and part of the rectum...

Pathology

Portal hypertension

In medicine, portal hypertension is hypertension in the portal vein and its tributaries.It is often defined as a portal pressure gradient of 10 mmHg or greater.-Causes:Causes can be divided into prehepatic, intrahepatic, and posthepatic...

is a condition in which the blood pressure of the portal venous system is too high. It is often the result of cirrhosis

Cirrhosis

Cirrhosis is a consequence of chronic liver disease characterized by replacement of liver tissue by fibrosis, scar tissue and regenerative nodules , leading to loss of liver function...

of the liver.

Function

Pathology

See also

Further reading