Mona Theodoraki

Organisation Of The Liver

Morphological Anatomy

Liver under right diaphragmatic dome, in right upper quadrantSurrounded by ribs and dome of diaphragmCapsule of liver very nerve rich so lots of pain when liver damaged

Blood Supply Of The Liver

Rich blood supply – 25% of resting cardiac outputDual blood supply – difficult for liver to become ischaemic20% arterial blood from hepatic artery (left and right branches)80% venous blood draining from gut through hepatic portal veinHPV drains gut – blood rich in absorbed nutrients which must pass through liver

Lobes Of The Liver

Anatomical lobes based on attachment of mesenteriesBoundary between territories of left and right branches of hepatic artery is importantPuts small lobes (caudate and quadrate) in with functional left lobe

Functional Anatomy

Couinaud classification8 functionally independent segmentsCentrally – portal vein, hepatic artery and bile ductPeripherally – hepatic veinEach segment can be resected without damaging those remainingNumbered clockwiseCaudate lobe (segment 1) is posteriorAnatomical variants frequently occur

Embryological Origins

Liver and biliary system share common origin with ventral part of pancreas at beginning of midgutSeptum transversum arises at embryonic junctional site – where ectoderm of amnion meets endoderm of yolk sac (externally), where foregut meets midgut (internally)Mesenchymal structure of septum transversum provides support upon which liver and blood supply can develop

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Biliary Tract

Biliary tract has spiral muscle structure which twists and untwistsAs it untwists it becomes patent (expanded/open) and allows bile to pass throughBiliary obstruction results in jaundice (see previous lecture)

Histological Structure

Liver consists of lobules consisting of cords (sheets) of liver epithelial cells (hepatocytes)Radiate from central vein (draining via main hepatic veins to IVC)Round the edges of adjoining lobules are portal triadsPortal triads consist of – arteriole, branch of portal vein, bile ductAll come from main triad entering liver at porta or hilum

Liver Cell Types

Hepatocytes – 80%Endothelial cells – lining blood vessels and sinusoidsCholangiocytes – lining biliary structuresKupffer cells – fixed phagocytes (liver macrophages)Hepatic stellate cells – vitamin A storage cells, may be activated to fibrogenic myofibroblastic phenotypeHepatocyte sheets near central vein of lobuleFlattened dense cell nuclei belong to phagocytic Kupffer cellsHepatocyte nuclei are paler and rounded

Lobule Vs. Acinus

LobuleHistological (morphological unit)Easily identifiedHepatic vein at centreAcinusFunctional unitLess clearly identifiedUnit of hepatocytes aligned around hepatic arterioles and portal venulesAcinus divided into zones dependent on proximity to arterial blood supply

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Liver Functions

Most functions carried out by hepatocytesBreakdown and recycling of red cells carried out by fixed macrophages (Kupffer cells) in endothelial lining of blood sinusoidsSinusoid – small blood vessel similar to capillary but with fenestrated endotheliumLarge multifunctional organFunctions carefully regulated to meet body requirementsKey role in – digestion, biosynthesis, degradation and detoxification, energy and metabolism

Space Of Disse

Space of Disse – location in liver between hepatocyte and sinusoidContains blood plasmaMicrovilli of hepatocytes extend into this space, allowing proteins and other plasma components from sinusoids to be absorbed by hepatocytesSpace may be obliterated in liver disease, leading to decreased uptake by hepatocytes of nutrients and wastes (eg. bilirubin)Space of Disse has phagocytes

Liver Structure In Disease

Activated stellate cellsDeposition of scar matrixLoss of fenestrae in hepatic sinusoidKupffer cell activationLoss of hepatocyte microvilli