HISTOLOGY Gastrointestinal & Nutrition Block GNT 223 Histology of Liver, Biliary System and Spleen, By Dr. Einas Yousef 2018/2019

Objectives By the end of the lecture, the student should be able to: 1. Describe the histological structure of liver with special emphasis on: Classical hepatic (liver) lobule. Hepatocytes. Portal tract (portal area). Hepatic (liver) blood sinusoids. Space of Disse (perisinusoidal space of Disse). Bile canalculi. 2. Identify & describe the histological features of: Intrahepatic biliary passages. Extrahepatic bile ducts. Gall bladder. 3. The histological structure of spleen with special emphasis on: The white pulp and the red Pulp.

Liver Porta hepatis The liver is the 2nd largest organ in the body (the largest is the skin). It is the largest gland in the body, weighting about 1.5 kg. The liver is an intraabodominal gland formed of two main lobes (Right and left lobes) and two associated small ones (caudate and quadrate lobes). It is an interface between the digestive system and the blood. The liver is the organ in which nutrients absorbed in the digestive tract are processed and stored for use by other parts of the body. So It is an interface between the digestive system and the blood.

Histology of Liver Stroma Capsule, trabeculae & Reticular CT The liver is surrounded by a thin CT capsule (Glisson’s capsule) and is covered partially with peritoneum. Glisson’s capsule is thickened at porta hepatis and sends trabeculae into the liver tissue dividing the parenchyma into incomplete lobules. Reticular CT: made up of reticular fibers & reticular cells. It forms a framework for the cell columns forming liver lobules. Glisson’s Capsule Trabecula 17-10-01

Histology of Liver B) Parenchyma The parenchymal tissue of the liver is formed of: 1- Hepatocytes 2- Blood vessels 3- Bile ducts 17-10-01

Hepatocytes Shape: Polyhedral cells with six or more surface. Organelles: The hepatocyte has one or two nuclei with extended chromatin and prominent nucleoli. It has acidophilic cytoplasm due to large number of mitochondria (richest cell in mitochondria) and SER. Hepatocytes are also rich in sER, rER, free ribosomes, Golgi apparatus and lysosomes. Inclusions: Glycogen and lipids: stored in hepatocytes which is the richest cell in the body in glycogen. Lipofusion pigments especially in old age. 4/20/2019

Hepatocytes Hepatocytes are radially arranged as cellular plates separated by the liver sinusoids. Any surface of hepatocytes may be either: In close contact with surface of other hepatocyte enclosing between them a bile canaliculi. In close contact with the wall of blood sinusoid through the space of Disse where there are numerous microvilli of the hepatocyte. Blood sinusoid

Sinusoidal lining cells Sinusoids are irregularly dilated vessels separating cords of hepatocytes. Lined with endothelial cells, Kupffer’s cells and reticulin fibers. Kupffer’s cells: They are phagocytic macrophages which are derived from blood monocytes. They lay within sinusoidal lumen attached to the endothelial surface. These cells has pseudopodia, rich in lysosomes, pinocytic and phagocytic vesicles. Function: metabolize aged erythrocytes, digest hemoglobin, destroy bacteria that enter the portal blood. 4/20/2019

Perisinusoidal Space of Disse It is the space between the hepatocytes and the wall of blood sinusoids. It contains: 1- Extracellular fluid. 2- Microvilli of the liver cells. 3- some reticular fibers. 4- Fat storing cells (Ito cells, hepatic lipocytes): stellate in shape and store vitamin A. Function: exchange of material between bloodstream and the hepatocytes. It holds back cells but proteins formed in liver cells can pass easily to the blood. 4/20/2019

Architectural units of the liver Classic hepatic lobule: Hexagonal in shape, drain blood from hepatic artery and portal vein to central (hepatic) vein. Portal lobule: Triangular in shape with one portal tract in the center. It is formed of a mass of liver tissue from three adjacent hepatic lobules that excretes its bile into one bile duct. Hepatic (portal) acinus: it is the functional unit of the liver. Part of two adjacent hepatic lobules. It is diamond in shape with apices include the central vein and the two adjoining portal areas. It surrounds a central vascular core which explains why the peripheral hepatocytes are richly supplied with blood while the central hepatocytes are poorly supplied with blood.

Classic Hepatic lobule Hexagonal mass of hepatic tissue. Central vein in the center and 3-6 portal triads at the angles. It consists of radially arranged cords or plats of liver cells radiating from the central vein to the periphery of the lobule and separated by blood sinusoids. Classic hepatic lobule 4/20/2019

Classic Hepatic lobule Blood flow from the periphery to the center (from hepatic artery and portal vein to the central vein). Bile flow from the center to the periphery. Areas near the portal triad are well supplied by oxygen and nutrients. Areas around the central vein are not well supplied. 4/20/2019

Portal tract Portal tract (Portal triad) occupies corners of the classic hepatic lobule. It contains: A venule (branch of portal vein) (largest structure), An arteriole (branch of hepatic artery) (smallest of the three), Bile duct Lymphatic vessels, nerves and capillaries may be found here as well. It is surrounded by a sheath of connective tissue 4/20/2019

Biliary Duct System B- Extrahepatic ducts It is a duct system that excretes the bile which is synthesized by hepatocytes. It is formed of: A- Intrahepatic ducts: 1- Bile canaliculi 2- Bile ductules (Hering’s canals) 3- Bile duct of portal canal B- Extrahepatic ducts 4- right and left hepatic ducts 5- Common hepatic duct (CHD) 6- Cystic duct 7- CHD join with cystic duct to form common bile duct 8- The common bile duct enter the second portion of duodenum at the duodenal papilla (Ampulla of Vater) where there is the sphincter of Oddi which regulates the bile flow to intestine.

Biliary duct system

Histology of Biliary duct system Canaliculi are lined by the plasma membrane of hepatocytes Canal of Hering’s is lined by the simple squamous epithelium. Bile duct of portal tract is lined by simple cubical then simple columnar epithelium Right & left hepatic ducts are lined by tall columnar epithelium

Functions of Liver All functions of the liver is performed only by hepatocyte. A- Endocrine Functions: (secretion of substances into blood) 1- Synthesis of glycogen and secretion of glucose (sER). 2- Secretion of blood proteins such as albumin, fibrinogen, prothrombin and most of blood globulin (formed by rER and secreted by Golgi apparatus). 3- Secretion of lipoproteins (synthesized by rER, sER and secreted by Golgi apparatus).

Functions of Liver B- Exocrine Functions: (Secretion of bile into bile system) 1-Bile secretion: bile is secreted by hepatocytes into bile canaliculi to reach to small intestine through the bile duct system (0.5-1L/day). Bile facilitates greatly the digestion and absorption of fat in small intestine. 2- Secretion of IgA: into intestine via bile. C- Metabolic functions 1- Detoxification and inactivation of various drugs and metabolites (inactivated in sER of hepatocytes) such as barbiturates and antihistamines. 2- Deamination of amino acids: the ammonia that is formed of metabolism of amino acids is toxic in high concentration. The hepatocytes transform it into water soluble urea which is secreted into blood and excreted by kidney. 3- Storage of metabolites such as glycogen, lipids and vitamins.

Gall bladder It is a hollow Pear shaped organ attached to the inferior surface of the liver by a thick C.T. layer. It is composed of: 1- Fundus 2- Body 3- Neck Fundus Body Neck اسم ورقم المقرر – Course Name and No. 4/20/2019

Histology of Gall bladder 1- Mucosa: Epithelium: Tall columnar epithelium with microvilli. (No goblet cells) Laminal propria: loose C.T. No glands in the mucosa except in the neck of the bladder. No muscularis mucosa 2- Musculosa: consists of irregularly arranged smooth muscle fibers. 3- Serosa & adventitia: Serosa covers most of the gall bladder except where it is attached to the liver. N.B. There is no submucosa in the wall of gall bladder Epithelium Lamina propria Musculosa Serosa or adventitia 4/20/2019

Functions of gall bladder 1- Storage and concentration of bile through absorption of water, sodium and chloride ions by the columnar cells then release it when necessary into the digestive tract. 2- Secretion of some mucus by mucous glands in the neck of the bladder and by the lining epithelium. اسم ورقم المقرر – Course Name and No. 4/20/2019

Spleen اسم ورقم المقرر – Course Name and No. 17-10-01

Spleen Largest lymphatic organ Located in the upper, left side of the abdominal cavity. Plays multiple supporting roles in the body such as blood filtration and helping fight certain kinds of bacteria The spleen is not vital to survival and it is possible to live without a spleen. The lymphoid organs are classified into two groups: A. Primary Lymphoid organs Organs where T and B lymphocytes are formed and mature. Red bone marrow and Thymus B. Secondary Lymphoid organs Receive immune cells from the primary lymphoid organs to make them active. Such as: Lymph node, Spleen & Tonsils. اسم ورقم المقرر – Course Name and No. 17-10-01

Histology of spleen Stroma Capsule, trabeculae & Reticular CT The spleen is surrounded by a capsule of dense CT and is covered with peritoneum. Trabeculae are scattered in the substances of spleen. Extend from the capsule or from the hilum. Reticular CT: made up of reticular fibers, reticular cells & macrophages. It provide internal support for the spleen. اسم ورقم المقرر – Course Name and No. 17-10-01

Histology of Spleen B) Parenchyma (Splenic pulp) The white and red pulps 1- The white pulp: Perivascular sheath: Lymphatic tissue which forms sheaths around arteries of the spleen. Formed mainly of T-lymphocytes. Lymphatic follicle: may show germinal centers, has artery called central or follicular artery. Formed mainly of B-lymphocytes. 17-10-01

Structure of Spleen 2- The red pulp: Splenic cords: are continuous, of varying thickness. Contain mainly macrophages, reticular cells, Blood cells (RBCs, WBCs & platelets) & Plasma cells Splenic venous blood sinusoids: lies between the splenic cords. They have wide gaps in their walls which allow free exchange of cells back and forth between the sinusoids and red pulp. 17-10-01

Functions of Spleen 1- Immunological reactions: Humoral immunity: Formation of antibodies by splenic Plasma cells Cellular immunity (Cell-mediated reactions): This is performed by splenic T-lymphocytes. 2- Filtration of blood, storage of iron & formation of bilirubin. 3- Haemopoietic function in the fetus: produce blood cells only during the fetal life. 4- Concentration of blood cells by separating them from the plasma 2- Haemoglobin is formed of heme (iron +Bilirubin) + globin. The spleen store Iron to reuse by bone marrow while it secrets the bilirubin in bile. 4- The human spleen sequesters 200-250 mL densely packed red blood cells. This concentrated blood cells expelled in the blood during strenuous exercise and diving. اسم ورقم المقرر – Course Name and No. 17-10-01

References Junqueira C., Carneiro J. (2005). Basic Histology, Text & Atlas, 11th ed. Gartner LP (2016). Color Textbook of Histology. 4th ed. Philadelphia: Saunders WB. Young B, O' Dowd G, Woodford P (2013). Wheater‟s Functional Histology. 6th ed. London: Churchill Livingstone. 17-11-19