Accessory Organs:

1.

2. Gall Bladder

3.

1. Liver (Structure and Functions)

 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 (), 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.

 The liver lies in the upper right part of the abdominal cavity.

 It occupies most of the right hypochondrium and epigastrium.

 In adults the liver weighs 2% of body mass.

 An overall wedge shape.

 The liver capsule plays an important part in maintaining the integrity of its shape.

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

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.

LOBATION AND SEGMENTATION: The liver has four lobes or eight segments:  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.

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 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 .  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. 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. Portal vein:  Portal vein is a valve less structure that is formed by the confluence of the superior mesenteric vein and the splenic vein.  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.  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.  The portal vein supplies the liver with 5% of its resting oxygen consumption but significantly more of its metabolic nutrition.

Hepatic Artery:  Provides the remaining 25% of the blood flow to the liver  Common hepatic artery arises from the celiac axis, ascends in the , 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.

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.  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.

Nerve Supply:  The liver has a dual nerve supply.  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.  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.

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.  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 plates.  Bile secreted by the hepatocytes is collected in a network of minute tubes (canaliculi).

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

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. .Connective tissue cells of the capsule and portal tracts.

Functions of Liver  The liver regulates most chemical levels in the blood and excretes a product called bile, this helps carry away waste products from the liver.  All the blood leaving the stomach and intestines passes through the liver. The liver processes this blood and breaks down, balances, and creates the nutrients.  Metabolizes drugs into forms that are easier to use for the rest of the body or that are nontoxic.

 Production of bile, which helps carry away waste and break down fats in the small intestine during digestion.

 Production of certain proteins for blood plasma.

 Production of cholesterol and special proteins to help carry fats through the body.

 Conversion of excess glucose into glycogen for storage (glycogen can later be converted back to glucose for energy) and to balance and make glucose as needed.

 Regulation of blood levels of amino acids, which form the building blocks of proteins.

 Processing of hemoglobin for use of its iron content (the liver stores iron).

 Conversion of poisonous ammonia to urea (urea is an end product of protein metabolism and is excreted in the urine).

 Clearing the blood of drugs and other poisonous substances.

 Resisting infections by making immune factors and removing bacteria from the bloodstream.

 Clearance of bilirubin, also from red blood cells. If there is an accumulation of bilirubin, the skin and eyes turn yellow.  Bile helps the small intestine break down and absorb fats, cholesterol, and some vitamins. Bile consists of bile salts, cholesterol, bilirubin, electrolytes, and water.  Bilirubin is formed by the breakdown of hemoglobin. The iron released from hemoglobin is stored in the liver or bone marrow and used to make the next generation of blood cells.  Vitamin K is necessary for the creation of certain coagulants that help clot the blood. Bile is essential for vitamin K absorption and is created in the liver. If the liver does not produce enough bile, clotting factors cannot be produced.  Bile breaks down fats and makes them easier to digest.  Carbohydrates are stored in the liver, where they are broken down into glucose and siphoned into the bloodstream to maintain normal glucose levels. They are stored as glycogen and released whenever a quick burst of energy is needed.  The liver stores vitamins A, D, E, K, and B12. It keeps significant amounts of these vitamins stored. The liver stores iron from hemoglobin in the form of ferritin, ready to make new red blood cells. The liver also stores and releases copper.  Bile helps break down proteins for digestion.  The liver filters and removes compounds from the body, including hormones, such as estrogen and aldosterone, and compounds from outside the body, including alcohol and other drugs.  The liver is part of the mononuclear phagocyte system. It contains high numbers of Kupffer cells that are involved in immune activity. These cells destroy any disease-causing agents that might enter the liver through the gut.

 Albumin is the most common protein in blood serum. It transports fatty acids and steroid hormones to help maintain the correct pressure and prevent the leaking of blood vessels.

 Synthesis of angiotensinogen: This hormone raises blood pressure by narrowing the blood vessels when alerted by production of an enzyme called renin in the kidneys.

2. Gall Bladder:  A storage sac.  The bile is secreted into it  The bile is stored here. How it works:  Food containing fat enters the digestive tract.  Salts are secreted into the small intestine to digest fats.  The bile emulsifies fats in partly digested food thereby assisting their absorption. 3. Pancreas:  The pancreas secretes a number of different enzymes into the small intestine.  Role is to digest carbohydrates lipids & proteins completely.  It also secretes bicarbonate ions. Role:  Neutralize the HCl from the stomach change the pH of the small intestine to a pH of 8.  The pancreas will secrete about 1.0 L. of pancreatic fluids per day.