The liver is the second largest organ in the body - only the skin is larger and heavier. The functions of the human liver are associated with digestion, metabolism, immunity and the storage of nutrients in the body. The liver is a vital organ, without which the body’s tissues quickly die from a lack of energy and nutrients. Fortunately, it has an incredible ability to regenerate and is able to grow very quickly in order to regain its functions and size. Let's look at the structure and function of the liver in more detail.
Human macroscopic anatomy
The human liver 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 extends beyond the midline of the body. The liver consists of very soft, pinkish-brown tissues enclosed in a capsule of connective tissue (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, the left and right triangular ligaments, and the round ligament. These compounds are not unique 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 with the diaphragm.
• Located on the lateral borders of the left and right lobes, the left and right triangular ligaments connect the organ to the diaphragm.
• A curved ligament runs down from the diaphragm through the front edge of the liver to its bottom. At the bottom of the organ, a 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 to the body during embryonic development.
The liver consists of two separate lobes - left and right. They are separated from each other by a curved ligament. The right lobe is about 6 times larger than the left. Each lobe is divided into sectors, which, in turn, are divided into segments of the liver. Thus, the body is divided into two parts, 5 sectors and 8 segments. In this case, the liver segments are numbered in Latin numbers.
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 sector and the paramedian right sector.
The right lateral sector is divided into two lateral segments that do not border the left lobe of the liver: the lateral upper-posterior segment of the right lobe (VII segment) and the lateral lower-posterior segment (VI segment).
The right paramedian sector also consists of two segments: the middle upper front and middle lower front segments of the liver (VIII and V, respectively).
Left lobe
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: left dorsal, left lateral, left paramedian.
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 front segments of the left lobe (IV and III, respectively).
You can examine the segmental structure of the liver in more detail on the diagrams below. For example, the figure shows one liver, which is visually divided into all its parts. The liver segments in the figure are numbered. Each number corresponds to a Latin segment number.
Picture 1:
Bile capillaries
Tubules carrying bile through the liver and gall bladder are called bile capillaries and form a branched structure - the system of bile ducts.
The bile produced by the liver cells flows into the microscopic channels - 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 are combined into one common hepatic duct, into which all bile flows.
The common hepatic duct finally connects to the cystic duct from the gallbladder. Together they form the 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 cystic duct by peristalsis, and remains in the gallbladder until it is needed for digestion.
Circulatory system
The blood supply to the liver is unique. Blood enters 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, gall bladder, small intestine and 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 the liver cells, blood collects in the hepatic veins, from which it enters the vena cava and returns to the heart.
The liver also has its own system of arteries and small arteries, which provide oxygen to its tissues in the same way as 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 multitude of capillary-like tubes - sinusoids. Like spokes in a 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 red blood cells passing through sinusoids.
• Hepatocytes (liver cells) are cuboidal epithelial cells that are between the sinusoids and make up the majority of the cells in the liver. Hepatocytes perform most of the functions of the liver - metabolism, storage, digestion and production of bile. The tiny collections of bile, known as its capillaries, run parallel to the sinusoids on the other side of the hepatocytes.
Liver pattern
We are already familiar with the theory. Let's now see what a person’s liver looks like. You will find photos and descriptions for them below. Since one picture cannot show the organ completely, we use several. It's okay if the two parts show the same part of the liver.
Figure 2:
Number 2 marks the human liver itself. Photos in this case would not be appropriate, therefore, we consider it according to the figure. The numbers are listed below, and what is shown below this number:
1 - the right hepatic duct; 2 - the liver; 3 - the left hepatic duct; 4 - common hepatic duct; 5 - common bile duct; 6 - pancreas; 7 - pancreatic duct; 8 - the duodenum; 9 - sphincter of Oddi; 10 - cystic duct; 11 - gall bladder.
Figure 3:
If you have ever seen an atlas of human anatomy, then you know that it contains approximately the same images. Here the liver is presented in front:
1 - inferior vena cava; 2 - a curved ligament; 3 - the right lobe; 4 - the left lobe; 5 - round ligament; 6 - gall bladder.
Figure 4:
In this figure, the liver is presented on the other hand. Again, the atlas of human anatomy contains almost the same figure:
1 - gall bladder; 2 - the right lobe; 3 - left lobe; 4 - cystic duct; 5 - hepatic duct; 6 - hepatic artery; 7 - hepatic portal vein; 8 - common bile duct; 9 - the inferior vena cava.
Figure 5:
This picture shows a very small part of the liver. Some explanations: the number 7 in the figure shows the triad portal - this is a group that combines the hepatic portal vein, the hepatic artery and the bile duct.
1 - hepatic sinusoid; 2 - liver 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. Liver segments are numbered with white numbers, each number corresponds to the Latin segment number:
1 - right hepatic vein; 2 - the left hepatic vein; 3 - middle hepatic vein; 4 - umbilical vein (residue); 5 - hepatic duct; 6 - the inferior vena cava; 7 - hepatic artery; 8 - portal vein; 9 - bile duct; 10 - cystic duct; 11 - gall bladder.
Physiology of the liver
The functions of the human liver are very diverse: it plays a serious role in digestion, in metabolism, and even in the storage of nutrients.
Digestion
The liver plays an active role in the digestion process 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 needed. When a meal containing fats reaches the duodenum, the cells of the duodenum release the hormone cholecystokinin, which relaxes the gallbladder. Bile, moving along the bile ducts, enters the duodenum, where it emulsifies large masses of fat. Emulsifying fats with bile turns large blocks of fat into small pieces that have a smaller surface area and are therefore easier to process.
Bilirubin, which is present in bile, is a product of the processing of worn red blood cells by the liver. Kupffer cells in the liver trap and destroy old, worn red blood cells and transfer them to hepatocytes. In the latter, the fate of hemoglobin is decided - it is divided into heme and globin groups. The globin protein is further destroyed and used as an energy source for the body. The iron-containing heme group cannot be processed by the body and is simply converted to bilirubin, which is added to bile. It is bilirubin that gives bile its distinctive greenish color. Intestinal bacteria further convert bilirubin into the brown pigment strekobilin, which gives the excrement a brown color.
Metabolism
A lot of complex tasks associated with metabolic processes are assigned to hepatocytes of the liver. Since all blood, leaving the digestive system, passes through the hepatic portal vein, the liver is responsible for the absorption of carbohydrate, lipids and proteins into biologically useful materials.
Our digestive system breaks down carbohydrates into glucose monosaccharide, which cells use as their main source of energy. Blood entering the liver through the hepatic portal vein is extremely rich in glucose from overcooked food. Hepatocytes absorb most of this glucose and store it as glycogen macromolecules, a branched polysaccharide that allows the liver to store large amounts of glucose and quickly release it between meals. The absorption and release of glucose by hepatocytes helps maintain homeostasis and lower blood glucose levels.
Fatty acids (lipids) of blood passing through the liver are absorbed and absorbed by hepatocytes to produce energy in the form of ATP. Glycerin, one of the components of a lipid, is converted by hepatocytes into glucose through the process of gluconeogenesis. Hepatocytes can also produce lipids such as cholesterol, phospholipids and lipoproteins, which 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 broken down into amino acids by the digestive system before they are transmitted to the hepatic portal vein. Amino acids that enter the liver require metabolic processing before they can be used as an energy source. Hepatocytes first remove the amine group from amino acids and convert it to ammonia, which is ultimately processed into urea.
Urea is less toxic than ammonia and can be excreted along with urine as an unnecessary digestion. The remaining parts of the amino acids are cleaved into ATP or converted into new glucose molecules through the gluconeogenesis process.
Detoxification
As blood from the digestive organs passes through the portal bloodstream of the liver, hepatocytes control blood levels and remove many potentially toxic substances before they can reach the rest of the body.
Enzymes in hepatocytes convert many of these toxins (such as alcoholic beverages or drugs) into their inactive metabolites. In order to maintain hormone levels within homeostatic limits, the liver also metabolizes and removes hormones produced by the glands of the body from the bloodstream.
Storage
The liver provides storage of many essential nutrients, vitamins and minerals obtained from the transfer of blood through the liver portal system. Glucose is transported in hepatocytes by the action of the hormone insulin and stored as a glycogen polysaccharide. Hepatocytes also absorb fatty acids from digested triglycerides. Storage of these substances allows the liver to maintain blood glucose homeostasis.
Our liver also stores vitamins and minerals (vitamins A, D, E, K and B 12, as well as iron and copper minerals) in order to ensure a constant flow of these important substances to the tissues of the body.
Production
The liver is responsible for the production of several vital plasma protein components: prothrombin, fibrinogen, and albumin. Prothrombin and fibrinogen proteins are coagulation factors involved in the formation of blood clots. Albumins are proteins that support the isotonic environment of the blood so that 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 that forms part of the mononuclear phagocytes of the system along with macrophages of the spleen and lymph nodes. Kupffer cells play an important role as they process bacteria, fungi, parasites, worn blood cells, and cell breakdown products.
Ultrasound of the liver: normal and deviations
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 cannot hurt, since there are no nerve endings in it, you may not even notice how the situation became 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, but in the end it turns out that he has cirrhosis or liver cancer. And this can not be changed.
Although the liver has the ability to recover, she herself can never cope with such diseases. Sometimes she needs your help.
To avoid unnecessary problems, it’s enough just to sometimes visit a doctor and do an ultrasound of the liver, the norm of which is described below. Remember that the most dangerous diseases are associated with the liver, for example, hepatitis, which, without proper treatment, can lead to such serious pathologies as cirrhosis and cancer.
Now let's go directly to the ultrasound and its standards. First of all, the specialist looks to see if the liver is displaced and what are its sizes.
It is impossible to indicate the exact size of the liver, since it is impossible to fully visualize this organ. The length of the entire organ should not exceed 18 cm. Doctors examine each part of the liver separately.
To begin with, on the ultrasound of the liver should be clearly visible two of its shares, as well as the sectors into which they are divided. In this case, the ligamentous apparatus (that is, all the ligaments) should not be visible. The study allows doctors to study all eight segments separately, as they are also well visible.
Norm of sizes of the right and left lobe
The left lobe should be about 7 cm in thickness and about 10 cm in height. An increase in size indicates a health problem, possibly your sore liver. The right lobe, the norm of which is about 12 cm in thickness and up to 15 cm in length, as you see, is much larger than the left.
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 be no more than 8 mm, the portal vein - about 12 mm, and the vena cava - up to 15 mm.
For doctors, not only the size of the organs is important, but also their structure, the contours of the organ and their tissue.
Human anatomy (whose liver is a very complex organ) is a rather fascinating thing. There is nothing more interesting than understanding the structure of oneself. Sometimes it can even protect against unwanted diseases. And if you are vigilant, problems can be avoided. Going to the doctor is not as scary as it seems. Be healthy!