Lobules of liver#Portal triad

The hepatic lobule can be described in terms of metabolic "zones", describing the hepatic acinus (terminal acinus). Each zone is centered on the line connecting two portal triads and extends outwards to the two adjacent central veins. The periportal zone I is nearest to the entering vascular supply and receives the most oxygenated blood, making it least sensitive to ischemic injury while making it very susceptible to viral hepatitis. Conversely, the centrilobular zone III has the poorest oxygenation, and will be most affected during a time of ischemia.{{cite book |author1=B.R. Bacon |author2=J.G. O'Grady |author3=A.M. Di Bisceglie |author4=J.R. Lake |title=Comprehensive Clinical Hepatology|year=2006|publisher=Elsevier Health Sciences |isbn=0-323-03675-9}}

A portal triad (also known as portal canal, portal field{{Citation needed|reason=This name is not mentioned in reference 1 or anywhere else|date=December 2018}}, portal area{{Citation needed|reason='In both cases peripheral connective tissue of portal areas contains the portal triad' was written in reference 1, which means portal triad is part of portal area|date=December 2018}}, or portal tract{{Citation needed|reason='The peripheral vessels are grouped in connective tissue of the portal tracts and include a branch of the portal vein, a branch of the hepatic artery, and a branch of the bile duct (the portal triad).' was written in reference 1, which means portal triad is part of portal tract|date=December 2018}}) is a distinctive arrangement within lobules. It consists of the following five structures:{{Cite book|title=Junqueira's Basic Histology text and atlas|last=Mescher|first=Anthony L.|publisher=McGraw-Hill Education|year=2013|isbn=978-0-07-180720-3|pages=333}}

• proper hepatic artery, an arteriole branch of the hepatic artery that supplies oxygen
• hepatic portal vein, a venule branch of the portal vein, with blood rich in nutrients but low in oxygen
• one or two small bile ductules of cuboidal epithelium, branches of the bile conducting system.
• lymphatic vessels
• branch of the vagus nerve

The misnomer "portal triad" traditionally has included only the first three structures, and was named before lymphatic vessels were discovered in the structure.{{Cite book|url=https://books.google.com/books?id=K7-6GM4ty0AC&q=The+misnomer+%22portal+triad%22&pg=PT454|title=Vander's Human Physiology, The Mechanisms of Body Function|date=26 September 2016|isbn=9781478436232}}{{Cite web|url=http://www.vivo.colostate.edu/hbooks/pathphys/digestion/liver/bloodsys.html|title=Physiology of the Hepatic Vascular System|website=www.vivo.colostate.edu|language=en|access-date=2018-12-04}} It can refer both to the largest branch of each of these vessels running inside the hepatoduodenal ligament, and to the smaller branches of these vessels inside the liver.

In the smaller portal triads, the four vessels lie in a network of connective tissue and are surrounded on all sides by hepatocytes. The ring of hepatocytes abutting the connective tissue of the triad is called the periportal limiting plate.

File:Portal triad.JPG|Portal triad

File:Gray1093.png|Labeled sketch of a portal canal

File:Leber Glisson (Ratte).jpg|Portal triad of a rat liver, 1 branch of hepatic artery, 2 branch of portal vein, 3 bile duct

File:Liver portal triad.png|Portal triad of mouse liver. 1= bile duct, 2= branch of hepatic artery, 3= branch of portal vein, 4= lymphatic vessels

The periportal space ({{langx|la|spatium periportale}}), or periportal space of Mall,{{cite book|author=Roderick N. M. MacSween|title=MacSween's pathology of the liver|url=https://books.google.com/books?id=08a3FiePGGQC&pg=PA44|access-date=23 May 2011|year=2007|publisher=Elsevier Health Sciences|isbn=978-0-443-10012-3|pages=44–}} is a space between the stroma of the portal canal and the outermost hepatocytes in the hepatic lobule, and is thought to be one of the sites where lymph originates in the liver.{{cite book | last1 = Ross | last2 = Pawlina | first1 = Michael H. | first2 = Wojciech | title = Histology: A Text and Atlas | publisher = Lippincott Williams & Wilkins | date = 2006 | page = [https://archive.org/details/histologytextatl0000ross_i4i2/page/426 426] | isbn = 0-7817-7221-4 | url = https://archive.org/details/histologytextatl0000ross_i4i2/page/426 }}

Fluid (residual blood plasma) that is not taken up by hepatocytes drains into the periportal space, and is taken up by the lymphatic vessels that accompany the other portal triad constituents.

File:Liver scheme1.jpg

Zones differ by function:

• zone I hepatocytes are specialized for oxidative liver functions such as gluconeogenesis, β-oxidation of fatty acids and cholesterol synthesis
• zone III cells are more important for glycolysis, lipogenesis and cytochrome P-450-based drug detoxification.{{cite book |editor1=E.R. Schiff |editor2=M.F. Sorrell |editor3=W.C. Maddrey |title=Schiff's Diseases of the Liver, Tenth Edition|year=2007 |publisher=Lippincott William & Wilkins|isbn=978-0-7817-6040-9}} This specialization is reflected histologically; the detoxifying zone III cells have the highest concentration of CYP2E1 and thus are most sensitive to NAPQI production in acetaminophen toxicity.{{cite book|editor=D.S. Basow|author1=M.J. Burns |author2=S.L. Friedman |author3=A.M. Larson |title=UpToDate|year=2009 |publisher=UpToDate|location=Waltham, MA|chapter=Acetaminophen (paracetamol) poisoning in adults: Pathophysiology, presentation, and diagnosis}}

Other zonal injury patterns include zone I deposition of hemosiderin in hemochromatosis and zone II necrosis in yellow fever.

Bridging fibrosis, a type of fibrosis seen in several types of liver injury, describes fibrosis from the central vein to the portal triad.{{cite web |title=The liver ~ Medical student education – Tissupath |url=http://tissupath.com.au/education-medical-student-liver/ |website=tissupath.com.au |access-date=20 June 2018}}

• Porta hepatis

{{Reflist}}

• [http://www.siumed.edu/~dking2/erg/liver.htm#lobules Histology at siumed.edu]
• [https://web.archive.org/web/20070125120420/http://www.cvm.okstate.edu/instruction/mm_curr/histology/HistologyReference/HRD2.htm Histology at okstate.edu]
• {{UIUCHistologySubject|923}}

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Category:Liver anatomy