Liver Anatomy

Liver Macroanatomy

The liverA large organ that produces bile, detoxifies blood, and stores nutrients. has a right and left lobe, although these lobes are not equal in size.  The falciform ligament separates the two lobes.  The round ligament A ligament that helps hold the uterus in place. connects to surrounding structures and secures the liver in place.  On the posterior side of the liver, the gall bladderA muscular organ that stores urine before excretion. is tucked into the larger right lobe. 

The vena cava receives the cleansed blood from the liver. It moves the blood back into systemic circulation to distribute the recently acquired nutrients.

Liver Vascularization

Imagine this: food moves through the digestive tract, and as it moves through the wall, it enters into capillariesThe smallest blood vessels where gas, nutrient, and waste exchange occurs between blood and tissues.. All of these capillaries converge and send all the blood to the liver. The liver then “cleanses” that blood by removing toxins and other substances. It releases the cleansed blood to the body.

The hepatic portal system carries blood from the small intestine to the liver for cleansing. It purifies the blood before being released to the body. The system is one-way. Blood from the small intestine flows through the hepatic portal veinThe main vein that transports blood from the digestive tract to the liver for processing. to the liver. There, it is processed before returning to the body. The spleen also contributes to cleansing the blood, albeit in a different manner.

Blood from the hepatic portal system enters the liver through the portal vein. This is distinct from the usual blood flow that comes from arteriesBlood vessels that carry oxygenated blood away from the heart (except pulmonary arteries, which carr. When someone has hepatitis, this vein can get backed up. This causes inflammation and malnutrition. The blood can’t properly flow from the small intestine to the liver.  Ultimately, fluid becomes trapped in the hepatic portal vein leading to portal hypertension and possible ascites.  Ascites is the build up of fluid that you see here in this person’s peritoneumThe membrane lining the abdominal cavity and organs..

Liver Lobules

The liver’s histology reveals hexagonal lobules, which are the functional units of the liver. These lobules contain plates of cellsThe basic structural and functional units of life. that fan out from a central line.  Imagine a book. Spread it open so the back and front covers touch. The pages fan out, creating an overall cylinder shape.  In this inset here, there are seven lobules and this even larger inset is showing just one lobule.

Each lobule is drained by a central vein. This vein merges with the central veinsBlood vessels that return deoxygenated blood to the heart (except pulmonary veins, which carry oxyge of other lobules. Together, they form the hepatic vein. This vein drains the cleansed blood into the vena cava. From there, it will be recirculated. The liver also receives oxygenated blood through the hepatic artery. This artery delivers oxygen and glucoseA simple sugar that is the main source of energy for cells. to liver cells. The portal vein carries blood needing to be cleansed. Both types of blood eventually return to the vena cava via the hepatic vein.

At the corner of the lobule hexagons, there are three vessels, called a portal triad.  Portal triads consist of an arteriole delivering oxygen-rich blood to the liver, as with any organ. They include a branch of the central vein or a venule. This carries blood from the hepatic portal system. They also consist of a bileA digestive fluid produced by the liver and stored in the gallbladder; it helps emulsify fats for di ductule. There is a branch of the vagus nerve. Additionally, they have the blind end of a lymphatic vessel.  Of course, the name portal triad was coined before we knew there were 5 structures, not 3. Sinusoidal capillaries in the liver are very porous.  Recall that these types of capillaries have intercellular clefts that are large enough for leukocytes to fit through

Liver Cells

The liver cells, called hepatocytesLiver cells responsible for detoxification, metabolism, and bile production., filter the blood coming from the hepatic portal system. Hepatocytes are full of smooth endoplasmic reticulumA membrane network involved in lipid synthesis, detoxification, and calcium storage., the organelle responsible for toxin removal.  Tolerance to alcohol occurs when hepatocytes add more smooth endoplasmic reticulum to match the need for detox.

The liver also contains stellate cells, which store fat. In cases of fatty liver disease, these cells become abnormally numerous. Kupffer cells, a type of macrophage, patrol the liver, consuming any invaders like pathogens. These cells also help detoxify the blood that flows from the hepatic portal system.