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Functional histology of liver

Functional histology of liver. Functions of the liver. Production of circulating plasma proteins. Albumins Lipoproteins [VLDLs, LDLs, HDLs] Glycoproteins e.g. transferrin Prothrombin Fibrinogen Non-immune globulins. Vitamin storage and conversion. Vitamin A [retinol]

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Functional histology of liver

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  1. Functional histology of liver

  2. Functions of the liver

  3. Production of circulating plasma proteins • Albumins • Lipoproteins [VLDLs, LDLs, HDLs] • Glycoproteins e.g. transferrin • Prothrombin • Fibrinogen • Non-immune globulins

  4. Vitamin storage and conversion • Vitamin A [retinol] • Vitamin D [cholecalciferol] • Vitamin K

  5. Degradation of drugs and toxins 2 processes • Oxidation • Conjugation with glucoronic acid, glycine and taurine [products become water soluble and removed by kidneys]

  6. Involvement in metabolic pathways • Glycogenolysis • Consumption of fatty acids by beta oxidation for energy • Production of ketone bodies – used as fuel by other organs • Urea synthesis • Synthesis and conversion of non-essential amino acids

  7. Bile production • Liver converts substrates delivered by blood from digestive tract, pancreas and spleen • Some of these products are involved in the production of bile

  8. Bile contains conjugated and degraded waste products that are returned to intestine for disposal, as well as substances that bind to metabolites in the intestine to aid in absorption

  9. Modification and structure and function of hormones • Conversion of Vitamin D to 25- hydroxycholecalciferol • Conversion of Thyroxine to its biologically active form, triiodothyronine • Modificationof action of Growth hormone by Growth hormone releasing hormone [GHRH] produced by liver

  10. Degradation of insulin and glucagon

  11. STRUCTURAL ORGANISATION • Parenchyma, consisting of organised plates of hepatocytes, which are normally one cell thick and separated by sinusoidal capillaries. In children, the liver cells are arranged I plates 2 cell thick • Connective tissue stroma, that is continuous with the fibrous capsule of Glisson. Blood vessels, nerves, lymphatic vessels and bile ducts travel with the stroma

  12. Sinusoidal capillaries (sinusoids), the vascular channels between plates of hepatocytes • Perisinusoidal spaces (spaces of Disse), between sinusoidal epithelium and hepatocytes

  13. Classic hepatic lobule

  14. Roughly hexagonal mass of tissue • Consists of stacks of anastomosing plates of hepatocytes, one cell thick, separated by the anastomosing system of sinusoids that perfuse the cells with the mixed portal and arterial blood.

  15. Each lobule measures about 2.0 × 0.7 mm. • At the center of the lobule is a relatively large venule, the terminal hepatic venule (central vein)into which the sinusoids drain.

  16. The plates of cells radiate from the central vein to the periphery of the lobule, as do the sinusoids. • At the angles of the hexagon are the portal areas (portal canals), loose stromal connective tissue characterized by the presence of the portal triads..

  17. This connective tissue is ultimately continuous with the fibrous capsule of the liver. • The portal canal is bordered by the outermost hepatocytes of the lobule

  18. The blood vessels and draining branches of the bile duct system course together in a relationship called portal triad. • This is a misnomer, as one or more lymphatic vessels always travel with the vein artery and bile duct

  19. At the edges of the portal canal, between the connective tissue stroma and the hepatocytes, is a small space called the space of Mall. • This space is thought to be one of the sites where lymph originates in the liver.

  20. In some species, e.g., the pig, the classic lobule is easily recognized because the portal areas are connected by relatively thick layers of connective tissue.

  21. In some species, e.g., the pig, the classic lobule is easily recognized because the portal areas are connected by relatively thick layers of connective tissue.

  22. In humans, however, there is normally very little interlobular connective tissue, and it is necessary, when examining histologic sections of liver, to draw imaginary lines between portal areas surrounding a central vein to get some sense of the size of the classic lobule

  23. Kupffer cells • Belong to MPS- derived from monocytes • SEM and TEM show that they form part of the vessel lining • Previously they were described as lying on the luminal surface of endothelial cells. This was probably based on the fact that processes of Kupffer cells occasionally overlap endothelial processes on the luminal side

  24. They do not form junctions with endothelial cells • They form 15% of liver cell population- most are located in the periportal region

  25. Functions • Metabolisation of aged RBCs and digestion of Hb • Secretion of proteins related to immunologic processes • Destruction of bacteria

  26. In the fetal liver, the spaces between blood vessels and hepatocytes contain blood-forming cells. • In cases of chronic anaemia in the adults, these cells may reappear in the perisinusoidal spaces

  27. Perisinusoidal space/ space of Disse • lies between basal surface of endothelial cells and Kupffer cells- site of exchange of materials between blood and liver cells • Small ,irregular microvilli from hepatocytes project into this space, which increase the available surface area for exchange of materials 6 times

  28. The portal lobule • emphasizes the exocrine functions of the liver • Morphologic axis of the portal lobule is the lobule is the interlobular bile duct of the portal triad of the “classic” lobule. • Its outer margins are imaginary lines drawn between the three central veins that are closest to that portal triad.

  29. These lines define a roughly triangular block of tissue that includes those portions of three classic lobules that secrete the bile that drains into its axial bile duct. • This concept allows a description of hepatic parenchymal structure comparable to that of other exocrine glands

  30. The liver acinus • Structural unit that provides the best correlation between blood perfusion, metabolic activity, and liver pathology • Lozenge shaped and represents the smallest functional unit of the hepatic parenchyma. • The short axis of the acinus is defined by the terminal branches of the portal tried that lie along the border between two classic lobules.

  31. The long axis is a line drawn between the two central veins closest to the short axis. • In a two-dimensional view the liver acinus occupies parts of adjacent classic lobules. • This concept allows a description of the exocrine secretory function of the liver comparable to that of the portal lobule.

  32. The hepatocytes in each liver acinus are described as being arranged in three concentric elliptical zones surrounding the short axis

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