Embryology of the Hepatopancreatobiliary System Prof Abdulameer AlNuaimi

Embryology of the Hepatopancreatobiliary System Prof. Abdulameer Al-Nuaimi E-mail: a. al-nuaimi@sheffield. ac. uk E. mail: abdulameerh@yahoo. com

Liver Diaph & Visc. Surfaces Falciform Lig. Diaphrag. Surface Caud. Lobe Lt. Triang. Lig. Venos. Rt. Triang Lig Rt. Lobe Lt. lobe Visceral surface Bare area Ant. Cor. Lig Post Cor. Lig Porta hepatis Quad. lobe Visceral surface Gallbladder www. google. co. uk/search?

Aorta Duct. Art. Pulm. Trunk Rt. At, Rt. Ven. Internal Lt. Ven.

www. google. co. uk/search? Hepatic duct Sagittal Section in the body Diaphragm Reflection of peritoneum from Liver to Diaphragm Bare area of the liver Diaphragm atic surface Reflection of peritoneum from Liver to the post. Abdominal wall Subphrenic space Post. Abdominal wall Hepatorenal space Ampulla of Vater Greater Sac Inferior (visceral) surface

Blood Supply of the Liver The liver receives blood from two sources. 1 - 25% of the blood supply to the liver is arterial blood from the hepatic artery (oxygenated). 2 - 75% of the blood entering the liver is venous blood from the hepatic portal vein (deoxygenated and containing nutrients). In the liver, the terminal branches of the portal vein and hepatic artery empty together in sinusoids surrounding the hepatic cells. Blood leaves the liver via the hepatic veins which end in the Inferior Vena Cava. This blood is, deoxygenated, detoxified, and containing normal (homeostatic) nutrient levels.

P. V. S. M. V. I. M. V. Portal system www. google. co. uk/search?

Histology of Liver The liver is divided into thousands of small units called lobules by thin layer of connective tissue. Each lobule is about 1 mm in diameter and roughly hexagonal in shape. The Lobule is composed of radiating double plates of liver cells (Hepatocytes) separated by a Vascular sinusoidal network. Each lobule has a central vein in the middle and portal triads at the vertices. Each portal triad contains branch of hepatic artery, portal vein and Bile duct.

Liver Lobules Portal Triad Central Vein www. google. co. uk/search?

Sinusoids have an incomplete lining of highly fenestrated endothelial cells, some of these cells are macrophagic In function (reticulo-endothelial cells), they are called Kupffer cells. The space between endothelium and hepatocytes is called the Space of Disse. In these spaces, lymph is collected and delivered to lymphatic capillaries. Lymph is collecting in hepatic duct outside the liver. Blood from the branches of hepatic artery and portal vein in the Portal triad, drains into sinusoids and then to the central vein. Central Veins carry the blood to hepatic veins which end in the Inferior vena cava. Bile is formed by liver cells and is discharged into the bile canaliculi within layers of the cell plates, and then drains into bile duct of the triads.

Histology of Liver www. google. co. uk/search?

Histology of Liver www. google. co. uk/search?

Development of Liver In the middle of the 3 rd week of pregnancy, the liver bud appears as an endodermal out growth from the distal part of the Foregut (Duodenum). Liver bud proliferates rapidly as an epithelial liver cords and penetrates the ventral mesentery. While hepatic cells are proliferating and penetrating the ventral mesentery, the connection between the liver diverticulum and the duodenum narrows and forming the Bile Duct. A small ventral outgrowth develops from the bile duct, this new growth forms the Gallbladder and Cystic Duct. Further growth of liver bud, allows the epithelial liver cords intermingle with the umbilical and vitelline veins. These veins form Hepatic Sinusoids.

Liver cords differentiates into Hepatocytes (liver paranchyma) and form the lining of the biliary ducts. Mesoderm of the ventral mesentery gives rise to Hematopoietic cells, Kupffer cells and connective tissue cells. The Ventral mesentery of the Foregut, is divided by liver into Lesser Omentum and Falciform Ligament. The liver is clothed by peritoneum except its cranial surface, which is never covered by peritoneum and remains in direct contact with the diaphragm; this area is the Bare Area of the Liver.

www. google. co. uk/search? Dorsal Pancreas Budding of Liver

At age of the 10 th week, the liver weight is about 10% of the total body weight. This is due to the presence of large numbers of sinusoids and involvement of the liver in hematopoietic function (production of white and red blood cells). At birth, the liver weighs about 5% that of the body weight, this is due to the existence of a small number of hematopoietic islands in the liver, and its hematopoietic activity is greatly reduced. Hepatic cells start production of Bile at age of the 12 th week.

During rotation of the Foregut, the duodenum changes to Cshaped Loop and rotates and swings to the right side of the body. The head of pancreas grows rapidly and fills in the concavity of the C-shaped duodenum. In this process the right surface of dorsal mesoduodenum fuses with peritoneum lining the posterior abdominal wall, then both layers eventually disappear, and the duodenum and head of pancreas become fixed in a retroperitoneal position to the right side of the midline. As a result of rotation of the duodenum, the entrance of the bile duct in the duodenum is changed from its initial anterior position to a posterior one. Then as a result of swinging and positional changes of duodenum to the right, the bile duct is shifted behind the duodenum and enters its posteromedial side.

Development of Liver and Pancreas www. google. co. uk/search?

Entrance of Co. Bile duct Co. B. D Extrahepatic bile duct Liver bud Co. B. D Liver Development of Duodenum www. google. co. uk/search?

Liver Com. Bile Duct www. google. co. uk/search?

The Pancreas is a soft lobulated organ located retroperitoneally across the posterior abdominal wall, it sits behind the stomach across the back of the abdomen. It is described as an organ having head, neck, body, and tail. The head is disc-shaped and lies within the concavity of the duodenum. Part of the head extends to the left behind the superior mesenteric vessels, it is called Uncinate process. The body extends to the left side and ends as a tail near the hilus of the spleen. The pancreas is made up of two types of glands, 1 -An exocrine gland that secretes digestive enzymes and Sodium bicarbonate into the duodenum through the main and accessory pancreatic ducts. Both ducts are usually interconnected.

2 - An endocrine gland, which consists of the islets of Langerhans, secretes hormones into the bloodstream. Islets of Langerhans are named for the German physician Paul Langerhans, who first described them in 1869. The normal human pancreas contains about 1, 000 islets. Cells of islets of Langerhans 1 -Beta cells (β-cells), they make about 65 -80% of the cells in the islets and produce Insulin. 2 -alpha cells (α-cells), 15 -20%, they produce an opposing hormone, Glucagon which releases glucose from the liver and fatty acids from fat tissue. 3 -Delta cells (δ-cells), 3 -10%, they secrete somatostatin a strong inhibitor of somatotropin, insulin, and glucagon; its role in metabolic regulation is not yet clear. Somatostatin is also produced by the hypothalamus and functions to inhibit secretion of growth hormone by the pituitary gland.

Pancreas P www. google. co. uk/search?

Development of Pancreas The Pancreas develops from the endodermal lining of the duodenum as a dorsal and ventral buds. The dorsal bud is in the dorsal mesentery and the ventral bud is in the ventral mesentery, close to the bile duct. When the duodenum rotates and become C-shaped, the ventral bud and the entrance of the common bile duct in the duodenum are shifted dorsally. The ventral bud comes to lie immediately below and behind the dorsal bud, finally the parenchyma and duct systems of both buds fuse together. Following swinging of the duodenum to the right, the pancreas and duodenum settles down on the posterior abdominal wall in a retroperitoneal position. The ventral pancreatic bud forms the Uncinate process and inferior part of the head of pancreas, where as the dorsal

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Entrance of Co. Bile duct Co. B. D Extrahepatic bile duct Liver bud Co. B. D Liver Development of Duodenum www. google. co. uk/search?

Pancreatic duct The main pancreatic duct is formed by the union of the ventral pancreatic duct with the distal part of the duct of dorsal bud. The proximal part of the dorsal pancreatic duct, either obliterates or persists to form the Accessory pancreatic duct. The main pancreatic duct, together with common bile duct, enter the Ampulla of Vater which enters the posteromedial wall of the duodenum at the site of Major Papilla. Accessory pancreatic duct when persist (in 10% of cases), drains the lower part of the head and uncinate process, it opens into the duodenum at Minor Papilla, 3 cm proximal to the opening of the main duct.

www. google. co. uk/search? Pancreatic duct Access. Panc. Duct Minor Papil Com. Bile Duct Major Papilla Main Panc. Duct. Access Pan. Duct Uncinate Process

Pancreatic islets of Langerhans develops from the parenchyma of pancreas at the third month of fetal life. Insulin secretion begins at the fifth month. Pancreatic connective tissue develops from the visceral surrounding mesoderm.

Variations of the opening of common bile duct and pancreatic duct into the duodenum (Contemp Surg 1987) A- In 85% of cases the common bile duct and pancreatic duct end in the Ampulla of Vater. B- In 5% of cases, Ampulla of Vater is not present. C- In 9% of cases, the common bile duct and pancreatic ducts open separately into the duodenum. 85% 5% 9% www. google. co. uk/search?

variations of the third portion of common bile duct to pancreas (Smanio, 1954). A, B - The bile duct is partially covered by a tongue of pancreatic tissue (44%). C- The bile duct is completely covered by pancreatic tissue (30%). D- The duct is uncovered by pancreatic tissue and located on the posterior surface of the pancreas (16. 5%). E- The common bile duct is covered by two tongues of pancreatic tissue (9%). 44% Posterior surface of the Head of pancreas and common bile duct www. google. co. uk/search? 30% 16. 5% 9%

Summary The liver bud appears as an endodermal out growth from the distal part of the Foregut (Duodenum). This gives rise to the liver and Extra hepatic biliary passages. During development, rotation and Rt swinging of duodenum, the bile duct entrance in duodenum is shifted from its initial anterior to a posteromedial position. The Pancreas develops from the endodermal lining of the duodenum as a dorsal and ventral buds. During rotation of duodenum, the ventral bud is shifted dorsally and fuses with the dorsal bud. islets of Langerhans develops from the parenchyma of pancreas at the third month of fetal life.

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