Practical Gastroenterology and Hepatology E-Book

• Herausgeber: John Wiley & Sons
• Kategorie: Fachliteratur
• Sprache: Englisch

Seitenzahl: 1050

Veröffentlichungsjahr: 2011

Beschreibung

This comprehensive resource for fellows/trainees and candidates for recertification in gastroenterology summarizes the field in a modern, fresh format. Prominent experts from around the globe write on their areas of expertise, and each chapter follows a uniform structure. The focus is on key knowledge, with the most important clinical facts highlighted in boxes. Color illustrations reinforce the text.

Leseprobe

Contents

Contributors

Preface

Foreword

Part 1: Pathobiology of the Intestine and Pancreas

1: The Liver and Biliary Apparatus: Basic Structural Anatomy and Variations,

Introduction

Developmental Anatomy and Variations of the Liver

References

2: Immunology of the Liver and Mechanisms of Inflammation,

Introduction

Innate Immunity of the Liver

Adaptive Immunity of the Liver

Antigen-presenting Cells and the Liver

Immunity, Inflammation, and Liver Fibrosis

References

Part 2 Diagnostic Approaches in Liver Disease

3: Approach to History Taking and Physical Examination in Liver and Biliary Disease,

Introduction

History Taking in Liver and Biliary Disease

Physical Examination

References

4: Assessment of Abnormal Liver Injury Tests,

Approach to Patient with Abnormal Liver Injury Tests

References

5: Imaging of the Liver and Biliary Tree,

Liver Pathology

Gall-bladder/Biliary Pathology

References

6: Endoscopic Techniques in Management of the Liver and Biliary Tree: Upper Gastrointestinal Endoscopy,

Introduction

Detection of Esophageal Varices and Primary Prophylaxis

Active Bleeding from Esophageal Varices

Endoscopic Technique

Gastric Varices

Gastric Antral Vascular Ectasia

References

7: Endoscopic Techniques in Management of the Liver and Biliary Tree: Endoscopic Retrograde Cholangiopancreatography and Biliary Manometry,

Equipment and Review of Technology

Bile Duct Stones

Bile Leaks

Primary Sclerosing Cholangitis

Benign Biliary Obstruction

Indeterminate Biliary Obstruction

Malignant Biliary Obstruction

Sphincter of Oddi Dysfunction

Complications of ERCP

Combined Percutaneous and Endoscopic Approaches (Rendezvous)

References

8: Endoscopic Techniques in Management of the Liver and Biliary Tree: Endoscopic Ultrasonography,

Introduction

Equipment and Review of Technology

EUS Evaluation of Hepatobiliary Disease

Therapeutic Applications

Complications

References

9: Liver Biopsy and Paracentesis,

Introduction

Liver Biopsy

Paracentesis

Reference

Part 3 Problem-based Approach to Liver Disease

10: Jaundice and Pruritus: A Diagnostic Approach,

Introduction

Evaluation

Management

References

11: Liver Mass Found on Abdominal Imaging,

Evaluation of Liver Masses

Benign Liver Lesions

Malignant Liver Lesions

Risks of Liver Imaging

References

12: Right Upper Quadrant Abdominal Pain,

Introduction

Biliary Diseases that Cause RUQ Pain

Hepatitic Diseases that Cause RUQ Pain

Gastric and Intestinal Diseases that Cause RUQ Pain

Pancreatic Diseases that Cause RUQ Pain

Pulmonary Diseases that Can Cause RUQ Pain

Cardiac Diseases that Can Cause RUQ Pain

Renal Diseases that Can Cause RUQ Pain

History and Physical Examination

Diagnostic Testing

References

13: Acute Liver Failure,

Introduction

Definition

Etiology

Pathophysiology

Clinical Features

Diagnosis

Therapeutics

General Supportive Care for All Patients with ALF

Intensive Care Depending on Coma Grade

Treatment of Intracranial Hypertension

Seizure management in ALF

Liver Support Devices

Prognostic Assessment and Timing of OLT

References

Part 4: Problem-based Approach to Diagnosis and Differential Diagnosis

14: Portal Hypertension,

Introduction

Varices

Ascites

Spontaneous Bacterial Peritonitis

Hepatorenal Syndrome

Hepatic Encephalopathy

Hepatopulmonary Syndrome: Portopulmonary Hypertension

References

15: Hepatocellular Carcinoma,

Epidemiology

Risk Factors

Pathogenesis of HCC

Clinical Features

Surveillance and Screening Tests for HCC

Diagnosis and Staging of HCC

Treatment

Conclusion

References

16: Pregnancy and Liver Disease,

Definition and Epidemiology

Pathophysiology

Clinical Features

Diagnosis

The HELLP Syndrome

Therapeutics

Prognosis

Special Circumstances Cirrhosis and Portal Hypertension

References

17: Biliary Atresia and Cystic Fibrosis: Transitioning Care from Pediatrics to Internal Medicine,

Biliary Atresia

Cystic Fibrosis

References

Part 5 Diseases of the Liver

18: Acute Viral Hepatitis: Hepatitis A, Hepatitis E, and Other Viruses,

Hepatitis A

Prognosis

Hepatitis E

Other viruses

References

19: Hepatitis B and C,

Management of Chronic Hepatitis B

Management of Chronic Hepatitis C

References

20: Bacterial and Other Non-viral Infections of the Liver,

Pyogenic Liver Abscess

Pylephlebitis

Amebic Liver Abscess

Acute Cholangitis

Granulomatous Hepatitis

Bacterial Infections of the Liver

Protozoa

Fungi

Helminths

References

21: Metabolic Liver Diseases,

Hereditary Hemochromatosis

Wilson Disease

α-Antitrypsin Deficiency

References

22: Hepatic Steatosis and Non-alcoholic Fatty Liver Disease,

Definition and Epidemiology

Pathophysiology

Clinical Features (Table 22.2) Symptoms and Signs

Assessment of Disease Severity

Diagnosis

Prognosis

Treatment (Table 22.4)

References

23: Drug-induced Liver Injury,

Definition and Epidemiology

Clinical Presentation and Clinical Evaluation of DILI

Diagnosis and Causality Assessment

Causative Drugs

Risk Factors

Prognosis

Management

References

24: Alcoholic Liver Disease,

Introduction

Definition and Epidemiology

Pathophysiology

Clinical Features

Diagnosis

Prognosis

Management

Other Treatment Options

Complications

References

25: Autoimmune Liver Diseases,

Autoimmune Hepatitis

Primary Biliary Cirrhosis

Primary Sclerosing Cholangitis

Celiac Disease

References

26: Vascular Diseases of the Liver,

Budd – Chiari Syndrome

Portal Vein Thrombosis

References

27: Hepatic Complications of Bone Marrow Transplantation,

Definition and Epidemiology

Pathophysiology

Clinical Features

Diagnosis

Therapy

Prognosis

Conclusions

References

28: Hepatic Manifestations of Systemic Diseases,

Cardiovascular Disorders

Pulmonary Disorders

Renal Disorders

Endocrine Disorders

Rheumatologic Disorders

Gastroenterologic Disorders

Hematologic Disorders

Infiltrative Systemic Disorders

Miscellaneous Disorders

References

Part 6 Liver Transplantation

29: Indications and Selection of Patients for Liver Transplantation,

Definition and Epidemiology

Pathophysiology

Clinical Features

Diagnosis

Therapeutics

References

30: What Hepatologists Should Know About Liver Transplant Surgery,

Introduction

Anatomy

Techniques of Liver Transplantation

Phases of Liver Transplantation

Surgical Complications of Liver Transplantation

Conclusion

References

31: Immunosuppression in Liver Transplantation,

Introduction

Dawn of a New Era

Corticosteroids

Antimetabolites

Antibody Induction

Monoclonal Anti-T-cell Antibodies

Miscellaneous

Current Therapeutic Strategies for Steroid Avoidance

Renal-sparing Protocols

Conversion from CNI to Sirolimus

Calcineurin Inhibitor Avoidance

Individualization of Drug Therapy

References

32: Liver Transplantation: Early and Long Term Management and Complications,

Immunosuppression

Graft Function

Vascular Complications

Biliary Complications

Rejection

Infectious Diseases Complications

Renal Complications

Cardiovascular Complications

Neurologic Complications

Gastrointestinal Complications

Nutritional Complications

Wound Complications

Disease Recurrence and Complications

Metabolic Complications

Malignancy (Table 32.3)

Vaccinations

Pregnancy

Compliance

References

Part 7 Problem-based Approach to Biliary Tract and Gall-bladder Disease

33: Gall Stones, Gall-bladder Polyps and Their Complications: Epidemiology, Pathogenesis, Diagnosis, and Management,

Gall Stones Epidemiology

Gall-bladder Polyps

References

34: Functional Gall-bladder and Sphincter of Oddi Disorders,

Definition and Epidemiology

Pathophysiology

Clinical Features

Diagnosis

Differential Diagnosis

Therapeutics

Management

Prognosis

References

35: Cancer of the Gall Bladder and Biliary Tree,

Gall bladder Cancer

Risk Factors

Cholangiocarcinoma

Conclusions

References

36: Biliary Strictures and Leaks,

Introduction

Biliary Leaks

Biliary Strictures

References

Index

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ISBN: 9781405182751

contributors

Saleh Alqahtani, MDAssistant Professor of MedicineDivision of Gastroenterology and HepatologyUm Alqura UniversityJeddah, Saudi Arabia

Paul Angulo, MDProfessor of MedicineSection Chief of Hepatology University of Kentucky Medical CenterLexington, KY, USA

Bashar A. Aqel, MDAssistant Professor of MedicineDivisions of Gastroenterology and HepatologyMayo ClinicScottsdale, AZ, USA

Todd H. Baron, MDProfessor of MedicineDivision of Gastroenterology and HepatologyMayo ClinicRochester, MN, USA

Mashal Jatoi Batheja, MDFellow in GastroenterologyDivision of GastroenterologyMayo ClinicScottsdale, AZ, USA

Einar S. Björnsson, MD, PhDProfessor of MedicineHead of Gastroenterology and HepatologyLandspitali University HospitalReykjavik, Iceland

Thomas J. Byrne, MDAssistant Professor of MedicineDivisions of Gastroenterology and HepatologyMayo ClinicScottsdale, AZ, USA

Elizabeth J. Carey, MDAssistant Professor of MedicineDivisions of Gastroenterology and HepatologyMayo ClinicScottsdale, AZ, USA

Naga Chalasani, MDProfessor and DirectorDivision of Gastroenterology and HepatologyIndiana University School of MedicineIndianapolis, IN, USA

Nayantara Coelho - Prabhu, MDFellow in GastroenterologyDivision of Gastroenterology and HepatologyMayo ClinicRochester, MN, USA

Kelly K. Curtis, MDFellow in Hematology/OncologyDivision of Hematology/OncologyMayo ClinicScottsdale, AZ, USA

David D. Douglas, MDAssociate Professor of MedicineDivisions of Gastroenterology and HepatologyMayo ClinicScottsdale, AZ, USA

Juan F. Gallegos - Orozco, MDFellow in GastroenterologyDivisions of Gastroenterology and HepatologyMayo ClinicScottsdale, AZ, USA

Ferga C. Gleeson, MDAssistant Professor of MedicineDivision of Gastroenterology and HepatologyMayo ClinicRochester, MN, USA

Andrea A. Gossard, MS, CNPAssistant Professor of MedicineDivision of Gastroenterology and HepatologyMayo ClinicRochester, MN, USA

John B. Gross, MDAssociate Professor of MedicineDivision of Gastroenterology and HepatologyMayo ClinicRochester, MN, USATimothy J. Gunneson, PA - CInstructor in MedicineWilliam J. von Liebig Transplant CenterMayo ClinicRochester, MN, USA

Denise M. Harnois, DOAssistant Professor of MedicineDepartment of TransplantMayo ClinicJacksonville, FL, USA

M. Edwyn Harrison, MDAssociate Professor of MedicineDivisions of Gastroenterology and HepatologyMayo ClinicScottsdale, AZ, USA

Stephen Crane Hauser, MDAssociate Professor of MedicineDivision of Gastroenterology and HepatologyMayo ClinicRochester, MN, USA

J. Eileen Hay, MDProfessor of MedicineDivision of Gastroenterology and HepatologyMayo ClinicRochester, MN, USA

Patrick S. Kamath, MDProfessor of MedicineDivision of Gastroenterology and HepatologyMayo ClinicRochester, MN, USA

W. Ray Kim, MDAssociate Professor of MedicineDivision of Gastroenterology and HepatologyMayo ClinicRochester, MN, USA

Shimon Kusne, MDProfessor of MedicineChair, Division of Infectious DiseasesMayo ClinicScottsdale, AZ, USA

Nirusha Lachman, PhDAssistant ProfessorDepartment of AnatomyMayo ClinicRochester, MN, USA

Konstantinos N. Lazaridis, MDAssociate Professor of MedicineCenter for Basic Research in Digestive DiseasesMayo ClinicRochester, MN, USA

Feng Li, MDFellow in GastroenterologyDivision of Gastroenterology and HepatologyUniversity of Maryland Medical CenterBaltimore, MD, USA

Ann McCullough, MDAssistant ProfessorDepartment of Laboratory Medicine and PathologyMayo ClinicScottsdale, AZ, USA

Kristin L. Mekeel, MDAssistant Professor of SurgeryDivision of Transplant, Hepatobiliary and Pancreatic SurgeryMayo ClinicScottsdale, AZ, USA

Ethan D. Miller, MDFellow in GastroenterologyDivisions of Gastroenterology and HepatologyMayo ClinicScottsdale, AZ, USA

David C. Mulligan, MDProfessor of Surgery and ChairDivision of Transplant, Hepatobiliary and Pancreatic SurgeryMayo ClinicScottsdale, AZ, USA

David M. Nagorney, MDProfessor of SurgeryDivision of General and Gastrointestinal SurgeryDepartment of SurgeryMayo ClinicRochester, MN, USA

Cuong C. Nguyen, MDAssociate Professor of MedicineDivision of GastroenterologyMayo ClinicScottsdale,AZ, USA

Chakri Panjala, MDFellow in GastroenterologyDivision of Gastroenterology and HepatologyDepartment of Internal MedicineMayo ClinicJacksonville, FL, USA

Helga Paula, MDResearch ProfessionalDivision of Gastroenterology and HepatologyMayo ClinicRochester, MN, USA

Wojciech Pawlina, MDProfessor and ChairDepartment of AnatomyMayo ClinicRochester, MN, USA

Bret T. Petersen, MDProfessor of MedicineDivision of Gastroenterology and HepatologyMayo ClinicRochester, MN, USA

David J. Post, PharmD, BCPSAssistant ProfessorDivision of Transplant MedicineMayo ClinicScottsdale, AZ, USA

John J. Poterucha, MDProfessor of MedicineDivision of Gastroenterology and HepatologyMayo ClinicRochester, MN, USA

Elizabeth Rajan, MDProfessor of MedicineDivision of Gastroenterology and HepatologyMayo ClinicRochester, MN, USA

Jorge Rakela, MDProfessor and ChairDivisions of Gastroenterology and HepatologyDepartment of Internal MedicineMayo ClinicScottsdale, AZ, USA

David J. Rea, MDInstructor in SurgeryDivision of Transplantation SurgeryMayo ClinicRochester, MN, USA

Lewis R. Roberts, MB ChB, PhDAssociate Professor of MedicineDivision of Gastroenterology and HepatologyMayo ClinicRochester, MN, USA

Charles B. Rosen, MDProfessor and ChairDivision of Transplantation SurgeryMayo ClinicRochester, MN, USA

William Sanchez, MDAssistant Professor of MedicineDivision of Gastroenterology and HepatologyMayo ClinicRochester, MN, USA

Maria Teresa A. Seville, MDInstructor in Medicine Division of Infectious DiseasesMayo ClinicScottsdale, AZ, USA

Vijay Shah, MDProfessor of MedicineDivision of Gastroenterology and HepatologyMayo ClinicRochester, MN, USA

Benjamin L. Shneider, MDProfessor of PediatricsDivision of Pediatric Gastroenterology, Hepatology andNutritionChildren’s Hospital of Pittsburgh of UPMCPittsburgh, PA, USA

Alvin C. Silva, MDAssistant Professor of RadiologyDirector, Abdominal ImagingDepartment of RadiologyMayo ClinicScottsdale, AZ, USA

James L. Slack, MDAssistant Professor of Medicine Division of Hematology/OncologyMayo ClinicScottsdale, AZ, USA

Jayant A. Talwalkar, MD, MPHAssociate Professor of MedicineDivision of Gastroenterology and HepatologyMayo ClinicRochester, MN, USA

Erin W. Thackeray, MDFellow in GastroenterologyDivision of Gastroenterology and HepatologyMayo ClinicRochester, MN, USA

Veena Venkat, MDAssistant Professor of PediatricsDivision of Pediatric Gastroenterology, Hepatology andNutritionChildren’s Hospital of Pittsburgh of UPMCPittsburgh, PA, USA

Kymberly D.S. Watt, MDAssistant Professor of MedicineWilliam J. von Liebig Transplant CenterMayo ClinicRochester, MN, USA

Preface

Welcome to Practical Gastroenterology and Hepatology, a new comprehensive three volume resource for everyone training in gastroenterology and for those certifying (or re-certifying) in the subspecialty. We have aimed to create three modern, easy to read and digest stand-alone textbooks. The entire set covers the waterfront, from clinical evaluation to advanced endoscopy to common and rare diseases every gastroenterologist must know.

Volume three deals with disorders of the liver and biliary tree. Each chapter highlights, where appropriate, a clinical case which demonstrates a common clinical situation, its approach, and management. Simple, easy to follow clinical algorithms are demonstrated throughout the relevant chapters. Endoscopy and surgery chapters provide excellent video examples, all available electronically.

Each chapter has been written by the best of the best in the field, and carefully peer reviewed and edited for accuracy and relevance. We have guided the writing of this textbook to help ensure experienced gastroenterologists, fellows, residents, medical students, internists, primary care physicians, as well as surgeons all will find something of interest and relevance.

Each volume and every chapter has followed a standard template structure. All chapters focus on key knowledge, and the most important clinical facts are highlighted in an introductory abstract and as take-home points at the end; irrelevant or unimportant information is omitted. The chapters are deliberately brief and readable; we want our readers to retain the material, and immediately be able to apply what they learn in practice. The chapters are illustrated in color, enhanced by a very pleasant layout. A Web based version has been created to complement the textbook including endoscopy images and movies.

In this volume, part one addresses the anatomy and immunopathology of the liver and biliary tree. The emphasis here is, as in all volumes, on the practical and clinically relevant, as opposed to the esoteric. Part two deals with the approach the clinician should take in diagnosis of diseases in the liver and biliary tract. Basic history and physical techniques, laboratory, imaging and endoscopy modalities are discussed. Part three covers problem -based approach to important manifestations of liver injury and disease such as jaundice, liver tumors, right upper quadrant pain and acute liver failure. Part four follows with approaches to manifestations of chronic disease such as portal hypertension and hepatocellular carcinoma in addition to specific clinical scenarios such as pregnancy in the setting of chronic liver disease and adult problems in the survivor of pediatric liver disease. Part five covers the wide spectrum of viral, autoimmune and metabolic diseases that the gastroenterologist is likely to encounter, all designed to be succinct and clinically oriented. Part six covers the very relevant topic of liver transplantation. The reader will be left with important clinical pearls in the selection and management of patients with cirrhosis in need of liver replacement. Surgical details and medical/pharmacological principles are outlined. Section seven addresses a problem-based approach to the management of biliary tract disorders, ranging from stones and strictures to cancer and functional pain syndromes.

We have been thrilled to work with a terrific team in the creation of this work, and very much hope you will enjoy reading this volume as much as we have enjoyed developing it for you.

Nicholas J. TalleyKeith D. LindorHugo E. Vargas

Foreword

The discipline of hepatology has blossomed into a comprehensive specialty that demands broad expertise. In that context, the textbook by Talley, Lindor and Vargas is timely and valuable. One need only peruse the topics within this section to realize how much has changed in the past few years—in particular, the emergence of liver transplantation as a life - saving intervention has rescued thousands of patients and buoyed clinicians by offering new hope and generating new principles of care for their patients. Viral hepatitis, acute liver failure, and non -alcoholic fatty liver are among the other important topics covered by this volume, reflecting the practical perspective of seasoned clinicians and thought leaders in the field. The work is infused with the excitement of hepatol-ogy and the practical wisdom of many of its practitioners. Therefore, it’s a great personal privilege to introduce this thoughtful effort to the readers who will richly benefit from its unique clarity and breadth.

Scott L. Friedman, M.D.Fishberg Professor and ChiefDivision of Liver DiseasesMount Sinai School of Medicine

Part 1

Pathobiolog y of the Liver and Biliary Tract

CHAPTER 1

The Liver and Biliary Apparatus: Basic Structural Anatomy and Variations

Nirusha Lachman and Wojciech Pawlina

Department of Anatomy, Mayo Clinic, Rochester, MN, USA

Summary

Understanding the anatomy of the liver may be complicated by the lack of anatomic consistency in its description. Although external observation of the liver presents a clear depiction of lobar division, appreciation of its functional anatomy is often made difficult by its complex intrahepatic architecture. In this chapter, the liver is approached through a clear delineation of the core features central to the clinical translation of its anatomy. The liver is described in terms of its location and surface anatomy, peritoneal relationships, surfaces and lobes, segmental anatomy, blood supply, and venous and lymphatic drainage. Descriptions combine gross anatomic features and histology with a commentary on the development and variations of the liver.

Introduction

The liver is one of the largest organs in the body, occupying at least 2 – 3% of the total adult body weight [1 – 3]. It weighs roughly 1200 – 1500 g in the average adult and, although not significant, reports have suggested that there may be population - specific variations in liver weight (1800–2600g) [1].

Location and Surface Anatomy (Figure 1.1 )

The liver appears wedge shaped, with its base to the right and its apex projecting to the left as it extends between the right and left upper quadrants. In its subdiaphragmatic position, the liver lies beneath the overlying ribs and cartilage. Its superior convex surface fills the concavity of the right dome of the diaphragm, reaching the fifth rib on the right and the fifth intercostal space, 7 – 8 cm from the midline, on the left. The upper margin may be traced at the level of the xiphisternal joint as it arches upward on each side. The right lateral margin therefore lies against the diaphragm and anterolateral thoracic wall, crossing the seventh to eleventh ribs along the midaxillary line. In comparison, the inferior border is sharp and may be followed just below the costal margin on the right extending to the left toward the fifth intercostal space. It is formed by a line joining the right lower, and upper left extremities [2 – 11].

Peritoneal Relationships

As the liver continues to grow and enlarges during its development, the ventral mesentery is modified to form membranous folds that not only enclose almost the entire liver but also provide diaphragmatic and visceral attachments. At its upper pole, however, the liver makes direct contact with the developing diaphragm and, as a result, is devoid of peritoneum. This area is referred to as the “ bare area ” and persists as the only portion of the liver surface with no membranous covering.

Figure 1.1 CT scans of liver in situ : (a) horizontal plane; (b) coronal plane. (c) Three - dimensional image of liver; (d) anterior view of liver in abdominal cavity. (Image (d) is courtesy of RF Morreale, 2008.)

Folds of peritoneum pass from the diaphragmatic and visceral surfaces, connecting the liver to two main structures (Figure 1.2 ): (1) the diaphragm and (2) the stomach. When entering the abdominal cavity during a dissection, a sickle - shaped anterior fold of peritoneum is visible. This is known as the falciform ligament. It consists of two layers of adherent peritoneum and attaches the liver to the supraumbilical part of the anterior abdominal wall, as well as to the inferior surface of the thoracic diaphragm. Inferiorly, the falciform ligament is unattached and contains the ligamentum teres (obliterated left umbilical vein). As the falciform ligament ascends superiorly, it produces the left triangular ligament, which extends toward the left tip of the liver, but stops short, about two - thirds of the way along the superior margin, and is related to the lesser omentum along its posterior fold. As the falciform ligament passes superiorly and to the right, it gives rise to the upper layer of the coronary ligament, so named because it encircles the bare area of the liver. The inferior line of peritoneal attachment passes superiorly toward the summit of the liver, where it meets the leaf of the falciform ligament. These ligaments then attach to a groove, which lodges the ligamentum venosum (remnant of the ductus venosus). The coronary ligament fuses at its apex to form a small, rather insignificant right triangular ligament [2–11].

Figure 1.2 Peritoneal ligaments. (Courtesy of RF Morreale, 2008.)

Visceral Surface

The visceral surface of the liver is best observed by superior rotation so that the inferior margin lies superiorly. Several key structures may be identified on this surface (Figure 1.3):

• Porta hepatis:

two layers of lesser omentum deviate to the right and enclose the portal triad (portal vein, hepatic artery, bileduct)

contains lymph nodes and nerves.

• Gall-bladder fossa:

located on the inferior slope of the visceral surface with cystic duct close to the right margin of porta hepatis

lies between the colic impression and the quadrate lobe.

• Quadrate lobe: between the gall-bladder fossa and fissure for ligamentum teres.

• Bare area: in contact with the diaphragm and right suprarenal gland.

In addition, the stomach, duodenum, hepatic flexure of the colon, and the right kidney form impressions on the visceral surface.

Lobes

Anatomically, the liver is divided into a larger right and a smaller left lobe using the line of attachment of the falciform ligament and fissures for ligamentum teres and ligamentum venosum. Functionally, the liver is divided along an oblique line that passes through the center of the bed of the gall bladder and the groove for the inferior vena cava (IVC) along the plane of the middle hepatic vein [12,13].

Figure 1.3 (a) Visceral surface of liver showing portal triad; (b) liver visceral surface impressions. (Courtesy of RF Morreale, 2008.)

The quadrate lobe is located on the superior part of the visceral surface, bound by the fissure for ligamentum teres on the left and the gall - bladder fossa on the right. Anatomically, it is considered part of the right lobe but remains, functionally, part of the left lobe.

The caudate lobe is located on the inferior part of the visceral surface of the liver, bound by the fissure for liga-mentum venosum on the left and by the groove for the IVC on the right. The caudate lobe exhibits a complex anatomy and is said to be embryologically and anatomically independent of the right and left lobes of the liver [14,15]. It therefore remains a separate anatomic segment. The right portion of the caudate lobe extends as the caudate process which forms the superior boundary of the epiploic foramen. Description of the functional segments of the liver has been based on blood supply (systemic and portal) and venous and biliary drainage. Although there are several descriptions of segmental anatomy, the most commonly applied nomenclature is based on Bismuth’s interpretation [16], where all hepatic segments, except for the caudate lobe, are defined by three vertical fissures and a single transverse fissure. Of these fissures, only one appears to be represented super-ficially (portoumbilical fissure) [12,13], while the others are related to three large hepatic veins. The right fissure, lying almost in the coronal plane, contains the right hepatic vein. The median fissure passes from the gall -bladder fossa to the left margin of the IVC. The left fissure runs from the left side of the IVC toward the left margin of the liver (a point between the dorsal third and ventral two - thirds), passing inferiorly to the start of the ligamentum venosum. The portoumbilical fissure is marked by the attachment of the falciform ligament [12]. The simplest way to understand the segmental anatomy of the liver is to view it in four sectors (a left medial and left lateral sector and a right anterior and right posterior sector) which are then divided into eight segments [12,13]. The left lateral sector lies to the left of the falciform ligament attachment and the grooves for ligamentum teres and ligamentum venosum, with the left medial sector lying between these lines and the plane of the gall bladder and the IVC. There is no external marking between the right anterior and posterior sectors. The plane runs obliquely, posteriorly and medially from the middle of the front of the right lobe toward the groove for the IVC. The segments may be identified as follows (Figure 1.4):

• Segment I: caudate lobe

• Segments II and III: left hepatic vein passes between segments

• Segments IVa and IVb: quadrate lobe

• Segments V and VI: inferior segments of right anterior and right posterior sectors

• Segments VII and VIII: superior segments of right anterior and right posterior sectors.

The following are basic points on hepatic nomenclature [2,12,13,16] :

• All hepatic segments except for the caudate lobe are defined by three vertical divisions and a single transverse division.

• The middle hepatic vein divides the liver into right and left hemi-livers.

• The right hemi-liver is divided by the right hepatic vein into anterior and posterior segments.

• The left hemi - liver is divided by the left hepatic vein into medial and lateral segments.

• Four segments are divided by a transverse line that passes through the right and left portal branches.

• In a frontal view, eight segments are numbered clockwise.

Microscopic Organization

Structurally, the liver is composed of the following:

• Parenchyma:

organized plates of hepatocytes

normally one cell thick (in adults, two cell layers in children aged 6 years).

• Connective tissue stroma:

contains blood vessels, nerves, lymphatic vessels, and bile ducts

continuous with the fibrous capsule of Glisson, covering the surface of the liver.

Figure 1.4 Liver segments. (Courtesy of RF Morreale, 2008.)

• Sinusoidal capillaries (sinusoids): vascular channels located between the plates of hepatocytes.

• Perisinusoidal spaces (spaces of Disse): located between the sinusoidal endothelium and hepatocytes.

The best approach to understanding the organization of the liver parenchyma is by visualizing a classic lobule. The architecture of this lobule is based on the distribution of the branches of the portal vein and hepatic artery within the liver and by the flow of blood when perfusing the liver [17-19].

Classic Liver Lobule

The liver lobule is roughly hexagonal, measures about 2.0 x 0.7 mm and consists of stacks of anastomosing plates of hepatocytes, one cell layer thick, separated by the anastomosing system of sinusoids that perfuse the cells with the mixed portal and arterial blood (Figure 1.5 ). At the center of the lobule is the terminal hepatic venule (central vein), into which the sinusoids drain. From the central vein, plates of cells radiate to the periphery of the lobule, as do sinusoids. Portal canals are located at the angles of the hexagon and bordered by the outermost hepatocytes of the lobule—loose stromal connective tissue (continuous with the fibrous capsule of the liver) characterized by the presence of the portal triads. Between the connective tissue stroma and the hepatocytes at the edges of the portal canal, a small space referred to as the space of Mall can be found. This space is thought to be one of the sites where lymph originates in the liver [17-19].

Figure 1.5 Organization of liver lobules (low magnification),×85. Arrowheads indicate the central vein.

Hepatocytes

Hepatocytes are large, polygonal cells measuring between 20 and 30 (im and constitute about 80% of the cell population of the liver.

Polygonal Structure. Two of its surfaces face the perisinusoidal space. The plasma membrane of the two surfaces faces a neighboring hepatocyte and a bile canaliculus. Assuming that the cell is cuboidal, the remaining two surfaces would also face neighboring cells and bile cana-liculi. The surfaces that face the perisinusoidal space correspond to the basal surface of other epithelial cells and those that face neighboring cells and bile canaliculi correspond to the lateral and apical surfaces, respectively, of other epithelial cells [17-19].

Hepatocyte Nuclei. Nuclei are large, spherical, and located in the center of the cell. In the adult liver, many cells are binucleate; two or more well - developed nucleoli are present in each nucleus. Cytoplasm is generally aci-dophilic [17-19].

Hepatocyte Organelles. The following organelles are visible through specific staining techniques [17 - 19] :

• Extensive smooth endoplasmic reticulum (sER) with varying metabolic activity. Under conditions of hepatocyte challenge by drugs, toxins, or metabolic stimulants, the sER may become the predominant organelle in the cell.

• Presence of mitochondria: as many as 800 - 1000 per cell.

• Large numbers of peroxisomes (200 - 300).

• Large Golgi apparatus consisting of as many as 50 Golgi units, each of which consists of three to five closely stacked cisternae, plus many large and small vesicles. Elements of the Golgi apparatus concentrated near the bile canaliculus are believed to be associated with the exo-crine secretion of bile.

• Heterogeneous population of lysosomes concentrated near the bile canaliculus.

• Deposits of glycogen (in a well-preserved hematoxylin and eosin (H & E) preparation; glycogen is also visible as irregular spaces, usually giving a fine foamy appearance to the cytoplasm).

• Lipid droplets of varying sizes. The number of lipid droplets increases after injection or ingestion of certain hepatotoxins, including ethanol.

• Various amounts of lipofuscin pigment within lysosomes

Blood Supply

The liver receives about 70% of its blood via the portal vein and 30% from the hepatic artery [2 – 5]. The hepatic artery commonly arises from the celiac trunk but may sometimes come off the superior mesenteric artery or as a separate branch of the aorta. It divides into right and left branches. The right branch passes behind the common hepatic duct and divides into anterior and posterior branches within the liver. The left branch divides into medial and lateral branches within the liver. Occasionally, these branches may arise from the superior mesenteric artery (15%) or the left gastric artery (20%) and may be additional or replace the normal branches [2,3]. There is no communication between the right and left halves of the liver. The arteries are said to be “end-arteries” [2,12]. Figure 1.6 shows the arterial pattern and Figure 1.7 shows the liver vascular tree.

Figure 1.6 (a) Liver arterial pattern; (b) liver venous pattern. (Courtesy of RF Morreale, 2008.)

Figure 1.7 Corrosion cast of liver vascular tree: (a) diaphragmatic surface; (b) visceral surface. (Courtesy of Hongjin Sui, 2008.)

The portal vein is formed by the union of the superior mesenteric and splenic veins behind the neck of the pancreas. It measures roughly 7 – 10 cm in length and has a diameter of 0.8 – 1.4 cm [2,3]. The portal vein has no valves. At the porta hepatis, the portal vein divides into right and left branches before it enters the liver. The right branch of portal vein is shorter than the left. It lies anterior to the caudate process, follows the distribution of the right hepatic artery and duct, and bifurcates into 17 anterior and posterior segmental branches, with further divisions into subsegmental parenchymal branches. The left branch of the portal vein is longer and has transverse and umbilical parts. It starts as the transverse part in the porta hepatis which, on its way to the left, gives off a caudate branch. After turning sharply at the level of the umbilical fissure, the umbilical part continues anteriorly in the direction of the round ligament to terminate in a blind end proximal to the inferior border of the liver, where it is joined by the round ligament [2 – 7,9,10].

Venous and Lymphatic Drainage

The venous drainage shows mixing of blood between the right and left halves of the liver. There are three main hepatic veins that drain into the IVC. A large central vein runs in between the right and left halves and receives blood from each. A right and left vein lie further laterally and, frequently, a middle hepatic vein joins the left vein close to the IVC. These veins have no extrahepatic course and drain into the IVC just below the central tendon of the diaphragm. In addition, there are several small hepatic veins that enter the IVC below the main veins, as well as a separate vein draining the caudate lobe. Anastomoses between the portal channels and the azygos system of veins have been observed in the bare area of the liver [2-5,11,12].

The lymphatic drainage may be summarized as follows [2]:

• Drainage into three to four nodes that lie in porta hepatis

• Drainage into pyloric nodes and celiac nodes

• Receives lymphatics from the gall bladder

• Communication with extraperitoneal lymphatics from bare area – perforate the diaphragm and drain into nodes of the posterior mediastinum; similar communications from the left triangular and falciform ligaments.

Interlobular Vessels

Interlobular vessels occupy the portal canals with only those that form the smallest portal triads sending blood into the sinusoids (Figure 1.8 ). Larger interlobular vessels branch into distributing vessels located at the periphery of the lobule. These distributing vessels send inlet vessels to the sinusoids. In the sinusoids, the blood flows cen-tripetally toward the central vein. As the central vein courses through the central axis of the classic liver lobule, it becomes larger and eventually empties into a sublobu-lar vein. Convergence of several sublobular veins forms larger hepatic veins which empty into the IVC [17 - 19].

Figure 1.8 (a) Portal triad: H & E,×650; (b) architecture of liver sinusoids and cords indicated by the arrows: H & E,×320. BD, bile ductule; HA, hepatic artery; PV, portal vein.

Structurally, the portal vein and the hepatic artery, with their tributaries and branches, are typical of veins and arteries in general. In addition to providing arterial blood directly to the sinusoids, the hepatic artery provides arterial blood to the connective tissue and other structures in the larger portal canals. Capillaries in these larger portal canals return the blood to the interlobular veins before they empty into the sinusoid [17 – 19].

The thin - walled central vein receives blood from the hepatic sinusoids. Its endothelial lining is surrounded by small amounts of spirally arranged connective tissue fibers. The sublobular vein, the vessel that receives blood from the terminal hepatic venules, has a distinct layer of connective tissue fibers (both collagenous and elastic) just external to the endothelium. The sublobular veins and the hepatic veins, into which they drain, travel alone. As a result of their solitary nature, they can be readily distinguished in a histologic section from the portal veins that are members of a triad. Hepatic veins have no valves [17–19].

Hepatic sinusoids are lined by a thin discontinuous endothelium with underlying discontinuous basal lamina that is absent over large areas. As opposed to other sinusoids, hepatic sinusoids contain a phagocytic cell derived from monocytes referred to as a Kupffer cell in the vessel lining. Kupffer cells do not form junctions with neighboring endothelial cells but processes of Kupffer cells often seem to span the sinusoidal lumen and may even partially occlude it [17].

Figure 1.9 Photomicrograph of liver with highlighted hepatocytes: toluidine blue, osmium fixation,×950. Asterisks indicate the hepatic sinusoids and arrowheads point to Kupffer cells.

The perisinusoidal space (space of Disse) is the site of exchange of materials between blood and liver cells (Figure 1.9 ). It lies between the basal surfaces of hepato-cytes and the basal surfaces of endothelial cells and Kupffer cells that line the sinusoids. Small, irregular microvilli project into this space from the basal surface of the hepatocytes. As a result of the large gaps in the endothelial layer and the absence of a continuous basal lamina, there is no significant barrier between the blood plasma in the sinusoid and the hepatocyte plasma membrane. Proteins and lipoproteins synthesized by the hepa-tocyte are transferred into the blood in the perisinusoidal space; this pathway is for liver secretions other than bile [17–19].

Figure 1.10 Gall bladder and biliary system.

Lymphatic Pathway

Plasma that remains in the perisinusoidal space drains into the periportal connective tissue where a small space, the space of Mall, is described between the stroma of the portal canal and the outermost hepatocytes. Lymphatic fluid then enters lymphatic capillaries which travel with the other components of the portal triad [17].

Lymph in progressively larger vessels follows the same direction as the bile (i.e., from the level of the hepatocytes toward the portal canals and eventually to the hilum of the liver). About 80% of the hepatic lymph follows this pathway and drains into the thoracic duct [17] (Figure 1.10).

Innervation

Sympathetic fibers from the celiac ganglion give off nerves that run with vessels in the free edge of the lesser omentum and enter the porta hepatis. Parasympathetic fibers arise from the hepatic branch of the anterior vagal trunk and reach porta hepatis via lesser omentum [2,3].

The Biliary Apparatus

The biliary apparatus consists of three hepatic ducts (right, left, and common), gall bladder and cystic duct, and the bile duct. In terms of their relationship, the right and left hepatic ducts go on to form the common hepatic duct to the right side of the porta hepatis. The common hepatic duct is joined on the right side by the cystic duct, which enters at an acute angle to form the bile duct [2 – 6] (Figure 1.11).

Figure 1.11 Photomicrograph of the liver showing bile canaliculi impregnated with gold. Gold stain x420.

The common bile duct is about 6 - 8 cm long and its normal diameter does not exceed 8 mm. For descriptive purposes, the bile duct may be divided into three parts [2,3]:

1 Supraduodenal: lies in the free edge of the lesser omentum in front of the portal vein and to the right of the hepatic artery.

2 Retroduodenal:

lies behind the first part of the duodenum, slopes down and to the right

portal vein lies to the left of the duct with the gastroduodenal artery

the IVC lies behind the duct.

3 Paraduodenal: slopes further to the right in a groove between the posterior surface of the head of the pancreas and the second part of the duodenum, and in front of the right renal vein.

Joins the pancreatic duct at a 60º angle at the hepatopan-creatic ampulla.

Innervation

Parasympathetic fibers run from the anterior vagal trunk and sympathetic from the celiac ganglion [2,3].

Microscopic Anatomy

The biliary system is formed from channels of increasing diameter, through which bile flows from the hepatocytes to the gall bladder and then to the intestines. These structures are not only passive conduits, but also capable of modifying bile flow and changing its composition in response to hormonal and neural stimulation.

Cholangiocytes (epithelial cells), which monitor bile flow and regulate its content, line the biliary system. These cells are identified by their organelle - scant cytoplasm, presence of tight junctions, and complete basal lamina. An apical domain of cholangiocytes appears similar to hepatocytes, with microvilli projecting into the lumen. In addition, each cholangiocyte contains primary cilia that sense changes in luminal flow, resulting in alterations of cholangiocyte secretion [17 – 19].

Bile flows from the region of the terminal hepatic venule (central vein) toward the portal canal (a direction opposite to the blood flow) (centrifugal flow). The smallest branches of the biliary system are the bile canaliculi, into which the hepatocytes secrete bile. They form a complete loop around four sides of the idealized six - sided hepatocytes. They are approximately 0.5 µm in luminal diameter and are isolated from the rest of the intercellular compartment by tight junctions (part of junctional complexes). Microvilli of the two adjacent hepatocytes extend into the canalicular lumen. Near the portal canal, bile canaliculi join together to form a larger channel, known as the canal of Hering. Its lining is made of two types of cells, hepatocytes and cholangiocytes. The main distinction between the canal of Hering and the bile ductule is whether the structure is partially or completely lined by cholangiocytes. Bile ductules carry bile to the interlobular bile ducts. These ducts range from 15 µm to 40µm in diameter and are lined by cholangiocytes, which are cuboidal near the lobules and gradually become columnar as the ducts near the porta hepatis. As the bile ducts get larger, they gradually acquire a dense connective tissue investment containing numerous elastic fibers. Smooth muscle cells appear in this connective tissue as the ducts approach the hilum. Interlobular ducts unite to form right and left hepatic ducts and, together, the common hepatic duct. The common hepatic duct is lined with tall columnar epithelial cells and possesses all the same layers of the alimentary canal, except the muscularis mucosae [17–19] (Figure 1.12).

The Gall Bladder

Gross Anatomy

The gall bladder is a pear - shaped organ that consists of a fundus, body, and neck. As already described, it lies in the fossa for the gall bladder on the visceral surface of the liver, adjacent to the quadrate lobe. The gall bladder is covered by the peritoneum over the liver, although sometimes it may hang free on a narrow mesentery and, only rarely, be embedded. It varies in size and shape, may be duplicated, with single or double cystic ducts, and very rarely absent. The fundus usually projects below the margin of the liver and may be located at the tip of the ninth costal cartilage where the transpyloric plane crosses the right costal margin. Internally, it is related to the left of the hepatic flexure of the transverse colon. The fundus is not normally palpable, except in disease. The body passes towards the right of the porta hepatis and is related to the first part of the duodenum. As the body narrows, it forms the neck which, with further narrowing, produces the cystic duct that passes backward and inferiorly to join the common hepatic duct in front of the right hepatic artery and its cystic branch [2,3,5 – 7].

Figure 1.12 Photomicrograph of wall of gall bladder. Rokitansky – Aschoff sinuses are indicated by an asterisk, and the lamina propria of mucosal folds by arrowheads. H & E,×100.

The gall bladder receives its blood supply from the cystic artery (commonly a branch of the right hepatic artery, but may arise from gastroduodenal artery or main trunk of the hepatic artery) and its venous drainage is via numerous cystic veins. The cystic artery may be located in the Calot triangle which also contains the cystic lymph node.

Microscopic Anatomy

The empty or partially filled gallbladder has numerous deep mucosal folds. Deep diverticula of the mucosa, called Rokitansky – Aschoff sinuses, are sometimes present and extend through muscularis externa. The mucosal surface consists of simple columnar epithelium. Tall epithelial cells exhibit numerous, but not well - developed, apical microvilli, well - developed junctional complexes, numerous mitochondria in the apical and basal cytoplasm, and complex plications on the lateral basal membrane. The lamina propria is also very cellular, containing large numbers of lymphocytes and plasma cells. It is particularly rich in fenestrated capillaries and small venules, but there are no lymphatic vessels in this layer. Mucin -secreting glands are sometimes present in the lamina propria, especially near the neck of the organ. Cells that appear identical to enteroendocrine cells of the intestine are also found in these glands. External to the lamina propria is muscularis externa with numerous collagen and elastic fibers, among somewhat randomly oriented bundles of smooth muscle cells. Despite its origin from a foregut - derived tube, the gall bladder does not have muscularis mucosae or submucosa. External to muscu-laris externa is a thick layer of dense connective tissue containing large blood vessels, extensive lymphatic network, and autonomic nerves. The connective tissue is also rich in elastic fibers and adipose tissue. The layer of tissue where the gall bladder attaches to the liver surface is referred to as the adventitia. The unattached surface is covered by a serosa or visceral peritoneum consisting of a layer of mesothelium and a thin layer of loose connective tissue [17–19].

Developmental Anatomy and Variations of the Liver

At the start of the fourth week of intrauterine life, the liver is one of the first organs to develop, undergoing rapid growth to fill the abdominal cavity and amounting to 10% of the total fetal weight by the ninth week of development [20–23].

The liver, biliary system, and gall bladder are said to arise as a ventral outgrowth from the caudal part of the foregut. This ventral outgrowth is described as being “ Y ” shaped and known as the hepatic diverticulum. At the same time, a thick mass of splanchnic mesoderm, the septum transversum, develops on the cranial aspect of the coelomic cavity (between the developing heart and the midgut). The cranial part of the septum transversum gives rise to the pericardial cavity (and, eventually, pericardium) and the diaphragm. The caudal part is, however, soon invaded by the developing liver and, as the liver grows, it is said to become surrounded by the septum transversum, which is then referred to as the ventral mesogastrium [20,21]. As the liver grows into the ventral mesogastrium, it divides into two parts. The larger, more cranial part is the primordium of the liver. The smaller, more caudal part gives rise to the gall bladder. The stalk of the hepatic diverticulum goes on to form the cystic duct and the stalk connecting the hepatic and cystic ducts to the duodenum forms the bile duct. It is important to note that, initially, the bile duct is attached to the ventral aspect of the duodenal loop. However, rotation of the duodenum carries the bile duct to its dorsal aspect, where it maintains its position throughout adult life [2,3,20-23].

As the endodermal cells now proliferate, they appear to give rise to intermingling cords of hepatocytes as well as the epithelial lining of the intrahepatic part of the biliary apparatus. These hepatic cords then anastomose around the early endothelial lined hepatic sinusoids [20-23].

The fibrous and hemopoietic tissue, as well as the Kupffer cells, are said to be derivatives of the mesen-chyme of the septum transversum. Hemopoiesis usually begins at around week 6 and bile formation, around week 12 of development [3,20,21].

As liver development is not subject to frequent deviation, variations in liver anatomy are rare. However, cases have been recorded and are summarized below [24] :

• The liver may have no lobar division.

• Accessory lobes may be present or division of the liver into 12 lobes may be possible.

• A detached portion forming a short accessory appendage on the left lobe may be observed. In this case, the appendage is usually covered by a fold of peritoneum containing blood vessels.

• The presence of two additional lobes has been reported: (a) lobus posterior – projecting through the epiploic foramen (lying behind the stomach); and (b) lobus vena cava – projecting along the course of the IVC.

• The left triangular ligament may contain liver tissue.

• A bridge of liver segment of varying size may connect the quadrate and left lobes.

• A smaller accessory liver may be found adherent to the pancreas.

• Isolated masses of liver have been observed on the wall of the gall bladder, ligamentum teres, spleen, and greater omentum.

Reports highlighting variations of liver and biliary anatomy and its importance in clinical procedures continue to add to the banks of existing knowledge [25–27].

Take - home points

The liver:

develops from a ventral outgrowth known as the hepatic diverticulum and grows into the ventral mesogastriumextends between right and left upper quadrants in a subdiaphragmatic position reaching as high as the fifth rib and as low as the eleventh rib on the rightis related to the peritoneum by the falciform, coronary, and triangular ligaments, and connected to ligamentum teres and ligamentum venosumreceives its blood supply from the hepatic artery (30%) and the portal vein (70%)consists of anatomic lobes and functional segmentsis connected to the biliary apparatus, which consists of the gall bladder, and hepatic, cystic, and bile ductsexhibits microscopic organization of hexagonally shaped lobules with a central veinmay have developmental anomalies and variations present but these are rare.

References

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CHAPTER 2

Immunology of the Liver and Mechanisms of Inflammation

Konstantinos N. Lazaridis

Center for Basic Research in Digestive Diseases, Mayo Clinic, Rochester, MN, USA

Summary

A decade ago the liver was simply considered as the main organ for metabolism and detoxification of endogenous and exogenous substances. Over the past 10 years studies have indicated that the liver also plays a key role in several immunologic events, some of which contribute to the development of autoimmune hepatic disease (i.e., primary biliary cirrhosis, primary sclerosing cholangitis, and autoimmune hepatitis), liver inflammation, and fibrosis. Innate immunity and adaptive immunity compromise a coordinated system that involves the liver parenchyma in both health and disease. To this extent, local immune and inflammatory events are key contributors to hepatic diseases and fibrosis. Improved understanding of these pathways provides the basis for better therapies of liver disease.

Introduction

Humans are protected from exogenous pathogens through the interplay of innate and adaptive immunity. Innate immunity represents a range of defense mechanisms that target pathogens in a non - specific manner and functions in the initial stages of an immune response. Adaptive immunity embodies a response of antigen -specific lymphocytes to antigen(s) of pathogens, including the development of memory lymphocytes against these antigens.

The liver is an organ with both immunological activity and reactivity. It not only represents an integral part of the immune system but its parenchyma could also be the grounds for several immune - mediated diseases. Hepatotropic virus - dependent diseases in which the host immune responses provoke inflammatory damage to virus - harboring hepatocytes, as well as autoimmune liver diseases that destroy the hepatic parenchyma, are examples of how malfunctional immunity could lead to organ - specific illness.

Innate Immunity of the Liver

The innate immune system has the capacity to recognize exogenous pathogens [1]. It comprises cells with killing capacities including monocytes, macrophages, neutrophils, and dendritic cells (DCs) as well as natural killer (NK) lymphocytes [2]. These cells possess pattern recognition receptors (PRRs) such as receptors for bacterial carbohydrates and toll - like receptors (TLRs) [3]. These molecules recognize components of microorganisms (e.g., lipopolysaccharides, glycolipids, flagellin) that lead to activation of immune cells (e.g., monocytes, macrophages, neutrophils, DCs, and NK cells), ultimately causing specific destruction of the activating organism or infected cell in the case of virus - harboring hepatocytes. This damage is achieved by either release of cytotoxic agents or phagocytosis. Another way in which the innate immune system detects pathogens is by activating receptors on NK cells [4]. These receptors recognize alterations of host cells secondary to damage from infection or tumor transformation, e.g., the molecule of NK group 2 member D (NKG2D) represents such a receptor, which recognizes the stress - inducible ligand molecule, the major histocompatibility class (MHC) I chain - related molecule (MICA) [5]. Interaction of these receptors with a ligand results in immediate killing of the infected or tumor cell by an NK cell.

In general, the innate immune response is activated in a very short period of time after liver injury from an invader (e.g., bacteria, virus). Those innate defense functions occur constantly and are more frequent in tissues with high exposure to foreign antigens (e.g., digestive system, hepatic parenchyma). A basic element of the innate immune system is its ability to recruit extra inflammatory cells from other sites of the body to the area of invasion or damage by exogenous agents. This function is achieved via chemical messengers that are released from activated cells of the innate immune system. including cytokines and chemokines [6]. These molecules not only act locally at the site of liver damage but also operate in a universal manner because of their release from the tissue of origin (e.g., hepatic parenchyma) into the systemic circulation, thus having an effect on other tissues and organs.

Adaptive Immunity of the Liver

When an invading bacterium or virus circumvents the innate immunity, adaptive immunity is initiated, the first step of which relates to activation of T lymphocytes. These cells remain in an inactive state until they encounter an infectious agent in the lymphoid tissues of the body. Detection of an antigen from a microorganism causes proliferation and differentiation of T lymphocytes into an effector stage. Na ï ve T lymphocytes are activated by antigen - presenting cells (APCs), which are able to capture, process, and display antigens of bacteria or viruses on the surfaces [7]. APCs present fragments of microorganism(s) on their plasma membrane together with MHC molecules. Subsequently, the T cells recognize the peptide/MHC complexes via specific T - cell receptors (TCRs). T cells demonstrate great diversity in antigen recognition, thus offering the immune system an enormous repertoire of effector cells with antigen specificity.