Liver anatomy and physiology

liver anatomy and physio

1. Liver: Anatomy and Physiology Dr. Himanshu Jangid

2. Liver : Introduction The liver is the largest of the abdominal viscera, occupying a substantial portion of the upper abdominal cavity. It performs a wide range of metabolic activities necessary for homeostasis, nutrition and immune defence . It is composed largely of epithelial cells ( hepatocytes ), which are bathed in blood derived from the hepatic portal veins and hepatic arteries. Hepatocytes are also associated with an extensive system of minute canals, which form the biliary system into which products are secreted.

3. The liver lies in the upper right part of the abdominal cavity. It occupies most of the right hypochondrium and epigastrium , frequently extends into the left hypochondrium as far as the left lateral line. In adults the liver weighs 2% of body mass. an overall wedge shape

4. The liver capsule plays an important part in maintaining the integrity of its shape. Once the capsule is lacerated, the liver tissue is easily parted and provides only limited support for surgical sutures. These features, in combination with its exceptional vascular supply, make the liver prone to potentially lethal injuries if it is split open.

5. EXTERNAL FEATURES The liver is attached to the anterior abdominal wall, diaphragm and other viscera by several ligaments, which are formed from condensations of the peritoneum : Falciform ligament Coronary ligament Triangular ligaments Lesser omentum

6. Porta hepatis The Porta hepatis is the area of the inferior surface through which all the neurovascular and biliary structures, except the hepatic veins, enter and leave the liver. It is situated between the quadrate lobe in front and the caudate process behind. Right and left hepatic bile ducts emerge from it. All these structures are enveloped in the perivascular fibrous capsule - hepatobiliary capsule of Glisson - a sheath of loose connective tissue which surrounds the vessels

7. The porta hepatis

8. LOBATION AND SEGMENTATION The liver has four lobes or eight segments , depending on whether it is defined by its gross anatomical appearance or by its internal architecture.

9. Gross anatomical lobes Right lobe The right lobe is the largest in volume and contributes to all surfaces Quadrate lobe The quadrate lobe is only visible from the inferior surface. it is functionally related to the left lobe. Caudate lobe this lobe is said to arise from the right lobe, but it is functionally separate Left lobe The left lobe is the smaller of the two 'main' lobes

10. Couinaud segments

11. Couinaud segments The liver is divided by the 'principal plane' into two halves of approximately equal size. The principal plane is defined by an imaginary parasagittal line from the gallbladder anteriorly to the inferior vena cava posteriorly . The usual functional division of the liver into right and left lobes lies along this plane. The liver is further subdivided into segments , each supplied by a principal branch of the hepatic artery, portal vein and bile duct.

12. Segments I, II, III and IV make up the functional left lobe, Segments V, VI, VII and VIII make up the functional right lobe. Segment I corresponds to the gross anatomical caudate lobe and segment IV to the quadrate lobe.

13. VASCULAR SUPPLY Two sources provide blood to the liver Hepatic artery Celiac trunk of aorta Portal vein Blood exits the liver via the central vein 25% of cardiac output Blood flow into the liver is controlled by number of factors Muscular sphincters Number of different stimuli, including the autonomic nervous system, circulating hormones, bile salts, and metabolites

14. Portal vein Portal vein is a valveless structure that is formed by the confluence of the superior mesenteric vein and the splenic vein. 75% of the total liver blood supply by volume 2 PV in liver Left 2,3,4 Right 5,6,7,8 Portal vein is formed by the union of the superior mesenteric vein and the splenic vein at the level of the second lumbar vertebra behind the head of pancreas Portal vein is contained within the hilum of the liver

15. Portal vein The portal vein gives rise to branching septal veins,. Blood from the septal veins enters directly into the parenchymal sinusoids between hepatocytes . Sinusoids are lined by fenestrated and discontinuous endothelial cells extrasinusoidal space of Disse , into which protrude abundant microvilli of hepatocytes Kupffer and presinusoidal stellate cells

16. The portal vein and its tributaries (semi-diagrammatic). Portions of the stomach, pancreas and left lobe of the liver and the transverse colon have been removed.

17. The portal vein supplies the liver with 5% of its resting oxygen consumption but significantly more of its metabolic nutrition. Progressive occlusion of the hepatic artery rarely results in complete necrosis of the liver, which is due principally to the blood supply derived from the portal vein.

18. Hepatic Artery Provides the remaining 25% of the blood flow to the liver Large amount of variability Common hepatic artery arises from the celiac axis, ascends in the hepatoduodenal ligament, and gives rise to the right gastric, gastroduodenal , and proper hepatic arteries; the proper hepatic artery then divides into the right and left hepatic arterial branches in the liver hilum Right artery off SMA (#1 variant)

19. Hepatic veins The liver has two venous systems. The portal system conveys venous blood from the majority of the gastrointestinal tract and its associated organs to the liver. The hepatic venous system drains blood from the liver parenchyma into the inferior vena cava.

20. The hepatic veins convey blood from the liver to the inferior vena cava. The right hepatic vein drains segments V, VI, VII and VIII. The left hepatic vein drains segments II and III with some drainage from segment IV. The hepatic veins have no valves.

21. Arrangement of the hepatic venous territories. Multiple lower group veins may be present. Individual segments may drain into more than one hepatic venous territory.

22. INNERVATION The liver has a dual innervation . Hepatic nerves, which arise from the hepatic plexus and contain sympathetic and parasympathetic ( vagal ) fibres Supply the parenchyma. They enter the liver at the porta hepatis and largely accompany the hepatic arteries and bile ducts.

23. INNERVATION The capsule is supplied by some fine branches of the lower intercostal nerves , which also supply the parietal peritoneum, particularly in the area of the 'bare area' and superior surface. This is seen clinically when distension or disruption of the liver capsule causes quite well localized sharp pain.

24. HEPATIC PLEXUS The hepatic plexus is the largest derivative of the coeliac plexus. It also receives branches from the anterior and posterior vagi . These branches not only supply vasomotor fibres to the hepatic vessels and biliary tree, but also innervate the hepatocytes directly and are involved in the control of some homeostatic mechanisms. The vagal fibres are motor to the musculature of the gallbladder and bile ducts and inhibitory to the sphincter of the bile duct.

25. REFERRED PAIN Pain arising from the parenchyma of the liver is poorly localized. In common with other structures of foregut origin, pain is referred to the central epigastrium . Stretch of or involvement of the liver capsule by inflammatory or neoplastic processes rapidly produces well-localized pain of a 'somatic' nature.

26. Functional Anatomy of Liver Liver is composed of hexagonal shaped units-lobules Radiate from central vein to the periphery Between the rows of hepatocytes are sinusoids which supply blood

27. Functional Anatomy of Liver In the mature liver, hepatocytes are arranged mainly in plates - or cords, Between the plates are venous sinusoids, which anastomose with each other via gaps in the hepatocyte plates. Bile secreted by the hepatocytes is collected in a network of minute tubes ( canaliculi ).

28. Portal Triad Branches of portal vein, hepatic artery and the biliary ducts bound together in the perivascular fibrous capsule

29. CELLS OF THE LIVER Cells of the liver include hepatocytes , hepatic stellate cells - also known as perisinusoidal lipocytes , or Ito cells - sinusoidal endothelial cells, macrophages ( Kupffer cells), the cells of the biliary tree - cuboidal to columnar epithelium - and connective tissue cells of the capsule and portal tracts.

30. Functions of the Liver Formation and secretion of bile Nutrient and vitamin metabolism      Glucose and other sugars   Amino acids   Lipids     Fatty acids     Cholesterol     Lipoproteins   Fat-soluble vitamins   Water-soluble vitamins

31. Inactivation of various substances      Toxins   Steroids   Other hormones Synthesis of plasma proteins    Acute-phase proteins   Albumin   Clotting factors   Steroid-binding and other hormone-binding proteins Immunity    Kupffer cells

32. Bile About 500 mL is secreted per day. Some of the components of the bile are reabsorbed in the intestine and then excreted again by the liver (enterohepatic circulation).

33. Composition of Human Hepatic Duct Bile

34. The glucuronides of the bile pigments, bilirubin and biliverdin, are responsible for the golden yellow color of bile. The bile salts are sodium and potassium salts of bile acids, and all those secreted into the bile are conjugated to glycine or taurine, a derivative of cysteine. The bile acids are synthesized from cholesterol.

35. P rimary bile acids F ormed in the liver are cholic acid and chenodeoxycholic acid. S econdary bile acids In the colon, bacteria convert cholic acid to deoxycholic acid and chenodeoxycholic acid to lithocholic acid .

36. Enterohepatic Circulation Enterohepatic circulation of bile salts. The solid lines entering the portal system represent bile salts of hepatic origin, whereas the dashed lines represent bile salts resulting from bacterial action.

37. Functions of the Gallbladder In normal individuals, bile flows into the gallbladder when the sphincter of Oddi is closed. In the gallbladder, the bile is concentrated by absorption of water. The degree of this concentration is shown by the increase in the concentration of solids liver bile is 97% water, whereas the average water content of gallbladder bile is 89%.

38. When the bile duct and cystic duct are clamped, the intrabiliary pressure rises to about 320 mm of bile in 30 minutes, and bile secretion stops . However, when the bile duct is clamped and the cystic duct is left open, water is reabsorbed in the gallbladder, and the intrabiliary pressure rises only to about 100 mm of bile in several hours. Acidification of the bile is another function of the gallbladder .

39. Comparison of Human Hepatic Duct Bile and Gallbladder Bile.

40. Regulation of Biliary Secretion C holagogues : Substances that cause contraction of the gallbladder When food enters the mouth, the resistance of the sphincter of Oddi decreases. Fatty acids and amino acids in the duodenum release CCK, which causes gallbladder contraction.

41. Effects of Cholecystectomy The periodic discharge of bile from the gallbladder aids digestion but is not essential for it. Cholecystectomized patients maintain good health and nutrition with a constant slow discharge of bile into the duodenum . B ile duct becomes somewhat dilated, and more bile tends to enter the duodenum after meals than at other times. Cholecystectomized patients can even tolerate fried foods, although they generally must avoid foods that are particularly high in fat content.

42. C holeretics : Substances that increase the secretion of bile The production of bile is increased by stimulation of the vagus nerves and by the hormone secretin, which increases the water and HCO 3 – content of bile. Bile salts themselves are among the most important physiologic choleretics.