Segments of the liver. Structure and function of the liver

The liver is the second largest organ in the body - only the skin is larger and heavier. Functions of the human liver are associated with digestion, metabolism, immunity and storage of nutrients in the body. The liver is a vital organ, without which body tissues quickly die from lack of energy and nutrients. Fortunately, it has an incredible ability to regenerate and is able to grow very quickly to regain its functions and size. Let's look at the structure and functions of the liver more.

Macroscopic anatomy of a human

The liver of a person is located on the right under the diaphragm and has a triangular shape. Most of its mass is located on the right side, and only a small part of it goes beyond the middle line of the body. The liver consists of very soft, rosy-brown tissues, encapsulated in a connective tissue capsule (glisson capsule). It is covered and strengthened by the peritoneum (serous membrane) of the abdominal cavity, which protects and holds it in place within the abdomen. The average size of the liver is about 18 cm in length and not more than 13 in thickness.

The peritoneum connects to the liver in four places: the coronary ligament, left and right triangular ligaments, and a round ligament. These compounds are not the only ones in the anatomical sense; Rather, they are compressed areas of the abdominal membrane that support the liver.

• A wide coronary ligament connects the central part of the liver to the diaphragm.

• Located on the lateral boundaries of the left and right lobes, the left and right triangular ligaments connect the organ to the diaphragm.

• A curved ligament passes down from the diaphragm through the front edge of the liver to its bottom. At the bottom of the organ, the curved ligament forms a round ligament and connects the liver to the navel. The round ligament is the remainder of the umbilical vein that carries blood into the body during embryonic development.

The liver consists of two separate lobes - left and right. They are separated from each other by a curved band. The right share is about 6 times larger than the left one. Each share is divided into sectors, which, in turn, are divided into segments of the liver. Thus, the organ is divided into two parts, 5 sectors and 8 segments. At the same time, the liver segments are numbered in Latin numerals.

Right share

As mentioned above, the right lobe of the liver is approximately 6 times larger than the left. It consists of two large sectors: the lateral right quadrant and the paramedian right quadrant.

The right lateral sector is divided into two lateral segments that do not border on the left lobe of the liver: the lateral upper and posterior segment of the right lobe (segment VII) and the lateral lower and posterior segment (segment VI).

The right paramedian sector also consists of two segments: the middle upper and the middle lower anterior segments of the liver (VIII and V, respectively).

Left share

Despite the fact that the left lobe of the liver is smaller than the right, it consists of more segments. It is divided into three sectors: the left dorsal, the left lateral, the left paramedian sector.

The left dorsal sector consists of one segment: the caudate segment of the left lobe (I).

The left lateral sector is also formed from one segment: the posterior segment of the left lobe (II).

The left paramedian sector is divided into two segments: the square and anterior segments of the left lobe (IV and III, respectively).

You can see the segmental structure of the liver in more detail on the diagrams below. For example, in the figure one shows a liver, which is visually divided into all its parts. The segments of the liver in the figure are numbered. Each number corresponds to the Latin segment number.

Picture 1:

Bile capillaries

The tubes carrying bile through the liver and gall bladder are called the bile capillaries and form a branched structure - the bile duct system.

The bile produced by the cells of the liver drains into microscopic canals - the bile capillaries, which combine into large bile ducts. These bile ducts then join together, forming large left and right branches that carry bile from the left and right lobes of the liver. Later they combine into one common hepatic duct, into which all the bile flows.

The common hepatic duct finally joins the bladder duct from the gallbladder. Together they form a common bile duct, carrying bile to the duodenum of the small intestine. Most of the bile produced by the liver is placed back into the vesicle by peristalsis, and remains in the gallbladder until it is required for digestion.

Circulatory system

The blood supply of the liver is unique. Blood enters into it from two sources: the portal vein (venous blood) and the hepatic artery (arterial blood).

The portal vein carries blood from the spleen, stomach, pancreas, gallbladder, small intestine and large omentum. Entering the gates of the liver, the venous vein is divided into a huge number of vessels, where the blood is processed before moving to other parts of the body. Leaving cells of the liver, the blood collects into the hepatic veins, from which it enters the hollow vein and again returns to the heart.

The liver also has its own system of arteries and small arteries that provide oxygen to its tissues just like any other organ.

Lobules

The internal structure of the liver consists of approximately 100,000 small hexagonal functional units, known as lobules. Each lobule consists of a central vein surrounded by 6 hepatic portal veins and 6 hepatic arteries. These blood vessels are connected by a set of tubule-like sinusoids. Like spokes in the wheel, they extend from the portal veins and arteries towards the central vein.

Each sinusoid passes through the liver tissue, which contains two main types of cells: Kupffer cells and hepatocytes.

• Kupffer cells are a type of macrophage. In simple words, they capture and break old, worn out red blood cells passing through the sinusoids.

• Hepatocytes (hepatic cells) are cuboidal epithelial cells that are located between sinusoids and make up the majority of cells in the liver. Hepatocytes perform most of the liver functions - metabolism, storage, digestion and production of bile. Tiny collections of bile, known as its capillaries, run parallel to the sinusoids on the other side of the hepatocytes.

The scheme

We have already familiarized ourselves with the theory. Let's now see what the human liver looks like. Photos and descriptions for them you will find below. Since one drawing can not show the organ completely, we use several. It's okay if two images show the same part of the liver.

Figure 2:

Number 2 marks the human liver itself. Photos in this case would not be appropriate, so consider it by drawing. Below are the figures, and that this figure shows:

1 - right hepatic duct; 2 - liver; 3 - left hepatic duct; 4 - common hepatic duct; 5 - common bile duct; 6 - pancreas; 7 - duct of the pancreas; 8 - duodenum; 9 - sphincter of Oddi; 10 - bladder duct; 11 - gall bladder.

Figure 3:

If you've ever seen an atlas of human anatomy, you know that it contains approximately the same images. Here the liver is presented in front:

1 - inferior vena cava; 2 - curved ligament; 3 - right share; 4 - the left share; 5 - round ligament; 6 - gall bladder.

Figure 4:

In this figure, the liver is represented on the other side. Again, the atlas of human anatomy contains almost the same pattern:

1 - gall bladder; 2 - the right share; 3 - the left share; 4 - bladder duct; 5 - hepatic duct; 6 - hepatic artery; 7 - hepatic portal vein; 8 - common bile duct; 9 - inferior vena cava.

Figure 5:

This picture shows a very small part of the liver. Some explanations: the figure 7 in the figure shows a triad portal - a group that combines the hepatic portal vein, hepatic artery and bile duct.

1 - hepatic sinusoid; 2 - hepatic cells; 3 - central vein; 4 - to the hepatic vein; 5 - bile capillaries; 6 - from intestinal capillaries; 7 - "triad portal"; 8 -hepatic portal vein; 9 - hepatic artery; 10 - bile duct.

Figure 6:

The inscriptions in English are translated as (from left to right): the right lateral sector, the right paramedian sector, the left paramedian sector and the left lateral sector. The white numbers numbered the segments of the liver, each number corresponds to the Latin segment number:

1 - right hepatic vein; 2 - left hepatic vein; 3 - the average hepatic vein; 4 - umbilical vein (rest); 5 - hepatic duct; 6 - inferior vena cava; 7 - hepatic artery; 8 - portal vein; 9 - bile duct; 10 - bladder duct; 11 - gall bladder.

Physiology of the liver

The functions of the human liver are very diverse: it plays a major role in digestion, metabolism, and even in the storage of nutrients.

Digestion

The liver plays an active role in the process of digestion through the production of bile. Bile is a mixture of water, bile salts , cholesterol and bilirubin pigment.

After hepatocytes in the liver produce bile, it passes through the bile ducts and remains in the gall bladder until it is needed. When the food containing fats reaches the duodenum, the cells of the duodenum release the hormone cholecystokinin, which relaxes the gallbladder. Bile, moving along the bile ducts, gets into the duodenum, where emulsifies large masses of fat. Emulsification of fat by bile converts large blocks of fat into small pieces that have a smaller surface area and are therefore easier to process.

Bilirubin, which exists in bile, is a product of processing by the liver of worn out red blood cells. Kupffer cells in the liver catch and destroy old, worn out red blood cells and transmit them to the hepatocytes. In the latter, the fate of hemoglobin is decided - it is divided into groups of heme and globin. The globin protein is further destroyed and used as an energy source for the body. The iron-containing group of heme can not be processed by the body and simply converted to bilirubin, which is added to the bile. It is bilirubin that gives bile its distinctive greenish color. Intestinal bacteria further transform bilirubin into a brown pigment of the cynocysts, which gives the excrement a brown color.

Metabolism

A lot of complicated tasks related to metabolic processes are assigned to hepatocytes of the liver. Since all the blood, leaving the digestive system, passes through the hepatic portal vein, the liver is responsible for assimilating carbohydrate, lipids and proteins into biologically useful materials.

Our digestive system splits carbohydrates into glucose monosaccharide, which cells use as the main energy source. The blood entering the liver through the hepatic portal vein is extremely rich in glucose from digested food. Hepatocytes absorb most of this glucose and store it as macromolecules of glycogen, a branched polysaccharide that allows the liver to conserve large amounts of glucose and quickly release it between meals. Absorption and release of glucose by hepatocytes help maintain homeostasis and lower blood glucose levels.

Fatty acids (lipids) of blood passing through the liver are absorbed and absorbed by the hepatocytes to produce energy in the form of ATP. Glycerin, one of the lipid components, is converted by hepatocytes into glucose through the process of gluconeogenesis. Hepatocytes can also produce lipids such as cholesterol, phospholipids and lipoproteins that are used by other cells throughout the body. Most of the cholesterol produced by hepatocytes is excreted from the body as a component of bile.

Dietary proteins are split into amino acids by the digestive system even before they are transferred to the hepatic portal vein. Amino acids entering the liver require metabolic treatment before they can be used as an energy source. Hepatocytes first remove the amino group from the amino acids and convert it to ammonia, which is eventually processed into urea.

Urea is less toxic than ammonia, and can be excreted together with urine as an unnecessary product of digestion. The remaining parts of the amino acids are cleaved to ATP or transformed into new glucose molecules through the process of gluconeogenesis.

Detoxification

As blood from the digestive organs passes through the portal bloodstream of the liver, hepatocytes control the blood content and remove many potentially toxic substances before they can reach the rest of the body.

Enzymes in hepatocytes convert many of these toxins (eg, alcoholic beverages or drugs) into their inactive metabolites. In order to maintain the level of hormones in homeostatic limits, the liver also absorbs and removes from the circulation of the hormones produced by the glands of its own organism.

Storage

The liver provides storage of many necessary nutrients, vitamins and minerals, received from blood transfer through the hepatic portal system. Glucose is transported in hepatocytes under the influence of the hormone insulin and stored in the form of glycogen polysaccharide. Hepatocytes also absorb fatty acids from digested triglycerides. The storage of these substances allows the liver to maintain glucose homeostasis in the blood.

Our liver also stores vitamins and minerals (vitamins A, D, E, K and B 12, as well as minerals of iron and copper) in order to ensure a constant inflow of these important substances to the tissues of the body.

Production

The liver is responsible for the production of several vital protein components of blood plasma: prothrombin, fibrinogen and albumins. Prothrombin and fibrinogen proteins are clotting factors involved in the formation of thrombi. Albumins are proteins that support the isotonic environment of the blood so that the body cells do not receive or lose water in the presence of body fluids.

Immunity

The liver functions as an organ of the immune system through the function of Kupffer cells. Kupffer cells are a macrophage forming part of the mononuclear phagocytes of the system along with macrophages of the spleen and lymph nodes. Kupffer cells play an important role, since they process bacteria, fungi, parasites, worn out blood cells and cell decay products.

Liver ultrasound: norm and abnormalities

The liver performs many important functions in our body, so it is very important that it is always normal. Given the fact that the liver can not hurt, since there are no nerve endings in it, you may not notice how the situation has become hopeless. It can simply collapse, gradually, but so that in the end it will be impossible to cure it.

There are a number of liver diseases, in which you do not even feel that something irreparable has happened. A person can live for a long time and consider himself healthy, and in the end it turns out that he has cirrhosis or liver cancer. And this can not be changed.

Although the liver and has the property to recover, she herself will never cope with such diseases. Sometimes she needs your help.

To avoid unnecessary problems, it is enough simply to visit a doctor sometimes and do an ultrasound of the liver, the norm of which is described below. Remember that the liver is associated with the most dangerous diseases, for example, hepatitis, which without proper treatment can lead to just such serious pathologies as cirrhosis and cancer.

Now let's go directly to ultrasound and its norms. First of all, the specialist looks at whether the liver is shifted and what its size is.

The exact dimensions of the liver can not be indicated, since it is impossible to fully visualize this organ. The length of the entire organ should not exceed 18 cm. Doctors treat each part of the liver separately.

To begin with, the liver ultrasound should clearly see its two parts, as well as the sectors to which they are divided. In this case, the ligamentous apparatus (i.e., all ligaments) should not be visible. The study allows physicians to study all eight segments separately, since they are also easily visible.

The norm of the sizes of the right and left share

The left share should be about 7 cm in thickness and about 10 cm in height. The increase in size indicates problems with your health, possibly, that you have an inflamed liver. The right lobe, whose norm is about 12 cm in thickness and up to 15 cm in length, as you can see, is much larger than the left one.

In addition to the organ itself, doctors must also look at the bile duct, as well as large vessels of the liver. The size of the bile duct, for example, should not be more than 8 mm, the portal vein - about 12 mm, and the hollow vein - up to 15 mm.

For doctors, not only the size of the organs, but also their structure, the contours of the organ and their tissue are important.

The anatomy of a man (whose liver is a very complex organ) is a fascinating thing. There is nothing more interesting than understanding the structure of yourself. Sometimes it can even save you from unwanted diseases. And if you are vigilant, problems can be avoided. Going to the doctor is not as bad as it seems. Be healthy!