Liver is the largest ‘gland’ of the digestive system. It is located right under the dome of the diaphragm, coated by the capsule. It is distinguished the liver’s convex upper surface adjacent to the diaphragm, and a lower, downwardly facing and in contact with the back and abdominal organs. On the part of the upper surface of the liver it can be seen its right and left lobes, the boundary of which is the crescent liver ligament. To the lower surface of the right lobe there is a gallbladder, close to the deep groove of the liver there are the gates, in which there are large blood and lymph vessels, nerves, bile ducts. The mass of a liver of an adult healthy person is about 3% of body weight, liver dimensions: 25-30 x 15-20 x 10-15 cm (Clemente).
Liver is a vital exocrine gland of the vertebrates, including humans, located in the abdominal cavity (abdomen) below the diaphragm and performing a wide variety of the physiological functions.
Anatomy
The liver consists of two parts: the left and right. In the right lobe it is recovered two more secondary lobes: square and caudate. According to the modern segmental scheme, proposed by Claude Quinn (1957), the liver is divided into eight segment, forming the right and left lobes. Liver segment is a pyramidal section of liver parenchyma with a distinct enough blood supply, innervation, and the outflow of bile. Caudate and square lobes, located behind and in front of the gate of the liver, according to this scheme correspond to SI and SIV of the left lobe. In addition, in the left lobe it is distinguished SII and SIII of the liver; the right lobe is divided into SV - SVIII, numbered around the liver gate clockwise (Abdel-Misih and Bloomston 643-653).
Thus, in connection with the development of surgery and hepatology now it is created the doctrine of the segmental structure of the liver, which has changed the old idea of the division of liver and only a fraction of cloves (Ritter). As noted in the liver has a tubular five systems:
1. biliary tract;
2. arteries;
3. the branches of the portal vein (portal system);
4. hepatic veins (caval system);
5. lymphatics (Clemente).
Portal and caval veins and system do not coincide with each other, and the remaining pipe systems accompany the portal vein branch and run parallel to each other and form secretory-vascular bundles, to which the nerves are joined. A part of the lymphatic vessels comes out with the hepatic veins (Tortora, Derrickson).
Liver segment is a pyramidal portion of its parenchyma, adjacent to the so-called hepatic triad: a branch of the portal vein of the second order, accompanying its own branch of the hepatic artery and the corresponding branch of the hepatic duct (Abdel-Misih and Bloomston 643-653).
The liver is divided into the following segments, starting from the sulcus venae cavae to the left, counter-clockwise:
• I - tailed segment of the left lobe corresponding to the same lobe of the liver;
• II - the posterior segment of the left lobe, which is localized in the posterior part of the same name lobe;
• III - the anterior segment of the left lobe, located in the same department of it;
• IV - a square segment of the left lobe, corresponding to the same name lobe of the liver;
• V - upper-middle anterior segment of the right lobe;
• VI - lower lateral-anterior segment of the right lobe;
• VII - lower lateral-posterior segment of the right lobe;
• VIII - middle upper-posterior segment of the right lobe (Tortora, Derrickson).
The segments, grouped radially around the gate of the liver, enter into the larger parts of the independent liver sections, called zones or sectors.
There are five such sectors:
1. the left lateral segment of the sector corresponds to the segment II (mono-segmental sector);
2. left paramedian sector, formed by the segments III and IV;
3. right paramedian sector, comprising to the V and VIII segments;
4. the right lateral sector, including segments VI and VII;
5. the left dorsal sector, corresponding to I segment (mono-segmental sector) (Abdel-Misih and Bloomston 643-653).
The segments of the liver are formed in the uterine period and clearly expressed at the time of birth. The doctrine of the segmental structure of liver deepens the old ideas of dividing its only into the lobes and cloves.
The histological structure of the liver
Hepatic lobule is a structural and functional unit of the liver. The main structural components of the liver lobules are:
hepatic plates (radial rows of hepatocytes);
intralobular sinusoidal hemocapillars (between the hepatic beams);
bile capillaries (Lat. ductuli beliferi) inside the hepatic beams, between two layers of the hepatocytes;
bile capillary expansion as they emerge from slices;
perisinusoidal space (or space of Disse), which is the space between the slit beams and hepatic sinusoidal hemocapillars;
central vein, formed by the merger intralobular sinusoidal hemocapillars (Self).
The features of the liver blood supply reflect its important biological function of detoxification: blood from the intestines, containing toxic substances consumed to the outside, as well as microbial waste products in the portal vein are delivered to the liver for the detoxification.
Then the portal vein is divided into the smaller interlobular veins. Arterial blood enters the liver through the own hepatic artery (a. Hepatica propria), branching to the interlobular arteries. Interlobular arteries and veins emit the blood into sinewaves, wherein thus mixed blood flows, the drainage of which occurs in the central vein. The central veins are collected into the hepatic veins in more inferior vena cava (Ritter).
The gallbladder is located under the gate of the liver. It extends to the outer edge of the liver and goes to the duodenum. The gallbladder is a pear shape, its length is 12-18 cm. Anatomically, the gallbladder is divided into a larger part - the bottom, the middle part - the body and the tapered part - the neck. Bladder neck transfers into the common cystic duct (Abdel-Misih and Bloomston 643-653).
Bile ducts, leaving the hepatic lobules, form the bile ducts, which merge into the right and left, then to the common hepatic duct. Hepatic duct is divided into two parts, one of which goes into the common bile duct and opens into the duodenum, and the other part goes into the cystic duct and ends by the gall bladder (Tortora, Derrickson).
The liver lobules produce the bile. Then the bile flows through the hepatic duct into the gallbladder, where it's stored. The gallbladder can collect up to 60 ml of bile.
There are liver and gallbladder bile. Hepatic bile is produced by 800-1000 ml per day. It is the liquid consistency and has a light brown color. Bile, entered to the gall bladder, is concentrated by the reabsorption of the liquid portion of the blood, so that it becomes thick and dark brown (Ritter).
The composition of bile includes water, bile acids (taurocholic and glycocholic sodium salt), bile pigments (bilirubin, biliverdin) and fats. It also comprises lecithin, cholesterol, mucus, potassium, sodium, magnesium, calcium and the enzyme - phosphatase. Out of the bile pigments it is formed the stool pigments (stercobilin) and urine pigments (urobilin) (Ritter).
Liver Functions
The liver performs the multiple functions, of which the most important function is metabolic (participation in interstitial metabolism), excretory and barrier. In the liver, it is carried out the synthesis of proteins (it is formed the blood albumin, the bulk of the blood clotting factors, and others). It occurs the most intense protein breakdown. The liver is involved in the metabolism of amino acids, the synthesis of glutamine and creatinine (Self).
It is carried the urea formation. The essential role in the metabolism of lipids is played by the liver, which is closely associated with the biliary liver function, because the bile is essential for the digestion and absorption of fats in the intestine (Busuttil, Klintmalm).
Mainly in the liver it is synthesized the triglycerides, phospholipids and bile acids; it is formed a significant part of the endogenous cholesterol; it passes the oxidation of triglycerides, the formation of the acetone bodies (Ritter).
Liver is also actively involved in the metabolism of carbohydrates: it is synthesized the sugar in it, glucose is oxidized, the synthesis and breakdown of glycogen. It is an important depot of glycogen in the body. The participation of the liver in the pigment metabolism is the formation of bilirubin, capture it from the blood, conjugation and excretion into the bile. It also plays an important role in the metabolism of hormones, biogenic amines, vitamins. It is closely associated with the liver and the formation of trace elements (Busuttil, Klintmalm).
The barrier function of the liver is aimed at the protection of the body from the damaging effects of the foreign agents and products of metabolism, maintaining a constant internal environment of the body. The barrier function is carried out by the security and neutralizing action of the liver. The protective effect is provided by the non-specific and specific (immune) mechanisms. Due to the non-specific mechanisms are removed from the blood by the phagocytosis of microorganisms and their toxins, immune complexes, and other fat droplets. Specific (immune) reactions are carried out through the protective activity of lymphocytes of lymph nodes of the liver and synthesized antibodies (Tortora, Derrickson).
Liver functions are the followings:
neutralization of the various foreign substances (xenobiotics), including allergens, toxins and poisons, by converting them into harmless, less toxic or more easily removed from the compound body;
neutralization and elimination of the excess hormones, neurotransmitters, vitamins, and toxic intermediate and end products of metabolism, such as ammonia, phenol, ethanol, acetone, acids and ketones;
participation in digestion, namely provision of glucose energy needs of the body, and energy conversions (free fatty acids, amino acids, glycerol, lactic acid and others) into the glucose (called gluconeogenesis);
the completion and storage of quick mobilization of energy reserves in the form of the glycogen depots and regulation of carbohydrate metabolism;
updating and storage depot for some vitamins (especially high hepatic reserves of fat soluble vitamins A, D, water-soluble vitamin B12), as well as a number of microcells depot cations - metals, particularly iron cations, copper and cobalt. Also, the liver is directly involved in the metabolism of vitamins A, B, C, D, E, K, PP and folic acid;
participation in the processes of hematopoiesis (only the fetus), in particular, the synthesis of many plasma proteins - albumin, alpha- and beta-globulin, transport proteins, hormones and various vitamins and protein coagulation anticoagulative system of blood, and many others; the liver is an important organ of hematopoiesis in the prenatal development;
synthesis of cholesterol and its esters, lipids and phospholipids, lipoproteins and regulation of lipid metabolism;
synthesis of bile acids, bilirubin production and secretion of bile;
liver serves as a depot for a fairly large volume of blood that can be thrown into the general bloodstream when blood loss or shock due to narrowing of the blood vessels supplying the liver;
synthesis of hormones and enzymes that are actively involved in the transformation of food into 12-duodenum and other parts of the small intestine;
in the fetal liver executes the hematopoietic function; detoxification function of the liver of the fetus is negligible, since it is performed by the placenta (Self).
Some idea of the liver anatomy gives its palpation. Normally, in the supine position while relaxing the muscles of the abdomen liver is usually palpable just below the costal arch on the right midclavicular line, and with a deep breath of its lower boundary falls to 1-4 cm.
The surface of the liver is smooth; the lower (front) edge is slightly sharp, smooth and painless. Poor location of the lower edge of the liver indicates its increase or omission. During the palpation of the liver it is necessary to follow all its lower edge. Modern research methods allow to significantly expand the idea of the anatomy and physiology of the liver (Busuttil, Klintmalm).
As a conclusion, it could be said that the liver is one of the most unique bodies. Of course, every organ of the body is indispensable in its own way, but the liver is unmatched by any one of them. Functional features of the liver are closely related to its particular anatomical structure. For example, the blood enters the liver not only through the arteries, as happens with all other organs, but also through the vein (Self).
In addition to the hepatic artery, extending from the aorta and supplying the liver with blood rich of oxygen, portal vein also comes to the liver, which delivers blood to the most of the abdominal organs. Venous blood in the portal vein is low in oxygen, but there are all the matter sucked into the bloodstream from the gastro-intestinal tract (such as nutrients and toxic). All substances, passing through the liver, are recognized as harmful or beneficial. The required amount of mineral (nutrients) remains in the liver ‘for its own needs,’ the rest is distributed throughout the body. Harmful substances are retained in the liver cells, which undergo a chemical reaction, which reduces their risk for the organism. Due to its anatomical and functional characteristics, the liver performs many important functions (Abdel-Misih and Bloomston 643-653).
The human body is arranged in such a way that all the bodies can be divided into vital and auxiliaries. Liver clearly belongs to the first group. Its importance in the maintaining of the viability of the organism can not be overstated. It is a powerful parenchymal organ that combines the functions of the digestive gland and peculiar biochemical laboratory.
Works Cited
Abdel-Misih, Sherif R. Z. and Mark Bloomston. "Liver Anatomy". Surgical Clinics of North America 90.4 (2010): 643-653. Web. 11 May 2016.
Busuttil, Ronald W., and Goran B. Klintmalm. Transplantation of the Liver. London: Elsevier Health Sciences, 2014. Print.
Clemente, Carmine D. Anatomy : a regional atlas of the human body. Philadelphia: Wolters Kluwer/Lippincott Williams & Wilkins Health, 2011. Print.
Ritter, Jessica A. Human Anatomy & Physiology + New Masteringa & p With Pearson Etext. City: Benjamin-Cummings Pub Co, 2012. Print.
Self, Will. Liver. New York: Bloomsbury, 2009. Print.
Tortora, Gerard J., and Bryan Derrickson. Principles of anatomy and physiology. Hoboken, NJ: John Wiley & Sons, 2010. Print.
