Gastrointestinal Tract - Liver Development: Difference between revisions
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Human data from Godlewski G, etal,<ref><pubmed>9407542</pubmed></ref> see also liver development in the rat during the embryonic period (Carnegie stages 15-23).<ref><pubmed>9718390</pubmed></ref> | |||
===Liver Bud=== | ===Liver Bud=== |
Revision as of 17:43, 25 August 2010
Introduction
This section of notes gives an overview of how the liver develops. The transverse septum (septum transversum) arises at an embryonic junctional site. The junctional region externally is where the ectoderm of the amnion meets the endoderm of the yolk sac. The junctional region internally is where the foregut meets the midgut. The mesenchymal structure of the transverse septum provides a support within which both blood vessels and the liver begin to form. This structure grows rapidly.
Arises at embryonic junction (septum transversum): externally is where ectoderm of amnion meets endoderm of yolk sac and internally is where the foregut meets the midgut
Mesenchymal structure of transverse septum provides a support within which both blood vessels and liver begin to form.
Liver Development Stages
Feature | |
hepatic diverticulum development | |
cell differentiation
septum transversum forming liver stroma hepatic diverticulum forming hepatic trabeculae | |
epithelial cord proliferation enmeshing stromal capillaries | |
hepatic gland and its vascular channels enlarge
hematopoietic function appeared | |
obturation due to epithelial proliferation
bile ducts became reorganized (continuity between liver cells and gut) | |
biliary ductules developed in periportal connective tissue
produces ductal plates that receive biliary capillaries (More? Timeline human development) |
Human data from Godlewski G, etal,[1] see also liver development in the rat during the embryonic period (Carnegie stages 15-23).[2]
Liver Bud
- Differentiates to form the hepatic diverticulum and hepatic primordium, generates the gall bladder then divides into right and left hepatic buds.
- Three connecting stalks (cystic duct, hepatic ducts) which fuse to form bile duct.
Hepatic Bud
- Left Hepatic Bud- left lobe, quadrate, caudate (both q and c anatomically Left)
- Right Hepatic Bud- right lobe
Liver Structural Origins
- Hepatic Buds - form hepatocytes, produce bile from week 13 (forms meconium of newborn)
- Vitelline Veins - form sinusoids
- Mesenchyme - form connective tissue and Kupffer cells
Function - Haemopoiesis
Embryonic liver also involved in blood formation, after the yolk sac and blood islands acting as a primary site.
Components of Liver Formation
Primitive Endoderm
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Data from mouse [3]
- Links: Endoderm | Mouse Development
Stage 13
The images below link to larger cross-sections of the mid-embryonic period (end week 4) stage 13 embryo starting just above the level of the liver and then in sequence through the liver to the level of the stomach. Note the relative position of the liver with respect to the abdominal cavity, the gall bladder and the heart.
The transverse septum differentiates to form the hepatic diverticulum and the hepatic primordium, these two structures together will go on to form different components of the mature liver and gall bladder. At this stage large vascular channels can be seen coursing through the liver primordium.
D3L | D4L | D5L | D6L | D7L | E1L |
G6L | G7L |
- Links: Carnegie stage 13 - serial sections | Embryo Serial Sections | Flash movies | Quicktime movies
Stage 22
The images below link to larger cross-sections of the end of the embryonic period (week 8) stage 22 embryo starting just above the level of the liver and then in sequence through the entire liver. (Note the sections are viewed from below, LR axis is reversed)
The rapidly developing liver also forms a visible surface bulge on the embryo directly under the heart bulge. The liver now occupies the entire ventral body cavity with parts of the gastrointestinal tract and urinary system "embedded" within its structure. Note in this image the large central ductus venosus.
E3L | E4L | E5L | E6L | E7L |
F1L | F2L | F3L | F4L | F5L |
- Links: Carnegie stage 22 - serial sections | Embryo Serial Sections | Flash movies | Quicktime movies
Selected Stage 22 Images
E3 Overview of liver region for selected high power views shown below. Note the position and size of the developing liver spanning the entire abdomen and within the liver the large central ductus venosus. | |
E4 Central veins of liver. Radiating appearance of hepatic sinusoids. unlabeled version | |
E5 Central vein with endothelial lining, containing nucleated erythrocytes, fetal red blood cells. The fetal liver has an important haemopoietic role. unlabeled version |
Liver Movies
Lesser Sac | Greater Omentum |
Quicktime version | Quicktime version |
Ductal Plate
The ductal plate is a primitive biliary epithelium which develops in mesenchyme adjacent to portal vein branches (periportal hepatoblasts). During liver development it is extensively reorganised (ductal plate remodelling) within the developing liver to form the intrahepatic bile ducts (IHBD). If remodelling does not occur, leading to excess of embryonic bile duct structures in the portal tract, these developmental abnormalities are described as "ductal plate malformation" (DPM).
Ductal Plate Malformations
- Interlobular bile ducts - autosomal recessive polycystic kidney disease
- Smaller interlobular ducts - von Meyenburg complexes
- Larger intrahepatic bile ducts - Caroli's disease
Bile Secretion
The epithelial cells that line the bile ducts are called cholangiocytes.
The pathway below describes the production and passage of bile for final excretion into the duodenum:
- hepatocytes produce bile
- secreted into bile canaliculi
- connected to intrahepatic bile ducts
- intrahepatic bile ducts connect to the hepatic duct
- then the cystic duct for storage in the gallbladder
- then the common bile duct into the duodenum
The term extrahepatic bile ducts (EHBDs) is used to describe the hepatic, cystic, and common bile ducts.
The developing bile ducts express VEGF while hepatoblasts express angiopoietin-1, these two signals are thought to regulate arterial vasculogenesis and remodeling of the hepatic artery respectively.[4]
Hepatocytes
These are the adult functional cells forming the majority of the liver (80% of the cells).
Many different functions including:
- Storage of substances including glucose (as glycogen), vitamin A (possibly in specialized adipocytes), vitamin B12, folic acid and iron.
- Lipid Turnover synthesis of plasmalipoproteins
- Plasma Protein Synthesis albumin, alpha and beta globulins, prothrombin, fibrinogen
- Metabolism fat soluble compounds (drugs, insecticides), steroid hormones turnover
- Secretion bile (about 1 litre/day)
Kupffer Cells
Kupffer Cells are a population of tissue macrophages found in the lumen of hepatic sinusoids, their role is endocytic against blood-borne materials entering the liver.
Primordial (primitive) macrophages arise in the yolk sac and then differentiate into fetal macrophages, either of these enter the blood and migrate into the developing liver.[5]
Kupffer Cells image
- Search PubMed Now: Kupffer cell development
Adult Liver Transplants
Approximately 6,000 liver transplant operations are performed in the United States (http://www.liverfoundation.org/education/info/transplant/) and about 600–700 in the UK every year (http://www.britishlivertrust.org.uk/home/the-liver/liver-transplantation/a-history-of-liver-transplantation-and-current-statistics.aspx). The main limitation on numbers are the availability of donor organs.[6]
Histology
The Liver Lobule
References
Reviews
Search Pubmed
Search Bookshelf Liver Development
Search Pubmed Now: Liver Development | Embryonic Liver Development
Glossary Links
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Cite this page: Hill, M.A. (2024, June 27) Embryology Gastrointestinal Tract - Liver Development. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/Gastrointestinal_Tract_-_Liver_Development
- © Dr Mark Hill 2024, UNSW Embryology ISBN: 978 0 7334 2609 4 - UNSW CRICOS Provider Code No. 00098G